Loading...
1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Generic ring buffer
4 *
5 * Copyright (C) 2008 Steven Rostedt <srostedt@redhat.com>
6 */
7#include <linux/trace_events.h>
8#include <linux/ring_buffer.h>
9#include <linux/trace_clock.h>
10#include <linux/sched/clock.h>
11#include <linux/trace_seq.h>
12#include <linux/spinlock.h>
13#include <linux/irq_work.h>
14#include <linux/uaccess.h>
15#include <linux/hardirq.h>
16#include <linux/kthread.h> /* for self test */
17#include <linux/module.h>
18#include <linux/percpu.h>
19#include <linux/mutex.h>
20#include <linux/delay.h>
21#include <linux/slab.h>
22#include <linux/init.h>
23#include <linux/hash.h>
24#include <linux/list.h>
25#include <linux/cpu.h>
26#include <linux/oom.h>
27
28#include <asm/local.h>
29
30static void update_pages_handler(struct work_struct *work);
31
32/*
33 * The ring buffer header is special. We must manually up keep it.
34 */
35int ring_buffer_print_entry_header(struct trace_seq *s)
36{
37 trace_seq_puts(s, "# compressed entry header\n");
38 trace_seq_puts(s, "\ttype_len : 5 bits\n");
39 trace_seq_puts(s, "\ttime_delta : 27 bits\n");
40 trace_seq_puts(s, "\tarray : 32 bits\n");
41 trace_seq_putc(s, '\n');
42 trace_seq_printf(s, "\tpadding : type == %d\n",
43 RINGBUF_TYPE_PADDING);
44 trace_seq_printf(s, "\ttime_extend : type == %d\n",
45 RINGBUF_TYPE_TIME_EXTEND);
46 trace_seq_printf(s, "\ttime_stamp : type == %d\n",
47 RINGBUF_TYPE_TIME_STAMP);
48 trace_seq_printf(s, "\tdata max type_len == %d\n",
49 RINGBUF_TYPE_DATA_TYPE_LEN_MAX);
50
51 return !trace_seq_has_overflowed(s);
52}
53
54/*
55 * The ring buffer is made up of a list of pages. A separate list of pages is
56 * allocated for each CPU. A writer may only write to a buffer that is
57 * associated with the CPU it is currently executing on. A reader may read
58 * from any per cpu buffer.
59 *
60 * The reader is special. For each per cpu buffer, the reader has its own
61 * reader page. When a reader has read the entire reader page, this reader
62 * page is swapped with another page in the ring buffer.
63 *
64 * Now, as long as the writer is off the reader page, the reader can do what
65 * ever it wants with that page. The writer will never write to that page
66 * again (as long as it is out of the ring buffer).
67 *
68 * Here's some silly ASCII art.
69 *
70 * +------+
71 * |reader| RING BUFFER
72 * |page |
73 * +------+ +---+ +---+ +---+
74 * | |-->| |-->| |
75 * +---+ +---+ +---+
76 * ^ |
77 * | |
78 * +---------------+
79 *
80 *
81 * +------+
82 * |reader| RING BUFFER
83 * |page |------------------v
84 * +------+ +---+ +---+ +---+
85 * | |-->| |-->| |
86 * +---+ +---+ +---+
87 * ^ |
88 * | |
89 * +---------------+
90 *
91 *
92 * +------+
93 * |reader| RING BUFFER
94 * |page |------------------v
95 * +------+ +---+ +---+ +---+
96 * ^ | |-->| |-->| |
97 * | +---+ +---+ +---+
98 * | |
99 * | |
100 * +------------------------------+
101 *
102 *
103 * +------+
104 * |buffer| RING BUFFER
105 * |page |------------------v
106 * +------+ +---+ +---+ +---+
107 * ^ | | | |-->| |
108 * | New +---+ +---+ +---+
109 * | Reader------^ |
110 * | page |
111 * +------------------------------+
112 *
113 *
114 * After we make this swap, the reader can hand this page off to the splice
115 * code and be done with it. It can even allocate a new page if it needs to
116 * and swap that into the ring buffer.
117 *
118 * We will be using cmpxchg soon to make all this lockless.
119 *
120 */
121
122/* Used for individual buffers (after the counter) */
123#define RB_BUFFER_OFF (1 << 20)
124
125#define BUF_PAGE_HDR_SIZE offsetof(struct buffer_data_page, data)
126
127#define RB_EVNT_HDR_SIZE (offsetof(struct ring_buffer_event, array))
128#define RB_ALIGNMENT 4U
129#define RB_MAX_SMALL_DATA (RB_ALIGNMENT * RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
130#define RB_EVNT_MIN_SIZE 8U /* two 32bit words */
131#define RB_ALIGN_DATA __aligned(RB_ALIGNMENT)
132
133/* define RINGBUF_TYPE_DATA for 'case RINGBUF_TYPE_DATA:' */
134#define RINGBUF_TYPE_DATA 0 ... RINGBUF_TYPE_DATA_TYPE_LEN_MAX
135
136enum {
137 RB_LEN_TIME_EXTEND = 8,
138 RB_LEN_TIME_STAMP = 8,
139};
140
141#define skip_time_extend(event) \
142 ((struct ring_buffer_event *)((char *)event + RB_LEN_TIME_EXTEND))
143
144#define extended_time(event) \
145 (event->type_len >= RINGBUF_TYPE_TIME_EXTEND)
146
147static inline int rb_null_event(struct ring_buffer_event *event)
148{
149 return event->type_len == RINGBUF_TYPE_PADDING && !event->time_delta;
150}
151
152static void rb_event_set_padding(struct ring_buffer_event *event)
153{
154 /* padding has a NULL time_delta */
155 event->type_len = RINGBUF_TYPE_PADDING;
156 event->time_delta = 0;
157}
158
159static unsigned
160rb_event_data_length(struct ring_buffer_event *event)
161{
162 unsigned length;
163
164 if (event->type_len)
165 length = event->type_len * RB_ALIGNMENT;
166 else
167 length = event->array[0];
168 return length + RB_EVNT_HDR_SIZE;
169}
170
171/*
172 * Return the length of the given event. Will return
173 * the length of the time extend if the event is a
174 * time extend.
175 */
176static inline unsigned
177rb_event_length(struct ring_buffer_event *event)
178{
179 switch (event->type_len) {
180 case RINGBUF_TYPE_PADDING:
181 if (rb_null_event(event))
182 /* undefined */
183 return -1;
184 return event->array[0] + RB_EVNT_HDR_SIZE;
185
186 case RINGBUF_TYPE_TIME_EXTEND:
187 return RB_LEN_TIME_EXTEND;
188
189 case RINGBUF_TYPE_TIME_STAMP:
190 return RB_LEN_TIME_STAMP;
191
192 case RINGBUF_TYPE_DATA:
193 return rb_event_data_length(event);
194 default:
195 BUG();
196 }
197 /* not hit */
198 return 0;
199}
200
201/*
202 * Return total length of time extend and data,
203 * or just the event length for all other events.
204 */
205static inline unsigned
206rb_event_ts_length(struct ring_buffer_event *event)
207{
208 unsigned len = 0;
209
210 if (extended_time(event)) {
211 /* time extends include the data event after it */
212 len = RB_LEN_TIME_EXTEND;
213 event = skip_time_extend(event);
214 }
215 return len + rb_event_length(event);
216}
217
218/**
219 * ring_buffer_event_length - return the length of the event
220 * @event: the event to get the length of
221 *
222 * Returns the size of the data load of a data event.
223 * If the event is something other than a data event, it
224 * returns the size of the event itself. With the exception
225 * of a TIME EXTEND, where it still returns the size of the
226 * data load of the data event after it.
227 */
228unsigned ring_buffer_event_length(struct ring_buffer_event *event)
229{
230 unsigned length;
231
232 if (extended_time(event))
233 event = skip_time_extend(event);
234
235 length = rb_event_length(event);
236 if (event->type_len > RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
237 return length;
238 length -= RB_EVNT_HDR_SIZE;
239 if (length > RB_MAX_SMALL_DATA + sizeof(event->array[0]))
240 length -= sizeof(event->array[0]);
241 return length;
242}
243EXPORT_SYMBOL_GPL(ring_buffer_event_length);
244
245/* inline for ring buffer fast paths */
246static __always_inline void *
247rb_event_data(struct ring_buffer_event *event)
248{
249 if (extended_time(event))
250 event = skip_time_extend(event);
251 BUG_ON(event->type_len > RINGBUF_TYPE_DATA_TYPE_LEN_MAX);
252 /* If length is in len field, then array[0] has the data */
253 if (event->type_len)
254 return (void *)&event->array[0];
255 /* Otherwise length is in array[0] and array[1] has the data */
256 return (void *)&event->array[1];
257}
258
259/**
260 * ring_buffer_event_data - return the data of the event
261 * @event: the event to get the data from
262 */
263void *ring_buffer_event_data(struct ring_buffer_event *event)
264{
265 return rb_event_data(event);
266}
267EXPORT_SYMBOL_GPL(ring_buffer_event_data);
268
269#define for_each_buffer_cpu(buffer, cpu) \
270 for_each_cpu(cpu, buffer->cpumask)
271
272#define TS_SHIFT 27
273#define TS_MASK ((1ULL << TS_SHIFT) - 1)
274#define TS_DELTA_TEST (~TS_MASK)
275
276/**
277 * ring_buffer_event_time_stamp - return the event's extended timestamp
278 * @event: the event to get the timestamp of
279 *
280 * Returns the extended timestamp associated with a data event.
281 * An extended time_stamp is a 64-bit timestamp represented
282 * internally in a special way that makes the best use of space
283 * contained within a ring buffer event. This function decodes
284 * it and maps it to a straight u64 value.
285 */
286u64 ring_buffer_event_time_stamp(struct ring_buffer_event *event)
287{
288 u64 ts;
289
290 ts = event->array[0];
291 ts <<= TS_SHIFT;
292 ts += event->time_delta;
293
294 return ts;
295}
296
297/* Flag when events were overwritten */
298#define RB_MISSED_EVENTS (1 << 31)
299/* Missed count stored at end */
300#define RB_MISSED_STORED (1 << 30)
301
302#define RB_MISSED_FLAGS (RB_MISSED_EVENTS|RB_MISSED_STORED)
303
304struct buffer_data_page {
305 u64 time_stamp; /* page time stamp */
306 local_t commit; /* write committed index */
307 unsigned char data[] RB_ALIGN_DATA; /* data of buffer page */
308};
309
310/*
311 * Note, the buffer_page list must be first. The buffer pages
312 * are allocated in cache lines, which means that each buffer
313 * page will be at the beginning of a cache line, and thus
314 * the least significant bits will be zero. We use this to
315 * add flags in the list struct pointers, to make the ring buffer
316 * lockless.
317 */
318struct buffer_page {
319 struct list_head list; /* list of buffer pages */
320 local_t write; /* index for next write */
321 unsigned read; /* index for next read */
322 local_t entries; /* entries on this page */
323 unsigned long real_end; /* real end of data */
324 struct buffer_data_page *page; /* Actual data page */
325};
326
327/*
328 * The buffer page counters, write and entries, must be reset
329 * atomically when crossing page boundaries. To synchronize this
330 * update, two counters are inserted into the number. One is
331 * the actual counter for the write position or count on the page.
332 *
333 * The other is a counter of updaters. Before an update happens
334 * the update partition of the counter is incremented. This will
335 * allow the updater to update the counter atomically.
336 *
337 * The counter is 20 bits, and the state data is 12.
338 */
339#define RB_WRITE_MASK 0xfffff
340#define RB_WRITE_INTCNT (1 << 20)
341
342static void rb_init_page(struct buffer_data_page *bpage)
343{
344 local_set(&bpage->commit, 0);
345}
346
347/*
348 * Also stolen from mm/slob.c. Thanks to Mathieu Desnoyers for pointing
349 * this issue out.
350 */
351static void free_buffer_page(struct buffer_page *bpage)
352{
353 free_page((unsigned long)bpage->page);
354 kfree(bpage);
355}
356
357/*
358 * We need to fit the time_stamp delta into 27 bits.
359 */
360static inline int test_time_stamp(u64 delta)
361{
362 if (delta & TS_DELTA_TEST)
363 return 1;
364 return 0;
365}
366
367#define BUF_PAGE_SIZE (PAGE_SIZE - BUF_PAGE_HDR_SIZE)
368
369/* Max payload is BUF_PAGE_SIZE - header (8bytes) */
370#define BUF_MAX_DATA_SIZE (BUF_PAGE_SIZE - (sizeof(u32) * 2))
371
372int ring_buffer_print_page_header(struct trace_seq *s)
373{
374 struct buffer_data_page field;
375
376 trace_seq_printf(s, "\tfield: u64 timestamp;\t"
377 "offset:0;\tsize:%u;\tsigned:%u;\n",
378 (unsigned int)sizeof(field.time_stamp),
379 (unsigned int)is_signed_type(u64));
380
381 trace_seq_printf(s, "\tfield: local_t commit;\t"
382 "offset:%u;\tsize:%u;\tsigned:%u;\n",
383 (unsigned int)offsetof(typeof(field), commit),
384 (unsigned int)sizeof(field.commit),
385 (unsigned int)is_signed_type(long));
386
387 trace_seq_printf(s, "\tfield: int overwrite;\t"
388 "offset:%u;\tsize:%u;\tsigned:%u;\n",
389 (unsigned int)offsetof(typeof(field), commit),
390 1,
391 (unsigned int)is_signed_type(long));
392
393 trace_seq_printf(s, "\tfield: char data;\t"
394 "offset:%u;\tsize:%u;\tsigned:%u;\n",
395 (unsigned int)offsetof(typeof(field), data),
396 (unsigned int)BUF_PAGE_SIZE,
397 (unsigned int)is_signed_type(char));
398
399 return !trace_seq_has_overflowed(s);
400}
401
402struct rb_irq_work {
403 struct irq_work work;
404 wait_queue_head_t waiters;
405 wait_queue_head_t full_waiters;
406 bool waiters_pending;
407 bool full_waiters_pending;
408 bool wakeup_full;
409};
410
411/*
412 * Structure to hold event state and handle nested events.
413 */
414struct rb_event_info {
415 u64 ts;
416 u64 delta;
417 unsigned long length;
418 struct buffer_page *tail_page;
419 int add_timestamp;
420};
421
422/*
423 * Used for which event context the event is in.
424 * NMI = 0
425 * IRQ = 1
426 * SOFTIRQ = 2
427 * NORMAL = 3
428 *
429 * See trace_recursive_lock() comment below for more details.
430 */
431enum {
432 RB_CTX_NMI,
433 RB_CTX_IRQ,
434 RB_CTX_SOFTIRQ,
435 RB_CTX_NORMAL,
436 RB_CTX_MAX
437};
438
439/*
440 * head_page == tail_page && head == tail then buffer is empty.
441 */
442struct ring_buffer_per_cpu {
443 int cpu;
444 atomic_t record_disabled;
445 struct ring_buffer *buffer;
446 raw_spinlock_t reader_lock; /* serialize readers */
447 arch_spinlock_t lock;
448 struct lock_class_key lock_key;
449 struct buffer_data_page *free_page;
450 unsigned long nr_pages;
451 unsigned int current_context;
452 struct list_head *pages;
453 struct buffer_page *head_page; /* read from head */
454 struct buffer_page *tail_page; /* write to tail */
455 struct buffer_page *commit_page; /* committed pages */
456 struct buffer_page *reader_page;
457 unsigned long lost_events;
458 unsigned long last_overrun;
459 unsigned long nest;
460 local_t entries_bytes;
461 local_t entries;
462 local_t overrun;
463 local_t commit_overrun;
464 local_t dropped_events;
465 local_t committing;
466 local_t commits;
467 local_t pages_touched;
468 local_t pages_read;
469 long last_pages_touch;
470 size_t shortest_full;
471 unsigned long read;
472 unsigned long read_bytes;
473 u64 write_stamp;
474 u64 read_stamp;
475 /* ring buffer pages to update, > 0 to add, < 0 to remove */
476 long nr_pages_to_update;
477 struct list_head new_pages; /* new pages to add */
478 struct work_struct update_pages_work;
479 struct completion update_done;
480
481 struct rb_irq_work irq_work;
482};
483
484struct ring_buffer {
485 unsigned flags;
486 int cpus;
487 atomic_t record_disabled;
488 atomic_t resize_disabled;
489 cpumask_var_t cpumask;
490
491 struct lock_class_key *reader_lock_key;
492
493 struct mutex mutex;
494
495 struct ring_buffer_per_cpu **buffers;
496
497 struct hlist_node node;
498 u64 (*clock)(void);
499
500 struct rb_irq_work irq_work;
501 bool time_stamp_abs;
502};
503
504struct ring_buffer_iter {
505 struct ring_buffer_per_cpu *cpu_buffer;
506 unsigned long head;
507 struct buffer_page *head_page;
508 struct buffer_page *cache_reader_page;
509 unsigned long cache_read;
510 u64 read_stamp;
511};
512
513/**
514 * ring_buffer_nr_pages - get the number of buffer pages in the ring buffer
515 * @buffer: The ring_buffer to get the number of pages from
516 * @cpu: The cpu of the ring_buffer to get the number of pages from
517 *
518 * Returns the number of pages used by a per_cpu buffer of the ring buffer.
519 */
520size_t ring_buffer_nr_pages(struct ring_buffer *buffer, int cpu)
521{
522 return buffer->buffers[cpu]->nr_pages;
523}
524
525/**
526 * ring_buffer_nr_pages_dirty - get the number of used pages in the ring buffer
527 * @buffer: The ring_buffer to get the number of pages from
528 * @cpu: The cpu of the ring_buffer to get the number of pages from
529 *
530 * Returns the number of pages that have content in the ring buffer.
531 */
532size_t ring_buffer_nr_dirty_pages(struct ring_buffer *buffer, int cpu)
533{
534 size_t read;
535 size_t cnt;
536
537 read = local_read(&buffer->buffers[cpu]->pages_read);
538 cnt = local_read(&buffer->buffers[cpu]->pages_touched);
539 /* The reader can read an empty page, but not more than that */
540 if (cnt < read) {
541 WARN_ON_ONCE(read > cnt + 1);
542 return 0;
543 }
544
545 return cnt - read;
546}
547
548/*
549 * rb_wake_up_waiters - wake up tasks waiting for ring buffer input
550 *
551 * Schedules a delayed work to wake up any task that is blocked on the
552 * ring buffer waiters queue.
553 */
554static void rb_wake_up_waiters(struct irq_work *work)
555{
556 struct rb_irq_work *rbwork = container_of(work, struct rb_irq_work, work);
557
558 wake_up_all(&rbwork->waiters);
559 if (rbwork->wakeup_full) {
560 rbwork->wakeup_full = false;
561 wake_up_all(&rbwork->full_waiters);
562 }
563}
564
565/**
566 * ring_buffer_wait - wait for input to the ring buffer
567 * @buffer: buffer to wait on
568 * @cpu: the cpu buffer to wait on
569 * @full: wait until a full page is available, if @cpu != RING_BUFFER_ALL_CPUS
570 *
571 * If @cpu == RING_BUFFER_ALL_CPUS then the task will wake up as soon
572 * as data is added to any of the @buffer's cpu buffers. Otherwise
573 * it will wait for data to be added to a specific cpu buffer.
574 */
575int ring_buffer_wait(struct ring_buffer *buffer, int cpu, int full)
576{
577 struct ring_buffer_per_cpu *uninitialized_var(cpu_buffer);
578 DEFINE_WAIT(wait);
579 struct rb_irq_work *work;
580 int ret = 0;
581
582 /*
583 * Depending on what the caller is waiting for, either any
584 * data in any cpu buffer, or a specific buffer, put the
585 * caller on the appropriate wait queue.
586 */
587 if (cpu == RING_BUFFER_ALL_CPUS) {
588 work = &buffer->irq_work;
589 /* Full only makes sense on per cpu reads */
590 full = 0;
591 } else {
592 if (!cpumask_test_cpu(cpu, buffer->cpumask))
593 return -ENODEV;
594 cpu_buffer = buffer->buffers[cpu];
595 work = &cpu_buffer->irq_work;
596 }
597
598
599 while (true) {
600 if (full)
601 prepare_to_wait(&work->full_waiters, &wait, TASK_INTERRUPTIBLE);
602 else
603 prepare_to_wait(&work->waiters, &wait, TASK_INTERRUPTIBLE);
604
605 /*
606 * The events can happen in critical sections where
607 * checking a work queue can cause deadlocks.
608 * After adding a task to the queue, this flag is set
609 * only to notify events to try to wake up the queue
610 * using irq_work.
611 *
612 * We don't clear it even if the buffer is no longer
613 * empty. The flag only causes the next event to run
614 * irq_work to do the work queue wake up. The worse
615 * that can happen if we race with !trace_empty() is that
616 * an event will cause an irq_work to try to wake up
617 * an empty queue.
618 *
619 * There's no reason to protect this flag either, as
620 * the work queue and irq_work logic will do the necessary
621 * synchronization for the wake ups. The only thing
622 * that is necessary is that the wake up happens after
623 * a task has been queued. It's OK for spurious wake ups.
624 */
625 if (full)
626 work->full_waiters_pending = true;
627 else
628 work->waiters_pending = true;
629
630 if (signal_pending(current)) {
631 ret = -EINTR;
632 break;
633 }
634
635 if (cpu == RING_BUFFER_ALL_CPUS && !ring_buffer_empty(buffer))
636 break;
637
638 if (cpu != RING_BUFFER_ALL_CPUS &&
639 !ring_buffer_empty_cpu(buffer, cpu)) {
640 unsigned long flags;
641 bool pagebusy;
642 size_t nr_pages;
643 size_t dirty;
644
645 if (!full)
646 break;
647
648 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
649 pagebusy = cpu_buffer->reader_page == cpu_buffer->commit_page;
650 nr_pages = cpu_buffer->nr_pages;
651 dirty = ring_buffer_nr_dirty_pages(buffer, cpu);
652 if (!cpu_buffer->shortest_full ||
653 cpu_buffer->shortest_full < full)
654 cpu_buffer->shortest_full = full;
655 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
656 if (!pagebusy &&
657 (!nr_pages || (dirty * 100) > full * nr_pages))
658 break;
659 }
660
661 schedule();
662 }
663
664 if (full)
665 finish_wait(&work->full_waiters, &wait);
666 else
667 finish_wait(&work->waiters, &wait);
668
669 return ret;
670}
671
672/**
673 * ring_buffer_poll_wait - poll on buffer input
674 * @buffer: buffer to wait on
675 * @cpu: the cpu buffer to wait on
676 * @filp: the file descriptor
677 * @poll_table: The poll descriptor
678 *
679 * If @cpu == RING_BUFFER_ALL_CPUS then the task will wake up as soon
680 * as data is added to any of the @buffer's cpu buffers. Otherwise
681 * it will wait for data to be added to a specific cpu buffer.
682 *
683 * Returns EPOLLIN | EPOLLRDNORM if data exists in the buffers,
684 * zero otherwise.
685 */
686__poll_t ring_buffer_poll_wait(struct ring_buffer *buffer, int cpu,
687 struct file *filp, poll_table *poll_table)
688{
689 struct ring_buffer_per_cpu *cpu_buffer;
690 struct rb_irq_work *work;
691
692 if (cpu == RING_BUFFER_ALL_CPUS)
693 work = &buffer->irq_work;
694 else {
695 if (!cpumask_test_cpu(cpu, buffer->cpumask))
696 return -EINVAL;
697
698 cpu_buffer = buffer->buffers[cpu];
699 work = &cpu_buffer->irq_work;
700 }
701
702 poll_wait(filp, &work->waiters, poll_table);
703 work->waiters_pending = true;
704 /*
705 * There's a tight race between setting the waiters_pending and
706 * checking if the ring buffer is empty. Once the waiters_pending bit
707 * is set, the next event will wake the task up, but we can get stuck
708 * if there's only a single event in.
709 *
710 * FIXME: Ideally, we need a memory barrier on the writer side as well,
711 * but adding a memory barrier to all events will cause too much of a
712 * performance hit in the fast path. We only need a memory barrier when
713 * the buffer goes from empty to having content. But as this race is
714 * extremely small, and it's not a problem if another event comes in, we
715 * will fix it later.
716 */
717 smp_mb();
718
719 if ((cpu == RING_BUFFER_ALL_CPUS && !ring_buffer_empty(buffer)) ||
720 (cpu != RING_BUFFER_ALL_CPUS && !ring_buffer_empty_cpu(buffer, cpu)))
721 return EPOLLIN | EPOLLRDNORM;
722 return 0;
723}
724
725/* buffer may be either ring_buffer or ring_buffer_per_cpu */
726#define RB_WARN_ON(b, cond) \
727 ({ \
728 int _____ret = unlikely(cond); \
729 if (_____ret) { \
730 if (__same_type(*(b), struct ring_buffer_per_cpu)) { \
731 struct ring_buffer_per_cpu *__b = \
732 (void *)b; \
733 atomic_inc(&__b->buffer->record_disabled); \
734 } else \
735 atomic_inc(&b->record_disabled); \
736 WARN_ON(1); \
737 } \
738 _____ret; \
739 })
740
741/* Up this if you want to test the TIME_EXTENTS and normalization */
742#define DEBUG_SHIFT 0
743
744static inline u64 rb_time_stamp(struct ring_buffer *buffer)
745{
746 /* shift to debug/test normalization and TIME_EXTENTS */
747 return buffer->clock() << DEBUG_SHIFT;
748}
749
750u64 ring_buffer_time_stamp(struct ring_buffer *buffer, int cpu)
751{
752 u64 time;
753
754 preempt_disable_notrace();
755 time = rb_time_stamp(buffer);
756 preempt_enable_notrace();
757
758 return time;
759}
760EXPORT_SYMBOL_GPL(ring_buffer_time_stamp);
761
762void ring_buffer_normalize_time_stamp(struct ring_buffer *buffer,
763 int cpu, u64 *ts)
764{
765 /* Just stupid testing the normalize function and deltas */
766 *ts >>= DEBUG_SHIFT;
767}
768EXPORT_SYMBOL_GPL(ring_buffer_normalize_time_stamp);
769
770/*
771 * Making the ring buffer lockless makes things tricky.
772 * Although writes only happen on the CPU that they are on,
773 * and they only need to worry about interrupts. Reads can
774 * happen on any CPU.
775 *
776 * The reader page is always off the ring buffer, but when the
777 * reader finishes with a page, it needs to swap its page with
778 * a new one from the buffer. The reader needs to take from
779 * the head (writes go to the tail). But if a writer is in overwrite
780 * mode and wraps, it must push the head page forward.
781 *
782 * Here lies the problem.
783 *
784 * The reader must be careful to replace only the head page, and
785 * not another one. As described at the top of the file in the
786 * ASCII art, the reader sets its old page to point to the next
787 * page after head. It then sets the page after head to point to
788 * the old reader page. But if the writer moves the head page
789 * during this operation, the reader could end up with the tail.
790 *
791 * We use cmpxchg to help prevent this race. We also do something
792 * special with the page before head. We set the LSB to 1.
793 *
794 * When the writer must push the page forward, it will clear the
795 * bit that points to the head page, move the head, and then set
796 * the bit that points to the new head page.
797 *
798 * We also don't want an interrupt coming in and moving the head
799 * page on another writer. Thus we use the second LSB to catch
800 * that too. Thus:
801 *
802 * head->list->prev->next bit 1 bit 0
803 * ------- -------
804 * Normal page 0 0
805 * Points to head page 0 1
806 * New head page 1 0
807 *
808 * Note we can not trust the prev pointer of the head page, because:
809 *
810 * +----+ +-----+ +-----+
811 * | |------>| T |---X--->| N |
812 * | |<------| | | |
813 * +----+ +-----+ +-----+
814 * ^ ^ |
815 * | +-----+ | |
816 * +----------| R |----------+ |
817 * | |<-----------+
818 * +-----+
819 *
820 * Key: ---X--> HEAD flag set in pointer
821 * T Tail page
822 * R Reader page
823 * N Next page
824 *
825 * (see __rb_reserve_next() to see where this happens)
826 *
827 * What the above shows is that the reader just swapped out
828 * the reader page with a page in the buffer, but before it
829 * could make the new header point back to the new page added
830 * it was preempted by a writer. The writer moved forward onto
831 * the new page added by the reader and is about to move forward
832 * again.
833 *
834 * You can see, it is legitimate for the previous pointer of
835 * the head (or any page) not to point back to itself. But only
836 * temporarily.
837 */
838
839#define RB_PAGE_NORMAL 0UL
840#define RB_PAGE_HEAD 1UL
841#define RB_PAGE_UPDATE 2UL
842
843
844#define RB_FLAG_MASK 3UL
845
846/* PAGE_MOVED is not part of the mask */
847#define RB_PAGE_MOVED 4UL
848
849/*
850 * rb_list_head - remove any bit
851 */
852static struct list_head *rb_list_head(struct list_head *list)
853{
854 unsigned long val = (unsigned long)list;
855
856 return (struct list_head *)(val & ~RB_FLAG_MASK);
857}
858
859/*
860 * rb_is_head_page - test if the given page is the head page
861 *
862 * Because the reader may move the head_page pointer, we can
863 * not trust what the head page is (it may be pointing to
864 * the reader page). But if the next page is a header page,
865 * its flags will be non zero.
866 */
867static inline int
868rb_is_head_page(struct ring_buffer_per_cpu *cpu_buffer,
869 struct buffer_page *page, struct list_head *list)
870{
871 unsigned long val;
872
873 val = (unsigned long)list->next;
874
875 if ((val & ~RB_FLAG_MASK) != (unsigned long)&page->list)
876 return RB_PAGE_MOVED;
877
878 return val & RB_FLAG_MASK;
879}
880
881/*
882 * rb_is_reader_page
883 *
884 * The unique thing about the reader page, is that, if the
885 * writer is ever on it, the previous pointer never points
886 * back to the reader page.
887 */
888static bool rb_is_reader_page(struct buffer_page *page)
889{
890 struct list_head *list = page->list.prev;
891
892 return rb_list_head(list->next) != &page->list;
893}
894
895/*
896 * rb_set_list_to_head - set a list_head to be pointing to head.
897 */
898static void rb_set_list_to_head(struct ring_buffer_per_cpu *cpu_buffer,
899 struct list_head *list)
900{
901 unsigned long *ptr;
902
903 ptr = (unsigned long *)&list->next;
904 *ptr |= RB_PAGE_HEAD;
905 *ptr &= ~RB_PAGE_UPDATE;
906}
907
908/*
909 * rb_head_page_activate - sets up head page
910 */
911static void rb_head_page_activate(struct ring_buffer_per_cpu *cpu_buffer)
912{
913 struct buffer_page *head;
914
915 head = cpu_buffer->head_page;
916 if (!head)
917 return;
918
919 /*
920 * Set the previous list pointer to have the HEAD flag.
921 */
922 rb_set_list_to_head(cpu_buffer, head->list.prev);
923}
924
925static void rb_list_head_clear(struct list_head *list)
926{
927 unsigned long *ptr = (unsigned long *)&list->next;
928
929 *ptr &= ~RB_FLAG_MASK;
930}
931
932/*
933 * rb_head_page_deactivate - clears head page ptr (for free list)
934 */
935static void
936rb_head_page_deactivate(struct ring_buffer_per_cpu *cpu_buffer)
937{
938 struct list_head *hd;
939
940 /* Go through the whole list and clear any pointers found. */
941 rb_list_head_clear(cpu_buffer->pages);
942
943 list_for_each(hd, cpu_buffer->pages)
944 rb_list_head_clear(hd);
945}
946
947static int rb_head_page_set(struct ring_buffer_per_cpu *cpu_buffer,
948 struct buffer_page *head,
949 struct buffer_page *prev,
950 int old_flag, int new_flag)
951{
952 struct list_head *list;
953 unsigned long val = (unsigned long)&head->list;
954 unsigned long ret;
955
956 list = &prev->list;
957
958 val &= ~RB_FLAG_MASK;
959
960 ret = cmpxchg((unsigned long *)&list->next,
961 val | old_flag, val | new_flag);
962
963 /* check if the reader took the page */
964 if ((ret & ~RB_FLAG_MASK) != val)
965 return RB_PAGE_MOVED;
966
967 return ret & RB_FLAG_MASK;
968}
969
970static int rb_head_page_set_update(struct ring_buffer_per_cpu *cpu_buffer,
971 struct buffer_page *head,
972 struct buffer_page *prev,
973 int old_flag)
974{
975 return rb_head_page_set(cpu_buffer, head, prev,
976 old_flag, RB_PAGE_UPDATE);
977}
978
979static int rb_head_page_set_head(struct ring_buffer_per_cpu *cpu_buffer,
980 struct buffer_page *head,
981 struct buffer_page *prev,
982 int old_flag)
983{
984 return rb_head_page_set(cpu_buffer, head, prev,
985 old_flag, RB_PAGE_HEAD);
986}
987
988static int rb_head_page_set_normal(struct ring_buffer_per_cpu *cpu_buffer,
989 struct buffer_page *head,
990 struct buffer_page *prev,
991 int old_flag)
992{
993 return rb_head_page_set(cpu_buffer, head, prev,
994 old_flag, RB_PAGE_NORMAL);
995}
996
997static inline void rb_inc_page(struct ring_buffer_per_cpu *cpu_buffer,
998 struct buffer_page **bpage)
999{
1000 struct list_head *p = rb_list_head((*bpage)->list.next);
1001
1002 *bpage = list_entry(p, struct buffer_page, list);
1003}
1004
1005static struct buffer_page *
1006rb_set_head_page(struct ring_buffer_per_cpu *cpu_buffer)
1007{
1008 struct buffer_page *head;
1009 struct buffer_page *page;
1010 struct list_head *list;
1011 int i;
1012
1013 if (RB_WARN_ON(cpu_buffer, !cpu_buffer->head_page))
1014 return NULL;
1015
1016 /* sanity check */
1017 list = cpu_buffer->pages;
1018 if (RB_WARN_ON(cpu_buffer, rb_list_head(list->prev->next) != list))
1019 return NULL;
1020
1021 page = head = cpu_buffer->head_page;
1022 /*
1023 * It is possible that the writer moves the header behind
1024 * where we started, and we miss in one loop.
1025 * A second loop should grab the header, but we'll do
1026 * three loops just because I'm paranoid.
1027 */
1028 for (i = 0; i < 3; i++) {
1029 do {
1030 if (rb_is_head_page(cpu_buffer, page, page->list.prev)) {
1031 cpu_buffer->head_page = page;
1032 return page;
1033 }
1034 rb_inc_page(cpu_buffer, &page);
1035 } while (page != head);
1036 }
1037
1038 RB_WARN_ON(cpu_buffer, 1);
1039
1040 return NULL;
1041}
1042
1043static int rb_head_page_replace(struct buffer_page *old,
1044 struct buffer_page *new)
1045{
1046 unsigned long *ptr = (unsigned long *)&old->list.prev->next;
1047 unsigned long val;
1048 unsigned long ret;
1049
1050 val = *ptr & ~RB_FLAG_MASK;
1051 val |= RB_PAGE_HEAD;
1052
1053 ret = cmpxchg(ptr, val, (unsigned long)&new->list);
1054
1055 return ret == val;
1056}
1057
1058/*
1059 * rb_tail_page_update - move the tail page forward
1060 */
1061static void rb_tail_page_update(struct ring_buffer_per_cpu *cpu_buffer,
1062 struct buffer_page *tail_page,
1063 struct buffer_page *next_page)
1064{
1065 unsigned long old_entries;
1066 unsigned long old_write;
1067
1068 /*
1069 * The tail page now needs to be moved forward.
1070 *
1071 * We need to reset the tail page, but without messing
1072 * with possible erasing of data brought in by interrupts
1073 * that have moved the tail page and are currently on it.
1074 *
1075 * We add a counter to the write field to denote this.
1076 */
1077 old_write = local_add_return(RB_WRITE_INTCNT, &next_page->write);
1078 old_entries = local_add_return(RB_WRITE_INTCNT, &next_page->entries);
1079
1080 local_inc(&cpu_buffer->pages_touched);
1081 /*
1082 * Just make sure we have seen our old_write and synchronize
1083 * with any interrupts that come in.
1084 */
1085 barrier();
1086
1087 /*
1088 * If the tail page is still the same as what we think
1089 * it is, then it is up to us to update the tail
1090 * pointer.
1091 */
1092 if (tail_page == READ_ONCE(cpu_buffer->tail_page)) {
1093 /* Zero the write counter */
1094 unsigned long val = old_write & ~RB_WRITE_MASK;
1095 unsigned long eval = old_entries & ~RB_WRITE_MASK;
1096
1097 /*
1098 * This will only succeed if an interrupt did
1099 * not come in and change it. In which case, we
1100 * do not want to modify it.
1101 *
1102 * We add (void) to let the compiler know that we do not care
1103 * about the return value of these functions. We use the
1104 * cmpxchg to only update if an interrupt did not already
1105 * do it for us. If the cmpxchg fails, we don't care.
1106 */
1107 (void)local_cmpxchg(&next_page->write, old_write, val);
1108 (void)local_cmpxchg(&next_page->entries, old_entries, eval);
1109
1110 /*
1111 * No need to worry about races with clearing out the commit.
1112 * it only can increment when a commit takes place. But that
1113 * only happens in the outer most nested commit.
1114 */
1115 local_set(&next_page->page->commit, 0);
1116
1117 /* Again, either we update tail_page or an interrupt does */
1118 (void)cmpxchg(&cpu_buffer->tail_page, tail_page, next_page);
1119 }
1120}
1121
1122static int rb_check_bpage(struct ring_buffer_per_cpu *cpu_buffer,
1123 struct buffer_page *bpage)
1124{
1125 unsigned long val = (unsigned long)bpage;
1126
1127 if (RB_WARN_ON(cpu_buffer, val & RB_FLAG_MASK))
1128 return 1;
1129
1130 return 0;
1131}
1132
1133/**
1134 * rb_check_list - make sure a pointer to a list has the last bits zero
1135 */
1136static int rb_check_list(struct ring_buffer_per_cpu *cpu_buffer,
1137 struct list_head *list)
1138{
1139 if (RB_WARN_ON(cpu_buffer, rb_list_head(list->prev) != list->prev))
1140 return 1;
1141 if (RB_WARN_ON(cpu_buffer, rb_list_head(list->next) != list->next))
1142 return 1;
1143 return 0;
1144}
1145
1146/**
1147 * rb_check_pages - integrity check of buffer pages
1148 * @cpu_buffer: CPU buffer with pages to test
1149 *
1150 * As a safety measure we check to make sure the data pages have not
1151 * been corrupted.
1152 */
1153static int rb_check_pages(struct ring_buffer_per_cpu *cpu_buffer)
1154{
1155 struct list_head *head = cpu_buffer->pages;
1156 struct buffer_page *bpage, *tmp;
1157
1158 /* Reset the head page if it exists */
1159 if (cpu_buffer->head_page)
1160 rb_set_head_page(cpu_buffer);
1161
1162 rb_head_page_deactivate(cpu_buffer);
1163
1164 if (RB_WARN_ON(cpu_buffer, head->next->prev != head))
1165 return -1;
1166 if (RB_WARN_ON(cpu_buffer, head->prev->next != head))
1167 return -1;
1168
1169 if (rb_check_list(cpu_buffer, head))
1170 return -1;
1171
1172 list_for_each_entry_safe(bpage, tmp, head, list) {
1173 if (RB_WARN_ON(cpu_buffer,
1174 bpage->list.next->prev != &bpage->list))
1175 return -1;
1176 if (RB_WARN_ON(cpu_buffer,
1177 bpage->list.prev->next != &bpage->list))
1178 return -1;
1179 if (rb_check_list(cpu_buffer, &bpage->list))
1180 return -1;
1181 }
1182
1183 rb_head_page_activate(cpu_buffer);
1184
1185 return 0;
1186}
1187
1188static int __rb_allocate_pages(long nr_pages, struct list_head *pages, int cpu)
1189{
1190 struct buffer_page *bpage, *tmp;
1191 bool user_thread = current->mm != NULL;
1192 gfp_t mflags;
1193 long i;
1194
1195 /*
1196 * Check if the available memory is there first.
1197 * Note, si_mem_available() only gives us a rough estimate of available
1198 * memory. It may not be accurate. But we don't care, we just want
1199 * to prevent doing any allocation when it is obvious that it is
1200 * not going to succeed.
1201 */
1202 i = si_mem_available();
1203 if (i < nr_pages)
1204 return -ENOMEM;
1205
1206 /*
1207 * __GFP_RETRY_MAYFAIL flag makes sure that the allocation fails
1208 * gracefully without invoking oom-killer and the system is not
1209 * destabilized.
1210 */
1211 mflags = GFP_KERNEL | __GFP_RETRY_MAYFAIL;
1212
1213 /*
1214 * If a user thread allocates too much, and si_mem_available()
1215 * reports there's enough memory, even though there is not.
1216 * Make sure the OOM killer kills this thread. This can happen
1217 * even with RETRY_MAYFAIL because another task may be doing
1218 * an allocation after this task has taken all memory.
1219 * This is the task the OOM killer needs to take out during this
1220 * loop, even if it was triggered by an allocation somewhere else.
1221 */
1222 if (user_thread)
1223 set_current_oom_origin();
1224 for (i = 0; i < nr_pages; i++) {
1225 struct page *page;
1226
1227 bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
1228 mflags, cpu_to_node(cpu));
1229 if (!bpage)
1230 goto free_pages;
1231
1232 list_add(&bpage->list, pages);
1233
1234 page = alloc_pages_node(cpu_to_node(cpu), mflags, 0);
1235 if (!page)
1236 goto free_pages;
1237 bpage->page = page_address(page);
1238 rb_init_page(bpage->page);
1239
1240 if (user_thread && fatal_signal_pending(current))
1241 goto free_pages;
1242 }
1243 if (user_thread)
1244 clear_current_oom_origin();
1245
1246 return 0;
1247
1248free_pages:
1249 list_for_each_entry_safe(bpage, tmp, pages, list) {
1250 list_del_init(&bpage->list);
1251 free_buffer_page(bpage);
1252 }
1253 if (user_thread)
1254 clear_current_oom_origin();
1255
1256 return -ENOMEM;
1257}
1258
1259static int rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
1260 unsigned long nr_pages)
1261{
1262 LIST_HEAD(pages);
1263
1264 WARN_ON(!nr_pages);
1265
1266 if (__rb_allocate_pages(nr_pages, &pages, cpu_buffer->cpu))
1267 return -ENOMEM;
1268
1269 /*
1270 * The ring buffer page list is a circular list that does not
1271 * start and end with a list head. All page list items point to
1272 * other pages.
1273 */
1274 cpu_buffer->pages = pages.next;
1275 list_del(&pages);
1276
1277 cpu_buffer->nr_pages = nr_pages;
1278
1279 rb_check_pages(cpu_buffer);
1280
1281 return 0;
1282}
1283
1284static struct ring_buffer_per_cpu *
1285rb_allocate_cpu_buffer(struct ring_buffer *buffer, long nr_pages, int cpu)
1286{
1287 struct ring_buffer_per_cpu *cpu_buffer;
1288 struct buffer_page *bpage;
1289 struct page *page;
1290 int ret;
1291
1292 cpu_buffer = kzalloc_node(ALIGN(sizeof(*cpu_buffer), cache_line_size()),
1293 GFP_KERNEL, cpu_to_node(cpu));
1294 if (!cpu_buffer)
1295 return NULL;
1296
1297 cpu_buffer->cpu = cpu;
1298 cpu_buffer->buffer = buffer;
1299 raw_spin_lock_init(&cpu_buffer->reader_lock);
1300 lockdep_set_class(&cpu_buffer->reader_lock, buffer->reader_lock_key);
1301 cpu_buffer->lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
1302 INIT_WORK(&cpu_buffer->update_pages_work, update_pages_handler);
1303 init_completion(&cpu_buffer->update_done);
1304 init_irq_work(&cpu_buffer->irq_work.work, rb_wake_up_waiters);
1305 init_waitqueue_head(&cpu_buffer->irq_work.waiters);
1306 init_waitqueue_head(&cpu_buffer->irq_work.full_waiters);
1307
1308 bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
1309 GFP_KERNEL, cpu_to_node(cpu));
1310 if (!bpage)
1311 goto fail_free_buffer;
1312
1313 rb_check_bpage(cpu_buffer, bpage);
1314
1315 cpu_buffer->reader_page = bpage;
1316 page = alloc_pages_node(cpu_to_node(cpu), GFP_KERNEL, 0);
1317 if (!page)
1318 goto fail_free_reader;
1319 bpage->page = page_address(page);
1320 rb_init_page(bpage->page);
1321
1322 INIT_LIST_HEAD(&cpu_buffer->reader_page->list);
1323 INIT_LIST_HEAD(&cpu_buffer->new_pages);
1324
1325 ret = rb_allocate_pages(cpu_buffer, nr_pages);
1326 if (ret < 0)
1327 goto fail_free_reader;
1328
1329 cpu_buffer->head_page
1330 = list_entry(cpu_buffer->pages, struct buffer_page, list);
1331 cpu_buffer->tail_page = cpu_buffer->commit_page = cpu_buffer->head_page;
1332
1333 rb_head_page_activate(cpu_buffer);
1334
1335 return cpu_buffer;
1336
1337 fail_free_reader:
1338 free_buffer_page(cpu_buffer->reader_page);
1339
1340 fail_free_buffer:
1341 kfree(cpu_buffer);
1342 return NULL;
1343}
1344
1345static void rb_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
1346{
1347 struct list_head *head = cpu_buffer->pages;
1348 struct buffer_page *bpage, *tmp;
1349
1350 free_buffer_page(cpu_buffer->reader_page);
1351
1352 rb_head_page_deactivate(cpu_buffer);
1353
1354 if (head) {
1355 list_for_each_entry_safe(bpage, tmp, head, list) {
1356 list_del_init(&bpage->list);
1357 free_buffer_page(bpage);
1358 }
1359 bpage = list_entry(head, struct buffer_page, list);
1360 free_buffer_page(bpage);
1361 }
1362
1363 kfree(cpu_buffer);
1364}
1365
1366/**
1367 * __ring_buffer_alloc - allocate a new ring_buffer
1368 * @size: the size in bytes per cpu that is needed.
1369 * @flags: attributes to set for the ring buffer.
1370 *
1371 * Currently the only flag that is available is the RB_FL_OVERWRITE
1372 * flag. This flag means that the buffer will overwrite old data
1373 * when the buffer wraps. If this flag is not set, the buffer will
1374 * drop data when the tail hits the head.
1375 */
1376struct ring_buffer *__ring_buffer_alloc(unsigned long size, unsigned flags,
1377 struct lock_class_key *key)
1378{
1379 struct ring_buffer *buffer;
1380 long nr_pages;
1381 int bsize;
1382 int cpu;
1383 int ret;
1384
1385 /* keep it in its own cache line */
1386 buffer = kzalloc(ALIGN(sizeof(*buffer), cache_line_size()),
1387 GFP_KERNEL);
1388 if (!buffer)
1389 return NULL;
1390
1391 if (!zalloc_cpumask_var(&buffer->cpumask, GFP_KERNEL))
1392 goto fail_free_buffer;
1393
1394 nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
1395 buffer->flags = flags;
1396 buffer->clock = trace_clock_local;
1397 buffer->reader_lock_key = key;
1398
1399 init_irq_work(&buffer->irq_work.work, rb_wake_up_waiters);
1400 init_waitqueue_head(&buffer->irq_work.waiters);
1401
1402 /* need at least two pages */
1403 if (nr_pages < 2)
1404 nr_pages = 2;
1405
1406 buffer->cpus = nr_cpu_ids;
1407
1408 bsize = sizeof(void *) * nr_cpu_ids;
1409 buffer->buffers = kzalloc(ALIGN(bsize, cache_line_size()),
1410 GFP_KERNEL);
1411 if (!buffer->buffers)
1412 goto fail_free_cpumask;
1413
1414 cpu = raw_smp_processor_id();
1415 cpumask_set_cpu(cpu, buffer->cpumask);
1416 buffer->buffers[cpu] = rb_allocate_cpu_buffer(buffer, nr_pages, cpu);
1417 if (!buffer->buffers[cpu])
1418 goto fail_free_buffers;
1419
1420 ret = cpuhp_state_add_instance(CPUHP_TRACE_RB_PREPARE, &buffer->node);
1421 if (ret < 0)
1422 goto fail_free_buffers;
1423
1424 mutex_init(&buffer->mutex);
1425
1426 return buffer;
1427
1428 fail_free_buffers:
1429 for_each_buffer_cpu(buffer, cpu) {
1430 if (buffer->buffers[cpu])
1431 rb_free_cpu_buffer(buffer->buffers[cpu]);
1432 }
1433 kfree(buffer->buffers);
1434
1435 fail_free_cpumask:
1436 free_cpumask_var(buffer->cpumask);
1437
1438 fail_free_buffer:
1439 kfree(buffer);
1440 return NULL;
1441}
1442EXPORT_SYMBOL_GPL(__ring_buffer_alloc);
1443
1444/**
1445 * ring_buffer_free - free a ring buffer.
1446 * @buffer: the buffer to free.
1447 */
1448void
1449ring_buffer_free(struct ring_buffer *buffer)
1450{
1451 int cpu;
1452
1453 cpuhp_state_remove_instance(CPUHP_TRACE_RB_PREPARE, &buffer->node);
1454
1455 for_each_buffer_cpu(buffer, cpu)
1456 rb_free_cpu_buffer(buffer->buffers[cpu]);
1457
1458 kfree(buffer->buffers);
1459 free_cpumask_var(buffer->cpumask);
1460
1461 kfree(buffer);
1462}
1463EXPORT_SYMBOL_GPL(ring_buffer_free);
1464
1465void ring_buffer_set_clock(struct ring_buffer *buffer,
1466 u64 (*clock)(void))
1467{
1468 buffer->clock = clock;
1469}
1470
1471void ring_buffer_set_time_stamp_abs(struct ring_buffer *buffer, bool abs)
1472{
1473 buffer->time_stamp_abs = abs;
1474}
1475
1476bool ring_buffer_time_stamp_abs(struct ring_buffer *buffer)
1477{
1478 return buffer->time_stamp_abs;
1479}
1480
1481static void rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer);
1482
1483static inline unsigned long rb_page_entries(struct buffer_page *bpage)
1484{
1485 return local_read(&bpage->entries) & RB_WRITE_MASK;
1486}
1487
1488static inline unsigned long rb_page_write(struct buffer_page *bpage)
1489{
1490 return local_read(&bpage->write) & RB_WRITE_MASK;
1491}
1492
1493static int
1494rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned long nr_pages)
1495{
1496 struct list_head *tail_page, *to_remove, *next_page;
1497 struct buffer_page *to_remove_page, *tmp_iter_page;
1498 struct buffer_page *last_page, *first_page;
1499 unsigned long nr_removed;
1500 unsigned long head_bit;
1501 int page_entries;
1502
1503 head_bit = 0;
1504
1505 raw_spin_lock_irq(&cpu_buffer->reader_lock);
1506 atomic_inc(&cpu_buffer->record_disabled);
1507 /*
1508 * We don't race with the readers since we have acquired the reader
1509 * lock. We also don't race with writers after disabling recording.
1510 * This makes it easy to figure out the first and the last page to be
1511 * removed from the list. We unlink all the pages in between including
1512 * the first and last pages. This is done in a busy loop so that we
1513 * lose the least number of traces.
1514 * The pages are freed after we restart recording and unlock readers.
1515 */
1516 tail_page = &cpu_buffer->tail_page->list;
1517
1518 /*
1519 * tail page might be on reader page, we remove the next page
1520 * from the ring buffer
1521 */
1522 if (cpu_buffer->tail_page == cpu_buffer->reader_page)
1523 tail_page = rb_list_head(tail_page->next);
1524 to_remove = tail_page;
1525
1526 /* start of pages to remove */
1527 first_page = list_entry(rb_list_head(to_remove->next),
1528 struct buffer_page, list);
1529
1530 for (nr_removed = 0; nr_removed < nr_pages; nr_removed++) {
1531 to_remove = rb_list_head(to_remove)->next;
1532 head_bit |= (unsigned long)to_remove & RB_PAGE_HEAD;
1533 }
1534
1535 next_page = rb_list_head(to_remove)->next;
1536
1537 /*
1538 * Now we remove all pages between tail_page and next_page.
1539 * Make sure that we have head_bit value preserved for the
1540 * next page
1541 */
1542 tail_page->next = (struct list_head *)((unsigned long)next_page |
1543 head_bit);
1544 next_page = rb_list_head(next_page);
1545 next_page->prev = tail_page;
1546
1547 /* make sure pages points to a valid page in the ring buffer */
1548 cpu_buffer->pages = next_page;
1549
1550 /* update head page */
1551 if (head_bit)
1552 cpu_buffer->head_page = list_entry(next_page,
1553 struct buffer_page, list);
1554
1555 /*
1556 * change read pointer to make sure any read iterators reset
1557 * themselves
1558 */
1559 cpu_buffer->read = 0;
1560
1561 /* pages are removed, resume tracing and then free the pages */
1562 atomic_dec(&cpu_buffer->record_disabled);
1563 raw_spin_unlock_irq(&cpu_buffer->reader_lock);
1564
1565 RB_WARN_ON(cpu_buffer, list_empty(cpu_buffer->pages));
1566
1567 /* last buffer page to remove */
1568 last_page = list_entry(rb_list_head(to_remove), struct buffer_page,
1569 list);
1570 tmp_iter_page = first_page;
1571
1572 do {
1573 cond_resched();
1574
1575 to_remove_page = tmp_iter_page;
1576 rb_inc_page(cpu_buffer, &tmp_iter_page);
1577
1578 /* update the counters */
1579 page_entries = rb_page_entries(to_remove_page);
1580 if (page_entries) {
1581 /*
1582 * If something was added to this page, it was full
1583 * since it is not the tail page. So we deduct the
1584 * bytes consumed in ring buffer from here.
1585 * Increment overrun to account for the lost events.
1586 */
1587 local_add(page_entries, &cpu_buffer->overrun);
1588 local_sub(BUF_PAGE_SIZE, &cpu_buffer->entries_bytes);
1589 }
1590
1591 /*
1592 * We have already removed references to this list item, just
1593 * free up the buffer_page and its page
1594 */
1595 free_buffer_page(to_remove_page);
1596 nr_removed--;
1597
1598 } while (to_remove_page != last_page);
1599
1600 RB_WARN_ON(cpu_buffer, nr_removed);
1601
1602 return nr_removed == 0;
1603}
1604
1605static int
1606rb_insert_pages(struct ring_buffer_per_cpu *cpu_buffer)
1607{
1608 struct list_head *pages = &cpu_buffer->new_pages;
1609 int retries, success;
1610
1611 raw_spin_lock_irq(&cpu_buffer->reader_lock);
1612 /*
1613 * We are holding the reader lock, so the reader page won't be swapped
1614 * in the ring buffer. Now we are racing with the writer trying to
1615 * move head page and the tail page.
1616 * We are going to adapt the reader page update process where:
1617 * 1. We first splice the start and end of list of new pages between
1618 * the head page and its previous page.
1619 * 2. We cmpxchg the prev_page->next to point from head page to the
1620 * start of new pages list.
1621 * 3. Finally, we update the head->prev to the end of new list.
1622 *
1623 * We will try this process 10 times, to make sure that we don't keep
1624 * spinning.
1625 */
1626 retries = 10;
1627 success = 0;
1628 while (retries--) {
1629 struct list_head *head_page, *prev_page, *r;
1630 struct list_head *last_page, *first_page;
1631 struct list_head *head_page_with_bit;
1632
1633 head_page = &rb_set_head_page(cpu_buffer)->list;
1634 if (!head_page)
1635 break;
1636 prev_page = head_page->prev;
1637
1638 first_page = pages->next;
1639 last_page = pages->prev;
1640
1641 head_page_with_bit = (struct list_head *)
1642 ((unsigned long)head_page | RB_PAGE_HEAD);
1643
1644 last_page->next = head_page_with_bit;
1645 first_page->prev = prev_page;
1646
1647 r = cmpxchg(&prev_page->next, head_page_with_bit, first_page);
1648
1649 if (r == head_page_with_bit) {
1650 /*
1651 * yay, we replaced the page pointer to our new list,
1652 * now, we just have to update to head page's prev
1653 * pointer to point to end of list
1654 */
1655 head_page->prev = last_page;
1656 success = 1;
1657 break;
1658 }
1659 }
1660
1661 if (success)
1662 INIT_LIST_HEAD(pages);
1663 /*
1664 * If we weren't successful in adding in new pages, warn and stop
1665 * tracing
1666 */
1667 RB_WARN_ON(cpu_buffer, !success);
1668 raw_spin_unlock_irq(&cpu_buffer->reader_lock);
1669
1670 /* free pages if they weren't inserted */
1671 if (!success) {
1672 struct buffer_page *bpage, *tmp;
1673 list_for_each_entry_safe(bpage, tmp, &cpu_buffer->new_pages,
1674 list) {
1675 list_del_init(&bpage->list);
1676 free_buffer_page(bpage);
1677 }
1678 }
1679 return success;
1680}
1681
1682static void rb_update_pages(struct ring_buffer_per_cpu *cpu_buffer)
1683{
1684 int success;
1685
1686 if (cpu_buffer->nr_pages_to_update > 0)
1687 success = rb_insert_pages(cpu_buffer);
1688 else
1689 success = rb_remove_pages(cpu_buffer,
1690 -cpu_buffer->nr_pages_to_update);
1691
1692 if (success)
1693 cpu_buffer->nr_pages += cpu_buffer->nr_pages_to_update;
1694}
1695
1696static void update_pages_handler(struct work_struct *work)
1697{
1698 struct ring_buffer_per_cpu *cpu_buffer = container_of(work,
1699 struct ring_buffer_per_cpu, update_pages_work);
1700 rb_update_pages(cpu_buffer);
1701 complete(&cpu_buffer->update_done);
1702}
1703
1704/**
1705 * ring_buffer_resize - resize the ring buffer
1706 * @buffer: the buffer to resize.
1707 * @size: the new size.
1708 * @cpu_id: the cpu buffer to resize
1709 *
1710 * Minimum size is 2 * BUF_PAGE_SIZE.
1711 *
1712 * Returns 0 on success and < 0 on failure.
1713 */
1714int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size,
1715 int cpu_id)
1716{
1717 struct ring_buffer_per_cpu *cpu_buffer;
1718 unsigned long nr_pages;
1719 int cpu, err = 0;
1720
1721 /*
1722 * Always succeed at resizing a non-existent buffer:
1723 */
1724 if (!buffer)
1725 return size;
1726
1727 /* Make sure the requested buffer exists */
1728 if (cpu_id != RING_BUFFER_ALL_CPUS &&
1729 !cpumask_test_cpu(cpu_id, buffer->cpumask))
1730 return size;
1731
1732 nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
1733
1734 /* we need a minimum of two pages */
1735 if (nr_pages < 2)
1736 nr_pages = 2;
1737
1738 size = nr_pages * BUF_PAGE_SIZE;
1739
1740 /*
1741 * Don't succeed if resizing is disabled, as a reader might be
1742 * manipulating the ring buffer and is expecting a sane state while
1743 * this is true.
1744 */
1745 if (atomic_read(&buffer->resize_disabled))
1746 return -EBUSY;
1747
1748 /* prevent another thread from changing buffer sizes */
1749 mutex_lock(&buffer->mutex);
1750
1751 if (cpu_id == RING_BUFFER_ALL_CPUS) {
1752 /* calculate the pages to update */
1753 for_each_buffer_cpu(buffer, cpu) {
1754 cpu_buffer = buffer->buffers[cpu];
1755
1756 cpu_buffer->nr_pages_to_update = nr_pages -
1757 cpu_buffer->nr_pages;
1758 /*
1759 * nothing more to do for removing pages or no update
1760 */
1761 if (cpu_buffer->nr_pages_to_update <= 0)
1762 continue;
1763 /*
1764 * to add pages, make sure all new pages can be
1765 * allocated without receiving ENOMEM
1766 */
1767 INIT_LIST_HEAD(&cpu_buffer->new_pages);
1768 if (__rb_allocate_pages(cpu_buffer->nr_pages_to_update,
1769 &cpu_buffer->new_pages, cpu)) {
1770 /* not enough memory for new pages */
1771 err = -ENOMEM;
1772 goto out_err;
1773 }
1774 }
1775
1776 get_online_cpus();
1777 /*
1778 * Fire off all the required work handlers
1779 * We can't schedule on offline CPUs, but it's not necessary
1780 * since we can change their buffer sizes without any race.
1781 */
1782 for_each_buffer_cpu(buffer, cpu) {
1783 cpu_buffer = buffer->buffers[cpu];
1784 if (!cpu_buffer->nr_pages_to_update)
1785 continue;
1786
1787 /* Can't run something on an offline CPU. */
1788 if (!cpu_online(cpu)) {
1789 rb_update_pages(cpu_buffer);
1790 cpu_buffer->nr_pages_to_update = 0;
1791 } else {
1792 schedule_work_on(cpu,
1793 &cpu_buffer->update_pages_work);
1794 }
1795 }
1796
1797 /* wait for all the updates to complete */
1798 for_each_buffer_cpu(buffer, cpu) {
1799 cpu_buffer = buffer->buffers[cpu];
1800 if (!cpu_buffer->nr_pages_to_update)
1801 continue;
1802
1803 if (cpu_online(cpu))
1804 wait_for_completion(&cpu_buffer->update_done);
1805 cpu_buffer->nr_pages_to_update = 0;
1806 }
1807
1808 put_online_cpus();
1809 } else {
1810 /* Make sure this CPU has been initialized */
1811 if (!cpumask_test_cpu(cpu_id, buffer->cpumask))
1812 goto out;
1813
1814 cpu_buffer = buffer->buffers[cpu_id];
1815
1816 if (nr_pages == cpu_buffer->nr_pages)
1817 goto out;
1818
1819 cpu_buffer->nr_pages_to_update = nr_pages -
1820 cpu_buffer->nr_pages;
1821
1822 INIT_LIST_HEAD(&cpu_buffer->new_pages);
1823 if (cpu_buffer->nr_pages_to_update > 0 &&
1824 __rb_allocate_pages(cpu_buffer->nr_pages_to_update,
1825 &cpu_buffer->new_pages, cpu_id)) {
1826 err = -ENOMEM;
1827 goto out_err;
1828 }
1829
1830 get_online_cpus();
1831
1832 /* Can't run something on an offline CPU. */
1833 if (!cpu_online(cpu_id))
1834 rb_update_pages(cpu_buffer);
1835 else {
1836 schedule_work_on(cpu_id,
1837 &cpu_buffer->update_pages_work);
1838 wait_for_completion(&cpu_buffer->update_done);
1839 }
1840
1841 cpu_buffer->nr_pages_to_update = 0;
1842 put_online_cpus();
1843 }
1844
1845 out:
1846 /*
1847 * The ring buffer resize can happen with the ring buffer
1848 * enabled, so that the update disturbs the tracing as little
1849 * as possible. But if the buffer is disabled, we do not need
1850 * to worry about that, and we can take the time to verify
1851 * that the buffer is not corrupt.
1852 */
1853 if (atomic_read(&buffer->record_disabled)) {
1854 atomic_inc(&buffer->record_disabled);
1855 /*
1856 * Even though the buffer was disabled, we must make sure
1857 * that it is truly disabled before calling rb_check_pages.
1858 * There could have been a race between checking
1859 * record_disable and incrementing it.
1860 */
1861 synchronize_rcu();
1862 for_each_buffer_cpu(buffer, cpu) {
1863 cpu_buffer = buffer->buffers[cpu];
1864 rb_check_pages(cpu_buffer);
1865 }
1866 atomic_dec(&buffer->record_disabled);
1867 }
1868
1869 mutex_unlock(&buffer->mutex);
1870 return size;
1871
1872 out_err:
1873 for_each_buffer_cpu(buffer, cpu) {
1874 struct buffer_page *bpage, *tmp;
1875
1876 cpu_buffer = buffer->buffers[cpu];
1877 cpu_buffer->nr_pages_to_update = 0;
1878
1879 if (list_empty(&cpu_buffer->new_pages))
1880 continue;
1881
1882 list_for_each_entry_safe(bpage, tmp, &cpu_buffer->new_pages,
1883 list) {
1884 list_del_init(&bpage->list);
1885 free_buffer_page(bpage);
1886 }
1887 }
1888 mutex_unlock(&buffer->mutex);
1889 return err;
1890}
1891EXPORT_SYMBOL_GPL(ring_buffer_resize);
1892
1893void ring_buffer_change_overwrite(struct ring_buffer *buffer, int val)
1894{
1895 mutex_lock(&buffer->mutex);
1896 if (val)
1897 buffer->flags |= RB_FL_OVERWRITE;
1898 else
1899 buffer->flags &= ~RB_FL_OVERWRITE;
1900 mutex_unlock(&buffer->mutex);
1901}
1902EXPORT_SYMBOL_GPL(ring_buffer_change_overwrite);
1903
1904static __always_inline void *__rb_page_index(struct buffer_page *bpage, unsigned index)
1905{
1906 return bpage->page->data + index;
1907}
1908
1909static __always_inline struct ring_buffer_event *
1910rb_reader_event(struct ring_buffer_per_cpu *cpu_buffer)
1911{
1912 return __rb_page_index(cpu_buffer->reader_page,
1913 cpu_buffer->reader_page->read);
1914}
1915
1916static __always_inline struct ring_buffer_event *
1917rb_iter_head_event(struct ring_buffer_iter *iter)
1918{
1919 return __rb_page_index(iter->head_page, iter->head);
1920}
1921
1922static __always_inline unsigned rb_page_commit(struct buffer_page *bpage)
1923{
1924 return local_read(&bpage->page->commit);
1925}
1926
1927/* Size is determined by what has been committed */
1928static __always_inline unsigned rb_page_size(struct buffer_page *bpage)
1929{
1930 return rb_page_commit(bpage);
1931}
1932
1933static __always_inline unsigned
1934rb_commit_index(struct ring_buffer_per_cpu *cpu_buffer)
1935{
1936 return rb_page_commit(cpu_buffer->commit_page);
1937}
1938
1939static __always_inline unsigned
1940rb_event_index(struct ring_buffer_event *event)
1941{
1942 unsigned long addr = (unsigned long)event;
1943
1944 return (addr & ~PAGE_MASK) - BUF_PAGE_HDR_SIZE;
1945}
1946
1947static void rb_inc_iter(struct ring_buffer_iter *iter)
1948{
1949 struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
1950
1951 /*
1952 * The iterator could be on the reader page (it starts there).
1953 * But the head could have moved, since the reader was
1954 * found. Check for this case and assign the iterator
1955 * to the head page instead of next.
1956 */
1957 if (iter->head_page == cpu_buffer->reader_page)
1958 iter->head_page = rb_set_head_page(cpu_buffer);
1959 else
1960 rb_inc_page(cpu_buffer, &iter->head_page);
1961
1962 iter->read_stamp = iter->head_page->page->time_stamp;
1963 iter->head = 0;
1964}
1965
1966/*
1967 * rb_handle_head_page - writer hit the head page
1968 *
1969 * Returns: +1 to retry page
1970 * 0 to continue
1971 * -1 on error
1972 */
1973static int
1974rb_handle_head_page(struct ring_buffer_per_cpu *cpu_buffer,
1975 struct buffer_page *tail_page,
1976 struct buffer_page *next_page)
1977{
1978 struct buffer_page *new_head;
1979 int entries;
1980 int type;
1981 int ret;
1982
1983 entries = rb_page_entries(next_page);
1984
1985 /*
1986 * The hard part is here. We need to move the head
1987 * forward, and protect against both readers on
1988 * other CPUs and writers coming in via interrupts.
1989 */
1990 type = rb_head_page_set_update(cpu_buffer, next_page, tail_page,
1991 RB_PAGE_HEAD);
1992
1993 /*
1994 * type can be one of four:
1995 * NORMAL - an interrupt already moved it for us
1996 * HEAD - we are the first to get here.
1997 * UPDATE - we are the interrupt interrupting
1998 * a current move.
1999 * MOVED - a reader on another CPU moved the next
2000 * pointer to its reader page. Give up
2001 * and try again.
2002 */
2003
2004 switch (type) {
2005 case RB_PAGE_HEAD:
2006 /*
2007 * We changed the head to UPDATE, thus
2008 * it is our responsibility to update
2009 * the counters.
2010 */
2011 local_add(entries, &cpu_buffer->overrun);
2012 local_sub(BUF_PAGE_SIZE, &cpu_buffer->entries_bytes);
2013
2014 /*
2015 * The entries will be zeroed out when we move the
2016 * tail page.
2017 */
2018
2019 /* still more to do */
2020 break;
2021
2022 case RB_PAGE_UPDATE:
2023 /*
2024 * This is an interrupt that interrupt the
2025 * previous update. Still more to do.
2026 */
2027 break;
2028 case RB_PAGE_NORMAL:
2029 /*
2030 * An interrupt came in before the update
2031 * and processed this for us.
2032 * Nothing left to do.
2033 */
2034 return 1;
2035 case RB_PAGE_MOVED:
2036 /*
2037 * The reader is on another CPU and just did
2038 * a swap with our next_page.
2039 * Try again.
2040 */
2041 return 1;
2042 default:
2043 RB_WARN_ON(cpu_buffer, 1); /* WTF??? */
2044 return -1;
2045 }
2046
2047 /*
2048 * Now that we are here, the old head pointer is
2049 * set to UPDATE. This will keep the reader from
2050 * swapping the head page with the reader page.
2051 * The reader (on another CPU) will spin till
2052 * we are finished.
2053 *
2054 * We just need to protect against interrupts
2055 * doing the job. We will set the next pointer
2056 * to HEAD. After that, we set the old pointer
2057 * to NORMAL, but only if it was HEAD before.
2058 * otherwise we are an interrupt, and only
2059 * want the outer most commit to reset it.
2060 */
2061 new_head = next_page;
2062 rb_inc_page(cpu_buffer, &new_head);
2063
2064 ret = rb_head_page_set_head(cpu_buffer, new_head, next_page,
2065 RB_PAGE_NORMAL);
2066
2067 /*
2068 * Valid returns are:
2069 * HEAD - an interrupt came in and already set it.
2070 * NORMAL - One of two things:
2071 * 1) We really set it.
2072 * 2) A bunch of interrupts came in and moved
2073 * the page forward again.
2074 */
2075 switch (ret) {
2076 case RB_PAGE_HEAD:
2077 case RB_PAGE_NORMAL:
2078 /* OK */
2079 break;
2080 default:
2081 RB_WARN_ON(cpu_buffer, 1);
2082 return -1;
2083 }
2084
2085 /*
2086 * It is possible that an interrupt came in,
2087 * set the head up, then more interrupts came in
2088 * and moved it again. When we get back here,
2089 * the page would have been set to NORMAL but we
2090 * just set it back to HEAD.
2091 *
2092 * How do you detect this? Well, if that happened
2093 * the tail page would have moved.
2094 */
2095 if (ret == RB_PAGE_NORMAL) {
2096 struct buffer_page *buffer_tail_page;
2097
2098 buffer_tail_page = READ_ONCE(cpu_buffer->tail_page);
2099 /*
2100 * If the tail had moved passed next, then we need
2101 * to reset the pointer.
2102 */
2103 if (buffer_tail_page != tail_page &&
2104 buffer_tail_page != next_page)
2105 rb_head_page_set_normal(cpu_buffer, new_head,
2106 next_page,
2107 RB_PAGE_HEAD);
2108 }
2109
2110 /*
2111 * If this was the outer most commit (the one that
2112 * changed the original pointer from HEAD to UPDATE),
2113 * then it is up to us to reset it to NORMAL.
2114 */
2115 if (type == RB_PAGE_HEAD) {
2116 ret = rb_head_page_set_normal(cpu_buffer, next_page,
2117 tail_page,
2118 RB_PAGE_UPDATE);
2119 if (RB_WARN_ON(cpu_buffer,
2120 ret != RB_PAGE_UPDATE))
2121 return -1;
2122 }
2123
2124 return 0;
2125}
2126
2127static inline void
2128rb_reset_tail(struct ring_buffer_per_cpu *cpu_buffer,
2129 unsigned long tail, struct rb_event_info *info)
2130{
2131 struct buffer_page *tail_page = info->tail_page;
2132 struct ring_buffer_event *event;
2133 unsigned long length = info->length;
2134
2135 /*
2136 * Only the event that crossed the page boundary
2137 * must fill the old tail_page with padding.
2138 */
2139 if (tail >= BUF_PAGE_SIZE) {
2140 /*
2141 * If the page was filled, then we still need
2142 * to update the real_end. Reset it to zero
2143 * and the reader will ignore it.
2144 */
2145 if (tail == BUF_PAGE_SIZE)
2146 tail_page->real_end = 0;
2147
2148 local_sub(length, &tail_page->write);
2149 return;
2150 }
2151
2152 event = __rb_page_index(tail_page, tail);
2153
2154 /* account for padding bytes */
2155 local_add(BUF_PAGE_SIZE - tail, &cpu_buffer->entries_bytes);
2156
2157 /*
2158 * Save the original length to the meta data.
2159 * This will be used by the reader to add lost event
2160 * counter.
2161 */
2162 tail_page->real_end = tail;
2163
2164 /*
2165 * If this event is bigger than the minimum size, then
2166 * we need to be careful that we don't subtract the
2167 * write counter enough to allow another writer to slip
2168 * in on this page.
2169 * We put in a discarded commit instead, to make sure
2170 * that this space is not used again.
2171 *
2172 * If we are less than the minimum size, we don't need to
2173 * worry about it.
2174 */
2175 if (tail > (BUF_PAGE_SIZE - RB_EVNT_MIN_SIZE)) {
2176 /* No room for any events */
2177
2178 /* Mark the rest of the page with padding */
2179 rb_event_set_padding(event);
2180
2181 /* Set the write back to the previous setting */
2182 local_sub(length, &tail_page->write);
2183 return;
2184 }
2185
2186 /* Put in a discarded event */
2187 event->array[0] = (BUF_PAGE_SIZE - tail) - RB_EVNT_HDR_SIZE;
2188 event->type_len = RINGBUF_TYPE_PADDING;
2189 /* time delta must be non zero */
2190 event->time_delta = 1;
2191
2192 /* Set write to end of buffer */
2193 length = (tail + length) - BUF_PAGE_SIZE;
2194 local_sub(length, &tail_page->write);
2195}
2196
2197static inline void rb_end_commit(struct ring_buffer_per_cpu *cpu_buffer);
2198
2199/*
2200 * This is the slow path, force gcc not to inline it.
2201 */
2202static noinline struct ring_buffer_event *
2203rb_move_tail(struct ring_buffer_per_cpu *cpu_buffer,
2204 unsigned long tail, struct rb_event_info *info)
2205{
2206 struct buffer_page *tail_page = info->tail_page;
2207 struct buffer_page *commit_page = cpu_buffer->commit_page;
2208 struct ring_buffer *buffer = cpu_buffer->buffer;
2209 struct buffer_page *next_page;
2210 int ret;
2211
2212 next_page = tail_page;
2213
2214 rb_inc_page(cpu_buffer, &next_page);
2215
2216 /*
2217 * If for some reason, we had an interrupt storm that made
2218 * it all the way around the buffer, bail, and warn
2219 * about it.
2220 */
2221 if (unlikely(next_page == commit_page)) {
2222 local_inc(&cpu_buffer->commit_overrun);
2223 goto out_reset;
2224 }
2225
2226 /*
2227 * This is where the fun begins!
2228 *
2229 * We are fighting against races between a reader that
2230 * could be on another CPU trying to swap its reader
2231 * page with the buffer head.
2232 *
2233 * We are also fighting against interrupts coming in and
2234 * moving the head or tail on us as well.
2235 *
2236 * If the next page is the head page then we have filled
2237 * the buffer, unless the commit page is still on the
2238 * reader page.
2239 */
2240 if (rb_is_head_page(cpu_buffer, next_page, &tail_page->list)) {
2241
2242 /*
2243 * If the commit is not on the reader page, then
2244 * move the header page.
2245 */
2246 if (!rb_is_reader_page(cpu_buffer->commit_page)) {
2247 /*
2248 * If we are not in overwrite mode,
2249 * this is easy, just stop here.
2250 */
2251 if (!(buffer->flags & RB_FL_OVERWRITE)) {
2252 local_inc(&cpu_buffer->dropped_events);
2253 goto out_reset;
2254 }
2255
2256 ret = rb_handle_head_page(cpu_buffer,
2257 tail_page,
2258 next_page);
2259 if (ret < 0)
2260 goto out_reset;
2261 if (ret)
2262 goto out_again;
2263 } else {
2264 /*
2265 * We need to be careful here too. The
2266 * commit page could still be on the reader
2267 * page. We could have a small buffer, and
2268 * have filled up the buffer with events
2269 * from interrupts and such, and wrapped.
2270 *
2271 * Note, if the tail page is also the on the
2272 * reader_page, we let it move out.
2273 */
2274 if (unlikely((cpu_buffer->commit_page !=
2275 cpu_buffer->tail_page) &&
2276 (cpu_buffer->commit_page ==
2277 cpu_buffer->reader_page))) {
2278 local_inc(&cpu_buffer->commit_overrun);
2279 goto out_reset;
2280 }
2281 }
2282 }
2283
2284 rb_tail_page_update(cpu_buffer, tail_page, next_page);
2285
2286 out_again:
2287
2288 rb_reset_tail(cpu_buffer, tail, info);
2289
2290 /* Commit what we have for now. */
2291 rb_end_commit(cpu_buffer);
2292 /* rb_end_commit() decs committing */
2293 local_inc(&cpu_buffer->committing);
2294
2295 /* fail and let the caller try again */
2296 return ERR_PTR(-EAGAIN);
2297
2298 out_reset:
2299 /* reset write */
2300 rb_reset_tail(cpu_buffer, tail, info);
2301
2302 return NULL;
2303}
2304
2305/* Slow path, do not inline */
2306static noinline struct ring_buffer_event *
2307rb_add_time_stamp(struct ring_buffer_event *event, u64 delta, bool abs)
2308{
2309 if (abs)
2310 event->type_len = RINGBUF_TYPE_TIME_STAMP;
2311 else
2312 event->type_len = RINGBUF_TYPE_TIME_EXTEND;
2313
2314 /* Not the first event on the page, or not delta? */
2315 if (abs || rb_event_index(event)) {
2316 event->time_delta = delta & TS_MASK;
2317 event->array[0] = delta >> TS_SHIFT;
2318 } else {
2319 /* nope, just zero it */
2320 event->time_delta = 0;
2321 event->array[0] = 0;
2322 }
2323
2324 return skip_time_extend(event);
2325}
2326
2327static inline bool rb_event_is_commit(struct ring_buffer_per_cpu *cpu_buffer,
2328 struct ring_buffer_event *event);
2329
2330/**
2331 * rb_update_event - update event type and data
2332 * @event: the event to update
2333 * @type: the type of event
2334 * @length: the size of the event field in the ring buffer
2335 *
2336 * Update the type and data fields of the event. The length
2337 * is the actual size that is written to the ring buffer,
2338 * and with this, we can determine what to place into the
2339 * data field.
2340 */
2341static void
2342rb_update_event(struct ring_buffer_per_cpu *cpu_buffer,
2343 struct ring_buffer_event *event,
2344 struct rb_event_info *info)
2345{
2346 unsigned length = info->length;
2347 u64 delta = info->delta;
2348
2349 /* Only a commit updates the timestamp */
2350 if (unlikely(!rb_event_is_commit(cpu_buffer, event)))
2351 delta = 0;
2352
2353 /*
2354 * If we need to add a timestamp, then we
2355 * add it to the start of the reserved space.
2356 */
2357 if (unlikely(info->add_timestamp)) {
2358 bool abs = ring_buffer_time_stamp_abs(cpu_buffer->buffer);
2359
2360 event = rb_add_time_stamp(event, info->delta, abs);
2361 length -= RB_LEN_TIME_EXTEND;
2362 delta = 0;
2363 }
2364
2365 event->time_delta = delta;
2366 length -= RB_EVNT_HDR_SIZE;
2367 if (length > RB_MAX_SMALL_DATA) {
2368 event->type_len = 0;
2369 event->array[0] = length;
2370 } else
2371 event->type_len = DIV_ROUND_UP(length, RB_ALIGNMENT);
2372}
2373
2374static unsigned rb_calculate_event_length(unsigned length)
2375{
2376 struct ring_buffer_event event; /* Used only for sizeof array */
2377
2378 /* zero length can cause confusions */
2379 if (!length)
2380 length++;
2381
2382 if (length > RB_MAX_SMALL_DATA)
2383 length += sizeof(event.array[0]);
2384
2385 length += RB_EVNT_HDR_SIZE;
2386 length = ALIGN(length, RB_ALIGNMENT);
2387
2388 /*
2389 * In case the time delta is larger than the 27 bits for it
2390 * in the header, we need to add a timestamp. If another
2391 * event comes in when trying to discard this one to increase
2392 * the length, then the timestamp will be added in the allocated
2393 * space of this event. If length is bigger than the size needed
2394 * for the TIME_EXTEND, then padding has to be used. The events
2395 * length must be either RB_LEN_TIME_EXTEND, or greater than or equal
2396 * to RB_LEN_TIME_EXTEND + 8, as 8 is the minimum size for padding.
2397 * As length is a multiple of 4, we only need to worry if it
2398 * is 12 (RB_LEN_TIME_EXTEND + 4).
2399 */
2400 if (length == RB_LEN_TIME_EXTEND + RB_ALIGNMENT)
2401 length += RB_ALIGNMENT;
2402
2403 return length;
2404}
2405
2406#ifndef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
2407static inline bool sched_clock_stable(void)
2408{
2409 return true;
2410}
2411#endif
2412
2413static inline int
2414rb_try_to_discard(struct ring_buffer_per_cpu *cpu_buffer,
2415 struct ring_buffer_event *event)
2416{
2417 unsigned long new_index, old_index;
2418 struct buffer_page *bpage;
2419 unsigned long index;
2420 unsigned long addr;
2421
2422 new_index = rb_event_index(event);
2423 old_index = new_index + rb_event_ts_length(event);
2424 addr = (unsigned long)event;
2425 addr &= PAGE_MASK;
2426
2427 bpage = READ_ONCE(cpu_buffer->tail_page);
2428
2429 if (bpage->page == (void *)addr && rb_page_write(bpage) == old_index) {
2430 unsigned long write_mask =
2431 local_read(&bpage->write) & ~RB_WRITE_MASK;
2432 unsigned long event_length = rb_event_length(event);
2433 /*
2434 * This is on the tail page. It is possible that
2435 * a write could come in and move the tail page
2436 * and write to the next page. That is fine
2437 * because we just shorten what is on this page.
2438 */
2439 old_index += write_mask;
2440 new_index += write_mask;
2441 index = local_cmpxchg(&bpage->write, old_index, new_index);
2442 if (index == old_index) {
2443 /* update counters */
2444 local_sub(event_length, &cpu_buffer->entries_bytes);
2445 return 1;
2446 }
2447 }
2448
2449 /* could not discard */
2450 return 0;
2451}
2452
2453static void rb_start_commit(struct ring_buffer_per_cpu *cpu_buffer)
2454{
2455 local_inc(&cpu_buffer->committing);
2456 local_inc(&cpu_buffer->commits);
2457}
2458
2459static __always_inline void
2460rb_set_commit_to_write(struct ring_buffer_per_cpu *cpu_buffer)
2461{
2462 unsigned long max_count;
2463
2464 /*
2465 * We only race with interrupts and NMIs on this CPU.
2466 * If we own the commit event, then we can commit
2467 * all others that interrupted us, since the interruptions
2468 * are in stack format (they finish before they come
2469 * back to us). This allows us to do a simple loop to
2470 * assign the commit to the tail.
2471 */
2472 again:
2473 max_count = cpu_buffer->nr_pages * 100;
2474
2475 while (cpu_buffer->commit_page != READ_ONCE(cpu_buffer->tail_page)) {
2476 if (RB_WARN_ON(cpu_buffer, !(--max_count)))
2477 return;
2478 if (RB_WARN_ON(cpu_buffer,
2479 rb_is_reader_page(cpu_buffer->tail_page)))
2480 return;
2481 local_set(&cpu_buffer->commit_page->page->commit,
2482 rb_page_write(cpu_buffer->commit_page));
2483 rb_inc_page(cpu_buffer, &cpu_buffer->commit_page);
2484 /* Only update the write stamp if the page has an event */
2485 if (rb_page_write(cpu_buffer->commit_page))
2486 cpu_buffer->write_stamp =
2487 cpu_buffer->commit_page->page->time_stamp;
2488 /* add barrier to keep gcc from optimizing too much */
2489 barrier();
2490 }
2491 while (rb_commit_index(cpu_buffer) !=
2492 rb_page_write(cpu_buffer->commit_page)) {
2493
2494 local_set(&cpu_buffer->commit_page->page->commit,
2495 rb_page_write(cpu_buffer->commit_page));
2496 RB_WARN_ON(cpu_buffer,
2497 local_read(&cpu_buffer->commit_page->page->commit) &
2498 ~RB_WRITE_MASK);
2499 barrier();
2500 }
2501
2502 /* again, keep gcc from optimizing */
2503 barrier();
2504
2505 /*
2506 * If an interrupt came in just after the first while loop
2507 * and pushed the tail page forward, we will be left with
2508 * a dangling commit that will never go forward.
2509 */
2510 if (unlikely(cpu_buffer->commit_page != READ_ONCE(cpu_buffer->tail_page)))
2511 goto again;
2512}
2513
2514static __always_inline void rb_end_commit(struct ring_buffer_per_cpu *cpu_buffer)
2515{
2516 unsigned long commits;
2517
2518 if (RB_WARN_ON(cpu_buffer,
2519 !local_read(&cpu_buffer->committing)))
2520 return;
2521
2522 again:
2523 commits = local_read(&cpu_buffer->commits);
2524 /* synchronize with interrupts */
2525 barrier();
2526 if (local_read(&cpu_buffer->committing) == 1)
2527 rb_set_commit_to_write(cpu_buffer);
2528
2529 local_dec(&cpu_buffer->committing);
2530
2531 /* synchronize with interrupts */
2532 barrier();
2533
2534 /*
2535 * Need to account for interrupts coming in between the
2536 * updating of the commit page and the clearing of the
2537 * committing counter.
2538 */
2539 if (unlikely(local_read(&cpu_buffer->commits) != commits) &&
2540 !local_read(&cpu_buffer->committing)) {
2541 local_inc(&cpu_buffer->committing);
2542 goto again;
2543 }
2544}
2545
2546static inline void rb_event_discard(struct ring_buffer_event *event)
2547{
2548 if (extended_time(event))
2549 event = skip_time_extend(event);
2550
2551 /* array[0] holds the actual length for the discarded event */
2552 event->array[0] = rb_event_data_length(event) - RB_EVNT_HDR_SIZE;
2553 event->type_len = RINGBUF_TYPE_PADDING;
2554 /* time delta must be non zero */
2555 if (!event->time_delta)
2556 event->time_delta = 1;
2557}
2558
2559static __always_inline bool
2560rb_event_is_commit(struct ring_buffer_per_cpu *cpu_buffer,
2561 struct ring_buffer_event *event)
2562{
2563 unsigned long addr = (unsigned long)event;
2564 unsigned long index;
2565
2566 index = rb_event_index(event);
2567 addr &= PAGE_MASK;
2568
2569 return cpu_buffer->commit_page->page == (void *)addr &&
2570 rb_commit_index(cpu_buffer) == index;
2571}
2572
2573static __always_inline void
2574rb_update_write_stamp(struct ring_buffer_per_cpu *cpu_buffer,
2575 struct ring_buffer_event *event)
2576{
2577 u64 delta;
2578
2579 /*
2580 * The event first in the commit queue updates the
2581 * time stamp.
2582 */
2583 if (rb_event_is_commit(cpu_buffer, event)) {
2584 /*
2585 * A commit event that is first on a page
2586 * updates the write timestamp with the page stamp
2587 */
2588 if (!rb_event_index(event))
2589 cpu_buffer->write_stamp =
2590 cpu_buffer->commit_page->page->time_stamp;
2591 else if (event->type_len == RINGBUF_TYPE_TIME_EXTEND) {
2592 delta = ring_buffer_event_time_stamp(event);
2593 cpu_buffer->write_stamp += delta;
2594 } else if (event->type_len == RINGBUF_TYPE_TIME_STAMP) {
2595 delta = ring_buffer_event_time_stamp(event);
2596 cpu_buffer->write_stamp = delta;
2597 } else
2598 cpu_buffer->write_stamp += event->time_delta;
2599 }
2600}
2601
2602static void rb_commit(struct ring_buffer_per_cpu *cpu_buffer,
2603 struct ring_buffer_event *event)
2604{
2605 local_inc(&cpu_buffer->entries);
2606 rb_update_write_stamp(cpu_buffer, event);
2607 rb_end_commit(cpu_buffer);
2608}
2609
2610static __always_inline void
2611rb_wakeups(struct ring_buffer *buffer, struct ring_buffer_per_cpu *cpu_buffer)
2612{
2613 size_t nr_pages;
2614 size_t dirty;
2615 size_t full;
2616
2617 if (buffer->irq_work.waiters_pending) {
2618 buffer->irq_work.waiters_pending = false;
2619 /* irq_work_queue() supplies it's own memory barriers */
2620 irq_work_queue(&buffer->irq_work.work);
2621 }
2622
2623 if (cpu_buffer->irq_work.waiters_pending) {
2624 cpu_buffer->irq_work.waiters_pending = false;
2625 /* irq_work_queue() supplies it's own memory barriers */
2626 irq_work_queue(&cpu_buffer->irq_work.work);
2627 }
2628
2629 if (cpu_buffer->last_pages_touch == local_read(&cpu_buffer->pages_touched))
2630 return;
2631
2632 if (cpu_buffer->reader_page == cpu_buffer->commit_page)
2633 return;
2634
2635 if (!cpu_buffer->irq_work.full_waiters_pending)
2636 return;
2637
2638 cpu_buffer->last_pages_touch = local_read(&cpu_buffer->pages_touched);
2639
2640 full = cpu_buffer->shortest_full;
2641 nr_pages = cpu_buffer->nr_pages;
2642 dirty = ring_buffer_nr_dirty_pages(buffer, cpu_buffer->cpu);
2643 if (full && nr_pages && (dirty * 100) <= full * nr_pages)
2644 return;
2645
2646 cpu_buffer->irq_work.wakeup_full = true;
2647 cpu_buffer->irq_work.full_waiters_pending = false;
2648 /* irq_work_queue() supplies it's own memory barriers */
2649 irq_work_queue(&cpu_buffer->irq_work.work);
2650}
2651
2652/*
2653 * The lock and unlock are done within a preempt disable section.
2654 * The current_context per_cpu variable can only be modified
2655 * by the current task between lock and unlock. But it can
2656 * be modified more than once via an interrupt. To pass this
2657 * information from the lock to the unlock without having to
2658 * access the 'in_interrupt()' functions again (which do show
2659 * a bit of overhead in something as critical as function tracing,
2660 * we use a bitmask trick.
2661 *
2662 * bit 0 = NMI context
2663 * bit 1 = IRQ context
2664 * bit 2 = SoftIRQ context
2665 * bit 3 = normal context.
2666 *
2667 * This works because this is the order of contexts that can
2668 * preempt other contexts. A SoftIRQ never preempts an IRQ
2669 * context.
2670 *
2671 * When the context is determined, the corresponding bit is
2672 * checked and set (if it was set, then a recursion of that context
2673 * happened).
2674 *
2675 * On unlock, we need to clear this bit. To do so, just subtract
2676 * 1 from the current_context and AND it to itself.
2677 *
2678 * (binary)
2679 * 101 - 1 = 100
2680 * 101 & 100 = 100 (clearing bit zero)
2681 *
2682 * 1010 - 1 = 1001
2683 * 1010 & 1001 = 1000 (clearing bit 1)
2684 *
2685 * The least significant bit can be cleared this way, and it
2686 * just so happens that it is the same bit corresponding to
2687 * the current context.
2688 */
2689
2690static __always_inline int
2691trace_recursive_lock(struct ring_buffer_per_cpu *cpu_buffer)
2692{
2693 unsigned int val = cpu_buffer->current_context;
2694 unsigned long pc = preempt_count();
2695 int bit;
2696
2697 if (!(pc & (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET)))
2698 bit = RB_CTX_NORMAL;
2699 else
2700 bit = pc & NMI_MASK ? RB_CTX_NMI :
2701 pc & HARDIRQ_MASK ? RB_CTX_IRQ : RB_CTX_SOFTIRQ;
2702
2703 if (unlikely(val & (1 << (bit + cpu_buffer->nest))))
2704 return 1;
2705
2706 val |= (1 << (bit + cpu_buffer->nest));
2707 cpu_buffer->current_context = val;
2708
2709 return 0;
2710}
2711
2712static __always_inline void
2713trace_recursive_unlock(struct ring_buffer_per_cpu *cpu_buffer)
2714{
2715 cpu_buffer->current_context &=
2716 cpu_buffer->current_context - (1 << cpu_buffer->nest);
2717}
2718
2719/* The recursive locking above uses 4 bits */
2720#define NESTED_BITS 4
2721
2722/**
2723 * ring_buffer_nest_start - Allow to trace while nested
2724 * @buffer: The ring buffer to modify
2725 *
2726 * The ring buffer has a safety mechanism to prevent recursion.
2727 * But there may be a case where a trace needs to be done while
2728 * tracing something else. In this case, calling this function
2729 * will allow this function to nest within a currently active
2730 * ring_buffer_lock_reserve().
2731 *
2732 * Call this function before calling another ring_buffer_lock_reserve() and
2733 * call ring_buffer_nest_end() after the nested ring_buffer_unlock_commit().
2734 */
2735void ring_buffer_nest_start(struct ring_buffer *buffer)
2736{
2737 struct ring_buffer_per_cpu *cpu_buffer;
2738 int cpu;
2739
2740 /* Enabled by ring_buffer_nest_end() */
2741 preempt_disable_notrace();
2742 cpu = raw_smp_processor_id();
2743 cpu_buffer = buffer->buffers[cpu];
2744 /* This is the shift value for the above recursive locking */
2745 cpu_buffer->nest += NESTED_BITS;
2746}
2747
2748/**
2749 * ring_buffer_nest_end - Allow to trace while nested
2750 * @buffer: The ring buffer to modify
2751 *
2752 * Must be called after ring_buffer_nest_start() and after the
2753 * ring_buffer_unlock_commit().
2754 */
2755void ring_buffer_nest_end(struct ring_buffer *buffer)
2756{
2757 struct ring_buffer_per_cpu *cpu_buffer;
2758 int cpu;
2759
2760 /* disabled by ring_buffer_nest_start() */
2761 cpu = raw_smp_processor_id();
2762 cpu_buffer = buffer->buffers[cpu];
2763 /* This is the shift value for the above recursive locking */
2764 cpu_buffer->nest -= NESTED_BITS;
2765 preempt_enable_notrace();
2766}
2767
2768/**
2769 * ring_buffer_unlock_commit - commit a reserved
2770 * @buffer: The buffer to commit to
2771 * @event: The event pointer to commit.
2772 *
2773 * This commits the data to the ring buffer, and releases any locks held.
2774 *
2775 * Must be paired with ring_buffer_lock_reserve.
2776 */
2777int ring_buffer_unlock_commit(struct ring_buffer *buffer,
2778 struct ring_buffer_event *event)
2779{
2780 struct ring_buffer_per_cpu *cpu_buffer;
2781 int cpu = raw_smp_processor_id();
2782
2783 cpu_buffer = buffer->buffers[cpu];
2784
2785 rb_commit(cpu_buffer, event);
2786
2787 rb_wakeups(buffer, cpu_buffer);
2788
2789 trace_recursive_unlock(cpu_buffer);
2790
2791 preempt_enable_notrace();
2792
2793 return 0;
2794}
2795EXPORT_SYMBOL_GPL(ring_buffer_unlock_commit);
2796
2797static noinline void
2798rb_handle_timestamp(struct ring_buffer_per_cpu *cpu_buffer,
2799 struct rb_event_info *info)
2800{
2801 WARN_ONCE(info->delta > (1ULL << 59),
2802 KERN_WARNING "Delta way too big! %llu ts=%llu write stamp = %llu\n%s",
2803 (unsigned long long)info->delta,
2804 (unsigned long long)info->ts,
2805 (unsigned long long)cpu_buffer->write_stamp,
2806 sched_clock_stable() ? "" :
2807 "If you just came from a suspend/resume,\n"
2808 "please switch to the trace global clock:\n"
2809 " echo global > /sys/kernel/debug/tracing/trace_clock\n"
2810 "or add trace_clock=global to the kernel command line\n");
2811 info->add_timestamp = 1;
2812}
2813
2814static struct ring_buffer_event *
2815__rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
2816 struct rb_event_info *info)
2817{
2818 struct ring_buffer_event *event;
2819 struct buffer_page *tail_page;
2820 unsigned long tail, write;
2821
2822 /*
2823 * If the time delta since the last event is too big to
2824 * hold in the time field of the event, then we append a
2825 * TIME EXTEND event ahead of the data event.
2826 */
2827 if (unlikely(info->add_timestamp))
2828 info->length += RB_LEN_TIME_EXTEND;
2829
2830 /* Don't let the compiler play games with cpu_buffer->tail_page */
2831 tail_page = info->tail_page = READ_ONCE(cpu_buffer->tail_page);
2832 write = local_add_return(info->length, &tail_page->write);
2833
2834 /* set write to only the index of the write */
2835 write &= RB_WRITE_MASK;
2836 tail = write - info->length;
2837
2838 /*
2839 * If this is the first commit on the page, then it has the same
2840 * timestamp as the page itself.
2841 */
2842 if (!tail && !ring_buffer_time_stamp_abs(cpu_buffer->buffer))
2843 info->delta = 0;
2844
2845 /* See if we shot pass the end of this buffer page */
2846 if (unlikely(write > BUF_PAGE_SIZE))
2847 return rb_move_tail(cpu_buffer, tail, info);
2848
2849 /* We reserved something on the buffer */
2850
2851 event = __rb_page_index(tail_page, tail);
2852 rb_update_event(cpu_buffer, event, info);
2853
2854 local_inc(&tail_page->entries);
2855
2856 /*
2857 * If this is the first commit on the page, then update
2858 * its timestamp.
2859 */
2860 if (!tail)
2861 tail_page->page->time_stamp = info->ts;
2862
2863 /* account for these added bytes */
2864 local_add(info->length, &cpu_buffer->entries_bytes);
2865
2866 return event;
2867}
2868
2869static __always_inline struct ring_buffer_event *
2870rb_reserve_next_event(struct ring_buffer *buffer,
2871 struct ring_buffer_per_cpu *cpu_buffer,
2872 unsigned long length)
2873{
2874 struct ring_buffer_event *event;
2875 struct rb_event_info info;
2876 int nr_loops = 0;
2877 u64 diff;
2878
2879 rb_start_commit(cpu_buffer);
2880
2881#ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
2882 /*
2883 * Due to the ability to swap a cpu buffer from a buffer
2884 * it is possible it was swapped before we committed.
2885 * (committing stops a swap). We check for it here and
2886 * if it happened, we have to fail the write.
2887 */
2888 barrier();
2889 if (unlikely(READ_ONCE(cpu_buffer->buffer) != buffer)) {
2890 local_dec(&cpu_buffer->committing);
2891 local_dec(&cpu_buffer->commits);
2892 return NULL;
2893 }
2894#endif
2895
2896 info.length = rb_calculate_event_length(length);
2897 again:
2898 info.add_timestamp = 0;
2899 info.delta = 0;
2900
2901 /*
2902 * We allow for interrupts to reenter here and do a trace.
2903 * If one does, it will cause this original code to loop
2904 * back here. Even with heavy interrupts happening, this
2905 * should only happen a few times in a row. If this happens
2906 * 1000 times in a row, there must be either an interrupt
2907 * storm or we have something buggy.
2908 * Bail!
2909 */
2910 if (RB_WARN_ON(cpu_buffer, ++nr_loops > 1000))
2911 goto out_fail;
2912
2913 info.ts = rb_time_stamp(cpu_buffer->buffer);
2914 diff = info.ts - cpu_buffer->write_stamp;
2915
2916 /* make sure this diff is calculated here */
2917 barrier();
2918
2919 if (ring_buffer_time_stamp_abs(buffer)) {
2920 info.delta = info.ts;
2921 rb_handle_timestamp(cpu_buffer, &info);
2922 } else /* Did the write stamp get updated already? */
2923 if (likely(info.ts >= cpu_buffer->write_stamp)) {
2924 info.delta = diff;
2925 if (unlikely(test_time_stamp(info.delta)))
2926 rb_handle_timestamp(cpu_buffer, &info);
2927 }
2928
2929 event = __rb_reserve_next(cpu_buffer, &info);
2930
2931 if (unlikely(PTR_ERR(event) == -EAGAIN)) {
2932 if (info.add_timestamp)
2933 info.length -= RB_LEN_TIME_EXTEND;
2934 goto again;
2935 }
2936
2937 if (!event)
2938 goto out_fail;
2939
2940 return event;
2941
2942 out_fail:
2943 rb_end_commit(cpu_buffer);
2944 return NULL;
2945}
2946
2947/**
2948 * ring_buffer_lock_reserve - reserve a part of the buffer
2949 * @buffer: the ring buffer to reserve from
2950 * @length: the length of the data to reserve (excluding event header)
2951 *
2952 * Returns a reserved event on the ring buffer to copy directly to.
2953 * The user of this interface will need to get the body to write into
2954 * and can use the ring_buffer_event_data() interface.
2955 *
2956 * The length is the length of the data needed, not the event length
2957 * which also includes the event header.
2958 *
2959 * Must be paired with ring_buffer_unlock_commit, unless NULL is returned.
2960 * If NULL is returned, then nothing has been allocated or locked.
2961 */
2962struct ring_buffer_event *
2963ring_buffer_lock_reserve(struct ring_buffer *buffer, unsigned long length)
2964{
2965 struct ring_buffer_per_cpu *cpu_buffer;
2966 struct ring_buffer_event *event;
2967 int cpu;
2968
2969 /* If we are tracing schedule, we don't want to recurse */
2970 preempt_disable_notrace();
2971
2972 if (unlikely(atomic_read(&buffer->record_disabled)))
2973 goto out;
2974
2975 cpu = raw_smp_processor_id();
2976
2977 if (unlikely(!cpumask_test_cpu(cpu, buffer->cpumask)))
2978 goto out;
2979
2980 cpu_buffer = buffer->buffers[cpu];
2981
2982 if (unlikely(atomic_read(&cpu_buffer->record_disabled)))
2983 goto out;
2984
2985 if (unlikely(length > BUF_MAX_DATA_SIZE))
2986 goto out;
2987
2988 if (unlikely(trace_recursive_lock(cpu_buffer)))
2989 goto out;
2990
2991 event = rb_reserve_next_event(buffer, cpu_buffer, length);
2992 if (!event)
2993 goto out_unlock;
2994
2995 return event;
2996
2997 out_unlock:
2998 trace_recursive_unlock(cpu_buffer);
2999 out:
3000 preempt_enable_notrace();
3001 return NULL;
3002}
3003EXPORT_SYMBOL_GPL(ring_buffer_lock_reserve);
3004
3005/*
3006 * Decrement the entries to the page that an event is on.
3007 * The event does not even need to exist, only the pointer
3008 * to the page it is on. This may only be called before the commit
3009 * takes place.
3010 */
3011static inline void
3012rb_decrement_entry(struct ring_buffer_per_cpu *cpu_buffer,
3013 struct ring_buffer_event *event)
3014{
3015 unsigned long addr = (unsigned long)event;
3016 struct buffer_page *bpage = cpu_buffer->commit_page;
3017 struct buffer_page *start;
3018
3019 addr &= PAGE_MASK;
3020
3021 /* Do the likely case first */
3022 if (likely(bpage->page == (void *)addr)) {
3023 local_dec(&bpage->entries);
3024 return;
3025 }
3026
3027 /*
3028 * Because the commit page may be on the reader page we
3029 * start with the next page and check the end loop there.
3030 */
3031 rb_inc_page(cpu_buffer, &bpage);
3032 start = bpage;
3033 do {
3034 if (bpage->page == (void *)addr) {
3035 local_dec(&bpage->entries);
3036 return;
3037 }
3038 rb_inc_page(cpu_buffer, &bpage);
3039 } while (bpage != start);
3040
3041 /* commit not part of this buffer?? */
3042 RB_WARN_ON(cpu_buffer, 1);
3043}
3044
3045/**
3046 * ring_buffer_commit_discard - discard an event that has not been committed
3047 * @buffer: the ring buffer
3048 * @event: non committed event to discard
3049 *
3050 * Sometimes an event that is in the ring buffer needs to be ignored.
3051 * This function lets the user discard an event in the ring buffer
3052 * and then that event will not be read later.
3053 *
3054 * This function only works if it is called before the item has been
3055 * committed. It will try to free the event from the ring buffer
3056 * if another event has not been added behind it.
3057 *
3058 * If another event has been added behind it, it will set the event
3059 * up as discarded, and perform the commit.
3060 *
3061 * If this function is called, do not call ring_buffer_unlock_commit on
3062 * the event.
3063 */
3064void ring_buffer_discard_commit(struct ring_buffer *buffer,
3065 struct ring_buffer_event *event)
3066{
3067 struct ring_buffer_per_cpu *cpu_buffer;
3068 int cpu;
3069
3070 /* The event is discarded regardless */
3071 rb_event_discard(event);
3072
3073 cpu = smp_processor_id();
3074 cpu_buffer = buffer->buffers[cpu];
3075
3076 /*
3077 * This must only be called if the event has not been
3078 * committed yet. Thus we can assume that preemption
3079 * is still disabled.
3080 */
3081 RB_WARN_ON(buffer, !local_read(&cpu_buffer->committing));
3082
3083 rb_decrement_entry(cpu_buffer, event);
3084 if (rb_try_to_discard(cpu_buffer, event))
3085 goto out;
3086
3087 /*
3088 * The commit is still visible by the reader, so we
3089 * must still update the timestamp.
3090 */
3091 rb_update_write_stamp(cpu_buffer, event);
3092 out:
3093 rb_end_commit(cpu_buffer);
3094
3095 trace_recursive_unlock(cpu_buffer);
3096
3097 preempt_enable_notrace();
3098
3099}
3100EXPORT_SYMBOL_GPL(ring_buffer_discard_commit);
3101
3102/**
3103 * ring_buffer_write - write data to the buffer without reserving
3104 * @buffer: The ring buffer to write to.
3105 * @length: The length of the data being written (excluding the event header)
3106 * @data: The data to write to the buffer.
3107 *
3108 * This is like ring_buffer_lock_reserve and ring_buffer_unlock_commit as
3109 * one function. If you already have the data to write to the buffer, it
3110 * may be easier to simply call this function.
3111 *
3112 * Note, like ring_buffer_lock_reserve, the length is the length of the data
3113 * and not the length of the event which would hold the header.
3114 */
3115int ring_buffer_write(struct ring_buffer *buffer,
3116 unsigned long length,
3117 void *data)
3118{
3119 struct ring_buffer_per_cpu *cpu_buffer;
3120 struct ring_buffer_event *event;
3121 void *body;
3122 int ret = -EBUSY;
3123 int cpu;
3124
3125 preempt_disable_notrace();
3126
3127 if (atomic_read(&buffer->record_disabled))
3128 goto out;
3129
3130 cpu = raw_smp_processor_id();
3131
3132 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3133 goto out;
3134
3135 cpu_buffer = buffer->buffers[cpu];
3136
3137 if (atomic_read(&cpu_buffer->record_disabled))
3138 goto out;
3139
3140 if (length > BUF_MAX_DATA_SIZE)
3141 goto out;
3142
3143 if (unlikely(trace_recursive_lock(cpu_buffer)))
3144 goto out;
3145
3146 event = rb_reserve_next_event(buffer, cpu_buffer, length);
3147 if (!event)
3148 goto out_unlock;
3149
3150 body = rb_event_data(event);
3151
3152 memcpy(body, data, length);
3153
3154 rb_commit(cpu_buffer, event);
3155
3156 rb_wakeups(buffer, cpu_buffer);
3157
3158 ret = 0;
3159
3160 out_unlock:
3161 trace_recursive_unlock(cpu_buffer);
3162
3163 out:
3164 preempt_enable_notrace();
3165
3166 return ret;
3167}
3168EXPORT_SYMBOL_GPL(ring_buffer_write);
3169
3170static bool rb_per_cpu_empty(struct ring_buffer_per_cpu *cpu_buffer)
3171{
3172 struct buffer_page *reader = cpu_buffer->reader_page;
3173 struct buffer_page *head = rb_set_head_page(cpu_buffer);
3174 struct buffer_page *commit = cpu_buffer->commit_page;
3175
3176 /* In case of error, head will be NULL */
3177 if (unlikely(!head))
3178 return true;
3179
3180 return reader->read == rb_page_commit(reader) &&
3181 (commit == reader ||
3182 (commit == head &&
3183 head->read == rb_page_commit(commit)));
3184}
3185
3186/**
3187 * ring_buffer_record_disable - stop all writes into the buffer
3188 * @buffer: The ring buffer to stop writes to.
3189 *
3190 * This prevents all writes to the buffer. Any attempt to write
3191 * to the buffer after this will fail and return NULL.
3192 *
3193 * The caller should call synchronize_rcu() after this.
3194 */
3195void ring_buffer_record_disable(struct ring_buffer *buffer)
3196{
3197 atomic_inc(&buffer->record_disabled);
3198}
3199EXPORT_SYMBOL_GPL(ring_buffer_record_disable);
3200
3201/**
3202 * ring_buffer_record_enable - enable writes to the buffer
3203 * @buffer: The ring buffer to enable writes
3204 *
3205 * Note, multiple disables will need the same number of enables
3206 * to truly enable the writing (much like preempt_disable).
3207 */
3208void ring_buffer_record_enable(struct ring_buffer *buffer)
3209{
3210 atomic_dec(&buffer->record_disabled);
3211}
3212EXPORT_SYMBOL_GPL(ring_buffer_record_enable);
3213
3214/**
3215 * ring_buffer_record_off - stop all writes into the buffer
3216 * @buffer: The ring buffer to stop writes to.
3217 *
3218 * This prevents all writes to the buffer. Any attempt to write
3219 * to the buffer after this will fail and return NULL.
3220 *
3221 * This is different than ring_buffer_record_disable() as
3222 * it works like an on/off switch, where as the disable() version
3223 * must be paired with a enable().
3224 */
3225void ring_buffer_record_off(struct ring_buffer *buffer)
3226{
3227 unsigned int rd;
3228 unsigned int new_rd;
3229
3230 do {
3231 rd = atomic_read(&buffer->record_disabled);
3232 new_rd = rd | RB_BUFFER_OFF;
3233 } while (atomic_cmpxchg(&buffer->record_disabled, rd, new_rd) != rd);
3234}
3235EXPORT_SYMBOL_GPL(ring_buffer_record_off);
3236
3237/**
3238 * ring_buffer_record_on - restart writes into the buffer
3239 * @buffer: The ring buffer to start writes to.
3240 *
3241 * This enables all writes to the buffer that was disabled by
3242 * ring_buffer_record_off().
3243 *
3244 * This is different than ring_buffer_record_enable() as
3245 * it works like an on/off switch, where as the enable() version
3246 * must be paired with a disable().
3247 */
3248void ring_buffer_record_on(struct ring_buffer *buffer)
3249{
3250 unsigned int rd;
3251 unsigned int new_rd;
3252
3253 do {
3254 rd = atomic_read(&buffer->record_disabled);
3255 new_rd = rd & ~RB_BUFFER_OFF;
3256 } while (atomic_cmpxchg(&buffer->record_disabled, rd, new_rd) != rd);
3257}
3258EXPORT_SYMBOL_GPL(ring_buffer_record_on);
3259
3260/**
3261 * ring_buffer_record_is_on - return true if the ring buffer can write
3262 * @buffer: The ring buffer to see if write is enabled
3263 *
3264 * Returns true if the ring buffer is in a state that it accepts writes.
3265 */
3266bool ring_buffer_record_is_on(struct ring_buffer *buffer)
3267{
3268 return !atomic_read(&buffer->record_disabled);
3269}
3270
3271/**
3272 * ring_buffer_record_is_set_on - return true if the ring buffer is set writable
3273 * @buffer: The ring buffer to see if write is set enabled
3274 *
3275 * Returns true if the ring buffer is set writable by ring_buffer_record_on().
3276 * Note that this does NOT mean it is in a writable state.
3277 *
3278 * It may return true when the ring buffer has been disabled by
3279 * ring_buffer_record_disable(), as that is a temporary disabling of
3280 * the ring buffer.
3281 */
3282bool ring_buffer_record_is_set_on(struct ring_buffer *buffer)
3283{
3284 return !(atomic_read(&buffer->record_disabled) & RB_BUFFER_OFF);
3285}
3286
3287/**
3288 * ring_buffer_record_disable_cpu - stop all writes into the cpu_buffer
3289 * @buffer: The ring buffer to stop writes to.
3290 * @cpu: The CPU buffer to stop
3291 *
3292 * This prevents all writes to the buffer. Any attempt to write
3293 * to the buffer after this will fail and return NULL.
3294 *
3295 * The caller should call synchronize_rcu() after this.
3296 */
3297void ring_buffer_record_disable_cpu(struct ring_buffer *buffer, int cpu)
3298{
3299 struct ring_buffer_per_cpu *cpu_buffer;
3300
3301 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3302 return;
3303
3304 cpu_buffer = buffer->buffers[cpu];
3305 atomic_inc(&cpu_buffer->record_disabled);
3306}
3307EXPORT_SYMBOL_GPL(ring_buffer_record_disable_cpu);
3308
3309/**
3310 * ring_buffer_record_enable_cpu - enable writes to the buffer
3311 * @buffer: The ring buffer to enable writes
3312 * @cpu: The CPU to enable.
3313 *
3314 * Note, multiple disables will need the same number of enables
3315 * to truly enable the writing (much like preempt_disable).
3316 */
3317void ring_buffer_record_enable_cpu(struct ring_buffer *buffer, int cpu)
3318{
3319 struct ring_buffer_per_cpu *cpu_buffer;
3320
3321 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3322 return;
3323
3324 cpu_buffer = buffer->buffers[cpu];
3325 atomic_dec(&cpu_buffer->record_disabled);
3326}
3327EXPORT_SYMBOL_GPL(ring_buffer_record_enable_cpu);
3328
3329/*
3330 * The total entries in the ring buffer is the running counter
3331 * of entries entered into the ring buffer, minus the sum of
3332 * the entries read from the ring buffer and the number of
3333 * entries that were overwritten.
3334 */
3335static inline unsigned long
3336rb_num_of_entries(struct ring_buffer_per_cpu *cpu_buffer)
3337{
3338 return local_read(&cpu_buffer->entries) -
3339 (local_read(&cpu_buffer->overrun) + cpu_buffer->read);
3340}
3341
3342/**
3343 * ring_buffer_oldest_event_ts - get the oldest event timestamp from the buffer
3344 * @buffer: The ring buffer
3345 * @cpu: The per CPU buffer to read from.
3346 */
3347u64 ring_buffer_oldest_event_ts(struct ring_buffer *buffer, int cpu)
3348{
3349 unsigned long flags;
3350 struct ring_buffer_per_cpu *cpu_buffer;
3351 struct buffer_page *bpage;
3352 u64 ret = 0;
3353
3354 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3355 return 0;
3356
3357 cpu_buffer = buffer->buffers[cpu];
3358 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
3359 /*
3360 * if the tail is on reader_page, oldest time stamp is on the reader
3361 * page
3362 */
3363 if (cpu_buffer->tail_page == cpu_buffer->reader_page)
3364 bpage = cpu_buffer->reader_page;
3365 else
3366 bpage = rb_set_head_page(cpu_buffer);
3367 if (bpage)
3368 ret = bpage->page->time_stamp;
3369 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
3370
3371 return ret;
3372}
3373EXPORT_SYMBOL_GPL(ring_buffer_oldest_event_ts);
3374
3375/**
3376 * ring_buffer_bytes_cpu - get the number of bytes consumed in a cpu buffer
3377 * @buffer: The ring buffer
3378 * @cpu: The per CPU buffer to read from.
3379 */
3380unsigned long ring_buffer_bytes_cpu(struct ring_buffer *buffer, int cpu)
3381{
3382 struct ring_buffer_per_cpu *cpu_buffer;
3383 unsigned long ret;
3384
3385 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3386 return 0;
3387
3388 cpu_buffer = buffer->buffers[cpu];
3389 ret = local_read(&cpu_buffer->entries_bytes) - cpu_buffer->read_bytes;
3390
3391 return ret;
3392}
3393EXPORT_SYMBOL_GPL(ring_buffer_bytes_cpu);
3394
3395/**
3396 * ring_buffer_entries_cpu - get the number of entries in a cpu buffer
3397 * @buffer: The ring buffer
3398 * @cpu: The per CPU buffer to get the entries from.
3399 */
3400unsigned long ring_buffer_entries_cpu(struct ring_buffer *buffer, int cpu)
3401{
3402 struct ring_buffer_per_cpu *cpu_buffer;
3403
3404 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3405 return 0;
3406
3407 cpu_buffer = buffer->buffers[cpu];
3408
3409 return rb_num_of_entries(cpu_buffer);
3410}
3411EXPORT_SYMBOL_GPL(ring_buffer_entries_cpu);
3412
3413/**
3414 * ring_buffer_overrun_cpu - get the number of overruns caused by the ring
3415 * buffer wrapping around (only if RB_FL_OVERWRITE is on).
3416 * @buffer: The ring buffer
3417 * @cpu: The per CPU buffer to get the number of overruns from
3418 */
3419unsigned long ring_buffer_overrun_cpu(struct ring_buffer *buffer, int cpu)
3420{
3421 struct ring_buffer_per_cpu *cpu_buffer;
3422 unsigned long ret;
3423
3424 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3425 return 0;
3426
3427 cpu_buffer = buffer->buffers[cpu];
3428 ret = local_read(&cpu_buffer->overrun);
3429
3430 return ret;
3431}
3432EXPORT_SYMBOL_GPL(ring_buffer_overrun_cpu);
3433
3434/**
3435 * ring_buffer_commit_overrun_cpu - get the number of overruns caused by
3436 * commits failing due to the buffer wrapping around while there are uncommitted
3437 * events, such as during an interrupt storm.
3438 * @buffer: The ring buffer
3439 * @cpu: The per CPU buffer to get the number of overruns from
3440 */
3441unsigned long
3442ring_buffer_commit_overrun_cpu(struct ring_buffer *buffer, int cpu)
3443{
3444 struct ring_buffer_per_cpu *cpu_buffer;
3445 unsigned long ret;
3446
3447 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3448 return 0;
3449
3450 cpu_buffer = buffer->buffers[cpu];
3451 ret = local_read(&cpu_buffer->commit_overrun);
3452
3453 return ret;
3454}
3455EXPORT_SYMBOL_GPL(ring_buffer_commit_overrun_cpu);
3456
3457/**
3458 * ring_buffer_dropped_events_cpu - get the number of dropped events caused by
3459 * the ring buffer filling up (only if RB_FL_OVERWRITE is off).
3460 * @buffer: The ring buffer
3461 * @cpu: The per CPU buffer to get the number of overruns from
3462 */
3463unsigned long
3464ring_buffer_dropped_events_cpu(struct ring_buffer *buffer, int cpu)
3465{
3466 struct ring_buffer_per_cpu *cpu_buffer;
3467 unsigned long ret;
3468
3469 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3470 return 0;
3471
3472 cpu_buffer = buffer->buffers[cpu];
3473 ret = local_read(&cpu_buffer->dropped_events);
3474
3475 return ret;
3476}
3477EXPORT_SYMBOL_GPL(ring_buffer_dropped_events_cpu);
3478
3479/**
3480 * ring_buffer_read_events_cpu - get the number of events successfully read
3481 * @buffer: The ring buffer
3482 * @cpu: The per CPU buffer to get the number of events read
3483 */
3484unsigned long
3485ring_buffer_read_events_cpu(struct ring_buffer *buffer, int cpu)
3486{
3487 struct ring_buffer_per_cpu *cpu_buffer;
3488
3489 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3490 return 0;
3491
3492 cpu_buffer = buffer->buffers[cpu];
3493 return cpu_buffer->read;
3494}
3495EXPORT_SYMBOL_GPL(ring_buffer_read_events_cpu);
3496
3497/**
3498 * ring_buffer_entries - get the number of entries in a buffer
3499 * @buffer: The ring buffer
3500 *
3501 * Returns the total number of entries in the ring buffer
3502 * (all CPU entries)
3503 */
3504unsigned long ring_buffer_entries(struct ring_buffer *buffer)
3505{
3506 struct ring_buffer_per_cpu *cpu_buffer;
3507 unsigned long entries = 0;
3508 int cpu;
3509
3510 /* if you care about this being correct, lock the buffer */
3511 for_each_buffer_cpu(buffer, cpu) {
3512 cpu_buffer = buffer->buffers[cpu];
3513 entries += rb_num_of_entries(cpu_buffer);
3514 }
3515
3516 return entries;
3517}
3518EXPORT_SYMBOL_GPL(ring_buffer_entries);
3519
3520/**
3521 * ring_buffer_overruns - get the number of overruns in buffer
3522 * @buffer: The ring buffer
3523 *
3524 * Returns the total number of overruns in the ring buffer
3525 * (all CPU entries)
3526 */
3527unsigned long ring_buffer_overruns(struct ring_buffer *buffer)
3528{
3529 struct ring_buffer_per_cpu *cpu_buffer;
3530 unsigned long overruns = 0;
3531 int cpu;
3532
3533 /* if you care about this being correct, lock the buffer */
3534 for_each_buffer_cpu(buffer, cpu) {
3535 cpu_buffer = buffer->buffers[cpu];
3536 overruns += local_read(&cpu_buffer->overrun);
3537 }
3538
3539 return overruns;
3540}
3541EXPORT_SYMBOL_GPL(ring_buffer_overruns);
3542
3543static void rb_iter_reset(struct ring_buffer_iter *iter)
3544{
3545 struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
3546
3547 /* Iterator usage is expected to have record disabled */
3548 iter->head_page = cpu_buffer->reader_page;
3549 iter->head = cpu_buffer->reader_page->read;
3550
3551 iter->cache_reader_page = iter->head_page;
3552 iter->cache_read = cpu_buffer->read;
3553
3554 if (iter->head)
3555 iter->read_stamp = cpu_buffer->read_stamp;
3556 else
3557 iter->read_stamp = iter->head_page->page->time_stamp;
3558}
3559
3560/**
3561 * ring_buffer_iter_reset - reset an iterator
3562 * @iter: The iterator to reset
3563 *
3564 * Resets the iterator, so that it will start from the beginning
3565 * again.
3566 */
3567void ring_buffer_iter_reset(struct ring_buffer_iter *iter)
3568{
3569 struct ring_buffer_per_cpu *cpu_buffer;
3570 unsigned long flags;
3571
3572 if (!iter)
3573 return;
3574
3575 cpu_buffer = iter->cpu_buffer;
3576
3577 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
3578 rb_iter_reset(iter);
3579 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
3580}
3581EXPORT_SYMBOL_GPL(ring_buffer_iter_reset);
3582
3583/**
3584 * ring_buffer_iter_empty - check if an iterator has no more to read
3585 * @iter: The iterator to check
3586 */
3587int ring_buffer_iter_empty(struct ring_buffer_iter *iter)
3588{
3589 struct ring_buffer_per_cpu *cpu_buffer;
3590 struct buffer_page *reader;
3591 struct buffer_page *head_page;
3592 struct buffer_page *commit_page;
3593 unsigned commit;
3594
3595 cpu_buffer = iter->cpu_buffer;
3596
3597 /* Remember, trace recording is off when iterator is in use */
3598 reader = cpu_buffer->reader_page;
3599 head_page = cpu_buffer->head_page;
3600 commit_page = cpu_buffer->commit_page;
3601 commit = rb_page_commit(commit_page);
3602
3603 return ((iter->head_page == commit_page && iter->head == commit) ||
3604 (iter->head_page == reader && commit_page == head_page &&
3605 head_page->read == commit &&
3606 iter->head == rb_page_commit(cpu_buffer->reader_page)));
3607}
3608EXPORT_SYMBOL_GPL(ring_buffer_iter_empty);
3609
3610static void
3611rb_update_read_stamp(struct ring_buffer_per_cpu *cpu_buffer,
3612 struct ring_buffer_event *event)
3613{
3614 u64 delta;
3615
3616 switch (event->type_len) {
3617 case RINGBUF_TYPE_PADDING:
3618 return;
3619
3620 case RINGBUF_TYPE_TIME_EXTEND:
3621 delta = ring_buffer_event_time_stamp(event);
3622 cpu_buffer->read_stamp += delta;
3623 return;
3624
3625 case RINGBUF_TYPE_TIME_STAMP:
3626 delta = ring_buffer_event_time_stamp(event);
3627 cpu_buffer->read_stamp = delta;
3628 return;
3629
3630 case RINGBUF_TYPE_DATA:
3631 cpu_buffer->read_stamp += event->time_delta;
3632 return;
3633
3634 default:
3635 BUG();
3636 }
3637 return;
3638}
3639
3640static void
3641rb_update_iter_read_stamp(struct ring_buffer_iter *iter,
3642 struct ring_buffer_event *event)
3643{
3644 u64 delta;
3645
3646 switch (event->type_len) {
3647 case RINGBUF_TYPE_PADDING:
3648 return;
3649
3650 case RINGBUF_TYPE_TIME_EXTEND:
3651 delta = ring_buffer_event_time_stamp(event);
3652 iter->read_stamp += delta;
3653 return;
3654
3655 case RINGBUF_TYPE_TIME_STAMP:
3656 delta = ring_buffer_event_time_stamp(event);
3657 iter->read_stamp = delta;
3658 return;
3659
3660 case RINGBUF_TYPE_DATA:
3661 iter->read_stamp += event->time_delta;
3662 return;
3663
3664 default:
3665 BUG();
3666 }
3667 return;
3668}
3669
3670static struct buffer_page *
3671rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
3672{
3673 struct buffer_page *reader = NULL;
3674 unsigned long overwrite;
3675 unsigned long flags;
3676 int nr_loops = 0;
3677 int ret;
3678
3679 local_irq_save(flags);
3680 arch_spin_lock(&cpu_buffer->lock);
3681
3682 again:
3683 /*
3684 * This should normally only loop twice. But because the
3685 * start of the reader inserts an empty page, it causes
3686 * a case where we will loop three times. There should be no
3687 * reason to loop four times (that I know of).
3688 */
3689 if (RB_WARN_ON(cpu_buffer, ++nr_loops > 3)) {
3690 reader = NULL;
3691 goto out;
3692 }
3693
3694 reader = cpu_buffer->reader_page;
3695
3696 /* If there's more to read, return this page */
3697 if (cpu_buffer->reader_page->read < rb_page_size(reader))
3698 goto out;
3699
3700 /* Never should we have an index greater than the size */
3701 if (RB_WARN_ON(cpu_buffer,
3702 cpu_buffer->reader_page->read > rb_page_size(reader)))
3703 goto out;
3704
3705 /* check if we caught up to the tail */
3706 reader = NULL;
3707 if (cpu_buffer->commit_page == cpu_buffer->reader_page)
3708 goto out;
3709
3710 /* Don't bother swapping if the ring buffer is empty */
3711 if (rb_num_of_entries(cpu_buffer) == 0)
3712 goto out;
3713
3714 /*
3715 * Reset the reader page to size zero.
3716 */
3717 local_set(&cpu_buffer->reader_page->write, 0);
3718 local_set(&cpu_buffer->reader_page->entries, 0);
3719 local_set(&cpu_buffer->reader_page->page->commit, 0);
3720 cpu_buffer->reader_page->real_end = 0;
3721
3722 spin:
3723 /*
3724 * Splice the empty reader page into the list around the head.
3725 */
3726 reader = rb_set_head_page(cpu_buffer);
3727 if (!reader)
3728 goto out;
3729 cpu_buffer->reader_page->list.next = rb_list_head(reader->list.next);
3730 cpu_buffer->reader_page->list.prev = reader->list.prev;
3731
3732 /*
3733 * cpu_buffer->pages just needs to point to the buffer, it
3734 * has no specific buffer page to point to. Lets move it out
3735 * of our way so we don't accidentally swap it.
3736 */
3737 cpu_buffer->pages = reader->list.prev;
3738
3739 /* The reader page will be pointing to the new head */
3740 rb_set_list_to_head(cpu_buffer, &cpu_buffer->reader_page->list);
3741
3742 /*
3743 * We want to make sure we read the overruns after we set up our
3744 * pointers to the next object. The writer side does a
3745 * cmpxchg to cross pages which acts as the mb on the writer
3746 * side. Note, the reader will constantly fail the swap
3747 * while the writer is updating the pointers, so this
3748 * guarantees that the overwrite recorded here is the one we
3749 * want to compare with the last_overrun.
3750 */
3751 smp_mb();
3752 overwrite = local_read(&(cpu_buffer->overrun));
3753
3754 /*
3755 * Here's the tricky part.
3756 *
3757 * We need to move the pointer past the header page.
3758 * But we can only do that if a writer is not currently
3759 * moving it. The page before the header page has the
3760 * flag bit '1' set if it is pointing to the page we want.
3761 * but if the writer is in the process of moving it
3762 * than it will be '2' or already moved '0'.
3763 */
3764
3765 ret = rb_head_page_replace(reader, cpu_buffer->reader_page);
3766
3767 /*
3768 * If we did not convert it, then we must try again.
3769 */
3770 if (!ret)
3771 goto spin;
3772
3773 /*
3774 * Yay! We succeeded in replacing the page.
3775 *
3776 * Now make the new head point back to the reader page.
3777 */
3778 rb_list_head(reader->list.next)->prev = &cpu_buffer->reader_page->list;
3779 rb_inc_page(cpu_buffer, &cpu_buffer->head_page);
3780
3781 local_inc(&cpu_buffer->pages_read);
3782
3783 /* Finally update the reader page to the new head */
3784 cpu_buffer->reader_page = reader;
3785 cpu_buffer->reader_page->read = 0;
3786
3787 if (overwrite != cpu_buffer->last_overrun) {
3788 cpu_buffer->lost_events = overwrite - cpu_buffer->last_overrun;
3789 cpu_buffer->last_overrun = overwrite;
3790 }
3791
3792 goto again;
3793
3794 out:
3795 /* Update the read_stamp on the first event */
3796 if (reader && reader->read == 0)
3797 cpu_buffer->read_stamp = reader->page->time_stamp;
3798
3799 arch_spin_unlock(&cpu_buffer->lock);
3800 local_irq_restore(flags);
3801
3802 return reader;
3803}
3804
3805static void rb_advance_reader(struct ring_buffer_per_cpu *cpu_buffer)
3806{
3807 struct ring_buffer_event *event;
3808 struct buffer_page *reader;
3809 unsigned length;
3810
3811 reader = rb_get_reader_page(cpu_buffer);
3812
3813 /* This function should not be called when buffer is empty */
3814 if (RB_WARN_ON(cpu_buffer, !reader))
3815 return;
3816
3817 event = rb_reader_event(cpu_buffer);
3818
3819 if (event->type_len <= RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
3820 cpu_buffer->read++;
3821
3822 rb_update_read_stamp(cpu_buffer, event);
3823
3824 length = rb_event_length(event);
3825 cpu_buffer->reader_page->read += length;
3826}
3827
3828static void rb_advance_iter(struct ring_buffer_iter *iter)
3829{
3830 struct ring_buffer_per_cpu *cpu_buffer;
3831 struct ring_buffer_event *event;
3832 unsigned length;
3833
3834 cpu_buffer = iter->cpu_buffer;
3835
3836 /*
3837 * Check if we are at the end of the buffer.
3838 */
3839 if (iter->head >= rb_page_size(iter->head_page)) {
3840 /* discarded commits can make the page empty */
3841 if (iter->head_page == cpu_buffer->commit_page)
3842 return;
3843 rb_inc_iter(iter);
3844 return;
3845 }
3846
3847 event = rb_iter_head_event(iter);
3848
3849 length = rb_event_length(event);
3850
3851 /*
3852 * This should not be called to advance the header if we are
3853 * at the tail of the buffer.
3854 */
3855 if (RB_WARN_ON(cpu_buffer,
3856 (iter->head_page == cpu_buffer->commit_page) &&
3857 (iter->head + length > rb_commit_index(cpu_buffer))))
3858 return;
3859
3860 rb_update_iter_read_stamp(iter, event);
3861
3862 iter->head += length;
3863
3864 /* check for end of page padding */
3865 if ((iter->head >= rb_page_size(iter->head_page)) &&
3866 (iter->head_page != cpu_buffer->commit_page))
3867 rb_inc_iter(iter);
3868}
3869
3870static int rb_lost_events(struct ring_buffer_per_cpu *cpu_buffer)
3871{
3872 return cpu_buffer->lost_events;
3873}
3874
3875static struct ring_buffer_event *
3876rb_buffer_peek(struct ring_buffer_per_cpu *cpu_buffer, u64 *ts,
3877 unsigned long *lost_events)
3878{
3879 struct ring_buffer_event *event;
3880 struct buffer_page *reader;
3881 int nr_loops = 0;
3882
3883 if (ts)
3884 *ts = 0;
3885 again:
3886 /*
3887 * We repeat when a time extend is encountered.
3888 * Since the time extend is always attached to a data event,
3889 * we should never loop more than once.
3890 * (We never hit the following condition more than twice).
3891 */
3892 if (RB_WARN_ON(cpu_buffer, ++nr_loops > 2))
3893 return NULL;
3894
3895 reader = rb_get_reader_page(cpu_buffer);
3896 if (!reader)
3897 return NULL;
3898
3899 event = rb_reader_event(cpu_buffer);
3900
3901 switch (event->type_len) {
3902 case RINGBUF_TYPE_PADDING:
3903 if (rb_null_event(event))
3904 RB_WARN_ON(cpu_buffer, 1);
3905 /*
3906 * Because the writer could be discarding every
3907 * event it creates (which would probably be bad)
3908 * if we were to go back to "again" then we may never
3909 * catch up, and will trigger the warn on, or lock
3910 * the box. Return the padding, and we will release
3911 * the current locks, and try again.
3912 */
3913 return event;
3914
3915 case RINGBUF_TYPE_TIME_EXTEND:
3916 /* Internal data, OK to advance */
3917 rb_advance_reader(cpu_buffer);
3918 goto again;
3919
3920 case RINGBUF_TYPE_TIME_STAMP:
3921 if (ts) {
3922 *ts = ring_buffer_event_time_stamp(event);
3923 ring_buffer_normalize_time_stamp(cpu_buffer->buffer,
3924 cpu_buffer->cpu, ts);
3925 }
3926 /* Internal data, OK to advance */
3927 rb_advance_reader(cpu_buffer);
3928 goto again;
3929
3930 case RINGBUF_TYPE_DATA:
3931 if (ts && !(*ts)) {
3932 *ts = cpu_buffer->read_stamp + event->time_delta;
3933 ring_buffer_normalize_time_stamp(cpu_buffer->buffer,
3934 cpu_buffer->cpu, ts);
3935 }
3936 if (lost_events)
3937 *lost_events = rb_lost_events(cpu_buffer);
3938 return event;
3939
3940 default:
3941 BUG();
3942 }
3943
3944 return NULL;
3945}
3946EXPORT_SYMBOL_GPL(ring_buffer_peek);
3947
3948static struct ring_buffer_event *
3949rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
3950{
3951 struct ring_buffer *buffer;
3952 struct ring_buffer_per_cpu *cpu_buffer;
3953 struct ring_buffer_event *event;
3954 int nr_loops = 0;
3955
3956 if (ts)
3957 *ts = 0;
3958
3959 cpu_buffer = iter->cpu_buffer;
3960 buffer = cpu_buffer->buffer;
3961
3962 /*
3963 * Check if someone performed a consuming read to
3964 * the buffer. A consuming read invalidates the iterator
3965 * and we need to reset the iterator in this case.
3966 */
3967 if (unlikely(iter->cache_read != cpu_buffer->read ||
3968 iter->cache_reader_page != cpu_buffer->reader_page))
3969 rb_iter_reset(iter);
3970
3971 again:
3972 if (ring_buffer_iter_empty(iter))
3973 return NULL;
3974
3975 /*
3976 * We repeat when a time extend is encountered or we hit
3977 * the end of the page. Since the time extend is always attached
3978 * to a data event, we should never loop more than three times.
3979 * Once for going to next page, once on time extend, and
3980 * finally once to get the event.
3981 * (We never hit the following condition more than thrice).
3982 */
3983 if (RB_WARN_ON(cpu_buffer, ++nr_loops > 3))
3984 return NULL;
3985
3986 if (rb_per_cpu_empty(cpu_buffer))
3987 return NULL;
3988
3989 if (iter->head >= rb_page_size(iter->head_page)) {
3990 rb_inc_iter(iter);
3991 goto again;
3992 }
3993
3994 event = rb_iter_head_event(iter);
3995
3996 switch (event->type_len) {
3997 case RINGBUF_TYPE_PADDING:
3998 if (rb_null_event(event)) {
3999 rb_inc_iter(iter);
4000 goto again;
4001 }
4002 rb_advance_iter(iter);
4003 return event;
4004
4005 case RINGBUF_TYPE_TIME_EXTEND:
4006 /* Internal data, OK to advance */
4007 rb_advance_iter(iter);
4008 goto again;
4009
4010 case RINGBUF_TYPE_TIME_STAMP:
4011 if (ts) {
4012 *ts = ring_buffer_event_time_stamp(event);
4013 ring_buffer_normalize_time_stamp(cpu_buffer->buffer,
4014 cpu_buffer->cpu, ts);
4015 }
4016 /* Internal data, OK to advance */
4017 rb_advance_iter(iter);
4018 goto again;
4019
4020 case RINGBUF_TYPE_DATA:
4021 if (ts && !(*ts)) {
4022 *ts = iter->read_stamp + event->time_delta;
4023 ring_buffer_normalize_time_stamp(buffer,
4024 cpu_buffer->cpu, ts);
4025 }
4026 return event;
4027
4028 default:
4029 BUG();
4030 }
4031
4032 return NULL;
4033}
4034EXPORT_SYMBOL_GPL(ring_buffer_iter_peek);
4035
4036static inline bool rb_reader_lock(struct ring_buffer_per_cpu *cpu_buffer)
4037{
4038 if (likely(!in_nmi())) {
4039 raw_spin_lock(&cpu_buffer->reader_lock);
4040 return true;
4041 }
4042
4043 /*
4044 * If an NMI die dumps out the content of the ring buffer
4045 * trylock must be used to prevent a deadlock if the NMI
4046 * preempted a task that holds the ring buffer locks. If
4047 * we get the lock then all is fine, if not, then continue
4048 * to do the read, but this can corrupt the ring buffer,
4049 * so it must be permanently disabled from future writes.
4050 * Reading from NMI is a oneshot deal.
4051 */
4052 if (raw_spin_trylock(&cpu_buffer->reader_lock))
4053 return true;
4054
4055 /* Continue without locking, but disable the ring buffer */
4056 atomic_inc(&cpu_buffer->record_disabled);
4057 return false;
4058}
4059
4060static inline void
4061rb_reader_unlock(struct ring_buffer_per_cpu *cpu_buffer, bool locked)
4062{
4063 if (likely(locked))
4064 raw_spin_unlock(&cpu_buffer->reader_lock);
4065 return;
4066}
4067
4068/**
4069 * ring_buffer_peek - peek at the next event to be read
4070 * @buffer: The ring buffer to read
4071 * @cpu: The cpu to peak at
4072 * @ts: The timestamp counter of this event.
4073 * @lost_events: a variable to store if events were lost (may be NULL)
4074 *
4075 * This will return the event that will be read next, but does
4076 * not consume the data.
4077 */
4078struct ring_buffer_event *
4079ring_buffer_peek(struct ring_buffer *buffer, int cpu, u64 *ts,
4080 unsigned long *lost_events)
4081{
4082 struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
4083 struct ring_buffer_event *event;
4084 unsigned long flags;
4085 bool dolock;
4086
4087 if (!cpumask_test_cpu(cpu, buffer->cpumask))
4088 return NULL;
4089
4090 again:
4091 local_irq_save(flags);
4092 dolock = rb_reader_lock(cpu_buffer);
4093 event = rb_buffer_peek(cpu_buffer, ts, lost_events);
4094 if (event && event->type_len == RINGBUF_TYPE_PADDING)
4095 rb_advance_reader(cpu_buffer);
4096 rb_reader_unlock(cpu_buffer, dolock);
4097 local_irq_restore(flags);
4098
4099 if (event && event->type_len == RINGBUF_TYPE_PADDING)
4100 goto again;
4101
4102 return event;
4103}
4104
4105/**
4106 * ring_buffer_iter_peek - peek at the next event to be read
4107 * @iter: The ring buffer iterator
4108 * @ts: The timestamp counter of this event.
4109 *
4110 * This will return the event that will be read next, but does
4111 * not increment the iterator.
4112 */
4113struct ring_buffer_event *
4114ring_buffer_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
4115{
4116 struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
4117 struct ring_buffer_event *event;
4118 unsigned long flags;
4119
4120 again:
4121 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
4122 event = rb_iter_peek(iter, ts);
4123 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
4124
4125 if (event && event->type_len == RINGBUF_TYPE_PADDING)
4126 goto again;
4127
4128 return event;
4129}
4130
4131/**
4132 * ring_buffer_consume - return an event and consume it
4133 * @buffer: The ring buffer to get the next event from
4134 * @cpu: the cpu to read the buffer from
4135 * @ts: a variable to store the timestamp (may be NULL)
4136 * @lost_events: a variable to store if events were lost (may be NULL)
4137 *
4138 * Returns the next event in the ring buffer, and that event is consumed.
4139 * Meaning, that sequential reads will keep returning a different event,
4140 * and eventually empty the ring buffer if the producer is slower.
4141 */
4142struct ring_buffer_event *
4143ring_buffer_consume(struct ring_buffer *buffer, int cpu, u64 *ts,
4144 unsigned long *lost_events)
4145{
4146 struct ring_buffer_per_cpu *cpu_buffer;
4147 struct ring_buffer_event *event = NULL;
4148 unsigned long flags;
4149 bool dolock;
4150
4151 again:
4152 /* might be called in atomic */
4153 preempt_disable();
4154
4155 if (!cpumask_test_cpu(cpu, buffer->cpumask))
4156 goto out;
4157
4158 cpu_buffer = buffer->buffers[cpu];
4159 local_irq_save(flags);
4160 dolock = rb_reader_lock(cpu_buffer);
4161
4162 event = rb_buffer_peek(cpu_buffer, ts, lost_events);
4163 if (event) {
4164 cpu_buffer->lost_events = 0;
4165 rb_advance_reader(cpu_buffer);
4166 }
4167
4168 rb_reader_unlock(cpu_buffer, dolock);
4169 local_irq_restore(flags);
4170
4171 out:
4172 preempt_enable();
4173
4174 if (event && event->type_len == RINGBUF_TYPE_PADDING)
4175 goto again;
4176
4177 return event;
4178}
4179EXPORT_SYMBOL_GPL(ring_buffer_consume);
4180
4181/**
4182 * ring_buffer_read_prepare - Prepare for a non consuming read of the buffer
4183 * @buffer: The ring buffer to read from
4184 * @cpu: The cpu buffer to iterate over
4185 * @flags: gfp flags to use for memory allocation
4186 *
4187 * This performs the initial preparations necessary to iterate
4188 * through the buffer. Memory is allocated, buffer recording
4189 * is disabled, and the iterator pointer is returned to the caller.
4190 *
4191 * Disabling buffer recording prevents the reading from being
4192 * corrupted. This is not a consuming read, so a producer is not
4193 * expected.
4194 *
4195 * After a sequence of ring_buffer_read_prepare calls, the user is
4196 * expected to make at least one call to ring_buffer_read_prepare_sync.
4197 * Afterwards, ring_buffer_read_start is invoked to get things going
4198 * for real.
4199 *
4200 * This overall must be paired with ring_buffer_read_finish.
4201 */
4202struct ring_buffer_iter *
4203ring_buffer_read_prepare(struct ring_buffer *buffer, int cpu, gfp_t flags)
4204{
4205 struct ring_buffer_per_cpu *cpu_buffer;
4206 struct ring_buffer_iter *iter;
4207
4208 if (!cpumask_test_cpu(cpu, buffer->cpumask))
4209 return NULL;
4210
4211 iter = kmalloc(sizeof(*iter), flags);
4212 if (!iter)
4213 return NULL;
4214
4215 cpu_buffer = buffer->buffers[cpu];
4216
4217 iter->cpu_buffer = cpu_buffer;
4218
4219 atomic_inc(&buffer->resize_disabled);
4220 atomic_inc(&cpu_buffer->record_disabled);
4221
4222 return iter;
4223}
4224EXPORT_SYMBOL_GPL(ring_buffer_read_prepare);
4225
4226/**
4227 * ring_buffer_read_prepare_sync - Synchronize a set of prepare calls
4228 *
4229 * All previously invoked ring_buffer_read_prepare calls to prepare
4230 * iterators will be synchronized. Afterwards, read_buffer_read_start
4231 * calls on those iterators are allowed.
4232 */
4233void
4234ring_buffer_read_prepare_sync(void)
4235{
4236 synchronize_rcu();
4237}
4238EXPORT_SYMBOL_GPL(ring_buffer_read_prepare_sync);
4239
4240/**
4241 * ring_buffer_read_start - start a non consuming read of the buffer
4242 * @iter: The iterator returned by ring_buffer_read_prepare
4243 *
4244 * This finalizes the startup of an iteration through the buffer.
4245 * The iterator comes from a call to ring_buffer_read_prepare and
4246 * an intervening ring_buffer_read_prepare_sync must have been
4247 * performed.
4248 *
4249 * Must be paired with ring_buffer_read_finish.
4250 */
4251void
4252ring_buffer_read_start(struct ring_buffer_iter *iter)
4253{
4254 struct ring_buffer_per_cpu *cpu_buffer;
4255 unsigned long flags;
4256
4257 if (!iter)
4258 return;
4259
4260 cpu_buffer = iter->cpu_buffer;
4261
4262 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
4263 arch_spin_lock(&cpu_buffer->lock);
4264 rb_iter_reset(iter);
4265 arch_spin_unlock(&cpu_buffer->lock);
4266 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
4267}
4268EXPORT_SYMBOL_GPL(ring_buffer_read_start);
4269
4270/**
4271 * ring_buffer_read_finish - finish reading the iterator of the buffer
4272 * @iter: The iterator retrieved by ring_buffer_start
4273 *
4274 * This re-enables the recording to the buffer, and frees the
4275 * iterator.
4276 */
4277void
4278ring_buffer_read_finish(struct ring_buffer_iter *iter)
4279{
4280 struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
4281 unsigned long flags;
4282
4283 /*
4284 * Ring buffer is disabled from recording, here's a good place
4285 * to check the integrity of the ring buffer.
4286 * Must prevent readers from trying to read, as the check
4287 * clears the HEAD page and readers require it.
4288 */
4289 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
4290 rb_check_pages(cpu_buffer);
4291 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
4292
4293 atomic_dec(&cpu_buffer->record_disabled);
4294 atomic_dec(&cpu_buffer->buffer->resize_disabled);
4295 kfree(iter);
4296}
4297EXPORT_SYMBOL_GPL(ring_buffer_read_finish);
4298
4299/**
4300 * ring_buffer_read - read the next item in the ring buffer by the iterator
4301 * @iter: The ring buffer iterator
4302 * @ts: The time stamp of the event read.
4303 *
4304 * This reads the next event in the ring buffer and increments the iterator.
4305 */
4306struct ring_buffer_event *
4307ring_buffer_read(struct ring_buffer_iter *iter, u64 *ts)
4308{
4309 struct ring_buffer_event *event;
4310 struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
4311 unsigned long flags;
4312
4313 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
4314 again:
4315 event = rb_iter_peek(iter, ts);
4316 if (!event)
4317 goto out;
4318
4319 if (event->type_len == RINGBUF_TYPE_PADDING)
4320 goto again;
4321
4322 rb_advance_iter(iter);
4323 out:
4324 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
4325
4326 return event;
4327}
4328EXPORT_SYMBOL_GPL(ring_buffer_read);
4329
4330/**
4331 * ring_buffer_size - return the size of the ring buffer (in bytes)
4332 * @buffer: The ring buffer.
4333 */
4334unsigned long ring_buffer_size(struct ring_buffer *buffer, int cpu)
4335{
4336 /*
4337 * Earlier, this method returned
4338 * BUF_PAGE_SIZE * buffer->nr_pages
4339 * Since the nr_pages field is now removed, we have converted this to
4340 * return the per cpu buffer value.
4341 */
4342 if (!cpumask_test_cpu(cpu, buffer->cpumask))
4343 return 0;
4344
4345 return BUF_PAGE_SIZE * buffer->buffers[cpu]->nr_pages;
4346}
4347EXPORT_SYMBOL_GPL(ring_buffer_size);
4348
4349static void
4350rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
4351{
4352 rb_head_page_deactivate(cpu_buffer);
4353
4354 cpu_buffer->head_page
4355 = list_entry(cpu_buffer->pages, struct buffer_page, list);
4356 local_set(&cpu_buffer->head_page->write, 0);
4357 local_set(&cpu_buffer->head_page->entries, 0);
4358 local_set(&cpu_buffer->head_page->page->commit, 0);
4359
4360 cpu_buffer->head_page->read = 0;
4361
4362 cpu_buffer->tail_page = cpu_buffer->head_page;
4363 cpu_buffer->commit_page = cpu_buffer->head_page;
4364
4365 INIT_LIST_HEAD(&cpu_buffer->reader_page->list);
4366 INIT_LIST_HEAD(&cpu_buffer->new_pages);
4367 local_set(&cpu_buffer->reader_page->write, 0);
4368 local_set(&cpu_buffer->reader_page->entries, 0);
4369 local_set(&cpu_buffer->reader_page->page->commit, 0);
4370 cpu_buffer->reader_page->read = 0;
4371
4372 local_set(&cpu_buffer->entries_bytes, 0);
4373 local_set(&cpu_buffer->overrun, 0);
4374 local_set(&cpu_buffer->commit_overrun, 0);
4375 local_set(&cpu_buffer->dropped_events, 0);
4376 local_set(&cpu_buffer->entries, 0);
4377 local_set(&cpu_buffer->committing, 0);
4378 local_set(&cpu_buffer->commits, 0);
4379 local_set(&cpu_buffer->pages_touched, 0);
4380 local_set(&cpu_buffer->pages_read, 0);
4381 cpu_buffer->last_pages_touch = 0;
4382 cpu_buffer->shortest_full = 0;
4383 cpu_buffer->read = 0;
4384 cpu_buffer->read_bytes = 0;
4385
4386 cpu_buffer->write_stamp = 0;
4387 cpu_buffer->read_stamp = 0;
4388
4389 cpu_buffer->lost_events = 0;
4390 cpu_buffer->last_overrun = 0;
4391
4392 rb_head_page_activate(cpu_buffer);
4393}
4394
4395/**
4396 * ring_buffer_reset_cpu - reset a ring buffer per CPU buffer
4397 * @buffer: The ring buffer to reset a per cpu buffer of
4398 * @cpu: The CPU buffer to be reset
4399 */
4400void ring_buffer_reset_cpu(struct ring_buffer *buffer, int cpu)
4401{
4402 struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
4403 unsigned long flags;
4404
4405 if (!cpumask_test_cpu(cpu, buffer->cpumask))
4406 return;
4407
4408 atomic_inc(&buffer->resize_disabled);
4409 atomic_inc(&cpu_buffer->record_disabled);
4410
4411 /* Make sure all commits have finished */
4412 synchronize_rcu();
4413
4414 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
4415
4416 if (RB_WARN_ON(cpu_buffer, local_read(&cpu_buffer->committing)))
4417 goto out;
4418
4419 arch_spin_lock(&cpu_buffer->lock);
4420
4421 rb_reset_cpu(cpu_buffer);
4422
4423 arch_spin_unlock(&cpu_buffer->lock);
4424
4425 out:
4426 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
4427
4428 atomic_dec(&cpu_buffer->record_disabled);
4429 atomic_dec(&buffer->resize_disabled);
4430}
4431EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu);
4432
4433/**
4434 * ring_buffer_reset - reset a ring buffer
4435 * @buffer: The ring buffer to reset all cpu buffers
4436 */
4437void ring_buffer_reset(struct ring_buffer *buffer)
4438{
4439 int cpu;
4440
4441 for_each_buffer_cpu(buffer, cpu)
4442 ring_buffer_reset_cpu(buffer, cpu);
4443}
4444EXPORT_SYMBOL_GPL(ring_buffer_reset);
4445
4446/**
4447 * rind_buffer_empty - is the ring buffer empty?
4448 * @buffer: The ring buffer to test
4449 */
4450bool ring_buffer_empty(struct ring_buffer *buffer)
4451{
4452 struct ring_buffer_per_cpu *cpu_buffer;
4453 unsigned long flags;
4454 bool dolock;
4455 int cpu;
4456 int ret;
4457
4458 /* yes this is racy, but if you don't like the race, lock the buffer */
4459 for_each_buffer_cpu(buffer, cpu) {
4460 cpu_buffer = buffer->buffers[cpu];
4461 local_irq_save(flags);
4462 dolock = rb_reader_lock(cpu_buffer);
4463 ret = rb_per_cpu_empty(cpu_buffer);
4464 rb_reader_unlock(cpu_buffer, dolock);
4465 local_irq_restore(flags);
4466
4467 if (!ret)
4468 return false;
4469 }
4470
4471 return true;
4472}
4473EXPORT_SYMBOL_GPL(ring_buffer_empty);
4474
4475/**
4476 * ring_buffer_empty_cpu - is a cpu buffer of a ring buffer empty?
4477 * @buffer: The ring buffer
4478 * @cpu: The CPU buffer to test
4479 */
4480bool ring_buffer_empty_cpu(struct ring_buffer *buffer, int cpu)
4481{
4482 struct ring_buffer_per_cpu *cpu_buffer;
4483 unsigned long flags;
4484 bool dolock;
4485 int ret;
4486
4487 if (!cpumask_test_cpu(cpu, buffer->cpumask))
4488 return true;
4489
4490 cpu_buffer = buffer->buffers[cpu];
4491 local_irq_save(flags);
4492 dolock = rb_reader_lock(cpu_buffer);
4493 ret = rb_per_cpu_empty(cpu_buffer);
4494 rb_reader_unlock(cpu_buffer, dolock);
4495 local_irq_restore(flags);
4496
4497 return ret;
4498}
4499EXPORT_SYMBOL_GPL(ring_buffer_empty_cpu);
4500
4501#ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
4502/**
4503 * ring_buffer_swap_cpu - swap a CPU buffer between two ring buffers
4504 * @buffer_a: One buffer to swap with
4505 * @buffer_b: The other buffer to swap with
4506 *
4507 * This function is useful for tracers that want to take a "snapshot"
4508 * of a CPU buffer and has another back up buffer lying around.
4509 * it is expected that the tracer handles the cpu buffer not being
4510 * used at the moment.
4511 */
4512int ring_buffer_swap_cpu(struct ring_buffer *buffer_a,
4513 struct ring_buffer *buffer_b, int cpu)
4514{
4515 struct ring_buffer_per_cpu *cpu_buffer_a;
4516 struct ring_buffer_per_cpu *cpu_buffer_b;
4517 int ret = -EINVAL;
4518
4519 if (!cpumask_test_cpu(cpu, buffer_a->cpumask) ||
4520 !cpumask_test_cpu(cpu, buffer_b->cpumask))
4521 goto out;
4522
4523 cpu_buffer_a = buffer_a->buffers[cpu];
4524 cpu_buffer_b = buffer_b->buffers[cpu];
4525
4526 /* At least make sure the two buffers are somewhat the same */
4527 if (cpu_buffer_a->nr_pages != cpu_buffer_b->nr_pages)
4528 goto out;
4529
4530 ret = -EAGAIN;
4531
4532 if (atomic_read(&buffer_a->record_disabled))
4533 goto out;
4534
4535 if (atomic_read(&buffer_b->record_disabled))
4536 goto out;
4537
4538 if (atomic_read(&cpu_buffer_a->record_disabled))
4539 goto out;
4540
4541 if (atomic_read(&cpu_buffer_b->record_disabled))
4542 goto out;
4543
4544 /*
4545 * We can't do a synchronize_rcu here because this
4546 * function can be called in atomic context.
4547 * Normally this will be called from the same CPU as cpu.
4548 * If not it's up to the caller to protect this.
4549 */
4550 atomic_inc(&cpu_buffer_a->record_disabled);
4551 atomic_inc(&cpu_buffer_b->record_disabled);
4552
4553 ret = -EBUSY;
4554 if (local_read(&cpu_buffer_a->committing))
4555 goto out_dec;
4556 if (local_read(&cpu_buffer_b->committing))
4557 goto out_dec;
4558
4559 buffer_a->buffers[cpu] = cpu_buffer_b;
4560 buffer_b->buffers[cpu] = cpu_buffer_a;
4561
4562 cpu_buffer_b->buffer = buffer_a;
4563 cpu_buffer_a->buffer = buffer_b;
4564
4565 ret = 0;
4566
4567out_dec:
4568 atomic_dec(&cpu_buffer_a->record_disabled);
4569 atomic_dec(&cpu_buffer_b->record_disabled);
4570out:
4571 return ret;
4572}
4573EXPORT_SYMBOL_GPL(ring_buffer_swap_cpu);
4574#endif /* CONFIG_RING_BUFFER_ALLOW_SWAP */
4575
4576/**
4577 * ring_buffer_alloc_read_page - allocate a page to read from buffer
4578 * @buffer: the buffer to allocate for.
4579 * @cpu: the cpu buffer to allocate.
4580 *
4581 * This function is used in conjunction with ring_buffer_read_page.
4582 * When reading a full page from the ring buffer, these functions
4583 * can be used to speed up the process. The calling function should
4584 * allocate a few pages first with this function. Then when it
4585 * needs to get pages from the ring buffer, it passes the result
4586 * of this function into ring_buffer_read_page, which will swap
4587 * the page that was allocated, with the read page of the buffer.
4588 *
4589 * Returns:
4590 * The page allocated, or ERR_PTR
4591 */
4592void *ring_buffer_alloc_read_page(struct ring_buffer *buffer, int cpu)
4593{
4594 struct ring_buffer_per_cpu *cpu_buffer;
4595 struct buffer_data_page *bpage = NULL;
4596 unsigned long flags;
4597 struct page *page;
4598
4599 if (!cpumask_test_cpu(cpu, buffer->cpumask))
4600 return ERR_PTR(-ENODEV);
4601
4602 cpu_buffer = buffer->buffers[cpu];
4603 local_irq_save(flags);
4604 arch_spin_lock(&cpu_buffer->lock);
4605
4606 if (cpu_buffer->free_page) {
4607 bpage = cpu_buffer->free_page;
4608 cpu_buffer->free_page = NULL;
4609 }
4610
4611 arch_spin_unlock(&cpu_buffer->lock);
4612 local_irq_restore(flags);
4613
4614 if (bpage)
4615 goto out;
4616
4617 page = alloc_pages_node(cpu_to_node(cpu),
4618 GFP_KERNEL | __GFP_NORETRY, 0);
4619 if (!page)
4620 return ERR_PTR(-ENOMEM);
4621
4622 bpage = page_address(page);
4623
4624 out:
4625 rb_init_page(bpage);
4626
4627 return bpage;
4628}
4629EXPORT_SYMBOL_GPL(ring_buffer_alloc_read_page);
4630
4631/**
4632 * ring_buffer_free_read_page - free an allocated read page
4633 * @buffer: the buffer the page was allocate for
4634 * @cpu: the cpu buffer the page came from
4635 * @data: the page to free
4636 *
4637 * Free a page allocated from ring_buffer_alloc_read_page.
4638 */
4639void ring_buffer_free_read_page(struct ring_buffer *buffer, int cpu, void *data)
4640{
4641 struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
4642 struct buffer_data_page *bpage = data;
4643 struct page *page = virt_to_page(bpage);
4644 unsigned long flags;
4645
4646 /* If the page is still in use someplace else, we can't reuse it */
4647 if (page_ref_count(page) > 1)
4648 goto out;
4649
4650 local_irq_save(flags);
4651 arch_spin_lock(&cpu_buffer->lock);
4652
4653 if (!cpu_buffer->free_page) {
4654 cpu_buffer->free_page = bpage;
4655 bpage = NULL;
4656 }
4657
4658 arch_spin_unlock(&cpu_buffer->lock);
4659 local_irq_restore(flags);
4660
4661 out:
4662 free_page((unsigned long)bpage);
4663}
4664EXPORT_SYMBOL_GPL(ring_buffer_free_read_page);
4665
4666/**
4667 * ring_buffer_read_page - extract a page from the ring buffer
4668 * @buffer: buffer to extract from
4669 * @data_page: the page to use allocated from ring_buffer_alloc_read_page
4670 * @len: amount to extract
4671 * @cpu: the cpu of the buffer to extract
4672 * @full: should the extraction only happen when the page is full.
4673 *
4674 * This function will pull out a page from the ring buffer and consume it.
4675 * @data_page must be the address of the variable that was returned
4676 * from ring_buffer_alloc_read_page. This is because the page might be used
4677 * to swap with a page in the ring buffer.
4678 *
4679 * for example:
4680 * rpage = ring_buffer_alloc_read_page(buffer, cpu);
4681 * if (IS_ERR(rpage))
4682 * return PTR_ERR(rpage);
4683 * ret = ring_buffer_read_page(buffer, &rpage, len, cpu, 0);
4684 * if (ret >= 0)
4685 * process_page(rpage, ret);
4686 *
4687 * When @full is set, the function will not return true unless
4688 * the writer is off the reader page.
4689 *
4690 * Note: it is up to the calling functions to handle sleeps and wakeups.
4691 * The ring buffer can be used anywhere in the kernel and can not
4692 * blindly call wake_up. The layer that uses the ring buffer must be
4693 * responsible for that.
4694 *
4695 * Returns:
4696 * >=0 if data has been transferred, returns the offset of consumed data.
4697 * <0 if no data has been transferred.
4698 */
4699int ring_buffer_read_page(struct ring_buffer *buffer,
4700 void **data_page, size_t len, int cpu, int full)
4701{
4702 struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
4703 struct ring_buffer_event *event;
4704 struct buffer_data_page *bpage;
4705 struct buffer_page *reader;
4706 unsigned long missed_events;
4707 unsigned long flags;
4708 unsigned int commit;
4709 unsigned int read;
4710 u64 save_timestamp;
4711 int ret = -1;
4712
4713 if (!cpumask_test_cpu(cpu, buffer->cpumask))
4714 goto out;
4715
4716 /*
4717 * If len is not big enough to hold the page header, then
4718 * we can not copy anything.
4719 */
4720 if (len <= BUF_PAGE_HDR_SIZE)
4721 goto out;
4722
4723 len -= BUF_PAGE_HDR_SIZE;
4724
4725 if (!data_page)
4726 goto out;
4727
4728 bpage = *data_page;
4729 if (!bpage)
4730 goto out;
4731
4732 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
4733
4734 reader = rb_get_reader_page(cpu_buffer);
4735 if (!reader)
4736 goto out_unlock;
4737
4738 event = rb_reader_event(cpu_buffer);
4739
4740 read = reader->read;
4741 commit = rb_page_commit(reader);
4742
4743 /* Check if any events were dropped */
4744 missed_events = cpu_buffer->lost_events;
4745
4746 /*
4747 * If this page has been partially read or
4748 * if len is not big enough to read the rest of the page or
4749 * a writer is still on the page, then
4750 * we must copy the data from the page to the buffer.
4751 * Otherwise, we can simply swap the page with the one passed in.
4752 */
4753 if (read || (len < (commit - read)) ||
4754 cpu_buffer->reader_page == cpu_buffer->commit_page) {
4755 struct buffer_data_page *rpage = cpu_buffer->reader_page->page;
4756 unsigned int rpos = read;
4757 unsigned int pos = 0;
4758 unsigned int size;
4759
4760 if (full)
4761 goto out_unlock;
4762
4763 if (len > (commit - read))
4764 len = (commit - read);
4765
4766 /* Always keep the time extend and data together */
4767 size = rb_event_ts_length(event);
4768
4769 if (len < size)
4770 goto out_unlock;
4771
4772 /* save the current timestamp, since the user will need it */
4773 save_timestamp = cpu_buffer->read_stamp;
4774
4775 /* Need to copy one event at a time */
4776 do {
4777 /* We need the size of one event, because
4778 * rb_advance_reader only advances by one event,
4779 * whereas rb_event_ts_length may include the size of
4780 * one or two events.
4781 * We have already ensured there's enough space if this
4782 * is a time extend. */
4783 size = rb_event_length(event);
4784 memcpy(bpage->data + pos, rpage->data + rpos, size);
4785
4786 len -= size;
4787
4788 rb_advance_reader(cpu_buffer);
4789 rpos = reader->read;
4790 pos += size;
4791
4792 if (rpos >= commit)
4793 break;
4794
4795 event = rb_reader_event(cpu_buffer);
4796 /* Always keep the time extend and data together */
4797 size = rb_event_ts_length(event);
4798 } while (len >= size);
4799
4800 /* update bpage */
4801 local_set(&bpage->commit, pos);
4802 bpage->time_stamp = save_timestamp;
4803
4804 /* we copied everything to the beginning */
4805 read = 0;
4806 } else {
4807 /* update the entry counter */
4808 cpu_buffer->read += rb_page_entries(reader);
4809 cpu_buffer->read_bytes += BUF_PAGE_SIZE;
4810
4811 /* swap the pages */
4812 rb_init_page(bpage);
4813 bpage = reader->page;
4814 reader->page = *data_page;
4815 local_set(&reader->write, 0);
4816 local_set(&reader->entries, 0);
4817 reader->read = 0;
4818 *data_page = bpage;
4819
4820 /*
4821 * Use the real_end for the data size,
4822 * This gives us a chance to store the lost events
4823 * on the page.
4824 */
4825 if (reader->real_end)
4826 local_set(&bpage->commit, reader->real_end);
4827 }
4828 ret = read;
4829
4830 cpu_buffer->lost_events = 0;
4831
4832 commit = local_read(&bpage->commit);
4833 /*
4834 * Set a flag in the commit field if we lost events
4835 */
4836 if (missed_events) {
4837 /* If there is room at the end of the page to save the
4838 * missed events, then record it there.
4839 */
4840 if (BUF_PAGE_SIZE - commit >= sizeof(missed_events)) {
4841 memcpy(&bpage->data[commit], &missed_events,
4842 sizeof(missed_events));
4843 local_add(RB_MISSED_STORED, &bpage->commit);
4844 commit += sizeof(missed_events);
4845 }
4846 local_add(RB_MISSED_EVENTS, &bpage->commit);
4847 }
4848
4849 /*
4850 * This page may be off to user land. Zero it out here.
4851 */
4852 if (commit < BUF_PAGE_SIZE)
4853 memset(&bpage->data[commit], 0, BUF_PAGE_SIZE - commit);
4854
4855 out_unlock:
4856 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
4857
4858 out:
4859 return ret;
4860}
4861EXPORT_SYMBOL_GPL(ring_buffer_read_page);
4862
4863/*
4864 * We only allocate new buffers, never free them if the CPU goes down.
4865 * If we were to free the buffer, then the user would lose any trace that was in
4866 * the buffer.
4867 */
4868int trace_rb_cpu_prepare(unsigned int cpu, struct hlist_node *node)
4869{
4870 struct ring_buffer *buffer;
4871 long nr_pages_same;
4872 int cpu_i;
4873 unsigned long nr_pages;
4874
4875 buffer = container_of(node, struct ring_buffer, node);
4876 if (cpumask_test_cpu(cpu, buffer->cpumask))
4877 return 0;
4878
4879 nr_pages = 0;
4880 nr_pages_same = 1;
4881 /* check if all cpu sizes are same */
4882 for_each_buffer_cpu(buffer, cpu_i) {
4883 /* fill in the size from first enabled cpu */
4884 if (nr_pages == 0)
4885 nr_pages = buffer->buffers[cpu_i]->nr_pages;
4886 if (nr_pages != buffer->buffers[cpu_i]->nr_pages) {
4887 nr_pages_same = 0;
4888 break;
4889 }
4890 }
4891 /* allocate minimum pages, user can later expand it */
4892 if (!nr_pages_same)
4893 nr_pages = 2;
4894 buffer->buffers[cpu] =
4895 rb_allocate_cpu_buffer(buffer, nr_pages, cpu);
4896 if (!buffer->buffers[cpu]) {
4897 WARN(1, "failed to allocate ring buffer on CPU %u\n",
4898 cpu);
4899 return -ENOMEM;
4900 }
4901 smp_wmb();
4902 cpumask_set_cpu(cpu, buffer->cpumask);
4903 return 0;
4904}
4905
4906#ifdef CONFIG_RING_BUFFER_STARTUP_TEST
4907/*
4908 * This is a basic integrity check of the ring buffer.
4909 * Late in the boot cycle this test will run when configured in.
4910 * It will kick off a thread per CPU that will go into a loop
4911 * writing to the per cpu ring buffer various sizes of data.
4912 * Some of the data will be large items, some small.
4913 *
4914 * Another thread is created that goes into a spin, sending out
4915 * IPIs to the other CPUs to also write into the ring buffer.
4916 * this is to test the nesting ability of the buffer.
4917 *
4918 * Basic stats are recorded and reported. If something in the
4919 * ring buffer should happen that's not expected, a big warning
4920 * is displayed and all ring buffers are disabled.
4921 */
4922static struct task_struct *rb_threads[NR_CPUS] __initdata;
4923
4924struct rb_test_data {
4925 struct ring_buffer *buffer;
4926 unsigned long events;
4927 unsigned long bytes_written;
4928 unsigned long bytes_alloc;
4929 unsigned long bytes_dropped;
4930 unsigned long events_nested;
4931 unsigned long bytes_written_nested;
4932 unsigned long bytes_alloc_nested;
4933 unsigned long bytes_dropped_nested;
4934 int min_size_nested;
4935 int max_size_nested;
4936 int max_size;
4937 int min_size;
4938 int cpu;
4939 int cnt;
4940};
4941
4942static struct rb_test_data rb_data[NR_CPUS] __initdata;
4943
4944/* 1 meg per cpu */
4945#define RB_TEST_BUFFER_SIZE 1048576
4946
4947static char rb_string[] __initdata =
4948 "abcdefghijklmnopqrstuvwxyz1234567890!@#$%^&*()?+\\"
4949 "?+|:';\",.<>/?abcdefghijklmnopqrstuvwxyz1234567890"
4950 "!@#$%^&*()?+\\?+|:';\",.<>/?abcdefghijklmnopqrstuv";
4951
4952static bool rb_test_started __initdata;
4953
4954struct rb_item {
4955 int size;
4956 char str[];
4957};
4958
4959static __init int rb_write_something(struct rb_test_data *data, bool nested)
4960{
4961 struct ring_buffer_event *event;
4962 struct rb_item *item;
4963 bool started;
4964 int event_len;
4965 int size;
4966 int len;
4967 int cnt;
4968
4969 /* Have nested writes different that what is written */
4970 cnt = data->cnt + (nested ? 27 : 0);
4971
4972 /* Multiply cnt by ~e, to make some unique increment */
4973 size = (cnt * 68 / 25) % (sizeof(rb_string) - 1);
4974
4975 len = size + sizeof(struct rb_item);
4976
4977 started = rb_test_started;
4978 /* read rb_test_started before checking buffer enabled */
4979 smp_rmb();
4980
4981 event = ring_buffer_lock_reserve(data->buffer, len);
4982 if (!event) {
4983 /* Ignore dropped events before test starts. */
4984 if (started) {
4985 if (nested)
4986 data->bytes_dropped += len;
4987 else
4988 data->bytes_dropped_nested += len;
4989 }
4990 return len;
4991 }
4992
4993 event_len = ring_buffer_event_length(event);
4994
4995 if (RB_WARN_ON(data->buffer, event_len < len))
4996 goto out;
4997
4998 item = ring_buffer_event_data(event);
4999 item->size = size;
5000 memcpy(item->str, rb_string, size);
5001
5002 if (nested) {
5003 data->bytes_alloc_nested += event_len;
5004 data->bytes_written_nested += len;
5005 data->events_nested++;
5006 if (!data->min_size_nested || len < data->min_size_nested)
5007 data->min_size_nested = len;
5008 if (len > data->max_size_nested)
5009 data->max_size_nested = len;
5010 } else {
5011 data->bytes_alloc += event_len;
5012 data->bytes_written += len;
5013 data->events++;
5014 if (!data->min_size || len < data->min_size)
5015 data->max_size = len;
5016 if (len > data->max_size)
5017 data->max_size = len;
5018 }
5019
5020 out:
5021 ring_buffer_unlock_commit(data->buffer, event);
5022
5023 return 0;
5024}
5025
5026static __init int rb_test(void *arg)
5027{
5028 struct rb_test_data *data = arg;
5029
5030 while (!kthread_should_stop()) {
5031 rb_write_something(data, false);
5032 data->cnt++;
5033
5034 set_current_state(TASK_INTERRUPTIBLE);
5035 /* Now sleep between a min of 100-300us and a max of 1ms */
5036 usleep_range(((data->cnt % 3) + 1) * 100, 1000);
5037 }
5038
5039 return 0;
5040}
5041
5042static __init void rb_ipi(void *ignore)
5043{
5044 struct rb_test_data *data;
5045 int cpu = smp_processor_id();
5046
5047 data = &rb_data[cpu];
5048 rb_write_something(data, true);
5049}
5050
5051static __init int rb_hammer_test(void *arg)
5052{
5053 while (!kthread_should_stop()) {
5054
5055 /* Send an IPI to all cpus to write data! */
5056 smp_call_function(rb_ipi, NULL, 1);
5057 /* No sleep, but for non preempt, let others run */
5058 schedule();
5059 }
5060
5061 return 0;
5062}
5063
5064static __init int test_ringbuffer(void)
5065{
5066 struct task_struct *rb_hammer;
5067 struct ring_buffer *buffer;
5068 int cpu;
5069 int ret = 0;
5070
5071 pr_info("Running ring buffer tests...\n");
5072
5073 buffer = ring_buffer_alloc(RB_TEST_BUFFER_SIZE, RB_FL_OVERWRITE);
5074 if (WARN_ON(!buffer))
5075 return 0;
5076
5077 /* Disable buffer so that threads can't write to it yet */
5078 ring_buffer_record_off(buffer);
5079
5080 for_each_online_cpu(cpu) {
5081 rb_data[cpu].buffer = buffer;
5082 rb_data[cpu].cpu = cpu;
5083 rb_data[cpu].cnt = cpu;
5084 rb_threads[cpu] = kthread_create(rb_test, &rb_data[cpu],
5085 "rbtester/%d", cpu);
5086 if (WARN_ON(IS_ERR(rb_threads[cpu]))) {
5087 pr_cont("FAILED\n");
5088 ret = PTR_ERR(rb_threads[cpu]);
5089 goto out_free;
5090 }
5091
5092 kthread_bind(rb_threads[cpu], cpu);
5093 wake_up_process(rb_threads[cpu]);
5094 }
5095
5096 /* Now create the rb hammer! */
5097 rb_hammer = kthread_run(rb_hammer_test, NULL, "rbhammer");
5098 if (WARN_ON(IS_ERR(rb_hammer))) {
5099 pr_cont("FAILED\n");
5100 ret = PTR_ERR(rb_hammer);
5101 goto out_free;
5102 }
5103
5104 ring_buffer_record_on(buffer);
5105 /*
5106 * Show buffer is enabled before setting rb_test_started.
5107 * Yes there's a small race window where events could be
5108 * dropped and the thread wont catch it. But when a ring
5109 * buffer gets enabled, there will always be some kind of
5110 * delay before other CPUs see it. Thus, we don't care about
5111 * those dropped events. We care about events dropped after
5112 * the threads see that the buffer is active.
5113 */
5114 smp_wmb();
5115 rb_test_started = true;
5116
5117 set_current_state(TASK_INTERRUPTIBLE);
5118 /* Just run for 10 seconds */;
5119 schedule_timeout(10 * HZ);
5120
5121 kthread_stop(rb_hammer);
5122
5123 out_free:
5124 for_each_online_cpu(cpu) {
5125 if (!rb_threads[cpu])
5126 break;
5127 kthread_stop(rb_threads[cpu]);
5128 }
5129 if (ret) {
5130 ring_buffer_free(buffer);
5131 return ret;
5132 }
5133
5134 /* Report! */
5135 pr_info("finished\n");
5136 for_each_online_cpu(cpu) {
5137 struct ring_buffer_event *event;
5138 struct rb_test_data *data = &rb_data[cpu];
5139 struct rb_item *item;
5140 unsigned long total_events;
5141 unsigned long total_dropped;
5142 unsigned long total_written;
5143 unsigned long total_alloc;
5144 unsigned long total_read = 0;
5145 unsigned long total_size = 0;
5146 unsigned long total_len = 0;
5147 unsigned long total_lost = 0;
5148 unsigned long lost;
5149 int big_event_size;
5150 int small_event_size;
5151
5152 ret = -1;
5153
5154 total_events = data->events + data->events_nested;
5155 total_written = data->bytes_written + data->bytes_written_nested;
5156 total_alloc = data->bytes_alloc + data->bytes_alloc_nested;
5157 total_dropped = data->bytes_dropped + data->bytes_dropped_nested;
5158
5159 big_event_size = data->max_size + data->max_size_nested;
5160 small_event_size = data->min_size + data->min_size_nested;
5161
5162 pr_info("CPU %d:\n", cpu);
5163 pr_info(" events: %ld\n", total_events);
5164 pr_info(" dropped bytes: %ld\n", total_dropped);
5165 pr_info(" alloced bytes: %ld\n", total_alloc);
5166 pr_info(" written bytes: %ld\n", total_written);
5167 pr_info(" biggest event: %d\n", big_event_size);
5168 pr_info(" smallest event: %d\n", small_event_size);
5169
5170 if (RB_WARN_ON(buffer, total_dropped))
5171 break;
5172
5173 ret = 0;
5174
5175 while ((event = ring_buffer_consume(buffer, cpu, NULL, &lost))) {
5176 total_lost += lost;
5177 item = ring_buffer_event_data(event);
5178 total_len += ring_buffer_event_length(event);
5179 total_size += item->size + sizeof(struct rb_item);
5180 if (memcmp(&item->str[0], rb_string, item->size) != 0) {
5181 pr_info("FAILED!\n");
5182 pr_info("buffer had: %.*s\n", item->size, item->str);
5183 pr_info("expected: %.*s\n", item->size, rb_string);
5184 RB_WARN_ON(buffer, 1);
5185 ret = -1;
5186 break;
5187 }
5188 total_read++;
5189 }
5190 if (ret)
5191 break;
5192
5193 ret = -1;
5194
5195 pr_info(" read events: %ld\n", total_read);
5196 pr_info(" lost events: %ld\n", total_lost);
5197 pr_info(" total events: %ld\n", total_lost + total_read);
5198 pr_info(" recorded len bytes: %ld\n", total_len);
5199 pr_info(" recorded size bytes: %ld\n", total_size);
5200 if (total_lost)
5201 pr_info(" With dropped events, record len and size may not match\n"
5202 " alloced and written from above\n");
5203 if (!total_lost) {
5204 if (RB_WARN_ON(buffer, total_len != total_alloc ||
5205 total_size != total_written))
5206 break;
5207 }
5208 if (RB_WARN_ON(buffer, total_lost + total_read != total_events))
5209 break;
5210
5211 ret = 0;
5212 }
5213 if (!ret)
5214 pr_info("Ring buffer PASSED!\n");
5215
5216 ring_buffer_free(buffer);
5217 return 0;
5218}
5219
5220late_initcall(test_ringbuffer);
5221#endif /* CONFIG_RING_BUFFER_STARTUP_TEST */
1/*
2 * Generic ring buffer
3 *
4 * Copyright (C) 2008 Steven Rostedt <srostedt@redhat.com>
5 */
6#include <linux/trace_events.h>
7#include <linux/ring_buffer.h>
8#include <linux/trace_clock.h>
9#include <linux/sched/clock.h>
10#include <linux/trace_seq.h>
11#include <linux/spinlock.h>
12#include <linux/irq_work.h>
13#include <linux/uaccess.h>
14#include <linux/hardirq.h>
15#include <linux/kthread.h> /* for self test */
16#include <linux/module.h>
17#include <linux/percpu.h>
18#include <linux/mutex.h>
19#include <linux/delay.h>
20#include <linux/slab.h>
21#include <linux/init.h>
22#include <linux/hash.h>
23#include <linux/list.h>
24#include <linux/cpu.h>
25#include <linux/oom.h>
26
27#include <asm/local.h>
28
29static void update_pages_handler(struct work_struct *work);
30
31/*
32 * The ring buffer header is special. We must manually up keep it.
33 */
34int ring_buffer_print_entry_header(struct trace_seq *s)
35{
36 trace_seq_puts(s, "# compressed entry header\n");
37 trace_seq_puts(s, "\ttype_len : 5 bits\n");
38 trace_seq_puts(s, "\ttime_delta : 27 bits\n");
39 trace_seq_puts(s, "\tarray : 32 bits\n");
40 trace_seq_putc(s, '\n');
41 trace_seq_printf(s, "\tpadding : type == %d\n",
42 RINGBUF_TYPE_PADDING);
43 trace_seq_printf(s, "\ttime_extend : type == %d\n",
44 RINGBUF_TYPE_TIME_EXTEND);
45 trace_seq_printf(s, "\ttime_stamp : type == %d\n",
46 RINGBUF_TYPE_TIME_STAMP);
47 trace_seq_printf(s, "\tdata max type_len == %d\n",
48 RINGBUF_TYPE_DATA_TYPE_LEN_MAX);
49
50 return !trace_seq_has_overflowed(s);
51}
52
53/*
54 * The ring buffer is made up of a list of pages. A separate list of pages is
55 * allocated for each CPU. A writer may only write to a buffer that is
56 * associated with the CPU it is currently executing on. A reader may read
57 * from any per cpu buffer.
58 *
59 * The reader is special. For each per cpu buffer, the reader has its own
60 * reader page. When a reader has read the entire reader page, this reader
61 * page is swapped with another page in the ring buffer.
62 *
63 * Now, as long as the writer is off the reader page, the reader can do what
64 * ever it wants with that page. The writer will never write to that page
65 * again (as long as it is out of the ring buffer).
66 *
67 * Here's some silly ASCII art.
68 *
69 * +------+
70 * |reader| RING BUFFER
71 * |page |
72 * +------+ +---+ +---+ +---+
73 * | |-->| |-->| |
74 * +---+ +---+ +---+
75 * ^ |
76 * | |
77 * +---------------+
78 *
79 *
80 * +------+
81 * |reader| RING BUFFER
82 * |page |------------------v
83 * +------+ +---+ +---+ +---+
84 * | |-->| |-->| |
85 * +---+ +---+ +---+
86 * ^ |
87 * | |
88 * +---------------+
89 *
90 *
91 * +------+
92 * |reader| RING BUFFER
93 * |page |------------------v
94 * +------+ +---+ +---+ +---+
95 * ^ | |-->| |-->| |
96 * | +---+ +---+ +---+
97 * | |
98 * | |
99 * +------------------------------+
100 *
101 *
102 * +------+
103 * |buffer| RING BUFFER
104 * |page |------------------v
105 * +------+ +---+ +---+ +---+
106 * ^ | | | |-->| |
107 * | New +---+ +---+ +---+
108 * | Reader------^ |
109 * | page |
110 * +------------------------------+
111 *
112 *
113 * After we make this swap, the reader can hand this page off to the splice
114 * code and be done with it. It can even allocate a new page if it needs to
115 * and swap that into the ring buffer.
116 *
117 * We will be using cmpxchg soon to make all this lockless.
118 *
119 */
120
121/* Used for individual buffers (after the counter) */
122#define RB_BUFFER_OFF (1 << 20)
123
124#define BUF_PAGE_HDR_SIZE offsetof(struct buffer_data_page, data)
125
126#define RB_EVNT_HDR_SIZE (offsetof(struct ring_buffer_event, array))
127#define RB_ALIGNMENT 4U
128#define RB_MAX_SMALL_DATA (RB_ALIGNMENT * RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
129#define RB_EVNT_MIN_SIZE 8U /* two 32bit words */
130
131#ifndef CONFIG_HAVE_64BIT_ALIGNED_ACCESS
132# define RB_FORCE_8BYTE_ALIGNMENT 0
133# define RB_ARCH_ALIGNMENT RB_ALIGNMENT
134#else
135# define RB_FORCE_8BYTE_ALIGNMENT 1
136# define RB_ARCH_ALIGNMENT 8U
137#endif
138
139#define RB_ALIGN_DATA __aligned(RB_ARCH_ALIGNMENT)
140
141/* define RINGBUF_TYPE_DATA for 'case RINGBUF_TYPE_DATA:' */
142#define RINGBUF_TYPE_DATA 0 ... RINGBUF_TYPE_DATA_TYPE_LEN_MAX
143
144enum {
145 RB_LEN_TIME_EXTEND = 8,
146 RB_LEN_TIME_STAMP = 8,
147};
148
149#define skip_time_extend(event) \
150 ((struct ring_buffer_event *)((char *)event + RB_LEN_TIME_EXTEND))
151
152#define extended_time(event) \
153 (event->type_len >= RINGBUF_TYPE_TIME_EXTEND)
154
155static inline int rb_null_event(struct ring_buffer_event *event)
156{
157 return event->type_len == RINGBUF_TYPE_PADDING && !event->time_delta;
158}
159
160static void rb_event_set_padding(struct ring_buffer_event *event)
161{
162 /* padding has a NULL time_delta */
163 event->type_len = RINGBUF_TYPE_PADDING;
164 event->time_delta = 0;
165}
166
167static unsigned
168rb_event_data_length(struct ring_buffer_event *event)
169{
170 unsigned length;
171
172 if (event->type_len)
173 length = event->type_len * RB_ALIGNMENT;
174 else
175 length = event->array[0];
176 return length + RB_EVNT_HDR_SIZE;
177}
178
179/*
180 * Return the length of the given event. Will return
181 * the length of the time extend if the event is a
182 * time extend.
183 */
184static inline unsigned
185rb_event_length(struct ring_buffer_event *event)
186{
187 switch (event->type_len) {
188 case RINGBUF_TYPE_PADDING:
189 if (rb_null_event(event))
190 /* undefined */
191 return -1;
192 return event->array[0] + RB_EVNT_HDR_SIZE;
193
194 case RINGBUF_TYPE_TIME_EXTEND:
195 return RB_LEN_TIME_EXTEND;
196
197 case RINGBUF_TYPE_TIME_STAMP:
198 return RB_LEN_TIME_STAMP;
199
200 case RINGBUF_TYPE_DATA:
201 return rb_event_data_length(event);
202 default:
203 BUG();
204 }
205 /* not hit */
206 return 0;
207}
208
209/*
210 * Return total length of time extend and data,
211 * or just the event length for all other events.
212 */
213static inline unsigned
214rb_event_ts_length(struct ring_buffer_event *event)
215{
216 unsigned len = 0;
217
218 if (extended_time(event)) {
219 /* time extends include the data event after it */
220 len = RB_LEN_TIME_EXTEND;
221 event = skip_time_extend(event);
222 }
223 return len + rb_event_length(event);
224}
225
226/**
227 * ring_buffer_event_length - return the length of the event
228 * @event: the event to get the length of
229 *
230 * Returns the size of the data load of a data event.
231 * If the event is something other than a data event, it
232 * returns the size of the event itself. With the exception
233 * of a TIME EXTEND, where it still returns the size of the
234 * data load of the data event after it.
235 */
236unsigned ring_buffer_event_length(struct ring_buffer_event *event)
237{
238 unsigned length;
239
240 if (extended_time(event))
241 event = skip_time_extend(event);
242
243 length = rb_event_length(event);
244 if (event->type_len > RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
245 return length;
246 length -= RB_EVNT_HDR_SIZE;
247 if (length > RB_MAX_SMALL_DATA + sizeof(event->array[0]))
248 length -= sizeof(event->array[0]);
249 return length;
250}
251EXPORT_SYMBOL_GPL(ring_buffer_event_length);
252
253/* inline for ring buffer fast paths */
254static __always_inline void *
255rb_event_data(struct ring_buffer_event *event)
256{
257 if (extended_time(event))
258 event = skip_time_extend(event);
259 BUG_ON(event->type_len > RINGBUF_TYPE_DATA_TYPE_LEN_MAX);
260 /* If length is in len field, then array[0] has the data */
261 if (event->type_len)
262 return (void *)&event->array[0];
263 /* Otherwise length is in array[0] and array[1] has the data */
264 return (void *)&event->array[1];
265}
266
267/**
268 * ring_buffer_event_data - return the data of the event
269 * @event: the event to get the data from
270 */
271void *ring_buffer_event_data(struct ring_buffer_event *event)
272{
273 return rb_event_data(event);
274}
275EXPORT_SYMBOL_GPL(ring_buffer_event_data);
276
277#define for_each_buffer_cpu(buffer, cpu) \
278 for_each_cpu(cpu, buffer->cpumask)
279
280#define TS_SHIFT 27
281#define TS_MASK ((1ULL << TS_SHIFT) - 1)
282#define TS_DELTA_TEST (~TS_MASK)
283
284/**
285 * ring_buffer_event_time_stamp - return the event's extended timestamp
286 * @event: the event to get the timestamp of
287 *
288 * Returns the extended timestamp associated with a data event.
289 * An extended time_stamp is a 64-bit timestamp represented
290 * internally in a special way that makes the best use of space
291 * contained within a ring buffer event. This function decodes
292 * it and maps it to a straight u64 value.
293 */
294u64 ring_buffer_event_time_stamp(struct ring_buffer_event *event)
295{
296 u64 ts;
297
298 ts = event->array[0];
299 ts <<= TS_SHIFT;
300 ts += event->time_delta;
301
302 return ts;
303}
304
305/* Flag when events were overwritten */
306#define RB_MISSED_EVENTS (1 << 31)
307/* Missed count stored at end */
308#define RB_MISSED_STORED (1 << 30)
309
310#define RB_MISSED_FLAGS (RB_MISSED_EVENTS|RB_MISSED_STORED)
311
312struct buffer_data_page {
313 u64 time_stamp; /* page time stamp */
314 local_t commit; /* write committed index */
315 unsigned char data[] RB_ALIGN_DATA; /* data of buffer page */
316};
317
318/*
319 * Note, the buffer_page list must be first. The buffer pages
320 * are allocated in cache lines, which means that each buffer
321 * page will be at the beginning of a cache line, and thus
322 * the least significant bits will be zero. We use this to
323 * add flags in the list struct pointers, to make the ring buffer
324 * lockless.
325 */
326struct buffer_page {
327 struct list_head list; /* list of buffer pages */
328 local_t write; /* index for next write */
329 unsigned read; /* index for next read */
330 local_t entries; /* entries on this page */
331 unsigned long real_end; /* real end of data */
332 struct buffer_data_page *page; /* Actual data page */
333};
334
335/*
336 * The buffer page counters, write and entries, must be reset
337 * atomically when crossing page boundaries. To synchronize this
338 * update, two counters are inserted into the number. One is
339 * the actual counter for the write position or count on the page.
340 *
341 * The other is a counter of updaters. Before an update happens
342 * the update partition of the counter is incremented. This will
343 * allow the updater to update the counter atomically.
344 *
345 * The counter is 20 bits, and the state data is 12.
346 */
347#define RB_WRITE_MASK 0xfffff
348#define RB_WRITE_INTCNT (1 << 20)
349
350static void rb_init_page(struct buffer_data_page *bpage)
351{
352 local_set(&bpage->commit, 0);
353}
354
355/**
356 * ring_buffer_page_len - the size of data on the page.
357 * @page: The page to read
358 *
359 * Returns the amount of data on the page, including buffer page header.
360 */
361size_t ring_buffer_page_len(void *page)
362{
363 struct buffer_data_page *bpage = page;
364
365 return (local_read(&bpage->commit) & ~RB_MISSED_FLAGS)
366 + BUF_PAGE_HDR_SIZE;
367}
368
369/*
370 * Also stolen from mm/slob.c. Thanks to Mathieu Desnoyers for pointing
371 * this issue out.
372 */
373static void free_buffer_page(struct buffer_page *bpage)
374{
375 free_page((unsigned long)bpage->page);
376 kfree(bpage);
377}
378
379/*
380 * We need to fit the time_stamp delta into 27 bits.
381 */
382static inline int test_time_stamp(u64 delta)
383{
384 if (delta & TS_DELTA_TEST)
385 return 1;
386 return 0;
387}
388
389#define BUF_PAGE_SIZE (PAGE_SIZE - BUF_PAGE_HDR_SIZE)
390
391/* Max payload is BUF_PAGE_SIZE - header (8bytes) */
392#define BUF_MAX_DATA_SIZE (BUF_PAGE_SIZE - (sizeof(u32) * 2))
393
394int ring_buffer_print_page_header(struct trace_seq *s)
395{
396 struct buffer_data_page field;
397
398 trace_seq_printf(s, "\tfield: u64 timestamp;\t"
399 "offset:0;\tsize:%u;\tsigned:%u;\n",
400 (unsigned int)sizeof(field.time_stamp),
401 (unsigned int)is_signed_type(u64));
402
403 trace_seq_printf(s, "\tfield: local_t commit;\t"
404 "offset:%u;\tsize:%u;\tsigned:%u;\n",
405 (unsigned int)offsetof(typeof(field), commit),
406 (unsigned int)sizeof(field.commit),
407 (unsigned int)is_signed_type(long));
408
409 trace_seq_printf(s, "\tfield: int overwrite;\t"
410 "offset:%u;\tsize:%u;\tsigned:%u;\n",
411 (unsigned int)offsetof(typeof(field), commit),
412 1,
413 (unsigned int)is_signed_type(long));
414
415 trace_seq_printf(s, "\tfield: char data;\t"
416 "offset:%u;\tsize:%u;\tsigned:%u;\n",
417 (unsigned int)offsetof(typeof(field), data),
418 (unsigned int)BUF_PAGE_SIZE,
419 (unsigned int)is_signed_type(char));
420
421 return !trace_seq_has_overflowed(s);
422}
423
424struct rb_irq_work {
425 struct irq_work work;
426 wait_queue_head_t waiters;
427 wait_queue_head_t full_waiters;
428 bool waiters_pending;
429 bool full_waiters_pending;
430 bool wakeup_full;
431};
432
433/*
434 * Structure to hold event state and handle nested events.
435 */
436struct rb_event_info {
437 u64 ts;
438 u64 delta;
439 unsigned long length;
440 struct buffer_page *tail_page;
441 int add_timestamp;
442};
443
444/*
445 * Used for which event context the event is in.
446 * NMI = 0
447 * IRQ = 1
448 * SOFTIRQ = 2
449 * NORMAL = 3
450 *
451 * See trace_recursive_lock() comment below for more details.
452 */
453enum {
454 RB_CTX_NMI,
455 RB_CTX_IRQ,
456 RB_CTX_SOFTIRQ,
457 RB_CTX_NORMAL,
458 RB_CTX_MAX
459};
460
461/*
462 * head_page == tail_page && head == tail then buffer is empty.
463 */
464struct ring_buffer_per_cpu {
465 int cpu;
466 atomic_t record_disabled;
467 struct ring_buffer *buffer;
468 raw_spinlock_t reader_lock; /* serialize readers */
469 arch_spinlock_t lock;
470 struct lock_class_key lock_key;
471 struct buffer_data_page *free_page;
472 unsigned long nr_pages;
473 unsigned int current_context;
474 struct list_head *pages;
475 struct buffer_page *head_page; /* read from head */
476 struct buffer_page *tail_page; /* write to tail */
477 struct buffer_page *commit_page; /* committed pages */
478 struct buffer_page *reader_page;
479 unsigned long lost_events;
480 unsigned long last_overrun;
481 unsigned long nest;
482 local_t entries_bytes;
483 local_t entries;
484 local_t overrun;
485 local_t commit_overrun;
486 local_t dropped_events;
487 local_t committing;
488 local_t commits;
489 unsigned long read;
490 unsigned long read_bytes;
491 u64 write_stamp;
492 u64 read_stamp;
493 /* ring buffer pages to update, > 0 to add, < 0 to remove */
494 long nr_pages_to_update;
495 struct list_head new_pages; /* new pages to add */
496 struct work_struct update_pages_work;
497 struct completion update_done;
498
499 struct rb_irq_work irq_work;
500};
501
502struct ring_buffer {
503 unsigned flags;
504 int cpus;
505 atomic_t record_disabled;
506 atomic_t resize_disabled;
507 cpumask_var_t cpumask;
508
509 struct lock_class_key *reader_lock_key;
510
511 struct mutex mutex;
512
513 struct ring_buffer_per_cpu **buffers;
514
515 struct hlist_node node;
516 u64 (*clock)(void);
517
518 struct rb_irq_work irq_work;
519 bool time_stamp_abs;
520};
521
522struct ring_buffer_iter {
523 struct ring_buffer_per_cpu *cpu_buffer;
524 unsigned long head;
525 struct buffer_page *head_page;
526 struct buffer_page *cache_reader_page;
527 unsigned long cache_read;
528 u64 read_stamp;
529};
530
531/*
532 * rb_wake_up_waiters - wake up tasks waiting for ring buffer input
533 *
534 * Schedules a delayed work to wake up any task that is blocked on the
535 * ring buffer waiters queue.
536 */
537static void rb_wake_up_waiters(struct irq_work *work)
538{
539 struct rb_irq_work *rbwork = container_of(work, struct rb_irq_work, work);
540
541 wake_up_all(&rbwork->waiters);
542 if (rbwork->wakeup_full) {
543 rbwork->wakeup_full = false;
544 wake_up_all(&rbwork->full_waiters);
545 }
546}
547
548/**
549 * ring_buffer_wait - wait for input to the ring buffer
550 * @buffer: buffer to wait on
551 * @cpu: the cpu buffer to wait on
552 * @full: wait until a full page is available, if @cpu != RING_BUFFER_ALL_CPUS
553 *
554 * If @cpu == RING_BUFFER_ALL_CPUS then the task will wake up as soon
555 * as data is added to any of the @buffer's cpu buffers. Otherwise
556 * it will wait for data to be added to a specific cpu buffer.
557 */
558int ring_buffer_wait(struct ring_buffer *buffer, int cpu, bool full)
559{
560 struct ring_buffer_per_cpu *uninitialized_var(cpu_buffer);
561 DEFINE_WAIT(wait);
562 struct rb_irq_work *work;
563 int ret = 0;
564
565 /*
566 * Depending on what the caller is waiting for, either any
567 * data in any cpu buffer, or a specific buffer, put the
568 * caller on the appropriate wait queue.
569 */
570 if (cpu == RING_BUFFER_ALL_CPUS) {
571 work = &buffer->irq_work;
572 /* Full only makes sense on per cpu reads */
573 full = false;
574 } else {
575 if (!cpumask_test_cpu(cpu, buffer->cpumask))
576 return -ENODEV;
577 cpu_buffer = buffer->buffers[cpu];
578 work = &cpu_buffer->irq_work;
579 }
580
581
582 while (true) {
583 if (full)
584 prepare_to_wait(&work->full_waiters, &wait, TASK_INTERRUPTIBLE);
585 else
586 prepare_to_wait(&work->waiters, &wait, TASK_INTERRUPTIBLE);
587
588 /*
589 * The events can happen in critical sections where
590 * checking a work queue can cause deadlocks.
591 * After adding a task to the queue, this flag is set
592 * only to notify events to try to wake up the queue
593 * using irq_work.
594 *
595 * We don't clear it even if the buffer is no longer
596 * empty. The flag only causes the next event to run
597 * irq_work to do the work queue wake up. The worse
598 * that can happen if we race with !trace_empty() is that
599 * an event will cause an irq_work to try to wake up
600 * an empty queue.
601 *
602 * There's no reason to protect this flag either, as
603 * the work queue and irq_work logic will do the necessary
604 * synchronization for the wake ups. The only thing
605 * that is necessary is that the wake up happens after
606 * a task has been queued. It's OK for spurious wake ups.
607 */
608 if (full)
609 work->full_waiters_pending = true;
610 else
611 work->waiters_pending = true;
612
613 if (signal_pending(current)) {
614 ret = -EINTR;
615 break;
616 }
617
618 if (cpu == RING_BUFFER_ALL_CPUS && !ring_buffer_empty(buffer))
619 break;
620
621 if (cpu != RING_BUFFER_ALL_CPUS &&
622 !ring_buffer_empty_cpu(buffer, cpu)) {
623 unsigned long flags;
624 bool pagebusy;
625
626 if (!full)
627 break;
628
629 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
630 pagebusy = cpu_buffer->reader_page == cpu_buffer->commit_page;
631 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
632
633 if (!pagebusy)
634 break;
635 }
636
637 schedule();
638 }
639
640 if (full)
641 finish_wait(&work->full_waiters, &wait);
642 else
643 finish_wait(&work->waiters, &wait);
644
645 return ret;
646}
647
648/**
649 * ring_buffer_poll_wait - poll on buffer input
650 * @buffer: buffer to wait on
651 * @cpu: the cpu buffer to wait on
652 * @filp: the file descriptor
653 * @poll_table: The poll descriptor
654 *
655 * If @cpu == RING_BUFFER_ALL_CPUS then the task will wake up as soon
656 * as data is added to any of the @buffer's cpu buffers. Otherwise
657 * it will wait for data to be added to a specific cpu buffer.
658 *
659 * Returns EPOLLIN | EPOLLRDNORM if data exists in the buffers,
660 * zero otherwise.
661 */
662__poll_t ring_buffer_poll_wait(struct ring_buffer *buffer, int cpu,
663 struct file *filp, poll_table *poll_table)
664{
665 struct ring_buffer_per_cpu *cpu_buffer;
666 struct rb_irq_work *work;
667
668 if (cpu == RING_BUFFER_ALL_CPUS)
669 work = &buffer->irq_work;
670 else {
671 if (!cpumask_test_cpu(cpu, buffer->cpumask))
672 return -EINVAL;
673
674 cpu_buffer = buffer->buffers[cpu];
675 work = &cpu_buffer->irq_work;
676 }
677
678 poll_wait(filp, &work->waiters, poll_table);
679 work->waiters_pending = true;
680 /*
681 * There's a tight race between setting the waiters_pending and
682 * checking if the ring buffer is empty. Once the waiters_pending bit
683 * is set, the next event will wake the task up, but we can get stuck
684 * if there's only a single event in.
685 *
686 * FIXME: Ideally, we need a memory barrier on the writer side as well,
687 * but adding a memory barrier to all events will cause too much of a
688 * performance hit in the fast path. We only need a memory barrier when
689 * the buffer goes from empty to having content. But as this race is
690 * extremely small, and it's not a problem if another event comes in, we
691 * will fix it later.
692 */
693 smp_mb();
694
695 if ((cpu == RING_BUFFER_ALL_CPUS && !ring_buffer_empty(buffer)) ||
696 (cpu != RING_BUFFER_ALL_CPUS && !ring_buffer_empty_cpu(buffer, cpu)))
697 return EPOLLIN | EPOLLRDNORM;
698 return 0;
699}
700
701/* buffer may be either ring_buffer or ring_buffer_per_cpu */
702#define RB_WARN_ON(b, cond) \
703 ({ \
704 int _____ret = unlikely(cond); \
705 if (_____ret) { \
706 if (__same_type(*(b), struct ring_buffer_per_cpu)) { \
707 struct ring_buffer_per_cpu *__b = \
708 (void *)b; \
709 atomic_inc(&__b->buffer->record_disabled); \
710 } else \
711 atomic_inc(&b->record_disabled); \
712 WARN_ON(1); \
713 } \
714 _____ret; \
715 })
716
717/* Up this if you want to test the TIME_EXTENTS and normalization */
718#define DEBUG_SHIFT 0
719
720static inline u64 rb_time_stamp(struct ring_buffer *buffer)
721{
722 /* shift to debug/test normalization and TIME_EXTENTS */
723 return buffer->clock() << DEBUG_SHIFT;
724}
725
726u64 ring_buffer_time_stamp(struct ring_buffer *buffer, int cpu)
727{
728 u64 time;
729
730 preempt_disable_notrace();
731 time = rb_time_stamp(buffer);
732 preempt_enable_no_resched_notrace();
733
734 return time;
735}
736EXPORT_SYMBOL_GPL(ring_buffer_time_stamp);
737
738void ring_buffer_normalize_time_stamp(struct ring_buffer *buffer,
739 int cpu, u64 *ts)
740{
741 /* Just stupid testing the normalize function and deltas */
742 *ts >>= DEBUG_SHIFT;
743}
744EXPORT_SYMBOL_GPL(ring_buffer_normalize_time_stamp);
745
746/*
747 * Making the ring buffer lockless makes things tricky.
748 * Although writes only happen on the CPU that they are on,
749 * and they only need to worry about interrupts. Reads can
750 * happen on any CPU.
751 *
752 * The reader page is always off the ring buffer, but when the
753 * reader finishes with a page, it needs to swap its page with
754 * a new one from the buffer. The reader needs to take from
755 * the head (writes go to the tail). But if a writer is in overwrite
756 * mode and wraps, it must push the head page forward.
757 *
758 * Here lies the problem.
759 *
760 * The reader must be careful to replace only the head page, and
761 * not another one. As described at the top of the file in the
762 * ASCII art, the reader sets its old page to point to the next
763 * page after head. It then sets the page after head to point to
764 * the old reader page. But if the writer moves the head page
765 * during this operation, the reader could end up with the tail.
766 *
767 * We use cmpxchg to help prevent this race. We also do something
768 * special with the page before head. We set the LSB to 1.
769 *
770 * When the writer must push the page forward, it will clear the
771 * bit that points to the head page, move the head, and then set
772 * the bit that points to the new head page.
773 *
774 * We also don't want an interrupt coming in and moving the head
775 * page on another writer. Thus we use the second LSB to catch
776 * that too. Thus:
777 *
778 * head->list->prev->next bit 1 bit 0
779 * ------- -------
780 * Normal page 0 0
781 * Points to head page 0 1
782 * New head page 1 0
783 *
784 * Note we can not trust the prev pointer of the head page, because:
785 *
786 * +----+ +-----+ +-----+
787 * | |------>| T |---X--->| N |
788 * | |<------| | | |
789 * +----+ +-----+ +-----+
790 * ^ ^ |
791 * | +-----+ | |
792 * +----------| R |----------+ |
793 * | |<-----------+
794 * +-----+
795 *
796 * Key: ---X--> HEAD flag set in pointer
797 * T Tail page
798 * R Reader page
799 * N Next page
800 *
801 * (see __rb_reserve_next() to see where this happens)
802 *
803 * What the above shows is that the reader just swapped out
804 * the reader page with a page in the buffer, but before it
805 * could make the new header point back to the new page added
806 * it was preempted by a writer. The writer moved forward onto
807 * the new page added by the reader and is about to move forward
808 * again.
809 *
810 * You can see, it is legitimate for the previous pointer of
811 * the head (or any page) not to point back to itself. But only
812 * temporarially.
813 */
814
815#define RB_PAGE_NORMAL 0UL
816#define RB_PAGE_HEAD 1UL
817#define RB_PAGE_UPDATE 2UL
818
819
820#define RB_FLAG_MASK 3UL
821
822/* PAGE_MOVED is not part of the mask */
823#define RB_PAGE_MOVED 4UL
824
825/*
826 * rb_list_head - remove any bit
827 */
828static struct list_head *rb_list_head(struct list_head *list)
829{
830 unsigned long val = (unsigned long)list;
831
832 return (struct list_head *)(val & ~RB_FLAG_MASK);
833}
834
835/*
836 * rb_is_head_page - test if the given page is the head page
837 *
838 * Because the reader may move the head_page pointer, we can
839 * not trust what the head page is (it may be pointing to
840 * the reader page). But if the next page is a header page,
841 * its flags will be non zero.
842 */
843static inline int
844rb_is_head_page(struct ring_buffer_per_cpu *cpu_buffer,
845 struct buffer_page *page, struct list_head *list)
846{
847 unsigned long val;
848
849 val = (unsigned long)list->next;
850
851 if ((val & ~RB_FLAG_MASK) != (unsigned long)&page->list)
852 return RB_PAGE_MOVED;
853
854 return val & RB_FLAG_MASK;
855}
856
857/*
858 * rb_is_reader_page
859 *
860 * The unique thing about the reader page, is that, if the
861 * writer is ever on it, the previous pointer never points
862 * back to the reader page.
863 */
864static bool rb_is_reader_page(struct buffer_page *page)
865{
866 struct list_head *list = page->list.prev;
867
868 return rb_list_head(list->next) != &page->list;
869}
870
871/*
872 * rb_set_list_to_head - set a list_head to be pointing to head.
873 */
874static void rb_set_list_to_head(struct ring_buffer_per_cpu *cpu_buffer,
875 struct list_head *list)
876{
877 unsigned long *ptr;
878
879 ptr = (unsigned long *)&list->next;
880 *ptr |= RB_PAGE_HEAD;
881 *ptr &= ~RB_PAGE_UPDATE;
882}
883
884/*
885 * rb_head_page_activate - sets up head page
886 */
887static void rb_head_page_activate(struct ring_buffer_per_cpu *cpu_buffer)
888{
889 struct buffer_page *head;
890
891 head = cpu_buffer->head_page;
892 if (!head)
893 return;
894
895 /*
896 * Set the previous list pointer to have the HEAD flag.
897 */
898 rb_set_list_to_head(cpu_buffer, head->list.prev);
899}
900
901static void rb_list_head_clear(struct list_head *list)
902{
903 unsigned long *ptr = (unsigned long *)&list->next;
904
905 *ptr &= ~RB_FLAG_MASK;
906}
907
908/*
909 * rb_head_page_dactivate - clears head page ptr (for free list)
910 */
911static void
912rb_head_page_deactivate(struct ring_buffer_per_cpu *cpu_buffer)
913{
914 struct list_head *hd;
915
916 /* Go through the whole list and clear any pointers found. */
917 rb_list_head_clear(cpu_buffer->pages);
918
919 list_for_each(hd, cpu_buffer->pages)
920 rb_list_head_clear(hd);
921}
922
923static int rb_head_page_set(struct ring_buffer_per_cpu *cpu_buffer,
924 struct buffer_page *head,
925 struct buffer_page *prev,
926 int old_flag, int new_flag)
927{
928 struct list_head *list;
929 unsigned long val = (unsigned long)&head->list;
930 unsigned long ret;
931
932 list = &prev->list;
933
934 val &= ~RB_FLAG_MASK;
935
936 ret = cmpxchg((unsigned long *)&list->next,
937 val | old_flag, val | new_flag);
938
939 /* check if the reader took the page */
940 if ((ret & ~RB_FLAG_MASK) != val)
941 return RB_PAGE_MOVED;
942
943 return ret & RB_FLAG_MASK;
944}
945
946static int rb_head_page_set_update(struct ring_buffer_per_cpu *cpu_buffer,
947 struct buffer_page *head,
948 struct buffer_page *prev,
949 int old_flag)
950{
951 return rb_head_page_set(cpu_buffer, head, prev,
952 old_flag, RB_PAGE_UPDATE);
953}
954
955static int rb_head_page_set_head(struct ring_buffer_per_cpu *cpu_buffer,
956 struct buffer_page *head,
957 struct buffer_page *prev,
958 int old_flag)
959{
960 return rb_head_page_set(cpu_buffer, head, prev,
961 old_flag, RB_PAGE_HEAD);
962}
963
964static int rb_head_page_set_normal(struct ring_buffer_per_cpu *cpu_buffer,
965 struct buffer_page *head,
966 struct buffer_page *prev,
967 int old_flag)
968{
969 return rb_head_page_set(cpu_buffer, head, prev,
970 old_flag, RB_PAGE_NORMAL);
971}
972
973static inline void rb_inc_page(struct ring_buffer_per_cpu *cpu_buffer,
974 struct buffer_page **bpage)
975{
976 struct list_head *p = rb_list_head((*bpage)->list.next);
977
978 *bpage = list_entry(p, struct buffer_page, list);
979}
980
981static struct buffer_page *
982rb_set_head_page(struct ring_buffer_per_cpu *cpu_buffer)
983{
984 struct buffer_page *head;
985 struct buffer_page *page;
986 struct list_head *list;
987 int i;
988
989 if (RB_WARN_ON(cpu_buffer, !cpu_buffer->head_page))
990 return NULL;
991
992 /* sanity check */
993 list = cpu_buffer->pages;
994 if (RB_WARN_ON(cpu_buffer, rb_list_head(list->prev->next) != list))
995 return NULL;
996
997 page = head = cpu_buffer->head_page;
998 /*
999 * It is possible that the writer moves the header behind
1000 * where we started, and we miss in one loop.
1001 * A second loop should grab the header, but we'll do
1002 * three loops just because I'm paranoid.
1003 */
1004 for (i = 0; i < 3; i++) {
1005 do {
1006 if (rb_is_head_page(cpu_buffer, page, page->list.prev)) {
1007 cpu_buffer->head_page = page;
1008 return page;
1009 }
1010 rb_inc_page(cpu_buffer, &page);
1011 } while (page != head);
1012 }
1013
1014 RB_WARN_ON(cpu_buffer, 1);
1015
1016 return NULL;
1017}
1018
1019static int rb_head_page_replace(struct buffer_page *old,
1020 struct buffer_page *new)
1021{
1022 unsigned long *ptr = (unsigned long *)&old->list.prev->next;
1023 unsigned long val;
1024 unsigned long ret;
1025
1026 val = *ptr & ~RB_FLAG_MASK;
1027 val |= RB_PAGE_HEAD;
1028
1029 ret = cmpxchg(ptr, val, (unsigned long)&new->list);
1030
1031 return ret == val;
1032}
1033
1034/*
1035 * rb_tail_page_update - move the tail page forward
1036 */
1037static void rb_tail_page_update(struct ring_buffer_per_cpu *cpu_buffer,
1038 struct buffer_page *tail_page,
1039 struct buffer_page *next_page)
1040{
1041 unsigned long old_entries;
1042 unsigned long old_write;
1043
1044 /*
1045 * The tail page now needs to be moved forward.
1046 *
1047 * We need to reset the tail page, but without messing
1048 * with possible erasing of data brought in by interrupts
1049 * that have moved the tail page and are currently on it.
1050 *
1051 * We add a counter to the write field to denote this.
1052 */
1053 old_write = local_add_return(RB_WRITE_INTCNT, &next_page->write);
1054 old_entries = local_add_return(RB_WRITE_INTCNT, &next_page->entries);
1055
1056 /*
1057 * Just make sure we have seen our old_write and synchronize
1058 * with any interrupts that come in.
1059 */
1060 barrier();
1061
1062 /*
1063 * If the tail page is still the same as what we think
1064 * it is, then it is up to us to update the tail
1065 * pointer.
1066 */
1067 if (tail_page == READ_ONCE(cpu_buffer->tail_page)) {
1068 /* Zero the write counter */
1069 unsigned long val = old_write & ~RB_WRITE_MASK;
1070 unsigned long eval = old_entries & ~RB_WRITE_MASK;
1071
1072 /*
1073 * This will only succeed if an interrupt did
1074 * not come in and change it. In which case, we
1075 * do not want to modify it.
1076 *
1077 * We add (void) to let the compiler know that we do not care
1078 * about the return value of these functions. We use the
1079 * cmpxchg to only update if an interrupt did not already
1080 * do it for us. If the cmpxchg fails, we don't care.
1081 */
1082 (void)local_cmpxchg(&next_page->write, old_write, val);
1083 (void)local_cmpxchg(&next_page->entries, old_entries, eval);
1084
1085 /*
1086 * No need to worry about races with clearing out the commit.
1087 * it only can increment when a commit takes place. But that
1088 * only happens in the outer most nested commit.
1089 */
1090 local_set(&next_page->page->commit, 0);
1091
1092 /* Again, either we update tail_page or an interrupt does */
1093 (void)cmpxchg(&cpu_buffer->tail_page, tail_page, next_page);
1094 }
1095}
1096
1097static int rb_check_bpage(struct ring_buffer_per_cpu *cpu_buffer,
1098 struct buffer_page *bpage)
1099{
1100 unsigned long val = (unsigned long)bpage;
1101
1102 if (RB_WARN_ON(cpu_buffer, val & RB_FLAG_MASK))
1103 return 1;
1104
1105 return 0;
1106}
1107
1108/**
1109 * rb_check_list - make sure a pointer to a list has the last bits zero
1110 */
1111static int rb_check_list(struct ring_buffer_per_cpu *cpu_buffer,
1112 struct list_head *list)
1113{
1114 if (RB_WARN_ON(cpu_buffer, rb_list_head(list->prev) != list->prev))
1115 return 1;
1116 if (RB_WARN_ON(cpu_buffer, rb_list_head(list->next) != list->next))
1117 return 1;
1118 return 0;
1119}
1120
1121/**
1122 * rb_check_pages - integrity check of buffer pages
1123 * @cpu_buffer: CPU buffer with pages to test
1124 *
1125 * As a safety measure we check to make sure the data pages have not
1126 * been corrupted.
1127 */
1128static int rb_check_pages(struct ring_buffer_per_cpu *cpu_buffer)
1129{
1130 struct list_head *head = cpu_buffer->pages;
1131 struct buffer_page *bpage, *tmp;
1132
1133 /* Reset the head page if it exists */
1134 if (cpu_buffer->head_page)
1135 rb_set_head_page(cpu_buffer);
1136
1137 rb_head_page_deactivate(cpu_buffer);
1138
1139 if (RB_WARN_ON(cpu_buffer, head->next->prev != head))
1140 return -1;
1141 if (RB_WARN_ON(cpu_buffer, head->prev->next != head))
1142 return -1;
1143
1144 if (rb_check_list(cpu_buffer, head))
1145 return -1;
1146
1147 list_for_each_entry_safe(bpage, tmp, head, list) {
1148 if (RB_WARN_ON(cpu_buffer,
1149 bpage->list.next->prev != &bpage->list))
1150 return -1;
1151 if (RB_WARN_ON(cpu_buffer,
1152 bpage->list.prev->next != &bpage->list))
1153 return -1;
1154 if (rb_check_list(cpu_buffer, &bpage->list))
1155 return -1;
1156 }
1157
1158 rb_head_page_activate(cpu_buffer);
1159
1160 return 0;
1161}
1162
1163static int __rb_allocate_pages(long nr_pages, struct list_head *pages, int cpu)
1164{
1165 struct buffer_page *bpage, *tmp;
1166 bool user_thread = current->mm != NULL;
1167 gfp_t mflags;
1168 long i;
1169
1170 /*
1171 * Check if the available memory is there first.
1172 * Note, si_mem_available() only gives us a rough estimate of available
1173 * memory. It may not be accurate. But we don't care, we just want
1174 * to prevent doing any allocation when it is obvious that it is
1175 * not going to succeed.
1176 */
1177 i = si_mem_available();
1178 if (i < nr_pages)
1179 return -ENOMEM;
1180
1181 /*
1182 * __GFP_RETRY_MAYFAIL flag makes sure that the allocation fails
1183 * gracefully without invoking oom-killer and the system is not
1184 * destabilized.
1185 */
1186 mflags = GFP_KERNEL | __GFP_RETRY_MAYFAIL;
1187
1188 /*
1189 * If a user thread allocates too much, and si_mem_available()
1190 * reports there's enough memory, even though there is not.
1191 * Make sure the OOM killer kills this thread. This can happen
1192 * even with RETRY_MAYFAIL because another task may be doing
1193 * an allocation after this task has taken all memory.
1194 * This is the task the OOM killer needs to take out during this
1195 * loop, even if it was triggered by an allocation somewhere else.
1196 */
1197 if (user_thread)
1198 set_current_oom_origin();
1199 for (i = 0; i < nr_pages; i++) {
1200 struct page *page;
1201
1202 bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
1203 mflags, cpu_to_node(cpu));
1204 if (!bpage)
1205 goto free_pages;
1206
1207 list_add(&bpage->list, pages);
1208
1209 page = alloc_pages_node(cpu_to_node(cpu), mflags, 0);
1210 if (!page)
1211 goto free_pages;
1212 bpage->page = page_address(page);
1213 rb_init_page(bpage->page);
1214
1215 if (user_thread && fatal_signal_pending(current))
1216 goto free_pages;
1217 }
1218 if (user_thread)
1219 clear_current_oom_origin();
1220
1221 return 0;
1222
1223free_pages:
1224 list_for_each_entry_safe(bpage, tmp, pages, list) {
1225 list_del_init(&bpage->list);
1226 free_buffer_page(bpage);
1227 }
1228 if (user_thread)
1229 clear_current_oom_origin();
1230
1231 return -ENOMEM;
1232}
1233
1234static int rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
1235 unsigned long nr_pages)
1236{
1237 LIST_HEAD(pages);
1238
1239 WARN_ON(!nr_pages);
1240
1241 if (__rb_allocate_pages(nr_pages, &pages, cpu_buffer->cpu))
1242 return -ENOMEM;
1243
1244 /*
1245 * The ring buffer page list is a circular list that does not
1246 * start and end with a list head. All page list items point to
1247 * other pages.
1248 */
1249 cpu_buffer->pages = pages.next;
1250 list_del(&pages);
1251
1252 cpu_buffer->nr_pages = nr_pages;
1253
1254 rb_check_pages(cpu_buffer);
1255
1256 return 0;
1257}
1258
1259static struct ring_buffer_per_cpu *
1260rb_allocate_cpu_buffer(struct ring_buffer *buffer, long nr_pages, int cpu)
1261{
1262 struct ring_buffer_per_cpu *cpu_buffer;
1263 struct buffer_page *bpage;
1264 struct page *page;
1265 int ret;
1266
1267 cpu_buffer = kzalloc_node(ALIGN(sizeof(*cpu_buffer), cache_line_size()),
1268 GFP_KERNEL, cpu_to_node(cpu));
1269 if (!cpu_buffer)
1270 return NULL;
1271
1272 cpu_buffer->cpu = cpu;
1273 cpu_buffer->buffer = buffer;
1274 raw_spin_lock_init(&cpu_buffer->reader_lock);
1275 lockdep_set_class(&cpu_buffer->reader_lock, buffer->reader_lock_key);
1276 cpu_buffer->lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
1277 INIT_WORK(&cpu_buffer->update_pages_work, update_pages_handler);
1278 init_completion(&cpu_buffer->update_done);
1279 init_irq_work(&cpu_buffer->irq_work.work, rb_wake_up_waiters);
1280 init_waitqueue_head(&cpu_buffer->irq_work.waiters);
1281 init_waitqueue_head(&cpu_buffer->irq_work.full_waiters);
1282
1283 bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
1284 GFP_KERNEL, cpu_to_node(cpu));
1285 if (!bpage)
1286 goto fail_free_buffer;
1287
1288 rb_check_bpage(cpu_buffer, bpage);
1289
1290 cpu_buffer->reader_page = bpage;
1291 page = alloc_pages_node(cpu_to_node(cpu), GFP_KERNEL, 0);
1292 if (!page)
1293 goto fail_free_reader;
1294 bpage->page = page_address(page);
1295 rb_init_page(bpage->page);
1296
1297 INIT_LIST_HEAD(&cpu_buffer->reader_page->list);
1298 INIT_LIST_HEAD(&cpu_buffer->new_pages);
1299
1300 ret = rb_allocate_pages(cpu_buffer, nr_pages);
1301 if (ret < 0)
1302 goto fail_free_reader;
1303
1304 cpu_buffer->head_page
1305 = list_entry(cpu_buffer->pages, struct buffer_page, list);
1306 cpu_buffer->tail_page = cpu_buffer->commit_page = cpu_buffer->head_page;
1307
1308 rb_head_page_activate(cpu_buffer);
1309
1310 return cpu_buffer;
1311
1312 fail_free_reader:
1313 free_buffer_page(cpu_buffer->reader_page);
1314
1315 fail_free_buffer:
1316 kfree(cpu_buffer);
1317 return NULL;
1318}
1319
1320static void rb_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
1321{
1322 struct list_head *head = cpu_buffer->pages;
1323 struct buffer_page *bpage, *tmp;
1324
1325 free_buffer_page(cpu_buffer->reader_page);
1326
1327 rb_head_page_deactivate(cpu_buffer);
1328
1329 if (head) {
1330 list_for_each_entry_safe(bpage, tmp, head, list) {
1331 list_del_init(&bpage->list);
1332 free_buffer_page(bpage);
1333 }
1334 bpage = list_entry(head, struct buffer_page, list);
1335 free_buffer_page(bpage);
1336 }
1337
1338 kfree(cpu_buffer);
1339}
1340
1341/**
1342 * __ring_buffer_alloc - allocate a new ring_buffer
1343 * @size: the size in bytes per cpu that is needed.
1344 * @flags: attributes to set for the ring buffer.
1345 *
1346 * Currently the only flag that is available is the RB_FL_OVERWRITE
1347 * flag. This flag means that the buffer will overwrite old data
1348 * when the buffer wraps. If this flag is not set, the buffer will
1349 * drop data when the tail hits the head.
1350 */
1351struct ring_buffer *__ring_buffer_alloc(unsigned long size, unsigned flags,
1352 struct lock_class_key *key)
1353{
1354 struct ring_buffer *buffer;
1355 long nr_pages;
1356 int bsize;
1357 int cpu;
1358 int ret;
1359
1360 /* keep it in its own cache line */
1361 buffer = kzalloc(ALIGN(sizeof(*buffer), cache_line_size()),
1362 GFP_KERNEL);
1363 if (!buffer)
1364 return NULL;
1365
1366 if (!zalloc_cpumask_var(&buffer->cpumask, GFP_KERNEL))
1367 goto fail_free_buffer;
1368
1369 nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
1370 buffer->flags = flags;
1371 buffer->clock = trace_clock_local;
1372 buffer->reader_lock_key = key;
1373
1374 init_irq_work(&buffer->irq_work.work, rb_wake_up_waiters);
1375 init_waitqueue_head(&buffer->irq_work.waiters);
1376
1377 /* need at least two pages */
1378 if (nr_pages < 2)
1379 nr_pages = 2;
1380
1381 buffer->cpus = nr_cpu_ids;
1382
1383 bsize = sizeof(void *) * nr_cpu_ids;
1384 buffer->buffers = kzalloc(ALIGN(bsize, cache_line_size()),
1385 GFP_KERNEL);
1386 if (!buffer->buffers)
1387 goto fail_free_cpumask;
1388
1389 cpu = raw_smp_processor_id();
1390 cpumask_set_cpu(cpu, buffer->cpumask);
1391 buffer->buffers[cpu] = rb_allocate_cpu_buffer(buffer, nr_pages, cpu);
1392 if (!buffer->buffers[cpu])
1393 goto fail_free_buffers;
1394
1395 ret = cpuhp_state_add_instance(CPUHP_TRACE_RB_PREPARE, &buffer->node);
1396 if (ret < 0)
1397 goto fail_free_buffers;
1398
1399 mutex_init(&buffer->mutex);
1400
1401 return buffer;
1402
1403 fail_free_buffers:
1404 for_each_buffer_cpu(buffer, cpu) {
1405 if (buffer->buffers[cpu])
1406 rb_free_cpu_buffer(buffer->buffers[cpu]);
1407 }
1408 kfree(buffer->buffers);
1409
1410 fail_free_cpumask:
1411 free_cpumask_var(buffer->cpumask);
1412
1413 fail_free_buffer:
1414 kfree(buffer);
1415 return NULL;
1416}
1417EXPORT_SYMBOL_GPL(__ring_buffer_alloc);
1418
1419/**
1420 * ring_buffer_free - free a ring buffer.
1421 * @buffer: the buffer to free.
1422 */
1423void
1424ring_buffer_free(struct ring_buffer *buffer)
1425{
1426 int cpu;
1427
1428 cpuhp_state_remove_instance(CPUHP_TRACE_RB_PREPARE, &buffer->node);
1429
1430 for_each_buffer_cpu(buffer, cpu)
1431 rb_free_cpu_buffer(buffer->buffers[cpu]);
1432
1433 kfree(buffer->buffers);
1434 free_cpumask_var(buffer->cpumask);
1435
1436 kfree(buffer);
1437}
1438EXPORT_SYMBOL_GPL(ring_buffer_free);
1439
1440void ring_buffer_set_clock(struct ring_buffer *buffer,
1441 u64 (*clock)(void))
1442{
1443 buffer->clock = clock;
1444}
1445
1446void ring_buffer_set_time_stamp_abs(struct ring_buffer *buffer, bool abs)
1447{
1448 buffer->time_stamp_abs = abs;
1449}
1450
1451bool ring_buffer_time_stamp_abs(struct ring_buffer *buffer)
1452{
1453 return buffer->time_stamp_abs;
1454}
1455
1456static void rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer);
1457
1458static inline unsigned long rb_page_entries(struct buffer_page *bpage)
1459{
1460 return local_read(&bpage->entries) & RB_WRITE_MASK;
1461}
1462
1463static inline unsigned long rb_page_write(struct buffer_page *bpage)
1464{
1465 return local_read(&bpage->write) & RB_WRITE_MASK;
1466}
1467
1468static int
1469rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned long nr_pages)
1470{
1471 struct list_head *tail_page, *to_remove, *next_page;
1472 struct buffer_page *to_remove_page, *tmp_iter_page;
1473 struct buffer_page *last_page, *first_page;
1474 unsigned long nr_removed;
1475 unsigned long head_bit;
1476 int page_entries;
1477
1478 head_bit = 0;
1479
1480 raw_spin_lock_irq(&cpu_buffer->reader_lock);
1481 atomic_inc(&cpu_buffer->record_disabled);
1482 /*
1483 * We don't race with the readers since we have acquired the reader
1484 * lock. We also don't race with writers after disabling recording.
1485 * This makes it easy to figure out the first and the last page to be
1486 * removed from the list. We unlink all the pages in between including
1487 * the first and last pages. This is done in a busy loop so that we
1488 * lose the least number of traces.
1489 * The pages are freed after we restart recording and unlock readers.
1490 */
1491 tail_page = &cpu_buffer->tail_page->list;
1492
1493 /*
1494 * tail page might be on reader page, we remove the next page
1495 * from the ring buffer
1496 */
1497 if (cpu_buffer->tail_page == cpu_buffer->reader_page)
1498 tail_page = rb_list_head(tail_page->next);
1499 to_remove = tail_page;
1500
1501 /* start of pages to remove */
1502 first_page = list_entry(rb_list_head(to_remove->next),
1503 struct buffer_page, list);
1504
1505 for (nr_removed = 0; nr_removed < nr_pages; nr_removed++) {
1506 to_remove = rb_list_head(to_remove)->next;
1507 head_bit |= (unsigned long)to_remove & RB_PAGE_HEAD;
1508 }
1509
1510 next_page = rb_list_head(to_remove)->next;
1511
1512 /*
1513 * Now we remove all pages between tail_page and next_page.
1514 * Make sure that we have head_bit value preserved for the
1515 * next page
1516 */
1517 tail_page->next = (struct list_head *)((unsigned long)next_page |
1518 head_bit);
1519 next_page = rb_list_head(next_page);
1520 next_page->prev = tail_page;
1521
1522 /* make sure pages points to a valid page in the ring buffer */
1523 cpu_buffer->pages = next_page;
1524
1525 /* update head page */
1526 if (head_bit)
1527 cpu_buffer->head_page = list_entry(next_page,
1528 struct buffer_page, list);
1529
1530 /*
1531 * change read pointer to make sure any read iterators reset
1532 * themselves
1533 */
1534 cpu_buffer->read = 0;
1535
1536 /* pages are removed, resume tracing and then free the pages */
1537 atomic_dec(&cpu_buffer->record_disabled);
1538 raw_spin_unlock_irq(&cpu_buffer->reader_lock);
1539
1540 RB_WARN_ON(cpu_buffer, list_empty(cpu_buffer->pages));
1541
1542 /* last buffer page to remove */
1543 last_page = list_entry(rb_list_head(to_remove), struct buffer_page,
1544 list);
1545 tmp_iter_page = first_page;
1546
1547 do {
1548 to_remove_page = tmp_iter_page;
1549 rb_inc_page(cpu_buffer, &tmp_iter_page);
1550
1551 /* update the counters */
1552 page_entries = rb_page_entries(to_remove_page);
1553 if (page_entries) {
1554 /*
1555 * If something was added to this page, it was full
1556 * since it is not the tail page. So we deduct the
1557 * bytes consumed in ring buffer from here.
1558 * Increment overrun to account for the lost events.
1559 */
1560 local_add(page_entries, &cpu_buffer->overrun);
1561 local_sub(BUF_PAGE_SIZE, &cpu_buffer->entries_bytes);
1562 }
1563
1564 /*
1565 * We have already removed references to this list item, just
1566 * free up the buffer_page and its page
1567 */
1568 free_buffer_page(to_remove_page);
1569 nr_removed--;
1570
1571 } while (to_remove_page != last_page);
1572
1573 RB_WARN_ON(cpu_buffer, nr_removed);
1574
1575 return nr_removed == 0;
1576}
1577
1578static int
1579rb_insert_pages(struct ring_buffer_per_cpu *cpu_buffer)
1580{
1581 struct list_head *pages = &cpu_buffer->new_pages;
1582 int retries, success;
1583
1584 raw_spin_lock_irq(&cpu_buffer->reader_lock);
1585 /*
1586 * We are holding the reader lock, so the reader page won't be swapped
1587 * in the ring buffer. Now we are racing with the writer trying to
1588 * move head page and the tail page.
1589 * We are going to adapt the reader page update process where:
1590 * 1. We first splice the start and end of list of new pages between
1591 * the head page and its previous page.
1592 * 2. We cmpxchg the prev_page->next to point from head page to the
1593 * start of new pages list.
1594 * 3. Finally, we update the head->prev to the end of new list.
1595 *
1596 * We will try this process 10 times, to make sure that we don't keep
1597 * spinning.
1598 */
1599 retries = 10;
1600 success = 0;
1601 while (retries--) {
1602 struct list_head *head_page, *prev_page, *r;
1603 struct list_head *last_page, *first_page;
1604 struct list_head *head_page_with_bit;
1605
1606 head_page = &rb_set_head_page(cpu_buffer)->list;
1607 if (!head_page)
1608 break;
1609 prev_page = head_page->prev;
1610
1611 first_page = pages->next;
1612 last_page = pages->prev;
1613
1614 head_page_with_bit = (struct list_head *)
1615 ((unsigned long)head_page | RB_PAGE_HEAD);
1616
1617 last_page->next = head_page_with_bit;
1618 first_page->prev = prev_page;
1619
1620 r = cmpxchg(&prev_page->next, head_page_with_bit, first_page);
1621
1622 if (r == head_page_with_bit) {
1623 /*
1624 * yay, we replaced the page pointer to our new list,
1625 * now, we just have to update to head page's prev
1626 * pointer to point to end of list
1627 */
1628 head_page->prev = last_page;
1629 success = 1;
1630 break;
1631 }
1632 }
1633
1634 if (success)
1635 INIT_LIST_HEAD(pages);
1636 /*
1637 * If we weren't successful in adding in new pages, warn and stop
1638 * tracing
1639 */
1640 RB_WARN_ON(cpu_buffer, !success);
1641 raw_spin_unlock_irq(&cpu_buffer->reader_lock);
1642
1643 /* free pages if they weren't inserted */
1644 if (!success) {
1645 struct buffer_page *bpage, *tmp;
1646 list_for_each_entry_safe(bpage, tmp, &cpu_buffer->new_pages,
1647 list) {
1648 list_del_init(&bpage->list);
1649 free_buffer_page(bpage);
1650 }
1651 }
1652 return success;
1653}
1654
1655static void rb_update_pages(struct ring_buffer_per_cpu *cpu_buffer)
1656{
1657 int success;
1658
1659 if (cpu_buffer->nr_pages_to_update > 0)
1660 success = rb_insert_pages(cpu_buffer);
1661 else
1662 success = rb_remove_pages(cpu_buffer,
1663 -cpu_buffer->nr_pages_to_update);
1664
1665 if (success)
1666 cpu_buffer->nr_pages += cpu_buffer->nr_pages_to_update;
1667}
1668
1669static void update_pages_handler(struct work_struct *work)
1670{
1671 struct ring_buffer_per_cpu *cpu_buffer = container_of(work,
1672 struct ring_buffer_per_cpu, update_pages_work);
1673 rb_update_pages(cpu_buffer);
1674 complete(&cpu_buffer->update_done);
1675}
1676
1677/**
1678 * ring_buffer_resize - resize the ring buffer
1679 * @buffer: the buffer to resize.
1680 * @size: the new size.
1681 * @cpu_id: the cpu buffer to resize
1682 *
1683 * Minimum size is 2 * BUF_PAGE_SIZE.
1684 *
1685 * Returns 0 on success and < 0 on failure.
1686 */
1687int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size,
1688 int cpu_id)
1689{
1690 struct ring_buffer_per_cpu *cpu_buffer;
1691 unsigned long nr_pages;
1692 int cpu, err = 0;
1693
1694 /*
1695 * Always succeed at resizing a non-existent buffer:
1696 */
1697 if (!buffer)
1698 return size;
1699
1700 /* Make sure the requested buffer exists */
1701 if (cpu_id != RING_BUFFER_ALL_CPUS &&
1702 !cpumask_test_cpu(cpu_id, buffer->cpumask))
1703 return size;
1704
1705 nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
1706
1707 /* we need a minimum of two pages */
1708 if (nr_pages < 2)
1709 nr_pages = 2;
1710
1711 size = nr_pages * BUF_PAGE_SIZE;
1712
1713 /*
1714 * Don't succeed if resizing is disabled, as a reader might be
1715 * manipulating the ring buffer and is expecting a sane state while
1716 * this is true.
1717 */
1718 if (atomic_read(&buffer->resize_disabled))
1719 return -EBUSY;
1720
1721 /* prevent another thread from changing buffer sizes */
1722 mutex_lock(&buffer->mutex);
1723
1724 if (cpu_id == RING_BUFFER_ALL_CPUS) {
1725 /* calculate the pages to update */
1726 for_each_buffer_cpu(buffer, cpu) {
1727 cpu_buffer = buffer->buffers[cpu];
1728
1729 cpu_buffer->nr_pages_to_update = nr_pages -
1730 cpu_buffer->nr_pages;
1731 /*
1732 * nothing more to do for removing pages or no update
1733 */
1734 if (cpu_buffer->nr_pages_to_update <= 0)
1735 continue;
1736 /*
1737 * to add pages, make sure all new pages can be
1738 * allocated without receiving ENOMEM
1739 */
1740 INIT_LIST_HEAD(&cpu_buffer->new_pages);
1741 if (__rb_allocate_pages(cpu_buffer->nr_pages_to_update,
1742 &cpu_buffer->new_pages, cpu)) {
1743 /* not enough memory for new pages */
1744 err = -ENOMEM;
1745 goto out_err;
1746 }
1747 }
1748
1749 get_online_cpus();
1750 /*
1751 * Fire off all the required work handlers
1752 * We can't schedule on offline CPUs, but it's not necessary
1753 * since we can change their buffer sizes without any race.
1754 */
1755 for_each_buffer_cpu(buffer, cpu) {
1756 cpu_buffer = buffer->buffers[cpu];
1757 if (!cpu_buffer->nr_pages_to_update)
1758 continue;
1759
1760 /* Can't run something on an offline CPU. */
1761 if (!cpu_online(cpu)) {
1762 rb_update_pages(cpu_buffer);
1763 cpu_buffer->nr_pages_to_update = 0;
1764 } else {
1765 schedule_work_on(cpu,
1766 &cpu_buffer->update_pages_work);
1767 }
1768 }
1769
1770 /* wait for all the updates to complete */
1771 for_each_buffer_cpu(buffer, cpu) {
1772 cpu_buffer = buffer->buffers[cpu];
1773 if (!cpu_buffer->nr_pages_to_update)
1774 continue;
1775
1776 if (cpu_online(cpu))
1777 wait_for_completion(&cpu_buffer->update_done);
1778 cpu_buffer->nr_pages_to_update = 0;
1779 }
1780
1781 put_online_cpus();
1782 } else {
1783 /* Make sure this CPU has been intitialized */
1784 if (!cpumask_test_cpu(cpu_id, buffer->cpumask))
1785 goto out;
1786
1787 cpu_buffer = buffer->buffers[cpu_id];
1788
1789 if (nr_pages == cpu_buffer->nr_pages)
1790 goto out;
1791
1792 cpu_buffer->nr_pages_to_update = nr_pages -
1793 cpu_buffer->nr_pages;
1794
1795 INIT_LIST_HEAD(&cpu_buffer->new_pages);
1796 if (cpu_buffer->nr_pages_to_update > 0 &&
1797 __rb_allocate_pages(cpu_buffer->nr_pages_to_update,
1798 &cpu_buffer->new_pages, cpu_id)) {
1799 err = -ENOMEM;
1800 goto out_err;
1801 }
1802
1803 get_online_cpus();
1804
1805 /* Can't run something on an offline CPU. */
1806 if (!cpu_online(cpu_id))
1807 rb_update_pages(cpu_buffer);
1808 else {
1809 schedule_work_on(cpu_id,
1810 &cpu_buffer->update_pages_work);
1811 wait_for_completion(&cpu_buffer->update_done);
1812 }
1813
1814 cpu_buffer->nr_pages_to_update = 0;
1815 put_online_cpus();
1816 }
1817
1818 out:
1819 /*
1820 * The ring buffer resize can happen with the ring buffer
1821 * enabled, so that the update disturbs the tracing as little
1822 * as possible. But if the buffer is disabled, we do not need
1823 * to worry about that, and we can take the time to verify
1824 * that the buffer is not corrupt.
1825 */
1826 if (atomic_read(&buffer->record_disabled)) {
1827 atomic_inc(&buffer->record_disabled);
1828 /*
1829 * Even though the buffer was disabled, we must make sure
1830 * that it is truly disabled before calling rb_check_pages.
1831 * There could have been a race between checking
1832 * record_disable and incrementing it.
1833 */
1834 synchronize_sched();
1835 for_each_buffer_cpu(buffer, cpu) {
1836 cpu_buffer = buffer->buffers[cpu];
1837 rb_check_pages(cpu_buffer);
1838 }
1839 atomic_dec(&buffer->record_disabled);
1840 }
1841
1842 mutex_unlock(&buffer->mutex);
1843 return size;
1844
1845 out_err:
1846 for_each_buffer_cpu(buffer, cpu) {
1847 struct buffer_page *bpage, *tmp;
1848
1849 cpu_buffer = buffer->buffers[cpu];
1850 cpu_buffer->nr_pages_to_update = 0;
1851
1852 if (list_empty(&cpu_buffer->new_pages))
1853 continue;
1854
1855 list_for_each_entry_safe(bpage, tmp, &cpu_buffer->new_pages,
1856 list) {
1857 list_del_init(&bpage->list);
1858 free_buffer_page(bpage);
1859 }
1860 }
1861 mutex_unlock(&buffer->mutex);
1862 return err;
1863}
1864EXPORT_SYMBOL_GPL(ring_buffer_resize);
1865
1866void ring_buffer_change_overwrite(struct ring_buffer *buffer, int val)
1867{
1868 mutex_lock(&buffer->mutex);
1869 if (val)
1870 buffer->flags |= RB_FL_OVERWRITE;
1871 else
1872 buffer->flags &= ~RB_FL_OVERWRITE;
1873 mutex_unlock(&buffer->mutex);
1874}
1875EXPORT_SYMBOL_GPL(ring_buffer_change_overwrite);
1876
1877static __always_inline void *__rb_page_index(struct buffer_page *bpage, unsigned index)
1878{
1879 return bpage->page->data + index;
1880}
1881
1882static __always_inline struct ring_buffer_event *
1883rb_reader_event(struct ring_buffer_per_cpu *cpu_buffer)
1884{
1885 return __rb_page_index(cpu_buffer->reader_page,
1886 cpu_buffer->reader_page->read);
1887}
1888
1889static __always_inline struct ring_buffer_event *
1890rb_iter_head_event(struct ring_buffer_iter *iter)
1891{
1892 return __rb_page_index(iter->head_page, iter->head);
1893}
1894
1895static __always_inline unsigned rb_page_commit(struct buffer_page *bpage)
1896{
1897 return local_read(&bpage->page->commit);
1898}
1899
1900/* Size is determined by what has been committed */
1901static __always_inline unsigned rb_page_size(struct buffer_page *bpage)
1902{
1903 return rb_page_commit(bpage);
1904}
1905
1906static __always_inline unsigned
1907rb_commit_index(struct ring_buffer_per_cpu *cpu_buffer)
1908{
1909 return rb_page_commit(cpu_buffer->commit_page);
1910}
1911
1912static __always_inline unsigned
1913rb_event_index(struct ring_buffer_event *event)
1914{
1915 unsigned long addr = (unsigned long)event;
1916
1917 return (addr & ~PAGE_MASK) - BUF_PAGE_HDR_SIZE;
1918}
1919
1920static void rb_inc_iter(struct ring_buffer_iter *iter)
1921{
1922 struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
1923
1924 /*
1925 * The iterator could be on the reader page (it starts there).
1926 * But the head could have moved, since the reader was
1927 * found. Check for this case and assign the iterator
1928 * to the head page instead of next.
1929 */
1930 if (iter->head_page == cpu_buffer->reader_page)
1931 iter->head_page = rb_set_head_page(cpu_buffer);
1932 else
1933 rb_inc_page(cpu_buffer, &iter->head_page);
1934
1935 iter->read_stamp = iter->head_page->page->time_stamp;
1936 iter->head = 0;
1937}
1938
1939/*
1940 * rb_handle_head_page - writer hit the head page
1941 *
1942 * Returns: +1 to retry page
1943 * 0 to continue
1944 * -1 on error
1945 */
1946static int
1947rb_handle_head_page(struct ring_buffer_per_cpu *cpu_buffer,
1948 struct buffer_page *tail_page,
1949 struct buffer_page *next_page)
1950{
1951 struct buffer_page *new_head;
1952 int entries;
1953 int type;
1954 int ret;
1955
1956 entries = rb_page_entries(next_page);
1957
1958 /*
1959 * The hard part is here. We need to move the head
1960 * forward, and protect against both readers on
1961 * other CPUs and writers coming in via interrupts.
1962 */
1963 type = rb_head_page_set_update(cpu_buffer, next_page, tail_page,
1964 RB_PAGE_HEAD);
1965
1966 /*
1967 * type can be one of four:
1968 * NORMAL - an interrupt already moved it for us
1969 * HEAD - we are the first to get here.
1970 * UPDATE - we are the interrupt interrupting
1971 * a current move.
1972 * MOVED - a reader on another CPU moved the next
1973 * pointer to its reader page. Give up
1974 * and try again.
1975 */
1976
1977 switch (type) {
1978 case RB_PAGE_HEAD:
1979 /*
1980 * We changed the head to UPDATE, thus
1981 * it is our responsibility to update
1982 * the counters.
1983 */
1984 local_add(entries, &cpu_buffer->overrun);
1985 local_sub(BUF_PAGE_SIZE, &cpu_buffer->entries_bytes);
1986
1987 /*
1988 * The entries will be zeroed out when we move the
1989 * tail page.
1990 */
1991
1992 /* still more to do */
1993 break;
1994
1995 case RB_PAGE_UPDATE:
1996 /*
1997 * This is an interrupt that interrupt the
1998 * previous update. Still more to do.
1999 */
2000 break;
2001 case RB_PAGE_NORMAL:
2002 /*
2003 * An interrupt came in before the update
2004 * and processed this for us.
2005 * Nothing left to do.
2006 */
2007 return 1;
2008 case RB_PAGE_MOVED:
2009 /*
2010 * The reader is on another CPU and just did
2011 * a swap with our next_page.
2012 * Try again.
2013 */
2014 return 1;
2015 default:
2016 RB_WARN_ON(cpu_buffer, 1); /* WTF??? */
2017 return -1;
2018 }
2019
2020 /*
2021 * Now that we are here, the old head pointer is
2022 * set to UPDATE. This will keep the reader from
2023 * swapping the head page with the reader page.
2024 * The reader (on another CPU) will spin till
2025 * we are finished.
2026 *
2027 * We just need to protect against interrupts
2028 * doing the job. We will set the next pointer
2029 * to HEAD. After that, we set the old pointer
2030 * to NORMAL, but only if it was HEAD before.
2031 * otherwise we are an interrupt, and only
2032 * want the outer most commit to reset it.
2033 */
2034 new_head = next_page;
2035 rb_inc_page(cpu_buffer, &new_head);
2036
2037 ret = rb_head_page_set_head(cpu_buffer, new_head, next_page,
2038 RB_PAGE_NORMAL);
2039
2040 /*
2041 * Valid returns are:
2042 * HEAD - an interrupt came in and already set it.
2043 * NORMAL - One of two things:
2044 * 1) We really set it.
2045 * 2) A bunch of interrupts came in and moved
2046 * the page forward again.
2047 */
2048 switch (ret) {
2049 case RB_PAGE_HEAD:
2050 case RB_PAGE_NORMAL:
2051 /* OK */
2052 break;
2053 default:
2054 RB_WARN_ON(cpu_buffer, 1);
2055 return -1;
2056 }
2057
2058 /*
2059 * It is possible that an interrupt came in,
2060 * set the head up, then more interrupts came in
2061 * and moved it again. When we get back here,
2062 * the page would have been set to NORMAL but we
2063 * just set it back to HEAD.
2064 *
2065 * How do you detect this? Well, if that happened
2066 * the tail page would have moved.
2067 */
2068 if (ret == RB_PAGE_NORMAL) {
2069 struct buffer_page *buffer_tail_page;
2070
2071 buffer_tail_page = READ_ONCE(cpu_buffer->tail_page);
2072 /*
2073 * If the tail had moved passed next, then we need
2074 * to reset the pointer.
2075 */
2076 if (buffer_tail_page != tail_page &&
2077 buffer_tail_page != next_page)
2078 rb_head_page_set_normal(cpu_buffer, new_head,
2079 next_page,
2080 RB_PAGE_HEAD);
2081 }
2082
2083 /*
2084 * If this was the outer most commit (the one that
2085 * changed the original pointer from HEAD to UPDATE),
2086 * then it is up to us to reset it to NORMAL.
2087 */
2088 if (type == RB_PAGE_HEAD) {
2089 ret = rb_head_page_set_normal(cpu_buffer, next_page,
2090 tail_page,
2091 RB_PAGE_UPDATE);
2092 if (RB_WARN_ON(cpu_buffer,
2093 ret != RB_PAGE_UPDATE))
2094 return -1;
2095 }
2096
2097 return 0;
2098}
2099
2100static inline void
2101rb_reset_tail(struct ring_buffer_per_cpu *cpu_buffer,
2102 unsigned long tail, struct rb_event_info *info)
2103{
2104 struct buffer_page *tail_page = info->tail_page;
2105 struct ring_buffer_event *event;
2106 unsigned long length = info->length;
2107
2108 /*
2109 * Only the event that crossed the page boundary
2110 * must fill the old tail_page with padding.
2111 */
2112 if (tail >= BUF_PAGE_SIZE) {
2113 /*
2114 * If the page was filled, then we still need
2115 * to update the real_end. Reset it to zero
2116 * and the reader will ignore it.
2117 */
2118 if (tail == BUF_PAGE_SIZE)
2119 tail_page->real_end = 0;
2120
2121 local_sub(length, &tail_page->write);
2122 return;
2123 }
2124
2125 event = __rb_page_index(tail_page, tail);
2126
2127 /* account for padding bytes */
2128 local_add(BUF_PAGE_SIZE - tail, &cpu_buffer->entries_bytes);
2129
2130 /*
2131 * Save the original length to the meta data.
2132 * This will be used by the reader to add lost event
2133 * counter.
2134 */
2135 tail_page->real_end = tail;
2136
2137 /*
2138 * If this event is bigger than the minimum size, then
2139 * we need to be careful that we don't subtract the
2140 * write counter enough to allow another writer to slip
2141 * in on this page.
2142 * We put in a discarded commit instead, to make sure
2143 * that this space is not used again.
2144 *
2145 * If we are less than the minimum size, we don't need to
2146 * worry about it.
2147 */
2148 if (tail > (BUF_PAGE_SIZE - RB_EVNT_MIN_SIZE)) {
2149 /* No room for any events */
2150
2151 /* Mark the rest of the page with padding */
2152 rb_event_set_padding(event);
2153
2154 /* Set the write back to the previous setting */
2155 local_sub(length, &tail_page->write);
2156 return;
2157 }
2158
2159 /* Put in a discarded event */
2160 event->array[0] = (BUF_PAGE_SIZE - tail) - RB_EVNT_HDR_SIZE;
2161 event->type_len = RINGBUF_TYPE_PADDING;
2162 /* time delta must be non zero */
2163 event->time_delta = 1;
2164
2165 /* Set write to end of buffer */
2166 length = (tail + length) - BUF_PAGE_SIZE;
2167 local_sub(length, &tail_page->write);
2168}
2169
2170static inline void rb_end_commit(struct ring_buffer_per_cpu *cpu_buffer);
2171
2172/*
2173 * This is the slow path, force gcc not to inline it.
2174 */
2175static noinline struct ring_buffer_event *
2176rb_move_tail(struct ring_buffer_per_cpu *cpu_buffer,
2177 unsigned long tail, struct rb_event_info *info)
2178{
2179 struct buffer_page *tail_page = info->tail_page;
2180 struct buffer_page *commit_page = cpu_buffer->commit_page;
2181 struct ring_buffer *buffer = cpu_buffer->buffer;
2182 struct buffer_page *next_page;
2183 int ret;
2184
2185 next_page = tail_page;
2186
2187 rb_inc_page(cpu_buffer, &next_page);
2188
2189 /*
2190 * If for some reason, we had an interrupt storm that made
2191 * it all the way around the buffer, bail, and warn
2192 * about it.
2193 */
2194 if (unlikely(next_page == commit_page)) {
2195 local_inc(&cpu_buffer->commit_overrun);
2196 goto out_reset;
2197 }
2198
2199 /*
2200 * This is where the fun begins!
2201 *
2202 * We are fighting against races between a reader that
2203 * could be on another CPU trying to swap its reader
2204 * page with the buffer head.
2205 *
2206 * We are also fighting against interrupts coming in and
2207 * moving the head or tail on us as well.
2208 *
2209 * If the next page is the head page then we have filled
2210 * the buffer, unless the commit page is still on the
2211 * reader page.
2212 */
2213 if (rb_is_head_page(cpu_buffer, next_page, &tail_page->list)) {
2214
2215 /*
2216 * If the commit is not on the reader page, then
2217 * move the header page.
2218 */
2219 if (!rb_is_reader_page(cpu_buffer->commit_page)) {
2220 /*
2221 * If we are not in overwrite mode,
2222 * this is easy, just stop here.
2223 */
2224 if (!(buffer->flags & RB_FL_OVERWRITE)) {
2225 local_inc(&cpu_buffer->dropped_events);
2226 goto out_reset;
2227 }
2228
2229 ret = rb_handle_head_page(cpu_buffer,
2230 tail_page,
2231 next_page);
2232 if (ret < 0)
2233 goto out_reset;
2234 if (ret)
2235 goto out_again;
2236 } else {
2237 /*
2238 * We need to be careful here too. The
2239 * commit page could still be on the reader
2240 * page. We could have a small buffer, and
2241 * have filled up the buffer with events
2242 * from interrupts and such, and wrapped.
2243 *
2244 * Note, if the tail page is also the on the
2245 * reader_page, we let it move out.
2246 */
2247 if (unlikely((cpu_buffer->commit_page !=
2248 cpu_buffer->tail_page) &&
2249 (cpu_buffer->commit_page ==
2250 cpu_buffer->reader_page))) {
2251 local_inc(&cpu_buffer->commit_overrun);
2252 goto out_reset;
2253 }
2254 }
2255 }
2256
2257 rb_tail_page_update(cpu_buffer, tail_page, next_page);
2258
2259 out_again:
2260
2261 rb_reset_tail(cpu_buffer, tail, info);
2262
2263 /* Commit what we have for now. */
2264 rb_end_commit(cpu_buffer);
2265 /* rb_end_commit() decs committing */
2266 local_inc(&cpu_buffer->committing);
2267
2268 /* fail and let the caller try again */
2269 return ERR_PTR(-EAGAIN);
2270
2271 out_reset:
2272 /* reset write */
2273 rb_reset_tail(cpu_buffer, tail, info);
2274
2275 return NULL;
2276}
2277
2278/* Slow path, do not inline */
2279static noinline struct ring_buffer_event *
2280rb_add_time_stamp(struct ring_buffer_event *event, u64 delta, bool abs)
2281{
2282 if (abs)
2283 event->type_len = RINGBUF_TYPE_TIME_STAMP;
2284 else
2285 event->type_len = RINGBUF_TYPE_TIME_EXTEND;
2286
2287 /* Not the first event on the page, or not delta? */
2288 if (abs || rb_event_index(event)) {
2289 event->time_delta = delta & TS_MASK;
2290 event->array[0] = delta >> TS_SHIFT;
2291 } else {
2292 /* nope, just zero it */
2293 event->time_delta = 0;
2294 event->array[0] = 0;
2295 }
2296
2297 return skip_time_extend(event);
2298}
2299
2300static inline bool rb_event_is_commit(struct ring_buffer_per_cpu *cpu_buffer,
2301 struct ring_buffer_event *event);
2302
2303/**
2304 * rb_update_event - update event type and data
2305 * @event: the event to update
2306 * @type: the type of event
2307 * @length: the size of the event field in the ring buffer
2308 *
2309 * Update the type and data fields of the event. The length
2310 * is the actual size that is written to the ring buffer,
2311 * and with this, we can determine what to place into the
2312 * data field.
2313 */
2314static void
2315rb_update_event(struct ring_buffer_per_cpu *cpu_buffer,
2316 struct ring_buffer_event *event,
2317 struct rb_event_info *info)
2318{
2319 unsigned length = info->length;
2320 u64 delta = info->delta;
2321
2322 /* Only a commit updates the timestamp */
2323 if (unlikely(!rb_event_is_commit(cpu_buffer, event)))
2324 delta = 0;
2325
2326 /*
2327 * If we need to add a timestamp, then we
2328 * add it to the start of the resevered space.
2329 */
2330 if (unlikely(info->add_timestamp)) {
2331 bool abs = ring_buffer_time_stamp_abs(cpu_buffer->buffer);
2332
2333 event = rb_add_time_stamp(event, info->delta, abs);
2334 length -= RB_LEN_TIME_EXTEND;
2335 delta = 0;
2336 }
2337
2338 event->time_delta = delta;
2339 length -= RB_EVNT_HDR_SIZE;
2340 if (length > RB_MAX_SMALL_DATA || RB_FORCE_8BYTE_ALIGNMENT) {
2341 event->type_len = 0;
2342 event->array[0] = length;
2343 } else
2344 event->type_len = DIV_ROUND_UP(length, RB_ALIGNMENT);
2345}
2346
2347static unsigned rb_calculate_event_length(unsigned length)
2348{
2349 struct ring_buffer_event event; /* Used only for sizeof array */
2350
2351 /* zero length can cause confusions */
2352 if (!length)
2353 length++;
2354
2355 if (length > RB_MAX_SMALL_DATA || RB_FORCE_8BYTE_ALIGNMENT)
2356 length += sizeof(event.array[0]);
2357
2358 length += RB_EVNT_HDR_SIZE;
2359 length = ALIGN(length, RB_ARCH_ALIGNMENT);
2360
2361 /*
2362 * In case the time delta is larger than the 27 bits for it
2363 * in the header, we need to add a timestamp. If another
2364 * event comes in when trying to discard this one to increase
2365 * the length, then the timestamp will be added in the allocated
2366 * space of this event. If length is bigger than the size needed
2367 * for the TIME_EXTEND, then padding has to be used. The events
2368 * length must be either RB_LEN_TIME_EXTEND, or greater than or equal
2369 * to RB_LEN_TIME_EXTEND + 8, as 8 is the minimum size for padding.
2370 * As length is a multiple of 4, we only need to worry if it
2371 * is 12 (RB_LEN_TIME_EXTEND + 4).
2372 */
2373 if (length == RB_LEN_TIME_EXTEND + RB_ALIGNMENT)
2374 length += RB_ALIGNMENT;
2375
2376 return length;
2377}
2378
2379#ifndef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
2380static inline bool sched_clock_stable(void)
2381{
2382 return true;
2383}
2384#endif
2385
2386static inline int
2387rb_try_to_discard(struct ring_buffer_per_cpu *cpu_buffer,
2388 struct ring_buffer_event *event)
2389{
2390 unsigned long new_index, old_index;
2391 struct buffer_page *bpage;
2392 unsigned long index;
2393 unsigned long addr;
2394
2395 new_index = rb_event_index(event);
2396 old_index = new_index + rb_event_ts_length(event);
2397 addr = (unsigned long)event;
2398 addr &= PAGE_MASK;
2399
2400 bpage = READ_ONCE(cpu_buffer->tail_page);
2401
2402 if (bpage->page == (void *)addr && rb_page_write(bpage) == old_index) {
2403 unsigned long write_mask =
2404 local_read(&bpage->write) & ~RB_WRITE_MASK;
2405 unsigned long event_length = rb_event_length(event);
2406 /*
2407 * This is on the tail page. It is possible that
2408 * a write could come in and move the tail page
2409 * and write to the next page. That is fine
2410 * because we just shorten what is on this page.
2411 */
2412 old_index += write_mask;
2413 new_index += write_mask;
2414 index = local_cmpxchg(&bpage->write, old_index, new_index);
2415 if (index == old_index) {
2416 /* update counters */
2417 local_sub(event_length, &cpu_buffer->entries_bytes);
2418 return 1;
2419 }
2420 }
2421
2422 /* could not discard */
2423 return 0;
2424}
2425
2426static void rb_start_commit(struct ring_buffer_per_cpu *cpu_buffer)
2427{
2428 local_inc(&cpu_buffer->committing);
2429 local_inc(&cpu_buffer->commits);
2430}
2431
2432static __always_inline void
2433rb_set_commit_to_write(struct ring_buffer_per_cpu *cpu_buffer)
2434{
2435 unsigned long max_count;
2436
2437 /*
2438 * We only race with interrupts and NMIs on this CPU.
2439 * If we own the commit event, then we can commit
2440 * all others that interrupted us, since the interruptions
2441 * are in stack format (they finish before they come
2442 * back to us). This allows us to do a simple loop to
2443 * assign the commit to the tail.
2444 */
2445 again:
2446 max_count = cpu_buffer->nr_pages * 100;
2447
2448 while (cpu_buffer->commit_page != READ_ONCE(cpu_buffer->tail_page)) {
2449 if (RB_WARN_ON(cpu_buffer, !(--max_count)))
2450 return;
2451 if (RB_WARN_ON(cpu_buffer,
2452 rb_is_reader_page(cpu_buffer->tail_page)))
2453 return;
2454 local_set(&cpu_buffer->commit_page->page->commit,
2455 rb_page_write(cpu_buffer->commit_page));
2456 rb_inc_page(cpu_buffer, &cpu_buffer->commit_page);
2457 /* Only update the write stamp if the page has an event */
2458 if (rb_page_write(cpu_buffer->commit_page))
2459 cpu_buffer->write_stamp =
2460 cpu_buffer->commit_page->page->time_stamp;
2461 /* add barrier to keep gcc from optimizing too much */
2462 barrier();
2463 }
2464 while (rb_commit_index(cpu_buffer) !=
2465 rb_page_write(cpu_buffer->commit_page)) {
2466
2467 local_set(&cpu_buffer->commit_page->page->commit,
2468 rb_page_write(cpu_buffer->commit_page));
2469 RB_WARN_ON(cpu_buffer,
2470 local_read(&cpu_buffer->commit_page->page->commit) &
2471 ~RB_WRITE_MASK);
2472 barrier();
2473 }
2474
2475 /* again, keep gcc from optimizing */
2476 barrier();
2477
2478 /*
2479 * If an interrupt came in just after the first while loop
2480 * and pushed the tail page forward, we will be left with
2481 * a dangling commit that will never go forward.
2482 */
2483 if (unlikely(cpu_buffer->commit_page != READ_ONCE(cpu_buffer->tail_page)))
2484 goto again;
2485}
2486
2487static __always_inline void rb_end_commit(struct ring_buffer_per_cpu *cpu_buffer)
2488{
2489 unsigned long commits;
2490
2491 if (RB_WARN_ON(cpu_buffer,
2492 !local_read(&cpu_buffer->committing)))
2493 return;
2494
2495 again:
2496 commits = local_read(&cpu_buffer->commits);
2497 /* synchronize with interrupts */
2498 barrier();
2499 if (local_read(&cpu_buffer->committing) == 1)
2500 rb_set_commit_to_write(cpu_buffer);
2501
2502 local_dec(&cpu_buffer->committing);
2503
2504 /* synchronize with interrupts */
2505 barrier();
2506
2507 /*
2508 * Need to account for interrupts coming in between the
2509 * updating of the commit page and the clearing of the
2510 * committing counter.
2511 */
2512 if (unlikely(local_read(&cpu_buffer->commits) != commits) &&
2513 !local_read(&cpu_buffer->committing)) {
2514 local_inc(&cpu_buffer->committing);
2515 goto again;
2516 }
2517}
2518
2519static inline void rb_event_discard(struct ring_buffer_event *event)
2520{
2521 if (extended_time(event))
2522 event = skip_time_extend(event);
2523
2524 /* array[0] holds the actual length for the discarded event */
2525 event->array[0] = rb_event_data_length(event) - RB_EVNT_HDR_SIZE;
2526 event->type_len = RINGBUF_TYPE_PADDING;
2527 /* time delta must be non zero */
2528 if (!event->time_delta)
2529 event->time_delta = 1;
2530}
2531
2532static __always_inline bool
2533rb_event_is_commit(struct ring_buffer_per_cpu *cpu_buffer,
2534 struct ring_buffer_event *event)
2535{
2536 unsigned long addr = (unsigned long)event;
2537 unsigned long index;
2538
2539 index = rb_event_index(event);
2540 addr &= PAGE_MASK;
2541
2542 return cpu_buffer->commit_page->page == (void *)addr &&
2543 rb_commit_index(cpu_buffer) == index;
2544}
2545
2546static __always_inline void
2547rb_update_write_stamp(struct ring_buffer_per_cpu *cpu_buffer,
2548 struct ring_buffer_event *event)
2549{
2550 u64 delta;
2551
2552 /*
2553 * The event first in the commit queue updates the
2554 * time stamp.
2555 */
2556 if (rb_event_is_commit(cpu_buffer, event)) {
2557 /*
2558 * A commit event that is first on a page
2559 * updates the write timestamp with the page stamp
2560 */
2561 if (!rb_event_index(event))
2562 cpu_buffer->write_stamp =
2563 cpu_buffer->commit_page->page->time_stamp;
2564 else if (event->type_len == RINGBUF_TYPE_TIME_EXTEND) {
2565 delta = ring_buffer_event_time_stamp(event);
2566 cpu_buffer->write_stamp += delta;
2567 } else if (event->type_len == RINGBUF_TYPE_TIME_STAMP) {
2568 delta = ring_buffer_event_time_stamp(event);
2569 cpu_buffer->write_stamp = delta;
2570 } else
2571 cpu_buffer->write_stamp += event->time_delta;
2572 }
2573}
2574
2575static void rb_commit(struct ring_buffer_per_cpu *cpu_buffer,
2576 struct ring_buffer_event *event)
2577{
2578 local_inc(&cpu_buffer->entries);
2579 rb_update_write_stamp(cpu_buffer, event);
2580 rb_end_commit(cpu_buffer);
2581}
2582
2583static __always_inline void
2584rb_wakeups(struct ring_buffer *buffer, struct ring_buffer_per_cpu *cpu_buffer)
2585{
2586 bool pagebusy;
2587
2588 if (buffer->irq_work.waiters_pending) {
2589 buffer->irq_work.waiters_pending = false;
2590 /* irq_work_queue() supplies it's own memory barriers */
2591 irq_work_queue(&buffer->irq_work.work);
2592 }
2593
2594 if (cpu_buffer->irq_work.waiters_pending) {
2595 cpu_buffer->irq_work.waiters_pending = false;
2596 /* irq_work_queue() supplies it's own memory barriers */
2597 irq_work_queue(&cpu_buffer->irq_work.work);
2598 }
2599
2600 pagebusy = cpu_buffer->reader_page == cpu_buffer->commit_page;
2601
2602 if (!pagebusy && cpu_buffer->irq_work.full_waiters_pending) {
2603 cpu_buffer->irq_work.wakeup_full = true;
2604 cpu_buffer->irq_work.full_waiters_pending = false;
2605 /* irq_work_queue() supplies it's own memory barriers */
2606 irq_work_queue(&cpu_buffer->irq_work.work);
2607 }
2608}
2609
2610/*
2611 * The lock and unlock are done within a preempt disable section.
2612 * The current_context per_cpu variable can only be modified
2613 * by the current task between lock and unlock. But it can
2614 * be modified more than once via an interrupt. To pass this
2615 * information from the lock to the unlock without having to
2616 * access the 'in_interrupt()' functions again (which do show
2617 * a bit of overhead in something as critical as function tracing,
2618 * we use a bitmask trick.
2619 *
2620 * bit 0 = NMI context
2621 * bit 1 = IRQ context
2622 * bit 2 = SoftIRQ context
2623 * bit 3 = normal context.
2624 *
2625 * This works because this is the order of contexts that can
2626 * preempt other contexts. A SoftIRQ never preempts an IRQ
2627 * context.
2628 *
2629 * When the context is determined, the corresponding bit is
2630 * checked and set (if it was set, then a recursion of that context
2631 * happened).
2632 *
2633 * On unlock, we need to clear this bit. To do so, just subtract
2634 * 1 from the current_context and AND it to itself.
2635 *
2636 * (binary)
2637 * 101 - 1 = 100
2638 * 101 & 100 = 100 (clearing bit zero)
2639 *
2640 * 1010 - 1 = 1001
2641 * 1010 & 1001 = 1000 (clearing bit 1)
2642 *
2643 * The least significant bit can be cleared this way, and it
2644 * just so happens that it is the same bit corresponding to
2645 * the current context.
2646 */
2647
2648static __always_inline int
2649trace_recursive_lock(struct ring_buffer_per_cpu *cpu_buffer)
2650{
2651 unsigned int val = cpu_buffer->current_context;
2652 unsigned long pc = preempt_count();
2653 int bit;
2654
2655 if (!(pc & (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET)))
2656 bit = RB_CTX_NORMAL;
2657 else
2658 bit = pc & NMI_MASK ? RB_CTX_NMI :
2659 pc & HARDIRQ_MASK ? RB_CTX_IRQ : RB_CTX_SOFTIRQ;
2660
2661 if (unlikely(val & (1 << (bit + cpu_buffer->nest))))
2662 return 1;
2663
2664 val |= (1 << (bit + cpu_buffer->nest));
2665 cpu_buffer->current_context = val;
2666
2667 return 0;
2668}
2669
2670static __always_inline void
2671trace_recursive_unlock(struct ring_buffer_per_cpu *cpu_buffer)
2672{
2673 cpu_buffer->current_context &=
2674 cpu_buffer->current_context - (1 << cpu_buffer->nest);
2675}
2676
2677/* The recursive locking above uses 4 bits */
2678#define NESTED_BITS 4
2679
2680/**
2681 * ring_buffer_nest_start - Allow to trace while nested
2682 * @buffer: The ring buffer to modify
2683 *
2684 * The ring buffer has a safty mechanism to prevent recursion.
2685 * But there may be a case where a trace needs to be done while
2686 * tracing something else. In this case, calling this function
2687 * will allow this function to nest within a currently active
2688 * ring_buffer_lock_reserve().
2689 *
2690 * Call this function before calling another ring_buffer_lock_reserve() and
2691 * call ring_buffer_nest_end() after the nested ring_buffer_unlock_commit().
2692 */
2693void ring_buffer_nest_start(struct ring_buffer *buffer)
2694{
2695 struct ring_buffer_per_cpu *cpu_buffer;
2696 int cpu;
2697
2698 /* Enabled by ring_buffer_nest_end() */
2699 preempt_disable_notrace();
2700 cpu = raw_smp_processor_id();
2701 cpu_buffer = buffer->buffers[cpu];
2702 /* This is the shift value for the above recusive locking */
2703 cpu_buffer->nest += NESTED_BITS;
2704}
2705
2706/**
2707 * ring_buffer_nest_end - Allow to trace while nested
2708 * @buffer: The ring buffer to modify
2709 *
2710 * Must be called after ring_buffer_nest_start() and after the
2711 * ring_buffer_unlock_commit().
2712 */
2713void ring_buffer_nest_end(struct ring_buffer *buffer)
2714{
2715 struct ring_buffer_per_cpu *cpu_buffer;
2716 int cpu;
2717
2718 /* disabled by ring_buffer_nest_start() */
2719 cpu = raw_smp_processor_id();
2720 cpu_buffer = buffer->buffers[cpu];
2721 /* This is the shift value for the above recusive locking */
2722 cpu_buffer->nest -= NESTED_BITS;
2723 preempt_enable_notrace();
2724}
2725
2726/**
2727 * ring_buffer_unlock_commit - commit a reserved
2728 * @buffer: The buffer to commit to
2729 * @event: The event pointer to commit.
2730 *
2731 * This commits the data to the ring buffer, and releases any locks held.
2732 *
2733 * Must be paired with ring_buffer_lock_reserve.
2734 */
2735int ring_buffer_unlock_commit(struct ring_buffer *buffer,
2736 struct ring_buffer_event *event)
2737{
2738 struct ring_buffer_per_cpu *cpu_buffer;
2739 int cpu = raw_smp_processor_id();
2740
2741 cpu_buffer = buffer->buffers[cpu];
2742
2743 rb_commit(cpu_buffer, event);
2744
2745 rb_wakeups(buffer, cpu_buffer);
2746
2747 trace_recursive_unlock(cpu_buffer);
2748
2749 preempt_enable_notrace();
2750
2751 return 0;
2752}
2753EXPORT_SYMBOL_GPL(ring_buffer_unlock_commit);
2754
2755static noinline void
2756rb_handle_timestamp(struct ring_buffer_per_cpu *cpu_buffer,
2757 struct rb_event_info *info)
2758{
2759 WARN_ONCE(info->delta > (1ULL << 59),
2760 KERN_WARNING "Delta way too big! %llu ts=%llu write stamp = %llu\n%s",
2761 (unsigned long long)info->delta,
2762 (unsigned long long)info->ts,
2763 (unsigned long long)cpu_buffer->write_stamp,
2764 sched_clock_stable() ? "" :
2765 "If you just came from a suspend/resume,\n"
2766 "please switch to the trace global clock:\n"
2767 " echo global > /sys/kernel/debug/tracing/trace_clock\n"
2768 "or add trace_clock=global to the kernel command line\n");
2769 info->add_timestamp = 1;
2770}
2771
2772static struct ring_buffer_event *
2773__rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
2774 struct rb_event_info *info)
2775{
2776 struct ring_buffer_event *event;
2777 struct buffer_page *tail_page;
2778 unsigned long tail, write;
2779
2780 /*
2781 * If the time delta since the last event is too big to
2782 * hold in the time field of the event, then we append a
2783 * TIME EXTEND event ahead of the data event.
2784 */
2785 if (unlikely(info->add_timestamp))
2786 info->length += RB_LEN_TIME_EXTEND;
2787
2788 /* Don't let the compiler play games with cpu_buffer->tail_page */
2789 tail_page = info->tail_page = READ_ONCE(cpu_buffer->tail_page);
2790 write = local_add_return(info->length, &tail_page->write);
2791
2792 /* set write to only the index of the write */
2793 write &= RB_WRITE_MASK;
2794 tail = write - info->length;
2795
2796 /*
2797 * If this is the first commit on the page, then it has the same
2798 * timestamp as the page itself.
2799 */
2800 if (!tail && !ring_buffer_time_stamp_abs(cpu_buffer->buffer))
2801 info->delta = 0;
2802
2803 /* See if we shot pass the end of this buffer page */
2804 if (unlikely(write > BUF_PAGE_SIZE))
2805 return rb_move_tail(cpu_buffer, tail, info);
2806
2807 /* We reserved something on the buffer */
2808
2809 event = __rb_page_index(tail_page, tail);
2810 rb_update_event(cpu_buffer, event, info);
2811
2812 local_inc(&tail_page->entries);
2813
2814 /*
2815 * If this is the first commit on the page, then update
2816 * its timestamp.
2817 */
2818 if (!tail)
2819 tail_page->page->time_stamp = info->ts;
2820
2821 /* account for these added bytes */
2822 local_add(info->length, &cpu_buffer->entries_bytes);
2823
2824 return event;
2825}
2826
2827static __always_inline struct ring_buffer_event *
2828rb_reserve_next_event(struct ring_buffer *buffer,
2829 struct ring_buffer_per_cpu *cpu_buffer,
2830 unsigned long length)
2831{
2832 struct ring_buffer_event *event;
2833 struct rb_event_info info;
2834 int nr_loops = 0;
2835 u64 diff;
2836
2837 rb_start_commit(cpu_buffer);
2838
2839#ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
2840 /*
2841 * Due to the ability to swap a cpu buffer from a buffer
2842 * it is possible it was swapped before we committed.
2843 * (committing stops a swap). We check for it here and
2844 * if it happened, we have to fail the write.
2845 */
2846 barrier();
2847 if (unlikely(READ_ONCE(cpu_buffer->buffer) != buffer)) {
2848 local_dec(&cpu_buffer->committing);
2849 local_dec(&cpu_buffer->commits);
2850 return NULL;
2851 }
2852#endif
2853
2854 info.length = rb_calculate_event_length(length);
2855 again:
2856 info.add_timestamp = 0;
2857 info.delta = 0;
2858
2859 /*
2860 * We allow for interrupts to reenter here and do a trace.
2861 * If one does, it will cause this original code to loop
2862 * back here. Even with heavy interrupts happening, this
2863 * should only happen a few times in a row. If this happens
2864 * 1000 times in a row, there must be either an interrupt
2865 * storm or we have something buggy.
2866 * Bail!
2867 */
2868 if (RB_WARN_ON(cpu_buffer, ++nr_loops > 1000))
2869 goto out_fail;
2870
2871 info.ts = rb_time_stamp(cpu_buffer->buffer);
2872 diff = info.ts - cpu_buffer->write_stamp;
2873
2874 /* make sure this diff is calculated here */
2875 barrier();
2876
2877 if (ring_buffer_time_stamp_abs(buffer)) {
2878 info.delta = info.ts;
2879 rb_handle_timestamp(cpu_buffer, &info);
2880 } else /* Did the write stamp get updated already? */
2881 if (likely(info.ts >= cpu_buffer->write_stamp)) {
2882 info.delta = diff;
2883 if (unlikely(test_time_stamp(info.delta)))
2884 rb_handle_timestamp(cpu_buffer, &info);
2885 }
2886
2887 event = __rb_reserve_next(cpu_buffer, &info);
2888
2889 if (unlikely(PTR_ERR(event) == -EAGAIN)) {
2890 if (info.add_timestamp)
2891 info.length -= RB_LEN_TIME_EXTEND;
2892 goto again;
2893 }
2894
2895 if (!event)
2896 goto out_fail;
2897
2898 return event;
2899
2900 out_fail:
2901 rb_end_commit(cpu_buffer);
2902 return NULL;
2903}
2904
2905/**
2906 * ring_buffer_lock_reserve - reserve a part of the buffer
2907 * @buffer: the ring buffer to reserve from
2908 * @length: the length of the data to reserve (excluding event header)
2909 *
2910 * Returns a reseverd event on the ring buffer to copy directly to.
2911 * The user of this interface will need to get the body to write into
2912 * and can use the ring_buffer_event_data() interface.
2913 *
2914 * The length is the length of the data needed, not the event length
2915 * which also includes the event header.
2916 *
2917 * Must be paired with ring_buffer_unlock_commit, unless NULL is returned.
2918 * If NULL is returned, then nothing has been allocated or locked.
2919 */
2920struct ring_buffer_event *
2921ring_buffer_lock_reserve(struct ring_buffer *buffer, unsigned long length)
2922{
2923 struct ring_buffer_per_cpu *cpu_buffer;
2924 struct ring_buffer_event *event;
2925 int cpu;
2926
2927 /* If we are tracing schedule, we don't want to recurse */
2928 preempt_disable_notrace();
2929
2930 if (unlikely(atomic_read(&buffer->record_disabled)))
2931 goto out;
2932
2933 cpu = raw_smp_processor_id();
2934
2935 if (unlikely(!cpumask_test_cpu(cpu, buffer->cpumask)))
2936 goto out;
2937
2938 cpu_buffer = buffer->buffers[cpu];
2939
2940 if (unlikely(atomic_read(&cpu_buffer->record_disabled)))
2941 goto out;
2942
2943 if (unlikely(length > BUF_MAX_DATA_SIZE))
2944 goto out;
2945
2946 if (unlikely(trace_recursive_lock(cpu_buffer)))
2947 goto out;
2948
2949 event = rb_reserve_next_event(buffer, cpu_buffer, length);
2950 if (!event)
2951 goto out_unlock;
2952
2953 return event;
2954
2955 out_unlock:
2956 trace_recursive_unlock(cpu_buffer);
2957 out:
2958 preempt_enable_notrace();
2959 return NULL;
2960}
2961EXPORT_SYMBOL_GPL(ring_buffer_lock_reserve);
2962
2963/*
2964 * Decrement the entries to the page that an event is on.
2965 * The event does not even need to exist, only the pointer
2966 * to the page it is on. This may only be called before the commit
2967 * takes place.
2968 */
2969static inline void
2970rb_decrement_entry(struct ring_buffer_per_cpu *cpu_buffer,
2971 struct ring_buffer_event *event)
2972{
2973 unsigned long addr = (unsigned long)event;
2974 struct buffer_page *bpage = cpu_buffer->commit_page;
2975 struct buffer_page *start;
2976
2977 addr &= PAGE_MASK;
2978
2979 /* Do the likely case first */
2980 if (likely(bpage->page == (void *)addr)) {
2981 local_dec(&bpage->entries);
2982 return;
2983 }
2984
2985 /*
2986 * Because the commit page may be on the reader page we
2987 * start with the next page and check the end loop there.
2988 */
2989 rb_inc_page(cpu_buffer, &bpage);
2990 start = bpage;
2991 do {
2992 if (bpage->page == (void *)addr) {
2993 local_dec(&bpage->entries);
2994 return;
2995 }
2996 rb_inc_page(cpu_buffer, &bpage);
2997 } while (bpage != start);
2998
2999 /* commit not part of this buffer?? */
3000 RB_WARN_ON(cpu_buffer, 1);
3001}
3002
3003/**
3004 * ring_buffer_commit_discard - discard an event that has not been committed
3005 * @buffer: the ring buffer
3006 * @event: non committed event to discard
3007 *
3008 * Sometimes an event that is in the ring buffer needs to be ignored.
3009 * This function lets the user discard an event in the ring buffer
3010 * and then that event will not be read later.
3011 *
3012 * This function only works if it is called before the the item has been
3013 * committed. It will try to free the event from the ring buffer
3014 * if another event has not been added behind it.
3015 *
3016 * If another event has been added behind it, it will set the event
3017 * up as discarded, and perform the commit.
3018 *
3019 * If this function is called, do not call ring_buffer_unlock_commit on
3020 * the event.
3021 */
3022void ring_buffer_discard_commit(struct ring_buffer *buffer,
3023 struct ring_buffer_event *event)
3024{
3025 struct ring_buffer_per_cpu *cpu_buffer;
3026 int cpu;
3027
3028 /* The event is discarded regardless */
3029 rb_event_discard(event);
3030
3031 cpu = smp_processor_id();
3032 cpu_buffer = buffer->buffers[cpu];
3033
3034 /*
3035 * This must only be called if the event has not been
3036 * committed yet. Thus we can assume that preemption
3037 * is still disabled.
3038 */
3039 RB_WARN_ON(buffer, !local_read(&cpu_buffer->committing));
3040
3041 rb_decrement_entry(cpu_buffer, event);
3042 if (rb_try_to_discard(cpu_buffer, event))
3043 goto out;
3044
3045 /*
3046 * The commit is still visible by the reader, so we
3047 * must still update the timestamp.
3048 */
3049 rb_update_write_stamp(cpu_buffer, event);
3050 out:
3051 rb_end_commit(cpu_buffer);
3052
3053 trace_recursive_unlock(cpu_buffer);
3054
3055 preempt_enable_notrace();
3056
3057}
3058EXPORT_SYMBOL_GPL(ring_buffer_discard_commit);
3059
3060/**
3061 * ring_buffer_write - write data to the buffer without reserving
3062 * @buffer: The ring buffer to write to.
3063 * @length: The length of the data being written (excluding the event header)
3064 * @data: The data to write to the buffer.
3065 *
3066 * This is like ring_buffer_lock_reserve and ring_buffer_unlock_commit as
3067 * one function. If you already have the data to write to the buffer, it
3068 * may be easier to simply call this function.
3069 *
3070 * Note, like ring_buffer_lock_reserve, the length is the length of the data
3071 * and not the length of the event which would hold the header.
3072 */
3073int ring_buffer_write(struct ring_buffer *buffer,
3074 unsigned long length,
3075 void *data)
3076{
3077 struct ring_buffer_per_cpu *cpu_buffer;
3078 struct ring_buffer_event *event;
3079 void *body;
3080 int ret = -EBUSY;
3081 int cpu;
3082
3083 preempt_disable_notrace();
3084
3085 if (atomic_read(&buffer->record_disabled))
3086 goto out;
3087
3088 cpu = raw_smp_processor_id();
3089
3090 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3091 goto out;
3092
3093 cpu_buffer = buffer->buffers[cpu];
3094
3095 if (atomic_read(&cpu_buffer->record_disabled))
3096 goto out;
3097
3098 if (length > BUF_MAX_DATA_SIZE)
3099 goto out;
3100
3101 if (unlikely(trace_recursive_lock(cpu_buffer)))
3102 goto out;
3103
3104 event = rb_reserve_next_event(buffer, cpu_buffer, length);
3105 if (!event)
3106 goto out_unlock;
3107
3108 body = rb_event_data(event);
3109
3110 memcpy(body, data, length);
3111
3112 rb_commit(cpu_buffer, event);
3113
3114 rb_wakeups(buffer, cpu_buffer);
3115
3116 ret = 0;
3117
3118 out_unlock:
3119 trace_recursive_unlock(cpu_buffer);
3120
3121 out:
3122 preempt_enable_notrace();
3123
3124 return ret;
3125}
3126EXPORT_SYMBOL_GPL(ring_buffer_write);
3127
3128static bool rb_per_cpu_empty(struct ring_buffer_per_cpu *cpu_buffer)
3129{
3130 struct buffer_page *reader = cpu_buffer->reader_page;
3131 struct buffer_page *head = rb_set_head_page(cpu_buffer);
3132 struct buffer_page *commit = cpu_buffer->commit_page;
3133
3134 /* In case of error, head will be NULL */
3135 if (unlikely(!head))
3136 return true;
3137
3138 return reader->read == rb_page_commit(reader) &&
3139 (commit == reader ||
3140 (commit == head &&
3141 head->read == rb_page_commit(commit)));
3142}
3143
3144/**
3145 * ring_buffer_record_disable - stop all writes into the buffer
3146 * @buffer: The ring buffer to stop writes to.
3147 *
3148 * This prevents all writes to the buffer. Any attempt to write
3149 * to the buffer after this will fail and return NULL.
3150 *
3151 * The caller should call synchronize_sched() after this.
3152 */
3153void ring_buffer_record_disable(struct ring_buffer *buffer)
3154{
3155 atomic_inc(&buffer->record_disabled);
3156}
3157EXPORT_SYMBOL_GPL(ring_buffer_record_disable);
3158
3159/**
3160 * ring_buffer_record_enable - enable writes to the buffer
3161 * @buffer: The ring buffer to enable writes
3162 *
3163 * Note, multiple disables will need the same number of enables
3164 * to truly enable the writing (much like preempt_disable).
3165 */
3166void ring_buffer_record_enable(struct ring_buffer *buffer)
3167{
3168 atomic_dec(&buffer->record_disabled);
3169}
3170EXPORT_SYMBOL_GPL(ring_buffer_record_enable);
3171
3172/**
3173 * ring_buffer_record_off - stop all writes into the buffer
3174 * @buffer: The ring buffer to stop writes to.
3175 *
3176 * This prevents all writes to the buffer. Any attempt to write
3177 * to the buffer after this will fail and return NULL.
3178 *
3179 * This is different than ring_buffer_record_disable() as
3180 * it works like an on/off switch, where as the disable() version
3181 * must be paired with a enable().
3182 */
3183void ring_buffer_record_off(struct ring_buffer *buffer)
3184{
3185 unsigned int rd;
3186 unsigned int new_rd;
3187
3188 do {
3189 rd = atomic_read(&buffer->record_disabled);
3190 new_rd = rd | RB_BUFFER_OFF;
3191 } while (atomic_cmpxchg(&buffer->record_disabled, rd, new_rd) != rd);
3192}
3193EXPORT_SYMBOL_GPL(ring_buffer_record_off);
3194
3195/**
3196 * ring_buffer_record_on - restart writes into the buffer
3197 * @buffer: The ring buffer to start writes to.
3198 *
3199 * This enables all writes to the buffer that was disabled by
3200 * ring_buffer_record_off().
3201 *
3202 * This is different than ring_buffer_record_enable() as
3203 * it works like an on/off switch, where as the enable() version
3204 * must be paired with a disable().
3205 */
3206void ring_buffer_record_on(struct ring_buffer *buffer)
3207{
3208 unsigned int rd;
3209 unsigned int new_rd;
3210
3211 do {
3212 rd = atomic_read(&buffer->record_disabled);
3213 new_rd = rd & ~RB_BUFFER_OFF;
3214 } while (atomic_cmpxchg(&buffer->record_disabled, rd, new_rd) != rd);
3215}
3216EXPORT_SYMBOL_GPL(ring_buffer_record_on);
3217
3218/**
3219 * ring_buffer_record_is_on - return true if the ring buffer can write
3220 * @buffer: The ring buffer to see if write is enabled
3221 *
3222 * Returns true if the ring buffer is in a state that it accepts writes.
3223 */
3224int ring_buffer_record_is_on(struct ring_buffer *buffer)
3225{
3226 return !atomic_read(&buffer->record_disabled);
3227}
3228
3229/**
3230 * ring_buffer_record_disable_cpu - stop all writes into the cpu_buffer
3231 * @buffer: The ring buffer to stop writes to.
3232 * @cpu: The CPU buffer to stop
3233 *
3234 * This prevents all writes to the buffer. Any attempt to write
3235 * to the buffer after this will fail and return NULL.
3236 *
3237 * The caller should call synchronize_sched() after this.
3238 */
3239void ring_buffer_record_disable_cpu(struct ring_buffer *buffer, int cpu)
3240{
3241 struct ring_buffer_per_cpu *cpu_buffer;
3242
3243 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3244 return;
3245
3246 cpu_buffer = buffer->buffers[cpu];
3247 atomic_inc(&cpu_buffer->record_disabled);
3248}
3249EXPORT_SYMBOL_GPL(ring_buffer_record_disable_cpu);
3250
3251/**
3252 * ring_buffer_record_enable_cpu - enable writes to the buffer
3253 * @buffer: The ring buffer to enable writes
3254 * @cpu: The CPU to enable.
3255 *
3256 * Note, multiple disables will need the same number of enables
3257 * to truly enable the writing (much like preempt_disable).
3258 */
3259void ring_buffer_record_enable_cpu(struct ring_buffer *buffer, int cpu)
3260{
3261 struct ring_buffer_per_cpu *cpu_buffer;
3262
3263 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3264 return;
3265
3266 cpu_buffer = buffer->buffers[cpu];
3267 atomic_dec(&cpu_buffer->record_disabled);
3268}
3269EXPORT_SYMBOL_GPL(ring_buffer_record_enable_cpu);
3270
3271/*
3272 * The total entries in the ring buffer is the running counter
3273 * of entries entered into the ring buffer, minus the sum of
3274 * the entries read from the ring buffer and the number of
3275 * entries that were overwritten.
3276 */
3277static inline unsigned long
3278rb_num_of_entries(struct ring_buffer_per_cpu *cpu_buffer)
3279{
3280 return local_read(&cpu_buffer->entries) -
3281 (local_read(&cpu_buffer->overrun) + cpu_buffer->read);
3282}
3283
3284/**
3285 * ring_buffer_oldest_event_ts - get the oldest event timestamp from the buffer
3286 * @buffer: The ring buffer
3287 * @cpu: The per CPU buffer to read from.
3288 */
3289u64 ring_buffer_oldest_event_ts(struct ring_buffer *buffer, int cpu)
3290{
3291 unsigned long flags;
3292 struct ring_buffer_per_cpu *cpu_buffer;
3293 struct buffer_page *bpage;
3294 u64 ret = 0;
3295
3296 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3297 return 0;
3298
3299 cpu_buffer = buffer->buffers[cpu];
3300 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
3301 /*
3302 * if the tail is on reader_page, oldest time stamp is on the reader
3303 * page
3304 */
3305 if (cpu_buffer->tail_page == cpu_buffer->reader_page)
3306 bpage = cpu_buffer->reader_page;
3307 else
3308 bpage = rb_set_head_page(cpu_buffer);
3309 if (bpage)
3310 ret = bpage->page->time_stamp;
3311 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
3312
3313 return ret;
3314}
3315EXPORT_SYMBOL_GPL(ring_buffer_oldest_event_ts);
3316
3317/**
3318 * ring_buffer_bytes_cpu - get the number of bytes consumed in a cpu buffer
3319 * @buffer: The ring buffer
3320 * @cpu: The per CPU buffer to read from.
3321 */
3322unsigned long ring_buffer_bytes_cpu(struct ring_buffer *buffer, int cpu)
3323{
3324 struct ring_buffer_per_cpu *cpu_buffer;
3325 unsigned long ret;
3326
3327 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3328 return 0;
3329
3330 cpu_buffer = buffer->buffers[cpu];
3331 ret = local_read(&cpu_buffer->entries_bytes) - cpu_buffer->read_bytes;
3332
3333 return ret;
3334}
3335EXPORT_SYMBOL_GPL(ring_buffer_bytes_cpu);
3336
3337/**
3338 * ring_buffer_entries_cpu - get the number of entries in a cpu buffer
3339 * @buffer: The ring buffer
3340 * @cpu: The per CPU buffer to get the entries from.
3341 */
3342unsigned long ring_buffer_entries_cpu(struct ring_buffer *buffer, int cpu)
3343{
3344 struct ring_buffer_per_cpu *cpu_buffer;
3345
3346 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3347 return 0;
3348
3349 cpu_buffer = buffer->buffers[cpu];
3350
3351 return rb_num_of_entries(cpu_buffer);
3352}
3353EXPORT_SYMBOL_GPL(ring_buffer_entries_cpu);
3354
3355/**
3356 * ring_buffer_overrun_cpu - get the number of overruns caused by the ring
3357 * buffer wrapping around (only if RB_FL_OVERWRITE is on).
3358 * @buffer: The ring buffer
3359 * @cpu: The per CPU buffer to get the number of overruns from
3360 */
3361unsigned long ring_buffer_overrun_cpu(struct ring_buffer *buffer, int cpu)
3362{
3363 struct ring_buffer_per_cpu *cpu_buffer;
3364 unsigned long ret;
3365
3366 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3367 return 0;
3368
3369 cpu_buffer = buffer->buffers[cpu];
3370 ret = local_read(&cpu_buffer->overrun);
3371
3372 return ret;
3373}
3374EXPORT_SYMBOL_GPL(ring_buffer_overrun_cpu);
3375
3376/**
3377 * ring_buffer_commit_overrun_cpu - get the number of overruns caused by
3378 * commits failing due to the buffer wrapping around while there are uncommitted
3379 * events, such as during an interrupt storm.
3380 * @buffer: The ring buffer
3381 * @cpu: The per CPU buffer to get the number of overruns from
3382 */
3383unsigned long
3384ring_buffer_commit_overrun_cpu(struct ring_buffer *buffer, int cpu)
3385{
3386 struct ring_buffer_per_cpu *cpu_buffer;
3387 unsigned long ret;
3388
3389 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3390 return 0;
3391
3392 cpu_buffer = buffer->buffers[cpu];
3393 ret = local_read(&cpu_buffer->commit_overrun);
3394
3395 return ret;
3396}
3397EXPORT_SYMBOL_GPL(ring_buffer_commit_overrun_cpu);
3398
3399/**
3400 * ring_buffer_dropped_events_cpu - get the number of dropped events caused by
3401 * the ring buffer filling up (only if RB_FL_OVERWRITE is off).
3402 * @buffer: The ring buffer
3403 * @cpu: The per CPU buffer to get the number of overruns from
3404 */
3405unsigned long
3406ring_buffer_dropped_events_cpu(struct ring_buffer *buffer, int cpu)
3407{
3408 struct ring_buffer_per_cpu *cpu_buffer;
3409 unsigned long ret;
3410
3411 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3412 return 0;
3413
3414 cpu_buffer = buffer->buffers[cpu];
3415 ret = local_read(&cpu_buffer->dropped_events);
3416
3417 return ret;
3418}
3419EXPORT_SYMBOL_GPL(ring_buffer_dropped_events_cpu);
3420
3421/**
3422 * ring_buffer_read_events_cpu - get the number of events successfully read
3423 * @buffer: The ring buffer
3424 * @cpu: The per CPU buffer to get the number of events read
3425 */
3426unsigned long
3427ring_buffer_read_events_cpu(struct ring_buffer *buffer, int cpu)
3428{
3429 struct ring_buffer_per_cpu *cpu_buffer;
3430
3431 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3432 return 0;
3433
3434 cpu_buffer = buffer->buffers[cpu];
3435 return cpu_buffer->read;
3436}
3437EXPORT_SYMBOL_GPL(ring_buffer_read_events_cpu);
3438
3439/**
3440 * ring_buffer_entries - get the number of entries in a buffer
3441 * @buffer: The ring buffer
3442 *
3443 * Returns the total number of entries in the ring buffer
3444 * (all CPU entries)
3445 */
3446unsigned long ring_buffer_entries(struct ring_buffer *buffer)
3447{
3448 struct ring_buffer_per_cpu *cpu_buffer;
3449 unsigned long entries = 0;
3450 int cpu;
3451
3452 /* if you care about this being correct, lock the buffer */
3453 for_each_buffer_cpu(buffer, cpu) {
3454 cpu_buffer = buffer->buffers[cpu];
3455 entries += rb_num_of_entries(cpu_buffer);
3456 }
3457
3458 return entries;
3459}
3460EXPORT_SYMBOL_GPL(ring_buffer_entries);
3461
3462/**
3463 * ring_buffer_overruns - get the number of overruns in buffer
3464 * @buffer: The ring buffer
3465 *
3466 * Returns the total number of overruns in the ring buffer
3467 * (all CPU entries)
3468 */
3469unsigned long ring_buffer_overruns(struct ring_buffer *buffer)
3470{
3471 struct ring_buffer_per_cpu *cpu_buffer;
3472 unsigned long overruns = 0;
3473 int cpu;
3474
3475 /* if you care about this being correct, lock the buffer */
3476 for_each_buffer_cpu(buffer, cpu) {
3477 cpu_buffer = buffer->buffers[cpu];
3478 overruns += local_read(&cpu_buffer->overrun);
3479 }
3480
3481 return overruns;
3482}
3483EXPORT_SYMBOL_GPL(ring_buffer_overruns);
3484
3485static void rb_iter_reset(struct ring_buffer_iter *iter)
3486{
3487 struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
3488
3489 /* Iterator usage is expected to have record disabled */
3490 iter->head_page = cpu_buffer->reader_page;
3491 iter->head = cpu_buffer->reader_page->read;
3492
3493 iter->cache_reader_page = iter->head_page;
3494 iter->cache_read = cpu_buffer->read;
3495
3496 if (iter->head)
3497 iter->read_stamp = cpu_buffer->read_stamp;
3498 else
3499 iter->read_stamp = iter->head_page->page->time_stamp;
3500}
3501
3502/**
3503 * ring_buffer_iter_reset - reset an iterator
3504 * @iter: The iterator to reset
3505 *
3506 * Resets the iterator, so that it will start from the beginning
3507 * again.
3508 */
3509void ring_buffer_iter_reset(struct ring_buffer_iter *iter)
3510{
3511 struct ring_buffer_per_cpu *cpu_buffer;
3512 unsigned long flags;
3513
3514 if (!iter)
3515 return;
3516
3517 cpu_buffer = iter->cpu_buffer;
3518
3519 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
3520 rb_iter_reset(iter);
3521 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
3522}
3523EXPORT_SYMBOL_GPL(ring_buffer_iter_reset);
3524
3525/**
3526 * ring_buffer_iter_empty - check if an iterator has no more to read
3527 * @iter: The iterator to check
3528 */
3529int ring_buffer_iter_empty(struct ring_buffer_iter *iter)
3530{
3531 struct ring_buffer_per_cpu *cpu_buffer;
3532 struct buffer_page *reader;
3533 struct buffer_page *head_page;
3534 struct buffer_page *commit_page;
3535 unsigned commit;
3536
3537 cpu_buffer = iter->cpu_buffer;
3538
3539 /* Remember, trace recording is off when iterator is in use */
3540 reader = cpu_buffer->reader_page;
3541 head_page = cpu_buffer->head_page;
3542 commit_page = cpu_buffer->commit_page;
3543 commit = rb_page_commit(commit_page);
3544
3545 return ((iter->head_page == commit_page && iter->head == commit) ||
3546 (iter->head_page == reader && commit_page == head_page &&
3547 head_page->read == commit &&
3548 iter->head == rb_page_commit(cpu_buffer->reader_page)));
3549}
3550EXPORT_SYMBOL_GPL(ring_buffer_iter_empty);
3551
3552static void
3553rb_update_read_stamp(struct ring_buffer_per_cpu *cpu_buffer,
3554 struct ring_buffer_event *event)
3555{
3556 u64 delta;
3557
3558 switch (event->type_len) {
3559 case RINGBUF_TYPE_PADDING:
3560 return;
3561
3562 case RINGBUF_TYPE_TIME_EXTEND:
3563 delta = ring_buffer_event_time_stamp(event);
3564 cpu_buffer->read_stamp += delta;
3565 return;
3566
3567 case RINGBUF_TYPE_TIME_STAMP:
3568 delta = ring_buffer_event_time_stamp(event);
3569 cpu_buffer->read_stamp = delta;
3570 return;
3571
3572 case RINGBUF_TYPE_DATA:
3573 cpu_buffer->read_stamp += event->time_delta;
3574 return;
3575
3576 default:
3577 BUG();
3578 }
3579 return;
3580}
3581
3582static void
3583rb_update_iter_read_stamp(struct ring_buffer_iter *iter,
3584 struct ring_buffer_event *event)
3585{
3586 u64 delta;
3587
3588 switch (event->type_len) {
3589 case RINGBUF_TYPE_PADDING:
3590 return;
3591
3592 case RINGBUF_TYPE_TIME_EXTEND:
3593 delta = ring_buffer_event_time_stamp(event);
3594 iter->read_stamp += delta;
3595 return;
3596
3597 case RINGBUF_TYPE_TIME_STAMP:
3598 delta = ring_buffer_event_time_stamp(event);
3599 iter->read_stamp = delta;
3600 return;
3601
3602 case RINGBUF_TYPE_DATA:
3603 iter->read_stamp += event->time_delta;
3604 return;
3605
3606 default:
3607 BUG();
3608 }
3609 return;
3610}
3611
3612static struct buffer_page *
3613rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
3614{
3615 struct buffer_page *reader = NULL;
3616 unsigned long overwrite;
3617 unsigned long flags;
3618 int nr_loops = 0;
3619 int ret;
3620
3621 local_irq_save(flags);
3622 arch_spin_lock(&cpu_buffer->lock);
3623
3624 again:
3625 /*
3626 * This should normally only loop twice. But because the
3627 * start of the reader inserts an empty page, it causes
3628 * a case where we will loop three times. There should be no
3629 * reason to loop four times (that I know of).
3630 */
3631 if (RB_WARN_ON(cpu_buffer, ++nr_loops > 3)) {
3632 reader = NULL;
3633 goto out;
3634 }
3635
3636 reader = cpu_buffer->reader_page;
3637
3638 /* If there's more to read, return this page */
3639 if (cpu_buffer->reader_page->read < rb_page_size(reader))
3640 goto out;
3641
3642 /* Never should we have an index greater than the size */
3643 if (RB_WARN_ON(cpu_buffer,
3644 cpu_buffer->reader_page->read > rb_page_size(reader)))
3645 goto out;
3646
3647 /* check if we caught up to the tail */
3648 reader = NULL;
3649 if (cpu_buffer->commit_page == cpu_buffer->reader_page)
3650 goto out;
3651
3652 /* Don't bother swapping if the ring buffer is empty */
3653 if (rb_num_of_entries(cpu_buffer) == 0)
3654 goto out;
3655
3656 /*
3657 * Reset the reader page to size zero.
3658 */
3659 local_set(&cpu_buffer->reader_page->write, 0);
3660 local_set(&cpu_buffer->reader_page->entries, 0);
3661 local_set(&cpu_buffer->reader_page->page->commit, 0);
3662 cpu_buffer->reader_page->real_end = 0;
3663
3664 spin:
3665 /*
3666 * Splice the empty reader page into the list around the head.
3667 */
3668 reader = rb_set_head_page(cpu_buffer);
3669 if (!reader)
3670 goto out;
3671 cpu_buffer->reader_page->list.next = rb_list_head(reader->list.next);
3672 cpu_buffer->reader_page->list.prev = reader->list.prev;
3673
3674 /*
3675 * cpu_buffer->pages just needs to point to the buffer, it
3676 * has no specific buffer page to point to. Lets move it out
3677 * of our way so we don't accidentally swap it.
3678 */
3679 cpu_buffer->pages = reader->list.prev;
3680
3681 /* The reader page will be pointing to the new head */
3682 rb_set_list_to_head(cpu_buffer, &cpu_buffer->reader_page->list);
3683
3684 /*
3685 * We want to make sure we read the overruns after we set up our
3686 * pointers to the next object. The writer side does a
3687 * cmpxchg to cross pages which acts as the mb on the writer
3688 * side. Note, the reader will constantly fail the swap
3689 * while the writer is updating the pointers, so this
3690 * guarantees that the overwrite recorded here is the one we
3691 * want to compare with the last_overrun.
3692 */
3693 smp_mb();
3694 overwrite = local_read(&(cpu_buffer->overrun));
3695
3696 /*
3697 * Here's the tricky part.
3698 *
3699 * We need to move the pointer past the header page.
3700 * But we can only do that if a writer is not currently
3701 * moving it. The page before the header page has the
3702 * flag bit '1' set if it is pointing to the page we want.
3703 * but if the writer is in the process of moving it
3704 * than it will be '2' or already moved '0'.
3705 */
3706
3707 ret = rb_head_page_replace(reader, cpu_buffer->reader_page);
3708
3709 /*
3710 * If we did not convert it, then we must try again.
3711 */
3712 if (!ret)
3713 goto spin;
3714
3715 /*
3716 * Yeah! We succeeded in replacing the page.
3717 *
3718 * Now make the new head point back to the reader page.
3719 */
3720 rb_list_head(reader->list.next)->prev = &cpu_buffer->reader_page->list;
3721 rb_inc_page(cpu_buffer, &cpu_buffer->head_page);
3722
3723 /* Finally update the reader page to the new head */
3724 cpu_buffer->reader_page = reader;
3725 cpu_buffer->reader_page->read = 0;
3726
3727 if (overwrite != cpu_buffer->last_overrun) {
3728 cpu_buffer->lost_events = overwrite - cpu_buffer->last_overrun;
3729 cpu_buffer->last_overrun = overwrite;
3730 }
3731
3732 goto again;
3733
3734 out:
3735 /* Update the read_stamp on the first event */
3736 if (reader && reader->read == 0)
3737 cpu_buffer->read_stamp = reader->page->time_stamp;
3738
3739 arch_spin_unlock(&cpu_buffer->lock);
3740 local_irq_restore(flags);
3741
3742 return reader;
3743}
3744
3745static void rb_advance_reader(struct ring_buffer_per_cpu *cpu_buffer)
3746{
3747 struct ring_buffer_event *event;
3748 struct buffer_page *reader;
3749 unsigned length;
3750
3751 reader = rb_get_reader_page(cpu_buffer);
3752
3753 /* This function should not be called when buffer is empty */
3754 if (RB_WARN_ON(cpu_buffer, !reader))
3755 return;
3756
3757 event = rb_reader_event(cpu_buffer);
3758
3759 if (event->type_len <= RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
3760 cpu_buffer->read++;
3761
3762 rb_update_read_stamp(cpu_buffer, event);
3763
3764 length = rb_event_length(event);
3765 cpu_buffer->reader_page->read += length;
3766}
3767
3768static void rb_advance_iter(struct ring_buffer_iter *iter)
3769{
3770 struct ring_buffer_per_cpu *cpu_buffer;
3771 struct ring_buffer_event *event;
3772 unsigned length;
3773
3774 cpu_buffer = iter->cpu_buffer;
3775
3776 /*
3777 * Check if we are at the end of the buffer.
3778 */
3779 if (iter->head >= rb_page_size(iter->head_page)) {
3780 /* discarded commits can make the page empty */
3781 if (iter->head_page == cpu_buffer->commit_page)
3782 return;
3783 rb_inc_iter(iter);
3784 return;
3785 }
3786
3787 event = rb_iter_head_event(iter);
3788
3789 length = rb_event_length(event);
3790
3791 /*
3792 * This should not be called to advance the header if we are
3793 * at the tail of the buffer.
3794 */
3795 if (RB_WARN_ON(cpu_buffer,
3796 (iter->head_page == cpu_buffer->commit_page) &&
3797 (iter->head + length > rb_commit_index(cpu_buffer))))
3798 return;
3799
3800 rb_update_iter_read_stamp(iter, event);
3801
3802 iter->head += length;
3803
3804 /* check for end of page padding */
3805 if ((iter->head >= rb_page_size(iter->head_page)) &&
3806 (iter->head_page != cpu_buffer->commit_page))
3807 rb_inc_iter(iter);
3808}
3809
3810static int rb_lost_events(struct ring_buffer_per_cpu *cpu_buffer)
3811{
3812 return cpu_buffer->lost_events;
3813}
3814
3815static struct ring_buffer_event *
3816rb_buffer_peek(struct ring_buffer_per_cpu *cpu_buffer, u64 *ts,
3817 unsigned long *lost_events)
3818{
3819 struct ring_buffer_event *event;
3820 struct buffer_page *reader;
3821 int nr_loops = 0;
3822
3823 if (ts)
3824 *ts = 0;
3825 again:
3826 /*
3827 * We repeat when a time extend is encountered.
3828 * Since the time extend is always attached to a data event,
3829 * we should never loop more than once.
3830 * (We never hit the following condition more than twice).
3831 */
3832 if (RB_WARN_ON(cpu_buffer, ++nr_loops > 2))
3833 return NULL;
3834
3835 reader = rb_get_reader_page(cpu_buffer);
3836 if (!reader)
3837 return NULL;
3838
3839 event = rb_reader_event(cpu_buffer);
3840
3841 switch (event->type_len) {
3842 case RINGBUF_TYPE_PADDING:
3843 if (rb_null_event(event))
3844 RB_WARN_ON(cpu_buffer, 1);
3845 /*
3846 * Because the writer could be discarding every
3847 * event it creates (which would probably be bad)
3848 * if we were to go back to "again" then we may never
3849 * catch up, and will trigger the warn on, or lock
3850 * the box. Return the padding, and we will release
3851 * the current locks, and try again.
3852 */
3853 return event;
3854
3855 case RINGBUF_TYPE_TIME_EXTEND:
3856 /* Internal data, OK to advance */
3857 rb_advance_reader(cpu_buffer);
3858 goto again;
3859
3860 case RINGBUF_TYPE_TIME_STAMP:
3861 if (ts) {
3862 *ts = ring_buffer_event_time_stamp(event);
3863 ring_buffer_normalize_time_stamp(cpu_buffer->buffer,
3864 cpu_buffer->cpu, ts);
3865 }
3866 /* Internal data, OK to advance */
3867 rb_advance_reader(cpu_buffer);
3868 goto again;
3869
3870 case RINGBUF_TYPE_DATA:
3871 if (ts && !(*ts)) {
3872 *ts = cpu_buffer->read_stamp + event->time_delta;
3873 ring_buffer_normalize_time_stamp(cpu_buffer->buffer,
3874 cpu_buffer->cpu, ts);
3875 }
3876 if (lost_events)
3877 *lost_events = rb_lost_events(cpu_buffer);
3878 return event;
3879
3880 default:
3881 BUG();
3882 }
3883
3884 return NULL;
3885}
3886EXPORT_SYMBOL_GPL(ring_buffer_peek);
3887
3888static struct ring_buffer_event *
3889rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
3890{
3891 struct ring_buffer *buffer;
3892 struct ring_buffer_per_cpu *cpu_buffer;
3893 struct ring_buffer_event *event;
3894 int nr_loops = 0;
3895
3896 if (ts)
3897 *ts = 0;
3898
3899 cpu_buffer = iter->cpu_buffer;
3900 buffer = cpu_buffer->buffer;
3901
3902 /*
3903 * Check if someone performed a consuming read to
3904 * the buffer. A consuming read invalidates the iterator
3905 * and we need to reset the iterator in this case.
3906 */
3907 if (unlikely(iter->cache_read != cpu_buffer->read ||
3908 iter->cache_reader_page != cpu_buffer->reader_page))
3909 rb_iter_reset(iter);
3910
3911 again:
3912 if (ring_buffer_iter_empty(iter))
3913 return NULL;
3914
3915 /*
3916 * We repeat when a time extend is encountered or we hit
3917 * the end of the page. Since the time extend is always attached
3918 * to a data event, we should never loop more than three times.
3919 * Once for going to next page, once on time extend, and
3920 * finally once to get the event.
3921 * (We never hit the following condition more than thrice).
3922 */
3923 if (RB_WARN_ON(cpu_buffer, ++nr_loops > 3))
3924 return NULL;
3925
3926 if (rb_per_cpu_empty(cpu_buffer))
3927 return NULL;
3928
3929 if (iter->head >= rb_page_size(iter->head_page)) {
3930 rb_inc_iter(iter);
3931 goto again;
3932 }
3933
3934 event = rb_iter_head_event(iter);
3935
3936 switch (event->type_len) {
3937 case RINGBUF_TYPE_PADDING:
3938 if (rb_null_event(event)) {
3939 rb_inc_iter(iter);
3940 goto again;
3941 }
3942 rb_advance_iter(iter);
3943 return event;
3944
3945 case RINGBUF_TYPE_TIME_EXTEND:
3946 /* Internal data, OK to advance */
3947 rb_advance_iter(iter);
3948 goto again;
3949
3950 case RINGBUF_TYPE_TIME_STAMP:
3951 if (ts) {
3952 *ts = ring_buffer_event_time_stamp(event);
3953 ring_buffer_normalize_time_stamp(cpu_buffer->buffer,
3954 cpu_buffer->cpu, ts);
3955 }
3956 /* Internal data, OK to advance */
3957 rb_advance_iter(iter);
3958 goto again;
3959
3960 case RINGBUF_TYPE_DATA:
3961 if (ts && !(*ts)) {
3962 *ts = iter->read_stamp + event->time_delta;
3963 ring_buffer_normalize_time_stamp(buffer,
3964 cpu_buffer->cpu, ts);
3965 }
3966 return event;
3967
3968 default:
3969 BUG();
3970 }
3971
3972 return NULL;
3973}
3974EXPORT_SYMBOL_GPL(ring_buffer_iter_peek);
3975
3976static inline bool rb_reader_lock(struct ring_buffer_per_cpu *cpu_buffer)
3977{
3978 if (likely(!in_nmi())) {
3979 raw_spin_lock(&cpu_buffer->reader_lock);
3980 return true;
3981 }
3982
3983 /*
3984 * If an NMI die dumps out the content of the ring buffer
3985 * trylock must be used to prevent a deadlock if the NMI
3986 * preempted a task that holds the ring buffer locks. If
3987 * we get the lock then all is fine, if not, then continue
3988 * to do the read, but this can corrupt the ring buffer,
3989 * so it must be permanently disabled from future writes.
3990 * Reading from NMI is a oneshot deal.
3991 */
3992 if (raw_spin_trylock(&cpu_buffer->reader_lock))
3993 return true;
3994
3995 /* Continue without locking, but disable the ring buffer */
3996 atomic_inc(&cpu_buffer->record_disabled);
3997 return false;
3998}
3999
4000static inline void
4001rb_reader_unlock(struct ring_buffer_per_cpu *cpu_buffer, bool locked)
4002{
4003 if (likely(locked))
4004 raw_spin_unlock(&cpu_buffer->reader_lock);
4005 return;
4006}
4007
4008/**
4009 * ring_buffer_peek - peek at the next event to be read
4010 * @buffer: The ring buffer to read
4011 * @cpu: The cpu to peak at
4012 * @ts: The timestamp counter of this event.
4013 * @lost_events: a variable to store if events were lost (may be NULL)
4014 *
4015 * This will return the event that will be read next, but does
4016 * not consume the data.
4017 */
4018struct ring_buffer_event *
4019ring_buffer_peek(struct ring_buffer *buffer, int cpu, u64 *ts,
4020 unsigned long *lost_events)
4021{
4022 struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
4023 struct ring_buffer_event *event;
4024 unsigned long flags;
4025 bool dolock;
4026
4027 if (!cpumask_test_cpu(cpu, buffer->cpumask))
4028 return NULL;
4029
4030 again:
4031 local_irq_save(flags);
4032 dolock = rb_reader_lock(cpu_buffer);
4033 event = rb_buffer_peek(cpu_buffer, ts, lost_events);
4034 if (event && event->type_len == RINGBUF_TYPE_PADDING)
4035 rb_advance_reader(cpu_buffer);
4036 rb_reader_unlock(cpu_buffer, dolock);
4037 local_irq_restore(flags);
4038
4039 if (event && event->type_len == RINGBUF_TYPE_PADDING)
4040 goto again;
4041
4042 return event;
4043}
4044
4045/**
4046 * ring_buffer_iter_peek - peek at the next event to be read
4047 * @iter: The ring buffer iterator
4048 * @ts: The timestamp counter of this event.
4049 *
4050 * This will return the event that will be read next, but does
4051 * not increment the iterator.
4052 */
4053struct ring_buffer_event *
4054ring_buffer_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
4055{
4056 struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
4057 struct ring_buffer_event *event;
4058 unsigned long flags;
4059
4060 again:
4061 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
4062 event = rb_iter_peek(iter, ts);
4063 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
4064
4065 if (event && event->type_len == RINGBUF_TYPE_PADDING)
4066 goto again;
4067
4068 return event;
4069}
4070
4071/**
4072 * ring_buffer_consume - return an event and consume it
4073 * @buffer: The ring buffer to get the next event from
4074 * @cpu: the cpu to read the buffer from
4075 * @ts: a variable to store the timestamp (may be NULL)
4076 * @lost_events: a variable to store if events were lost (may be NULL)
4077 *
4078 * Returns the next event in the ring buffer, and that event is consumed.
4079 * Meaning, that sequential reads will keep returning a different event,
4080 * and eventually empty the ring buffer if the producer is slower.
4081 */
4082struct ring_buffer_event *
4083ring_buffer_consume(struct ring_buffer *buffer, int cpu, u64 *ts,
4084 unsigned long *lost_events)
4085{
4086 struct ring_buffer_per_cpu *cpu_buffer;
4087 struct ring_buffer_event *event = NULL;
4088 unsigned long flags;
4089 bool dolock;
4090
4091 again:
4092 /* might be called in atomic */
4093 preempt_disable();
4094
4095 if (!cpumask_test_cpu(cpu, buffer->cpumask))
4096 goto out;
4097
4098 cpu_buffer = buffer->buffers[cpu];
4099 local_irq_save(flags);
4100 dolock = rb_reader_lock(cpu_buffer);
4101
4102 event = rb_buffer_peek(cpu_buffer, ts, lost_events);
4103 if (event) {
4104 cpu_buffer->lost_events = 0;
4105 rb_advance_reader(cpu_buffer);
4106 }
4107
4108 rb_reader_unlock(cpu_buffer, dolock);
4109 local_irq_restore(flags);
4110
4111 out:
4112 preempt_enable();
4113
4114 if (event && event->type_len == RINGBUF_TYPE_PADDING)
4115 goto again;
4116
4117 return event;
4118}
4119EXPORT_SYMBOL_GPL(ring_buffer_consume);
4120
4121/**
4122 * ring_buffer_read_prepare - Prepare for a non consuming read of the buffer
4123 * @buffer: The ring buffer to read from
4124 * @cpu: The cpu buffer to iterate over
4125 *
4126 * This performs the initial preparations necessary to iterate
4127 * through the buffer. Memory is allocated, buffer recording
4128 * is disabled, and the iterator pointer is returned to the caller.
4129 *
4130 * Disabling buffer recordng prevents the reading from being
4131 * corrupted. This is not a consuming read, so a producer is not
4132 * expected.
4133 *
4134 * After a sequence of ring_buffer_read_prepare calls, the user is
4135 * expected to make at least one call to ring_buffer_read_prepare_sync.
4136 * Afterwards, ring_buffer_read_start is invoked to get things going
4137 * for real.
4138 *
4139 * This overall must be paired with ring_buffer_read_finish.
4140 */
4141struct ring_buffer_iter *
4142ring_buffer_read_prepare(struct ring_buffer *buffer, int cpu)
4143{
4144 struct ring_buffer_per_cpu *cpu_buffer;
4145 struct ring_buffer_iter *iter;
4146
4147 if (!cpumask_test_cpu(cpu, buffer->cpumask))
4148 return NULL;
4149
4150 iter = kmalloc(sizeof(*iter), GFP_KERNEL);
4151 if (!iter)
4152 return NULL;
4153
4154 cpu_buffer = buffer->buffers[cpu];
4155
4156 iter->cpu_buffer = cpu_buffer;
4157
4158 atomic_inc(&buffer->resize_disabled);
4159 atomic_inc(&cpu_buffer->record_disabled);
4160
4161 return iter;
4162}
4163EXPORT_SYMBOL_GPL(ring_buffer_read_prepare);
4164
4165/**
4166 * ring_buffer_read_prepare_sync - Synchronize a set of prepare calls
4167 *
4168 * All previously invoked ring_buffer_read_prepare calls to prepare
4169 * iterators will be synchronized. Afterwards, read_buffer_read_start
4170 * calls on those iterators are allowed.
4171 */
4172void
4173ring_buffer_read_prepare_sync(void)
4174{
4175 synchronize_sched();
4176}
4177EXPORT_SYMBOL_GPL(ring_buffer_read_prepare_sync);
4178
4179/**
4180 * ring_buffer_read_start - start a non consuming read of the buffer
4181 * @iter: The iterator returned by ring_buffer_read_prepare
4182 *
4183 * This finalizes the startup of an iteration through the buffer.
4184 * The iterator comes from a call to ring_buffer_read_prepare and
4185 * an intervening ring_buffer_read_prepare_sync must have been
4186 * performed.
4187 *
4188 * Must be paired with ring_buffer_read_finish.
4189 */
4190void
4191ring_buffer_read_start(struct ring_buffer_iter *iter)
4192{
4193 struct ring_buffer_per_cpu *cpu_buffer;
4194 unsigned long flags;
4195
4196 if (!iter)
4197 return;
4198
4199 cpu_buffer = iter->cpu_buffer;
4200
4201 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
4202 arch_spin_lock(&cpu_buffer->lock);
4203 rb_iter_reset(iter);
4204 arch_spin_unlock(&cpu_buffer->lock);
4205 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
4206}
4207EXPORT_SYMBOL_GPL(ring_buffer_read_start);
4208
4209/**
4210 * ring_buffer_read_finish - finish reading the iterator of the buffer
4211 * @iter: The iterator retrieved by ring_buffer_start
4212 *
4213 * This re-enables the recording to the buffer, and frees the
4214 * iterator.
4215 */
4216void
4217ring_buffer_read_finish(struct ring_buffer_iter *iter)
4218{
4219 struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
4220 unsigned long flags;
4221
4222 /*
4223 * Ring buffer is disabled from recording, here's a good place
4224 * to check the integrity of the ring buffer.
4225 * Must prevent readers from trying to read, as the check
4226 * clears the HEAD page and readers require it.
4227 */
4228 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
4229 rb_check_pages(cpu_buffer);
4230 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
4231
4232 atomic_dec(&cpu_buffer->record_disabled);
4233 atomic_dec(&cpu_buffer->buffer->resize_disabled);
4234 kfree(iter);
4235}
4236EXPORT_SYMBOL_GPL(ring_buffer_read_finish);
4237
4238/**
4239 * ring_buffer_read - read the next item in the ring buffer by the iterator
4240 * @iter: The ring buffer iterator
4241 * @ts: The time stamp of the event read.
4242 *
4243 * This reads the next event in the ring buffer and increments the iterator.
4244 */
4245struct ring_buffer_event *
4246ring_buffer_read(struct ring_buffer_iter *iter, u64 *ts)
4247{
4248 struct ring_buffer_event *event;
4249 struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
4250 unsigned long flags;
4251
4252 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
4253 again:
4254 event = rb_iter_peek(iter, ts);
4255 if (!event)
4256 goto out;
4257
4258 if (event->type_len == RINGBUF_TYPE_PADDING)
4259 goto again;
4260
4261 rb_advance_iter(iter);
4262 out:
4263 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
4264
4265 return event;
4266}
4267EXPORT_SYMBOL_GPL(ring_buffer_read);
4268
4269/**
4270 * ring_buffer_size - return the size of the ring buffer (in bytes)
4271 * @buffer: The ring buffer.
4272 */
4273unsigned long ring_buffer_size(struct ring_buffer *buffer, int cpu)
4274{
4275 /*
4276 * Earlier, this method returned
4277 * BUF_PAGE_SIZE * buffer->nr_pages
4278 * Since the nr_pages field is now removed, we have converted this to
4279 * return the per cpu buffer value.
4280 */
4281 if (!cpumask_test_cpu(cpu, buffer->cpumask))
4282 return 0;
4283
4284 return BUF_PAGE_SIZE * buffer->buffers[cpu]->nr_pages;
4285}
4286EXPORT_SYMBOL_GPL(ring_buffer_size);
4287
4288static void
4289rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
4290{
4291 rb_head_page_deactivate(cpu_buffer);
4292
4293 cpu_buffer->head_page
4294 = list_entry(cpu_buffer->pages, struct buffer_page, list);
4295 local_set(&cpu_buffer->head_page->write, 0);
4296 local_set(&cpu_buffer->head_page->entries, 0);
4297 local_set(&cpu_buffer->head_page->page->commit, 0);
4298
4299 cpu_buffer->head_page->read = 0;
4300
4301 cpu_buffer->tail_page = cpu_buffer->head_page;
4302 cpu_buffer->commit_page = cpu_buffer->head_page;
4303
4304 INIT_LIST_HEAD(&cpu_buffer->reader_page->list);
4305 INIT_LIST_HEAD(&cpu_buffer->new_pages);
4306 local_set(&cpu_buffer->reader_page->write, 0);
4307 local_set(&cpu_buffer->reader_page->entries, 0);
4308 local_set(&cpu_buffer->reader_page->page->commit, 0);
4309 cpu_buffer->reader_page->read = 0;
4310
4311 local_set(&cpu_buffer->entries_bytes, 0);
4312 local_set(&cpu_buffer->overrun, 0);
4313 local_set(&cpu_buffer->commit_overrun, 0);
4314 local_set(&cpu_buffer->dropped_events, 0);
4315 local_set(&cpu_buffer->entries, 0);
4316 local_set(&cpu_buffer->committing, 0);
4317 local_set(&cpu_buffer->commits, 0);
4318 cpu_buffer->read = 0;
4319 cpu_buffer->read_bytes = 0;
4320
4321 cpu_buffer->write_stamp = 0;
4322 cpu_buffer->read_stamp = 0;
4323
4324 cpu_buffer->lost_events = 0;
4325 cpu_buffer->last_overrun = 0;
4326
4327 rb_head_page_activate(cpu_buffer);
4328}
4329
4330/**
4331 * ring_buffer_reset_cpu - reset a ring buffer per CPU buffer
4332 * @buffer: The ring buffer to reset a per cpu buffer of
4333 * @cpu: The CPU buffer to be reset
4334 */
4335void ring_buffer_reset_cpu(struct ring_buffer *buffer, int cpu)
4336{
4337 struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
4338 unsigned long flags;
4339
4340 if (!cpumask_test_cpu(cpu, buffer->cpumask))
4341 return;
4342
4343 atomic_inc(&buffer->resize_disabled);
4344 atomic_inc(&cpu_buffer->record_disabled);
4345
4346 /* Make sure all commits have finished */
4347 synchronize_sched();
4348
4349 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
4350
4351 if (RB_WARN_ON(cpu_buffer, local_read(&cpu_buffer->committing)))
4352 goto out;
4353
4354 arch_spin_lock(&cpu_buffer->lock);
4355
4356 rb_reset_cpu(cpu_buffer);
4357
4358 arch_spin_unlock(&cpu_buffer->lock);
4359
4360 out:
4361 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
4362
4363 atomic_dec(&cpu_buffer->record_disabled);
4364 atomic_dec(&buffer->resize_disabled);
4365}
4366EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu);
4367
4368/**
4369 * ring_buffer_reset - reset a ring buffer
4370 * @buffer: The ring buffer to reset all cpu buffers
4371 */
4372void ring_buffer_reset(struct ring_buffer *buffer)
4373{
4374 int cpu;
4375
4376 for_each_buffer_cpu(buffer, cpu)
4377 ring_buffer_reset_cpu(buffer, cpu);
4378}
4379EXPORT_SYMBOL_GPL(ring_buffer_reset);
4380
4381/**
4382 * rind_buffer_empty - is the ring buffer empty?
4383 * @buffer: The ring buffer to test
4384 */
4385bool ring_buffer_empty(struct ring_buffer *buffer)
4386{
4387 struct ring_buffer_per_cpu *cpu_buffer;
4388 unsigned long flags;
4389 bool dolock;
4390 int cpu;
4391 int ret;
4392
4393 /* yes this is racy, but if you don't like the race, lock the buffer */
4394 for_each_buffer_cpu(buffer, cpu) {
4395 cpu_buffer = buffer->buffers[cpu];
4396 local_irq_save(flags);
4397 dolock = rb_reader_lock(cpu_buffer);
4398 ret = rb_per_cpu_empty(cpu_buffer);
4399 rb_reader_unlock(cpu_buffer, dolock);
4400 local_irq_restore(flags);
4401
4402 if (!ret)
4403 return false;
4404 }
4405
4406 return true;
4407}
4408EXPORT_SYMBOL_GPL(ring_buffer_empty);
4409
4410/**
4411 * ring_buffer_empty_cpu - is a cpu buffer of a ring buffer empty?
4412 * @buffer: The ring buffer
4413 * @cpu: The CPU buffer to test
4414 */
4415bool ring_buffer_empty_cpu(struct ring_buffer *buffer, int cpu)
4416{
4417 struct ring_buffer_per_cpu *cpu_buffer;
4418 unsigned long flags;
4419 bool dolock;
4420 int ret;
4421
4422 if (!cpumask_test_cpu(cpu, buffer->cpumask))
4423 return true;
4424
4425 cpu_buffer = buffer->buffers[cpu];
4426 local_irq_save(flags);
4427 dolock = rb_reader_lock(cpu_buffer);
4428 ret = rb_per_cpu_empty(cpu_buffer);
4429 rb_reader_unlock(cpu_buffer, dolock);
4430 local_irq_restore(flags);
4431
4432 return ret;
4433}
4434EXPORT_SYMBOL_GPL(ring_buffer_empty_cpu);
4435
4436#ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
4437/**
4438 * ring_buffer_swap_cpu - swap a CPU buffer between two ring buffers
4439 * @buffer_a: One buffer to swap with
4440 * @buffer_b: The other buffer to swap with
4441 *
4442 * This function is useful for tracers that want to take a "snapshot"
4443 * of a CPU buffer and has another back up buffer lying around.
4444 * it is expected that the tracer handles the cpu buffer not being
4445 * used at the moment.
4446 */
4447int ring_buffer_swap_cpu(struct ring_buffer *buffer_a,
4448 struct ring_buffer *buffer_b, int cpu)
4449{
4450 struct ring_buffer_per_cpu *cpu_buffer_a;
4451 struct ring_buffer_per_cpu *cpu_buffer_b;
4452 int ret = -EINVAL;
4453
4454 if (!cpumask_test_cpu(cpu, buffer_a->cpumask) ||
4455 !cpumask_test_cpu(cpu, buffer_b->cpumask))
4456 goto out;
4457
4458 cpu_buffer_a = buffer_a->buffers[cpu];
4459 cpu_buffer_b = buffer_b->buffers[cpu];
4460
4461 /* At least make sure the two buffers are somewhat the same */
4462 if (cpu_buffer_a->nr_pages != cpu_buffer_b->nr_pages)
4463 goto out;
4464
4465 ret = -EAGAIN;
4466
4467 if (atomic_read(&buffer_a->record_disabled))
4468 goto out;
4469
4470 if (atomic_read(&buffer_b->record_disabled))
4471 goto out;
4472
4473 if (atomic_read(&cpu_buffer_a->record_disabled))
4474 goto out;
4475
4476 if (atomic_read(&cpu_buffer_b->record_disabled))
4477 goto out;
4478
4479 /*
4480 * We can't do a synchronize_sched here because this
4481 * function can be called in atomic context.
4482 * Normally this will be called from the same CPU as cpu.
4483 * If not it's up to the caller to protect this.
4484 */
4485 atomic_inc(&cpu_buffer_a->record_disabled);
4486 atomic_inc(&cpu_buffer_b->record_disabled);
4487
4488 ret = -EBUSY;
4489 if (local_read(&cpu_buffer_a->committing))
4490 goto out_dec;
4491 if (local_read(&cpu_buffer_b->committing))
4492 goto out_dec;
4493
4494 buffer_a->buffers[cpu] = cpu_buffer_b;
4495 buffer_b->buffers[cpu] = cpu_buffer_a;
4496
4497 cpu_buffer_b->buffer = buffer_a;
4498 cpu_buffer_a->buffer = buffer_b;
4499
4500 ret = 0;
4501
4502out_dec:
4503 atomic_dec(&cpu_buffer_a->record_disabled);
4504 atomic_dec(&cpu_buffer_b->record_disabled);
4505out:
4506 return ret;
4507}
4508EXPORT_SYMBOL_GPL(ring_buffer_swap_cpu);
4509#endif /* CONFIG_RING_BUFFER_ALLOW_SWAP */
4510
4511/**
4512 * ring_buffer_alloc_read_page - allocate a page to read from buffer
4513 * @buffer: the buffer to allocate for.
4514 * @cpu: the cpu buffer to allocate.
4515 *
4516 * This function is used in conjunction with ring_buffer_read_page.
4517 * When reading a full page from the ring buffer, these functions
4518 * can be used to speed up the process. The calling function should
4519 * allocate a few pages first with this function. Then when it
4520 * needs to get pages from the ring buffer, it passes the result
4521 * of this function into ring_buffer_read_page, which will swap
4522 * the page that was allocated, with the read page of the buffer.
4523 *
4524 * Returns:
4525 * The page allocated, or ERR_PTR
4526 */
4527void *ring_buffer_alloc_read_page(struct ring_buffer *buffer, int cpu)
4528{
4529 struct ring_buffer_per_cpu *cpu_buffer;
4530 struct buffer_data_page *bpage = NULL;
4531 unsigned long flags;
4532 struct page *page;
4533
4534 if (!cpumask_test_cpu(cpu, buffer->cpumask))
4535 return ERR_PTR(-ENODEV);
4536
4537 cpu_buffer = buffer->buffers[cpu];
4538 local_irq_save(flags);
4539 arch_spin_lock(&cpu_buffer->lock);
4540
4541 if (cpu_buffer->free_page) {
4542 bpage = cpu_buffer->free_page;
4543 cpu_buffer->free_page = NULL;
4544 }
4545
4546 arch_spin_unlock(&cpu_buffer->lock);
4547 local_irq_restore(flags);
4548
4549 if (bpage)
4550 goto out;
4551
4552 page = alloc_pages_node(cpu_to_node(cpu),
4553 GFP_KERNEL | __GFP_NORETRY, 0);
4554 if (!page)
4555 return ERR_PTR(-ENOMEM);
4556
4557 bpage = page_address(page);
4558
4559 out:
4560 rb_init_page(bpage);
4561
4562 return bpage;
4563}
4564EXPORT_SYMBOL_GPL(ring_buffer_alloc_read_page);
4565
4566/**
4567 * ring_buffer_free_read_page - free an allocated read page
4568 * @buffer: the buffer the page was allocate for
4569 * @cpu: the cpu buffer the page came from
4570 * @data: the page to free
4571 *
4572 * Free a page allocated from ring_buffer_alloc_read_page.
4573 */
4574void ring_buffer_free_read_page(struct ring_buffer *buffer, int cpu, void *data)
4575{
4576 struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
4577 struct buffer_data_page *bpage = data;
4578 struct page *page = virt_to_page(bpage);
4579 unsigned long flags;
4580
4581 /* If the page is still in use someplace else, we can't reuse it */
4582 if (page_ref_count(page) > 1)
4583 goto out;
4584
4585 local_irq_save(flags);
4586 arch_spin_lock(&cpu_buffer->lock);
4587
4588 if (!cpu_buffer->free_page) {
4589 cpu_buffer->free_page = bpage;
4590 bpage = NULL;
4591 }
4592
4593 arch_spin_unlock(&cpu_buffer->lock);
4594 local_irq_restore(flags);
4595
4596 out:
4597 free_page((unsigned long)bpage);
4598}
4599EXPORT_SYMBOL_GPL(ring_buffer_free_read_page);
4600
4601/**
4602 * ring_buffer_read_page - extract a page from the ring buffer
4603 * @buffer: buffer to extract from
4604 * @data_page: the page to use allocated from ring_buffer_alloc_read_page
4605 * @len: amount to extract
4606 * @cpu: the cpu of the buffer to extract
4607 * @full: should the extraction only happen when the page is full.
4608 *
4609 * This function will pull out a page from the ring buffer and consume it.
4610 * @data_page must be the address of the variable that was returned
4611 * from ring_buffer_alloc_read_page. This is because the page might be used
4612 * to swap with a page in the ring buffer.
4613 *
4614 * for example:
4615 * rpage = ring_buffer_alloc_read_page(buffer, cpu);
4616 * if (IS_ERR(rpage))
4617 * return PTR_ERR(rpage);
4618 * ret = ring_buffer_read_page(buffer, &rpage, len, cpu, 0);
4619 * if (ret >= 0)
4620 * process_page(rpage, ret);
4621 *
4622 * When @full is set, the function will not return true unless
4623 * the writer is off the reader page.
4624 *
4625 * Note: it is up to the calling functions to handle sleeps and wakeups.
4626 * The ring buffer can be used anywhere in the kernel and can not
4627 * blindly call wake_up. The layer that uses the ring buffer must be
4628 * responsible for that.
4629 *
4630 * Returns:
4631 * >=0 if data has been transferred, returns the offset of consumed data.
4632 * <0 if no data has been transferred.
4633 */
4634int ring_buffer_read_page(struct ring_buffer *buffer,
4635 void **data_page, size_t len, int cpu, int full)
4636{
4637 struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
4638 struct ring_buffer_event *event;
4639 struct buffer_data_page *bpage;
4640 struct buffer_page *reader;
4641 unsigned long missed_events;
4642 unsigned long flags;
4643 unsigned int commit;
4644 unsigned int read;
4645 u64 save_timestamp;
4646 int ret = -1;
4647
4648 if (!cpumask_test_cpu(cpu, buffer->cpumask))
4649 goto out;
4650
4651 /*
4652 * If len is not big enough to hold the page header, then
4653 * we can not copy anything.
4654 */
4655 if (len <= BUF_PAGE_HDR_SIZE)
4656 goto out;
4657
4658 len -= BUF_PAGE_HDR_SIZE;
4659
4660 if (!data_page)
4661 goto out;
4662
4663 bpage = *data_page;
4664 if (!bpage)
4665 goto out;
4666
4667 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
4668
4669 reader = rb_get_reader_page(cpu_buffer);
4670 if (!reader)
4671 goto out_unlock;
4672
4673 event = rb_reader_event(cpu_buffer);
4674
4675 read = reader->read;
4676 commit = rb_page_commit(reader);
4677
4678 /* Check if any events were dropped */
4679 missed_events = cpu_buffer->lost_events;
4680
4681 /*
4682 * If this page has been partially read or
4683 * if len is not big enough to read the rest of the page or
4684 * a writer is still on the page, then
4685 * we must copy the data from the page to the buffer.
4686 * Otherwise, we can simply swap the page with the one passed in.
4687 */
4688 if (read || (len < (commit - read)) ||
4689 cpu_buffer->reader_page == cpu_buffer->commit_page) {
4690 struct buffer_data_page *rpage = cpu_buffer->reader_page->page;
4691 unsigned int rpos = read;
4692 unsigned int pos = 0;
4693 unsigned int size;
4694
4695 if (full)
4696 goto out_unlock;
4697
4698 if (len > (commit - read))
4699 len = (commit - read);
4700
4701 /* Always keep the time extend and data together */
4702 size = rb_event_ts_length(event);
4703
4704 if (len < size)
4705 goto out_unlock;
4706
4707 /* save the current timestamp, since the user will need it */
4708 save_timestamp = cpu_buffer->read_stamp;
4709
4710 /* Need to copy one event at a time */
4711 do {
4712 /* We need the size of one event, because
4713 * rb_advance_reader only advances by one event,
4714 * whereas rb_event_ts_length may include the size of
4715 * one or two events.
4716 * We have already ensured there's enough space if this
4717 * is a time extend. */
4718 size = rb_event_length(event);
4719 memcpy(bpage->data + pos, rpage->data + rpos, size);
4720
4721 len -= size;
4722
4723 rb_advance_reader(cpu_buffer);
4724 rpos = reader->read;
4725 pos += size;
4726
4727 if (rpos >= commit)
4728 break;
4729
4730 event = rb_reader_event(cpu_buffer);
4731 /* Always keep the time extend and data together */
4732 size = rb_event_ts_length(event);
4733 } while (len >= size);
4734
4735 /* update bpage */
4736 local_set(&bpage->commit, pos);
4737 bpage->time_stamp = save_timestamp;
4738
4739 /* we copied everything to the beginning */
4740 read = 0;
4741 } else {
4742 /* update the entry counter */
4743 cpu_buffer->read += rb_page_entries(reader);
4744 cpu_buffer->read_bytes += BUF_PAGE_SIZE;
4745
4746 /* swap the pages */
4747 rb_init_page(bpage);
4748 bpage = reader->page;
4749 reader->page = *data_page;
4750 local_set(&reader->write, 0);
4751 local_set(&reader->entries, 0);
4752 reader->read = 0;
4753 *data_page = bpage;
4754
4755 /*
4756 * Use the real_end for the data size,
4757 * This gives us a chance to store the lost events
4758 * on the page.
4759 */
4760 if (reader->real_end)
4761 local_set(&bpage->commit, reader->real_end);
4762 }
4763 ret = read;
4764
4765 cpu_buffer->lost_events = 0;
4766
4767 commit = local_read(&bpage->commit);
4768 /*
4769 * Set a flag in the commit field if we lost events
4770 */
4771 if (missed_events) {
4772 /* If there is room at the end of the page to save the
4773 * missed events, then record it there.
4774 */
4775 if (BUF_PAGE_SIZE - commit >= sizeof(missed_events)) {
4776 memcpy(&bpage->data[commit], &missed_events,
4777 sizeof(missed_events));
4778 local_add(RB_MISSED_STORED, &bpage->commit);
4779 commit += sizeof(missed_events);
4780 }
4781 local_add(RB_MISSED_EVENTS, &bpage->commit);
4782 }
4783
4784 /*
4785 * This page may be off to user land. Zero it out here.
4786 */
4787 if (commit < BUF_PAGE_SIZE)
4788 memset(&bpage->data[commit], 0, BUF_PAGE_SIZE - commit);
4789
4790 out_unlock:
4791 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
4792
4793 out:
4794 return ret;
4795}
4796EXPORT_SYMBOL_GPL(ring_buffer_read_page);
4797
4798/*
4799 * We only allocate new buffers, never free them if the CPU goes down.
4800 * If we were to free the buffer, then the user would lose any trace that was in
4801 * the buffer.
4802 */
4803int trace_rb_cpu_prepare(unsigned int cpu, struct hlist_node *node)
4804{
4805 struct ring_buffer *buffer;
4806 long nr_pages_same;
4807 int cpu_i;
4808 unsigned long nr_pages;
4809
4810 buffer = container_of(node, struct ring_buffer, node);
4811 if (cpumask_test_cpu(cpu, buffer->cpumask))
4812 return 0;
4813
4814 nr_pages = 0;
4815 nr_pages_same = 1;
4816 /* check if all cpu sizes are same */
4817 for_each_buffer_cpu(buffer, cpu_i) {
4818 /* fill in the size from first enabled cpu */
4819 if (nr_pages == 0)
4820 nr_pages = buffer->buffers[cpu_i]->nr_pages;
4821 if (nr_pages != buffer->buffers[cpu_i]->nr_pages) {
4822 nr_pages_same = 0;
4823 break;
4824 }
4825 }
4826 /* allocate minimum pages, user can later expand it */
4827 if (!nr_pages_same)
4828 nr_pages = 2;
4829 buffer->buffers[cpu] =
4830 rb_allocate_cpu_buffer(buffer, nr_pages, cpu);
4831 if (!buffer->buffers[cpu]) {
4832 WARN(1, "failed to allocate ring buffer on CPU %u\n",
4833 cpu);
4834 return -ENOMEM;
4835 }
4836 smp_wmb();
4837 cpumask_set_cpu(cpu, buffer->cpumask);
4838 return 0;
4839}
4840
4841#ifdef CONFIG_RING_BUFFER_STARTUP_TEST
4842/*
4843 * This is a basic integrity check of the ring buffer.
4844 * Late in the boot cycle this test will run when configured in.
4845 * It will kick off a thread per CPU that will go into a loop
4846 * writing to the per cpu ring buffer various sizes of data.
4847 * Some of the data will be large items, some small.
4848 *
4849 * Another thread is created that goes into a spin, sending out
4850 * IPIs to the other CPUs to also write into the ring buffer.
4851 * this is to test the nesting ability of the buffer.
4852 *
4853 * Basic stats are recorded and reported. If something in the
4854 * ring buffer should happen that's not expected, a big warning
4855 * is displayed and all ring buffers are disabled.
4856 */
4857static struct task_struct *rb_threads[NR_CPUS] __initdata;
4858
4859struct rb_test_data {
4860 struct ring_buffer *buffer;
4861 unsigned long events;
4862 unsigned long bytes_written;
4863 unsigned long bytes_alloc;
4864 unsigned long bytes_dropped;
4865 unsigned long events_nested;
4866 unsigned long bytes_written_nested;
4867 unsigned long bytes_alloc_nested;
4868 unsigned long bytes_dropped_nested;
4869 int min_size_nested;
4870 int max_size_nested;
4871 int max_size;
4872 int min_size;
4873 int cpu;
4874 int cnt;
4875};
4876
4877static struct rb_test_data rb_data[NR_CPUS] __initdata;
4878
4879/* 1 meg per cpu */
4880#define RB_TEST_BUFFER_SIZE 1048576
4881
4882static char rb_string[] __initdata =
4883 "abcdefghijklmnopqrstuvwxyz1234567890!@#$%^&*()?+\\"
4884 "?+|:';\",.<>/?abcdefghijklmnopqrstuvwxyz1234567890"
4885 "!@#$%^&*()?+\\?+|:';\",.<>/?abcdefghijklmnopqrstuv";
4886
4887static bool rb_test_started __initdata;
4888
4889struct rb_item {
4890 int size;
4891 char str[];
4892};
4893
4894static __init int rb_write_something(struct rb_test_data *data, bool nested)
4895{
4896 struct ring_buffer_event *event;
4897 struct rb_item *item;
4898 bool started;
4899 int event_len;
4900 int size;
4901 int len;
4902 int cnt;
4903
4904 /* Have nested writes different that what is written */
4905 cnt = data->cnt + (nested ? 27 : 0);
4906
4907 /* Multiply cnt by ~e, to make some unique increment */
4908 size = (data->cnt * 68 / 25) % (sizeof(rb_string) - 1);
4909
4910 len = size + sizeof(struct rb_item);
4911
4912 started = rb_test_started;
4913 /* read rb_test_started before checking buffer enabled */
4914 smp_rmb();
4915
4916 event = ring_buffer_lock_reserve(data->buffer, len);
4917 if (!event) {
4918 /* Ignore dropped events before test starts. */
4919 if (started) {
4920 if (nested)
4921 data->bytes_dropped += len;
4922 else
4923 data->bytes_dropped_nested += len;
4924 }
4925 return len;
4926 }
4927
4928 event_len = ring_buffer_event_length(event);
4929
4930 if (RB_WARN_ON(data->buffer, event_len < len))
4931 goto out;
4932
4933 item = ring_buffer_event_data(event);
4934 item->size = size;
4935 memcpy(item->str, rb_string, size);
4936
4937 if (nested) {
4938 data->bytes_alloc_nested += event_len;
4939 data->bytes_written_nested += len;
4940 data->events_nested++;
4941 if (!data->min_size_nested || len < data->min_size_nested)
4942 data->min_size_nested = len;
4943 if (len > data->max_size_nested)
4944 data->max_size_nested = len;
4945 } else {
4946 data->bytes_alloc += event_len;
4947 data->bytes_written += len;
4948 data->events++;
4949 if (!data->min_size || len < data->min_size)
4950 data->max_size = len;
4951 if (len > data->max_size)
4952 data->max_size = len;
4953 }
4954
4955 out:
4956 ring_buffer_unlock_commit(data->buffer, event);
4957
4958 return 0;
4959}
4960
4961static __init int rb_test(void *arg)
4962{
4963 struct rb_test_data *data = arg;
4964
4965 while (!kthread_should_stop()) {
4966 rb_write_something(data, false);
4967 data->cnt++;
4968
4969 set_current_state(TASK_INTERRUPTIBLE);
4970 /* Now sleep between a min of 100-300us and a max of 1ms */
4971 usleep_range(((data->cnt % 3) + 1) * 100, 1000);
4972 }
4973
4974 return 0;
4975}
4976
4977static __init void rb_ipi(void *ignore)
4978{
4979 struct rb_test_data *data;
4980 int cpu = smp_processor_id();
4981
4982 data = &rb_data[cpu];
4983 rb_write_something(data, true);
4984}
4985
4986static __init int rb_hammer_test(void *arg)
4987{
4988 while (!kthread_should_stop()) {
4989
4990 /* Send an IPI to all cpus to write data! */
4991 smp_call_function(rb_ipi, NULL, 1);
4992 /* No sleep, but for non preempt, let others run */
4993 schedule();
4994 }
4995
4996 return 0;
4997}
4998
4999static __init int test_ringbuffer(void)
5000{
5001 struct task_struct *rb_hammer;
5002 struct ring_buffer *buffer;
5003 int cpu;
5004 int ret = 0;
5005
5006 pr_info("Running ring buffer tests...\n");
5007
5008 buffer = ring_buffer_alloc(RB_TEST_BUFFER_SIZE, RB_FL_OVERWRITE);
5009 if (WARN_ON(!buffer))
5010 return 0;
5011
5012 /* Disable buffer so that threads can't write to it yet */
5013 ring_buffer_record_off(buffer);
5014
5015 for_each_online_cpu(cpu) {
5016 rb_data[cpu].buffer = buffer;
5017 rb_data[cpu].cpu = cpu;
5018 rb_data[cpu].cnt = cpu;
5019 rb_threads[cpu] = kthread_create(rb_test, &rb_data[cpu],
5020 "rbtester/%d", cpu);
5021 if (WARN_ON(IS_ERR(rb_threads[cpu]))) {
5022 pr_cont("FAILED\n");
5023 ret = PTR_ERR(rb_threads[cpu]);
5024 goto out_free;
5025 }
5026
5027 kthread_bind(rb_threads[cpu], cpu);
5028 wake_up_process(rb_threads[cpu]);
5029 }
5030
5031 /* Now create the rb hammer! */
5032 rb_hammer = kthread_run(rb_hammer_test, NULL, "rbhammer");
5033 if (WARN_ON(IS_ERR(rb_hammer))) {
5034 pr_cont("FAILED\n");
5035 ret = PTR_ERR(rb_hammer);
5036 goto out_free;
5037 }
5038
5039 ring_buffer_record_on(buffer);
5040 /*
5041 * Show buffer is enabled before setting rb_test_started.
5042 * Yes there's a small race window where events could be
5043 * dropped and the thread wont catch it. But when a ring
5044 * buffer gets enabled, there will always be some kind of
5045 * delay before other CPUs see it. Thus, we don't care about
5046 * those dropped events. We care about events dropped after
5047 * the threads see that the buffer is active.
5048 */
5049 smp_wmb();
5050 rb_test_started = true;
5051
5052 set_current_state(TASK_INTERRUPTIBLE);
5053 /* Just run for 10 seconds */;
5054 schedule_timeout(10 * HZ);
5055
5056 kthread_stop(rb_hammer);
5057
5058 out_free:
5059 for_each_online_cpu(cpu) {
5060 if (!rb_threads[cpu])
5061 break;
5062 kthread_stop(rb_threads[cpu]);
5063 }
5064 if (ret) {
5065 ring_buffer_free(buffer);
5066 return ret;
5067 }
5068
5069 /* Report! */
5070 pr_info("finished\n");
5071 for_each_online_cpu(cpu) {
5072 struct ring_buffer_event *event;
5073 struct rb_test_data *data = &rb_data[cpu];
5074 struct rb_item *item;
5075 unsigned long total_events;
5076 unsigned long total_dropped;
5077 unsigned long total_written;
5078 unsigned long total_alloc;
5079 unsigned long total_read = 0;
5080 unsigned long total_size = 0;
5081 unsigned long total_len = 0;
5082 unsigned long total_lost = 0;
5083 unsigned long lost;
5084 int big_event_size;
5085 int small_event_size;
5086
5087 ret = -1;
5088
5089 total_events = data->events + data->events_nested;
5090 total_written = data->bytes_written + data->bytes_written_nested;
5091 total_alloc = data->bytes_alloc + data->bytes_alloc_nested;
5092 total_dropped = data->bytes_dropped + data->bytes_dropped_nested;
5093
5094 big_event_size = data->max_size + data->max_size_nested;
5095 small_event_size = data->min_size + data->min_size_nested;
5096
5097 pr_info("CPU %d:\n", cpu);
5098 pr_info(" events: %ld\n", total_events);
5099 pr_info(" dropped bytes: %ld\n", total_dropped);
5100 pr_info(" alloced bytes: %ld\n", total_alloc);
5101 pr_info(" written bytes: %ld\n", total_written);
5102 pr_info(" biggest event: %d\n", big_event_size);
5103 pr_info(" smallest event: %d\n", small_event_size);
5104
5105 if (RB_WARN_ON(buffer, total_dropped))
5106 break;
5107
5108 ret = 0;
5109
5110 while ((event = ring_buffer_consume(buffer, cpu, NULL, &lost))) {
5111 total_lost += lost;
5112 item = ring_buffer_event_data(event);
5113 total_len += ring_buffer_event_length(event);
5114 total_size += item->size + sizeof(struct rb_item);
5115 if (memcmp(&item->str[0], rb_string, item->size) != 0) {
5116 pr_info("FAILED!\n");
5117 pr_info("buffer had: %.*s\n", item->size, item->str);
5118 pr_info("expected: %.*s\n", item->size, rb_string);
5119 RB_WARN_ON(buffer, 1);
5120 ret = -1;
5121 break;
5122 }
5123 total_read++;
5124 }
5125 if (ret)
5126 break;
5127
5128 ret = -1;
5129
5130 pr_info(" read events: %ld\n", total_read);
5131 pr_info(" lost events: %ld\n", total_lost);
5132 pr_info(" total events: %ld\n", total_lost + total_read);
5133 pr_info(" recorded len bytes: %ld\n", total_len);
5134 pr_info(" recorded size bytes: %ld\n", total_size);
5135 if (total_lost)
5136 pr_info(" With dropped events, record len and size may not match\n"
5137 " alloced and written from above\n");
5138 if (!total_lost) {
5139 if (RB_WARN_ON(buffer, total_len != total_alloc ||
5140 total_size != total_written))
5141 break;
5142 }
5143 if (RB_WARN_ON(buffer, total_lost + total_read != total_events))
5144 break;
5145
5146 ret = 0;
5147 }
5148 if (!ret)
5149 pr_info("Ring buffer PASSED!\n");
5150
5151 ring_buffer_free(buffer);
5152 return 0;
5153}
5154
5155late_initcall(test_ringbuffer);
5156#endif /* CONFIG_RING_BUFFER_STARTUP_TEST */