Loading...
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/trace_seq.h>
10#include <linux/spinlock.h>
11#include <linux/irq_work.h>
12#include <linux/uaccess.h>
13#include <linux/hardirq.h>
14#include <linux/kthread.h> /* for self test */
15#include <linux/kmemcheck.h>
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
26#include <asm/local.h>
27
28static void update_pages_handler(struct work_struct *work);
29
30/*
31 * The ring buffer header is special. We must manually up keep it.
32 */
33int ring_buffer_print_entry_header(struct trace_seq *s)
34{
35 trace_seq_puts(s, "# compressed entry header\n");
36 trace_seq_puts(s, "\ttype_len : 5 bits\n");
37 trace_seq_puts(s, "\ttime_delta : 27 bits\n");
38 trace_seq_puts(s, "\tarray : 32 bits\n");
39 trace_seq_putc(s, '\n');
40 trace_seq_printf(s, "\tpadding : type == %d\n",
41 RINGBUF_TYPE_PADDING);
42 trace_seq_printf(s, "\ttime_extend : type == %d\n",
43 RINGBUF_TYPE_TIME_EXTEND);
44 trace_seq_printf(s, "\tdata max type_len == %d\n",
45 RINGBUF_TYPE_DATA_TYPE_LEN_MAX);
46
47 return !trace_seq_has_overflowed(s);
48}
49
50/*
51 * The ring buffer is made up of a list of pages. A separate list of pages is
52 * allocated for each CPU. A writer may only write to a buffer that is
53 * associated with the CPU it is currently executing on. A reader may read
54 * from any per cpu buffer.
55 *
56 * The reader is special. For each per cpu buffer, the reader has its own
57 * reader page. When a reader has read the entire reader page, this reader
58 * page is swapped with another page in the ring buffer.
59 *
60 * Now, as long as the writer is off the reader page, the reader can do what
61 * ever it wants with that page. The writer will never write to that page
62 * again (as long as it is out of the ring buffer).
63 *
64 * Here's some silly ASCII art.
65 *
66 * +------+
67 * |reader| RING BUFFER
68 * |page |
69 * +------+ +---+ +---+ +---+
70 * | |-->| |-->| |
71 * +---+ +---+ +---+
72 * ^ |
73 * | |
74 * +---------------+
75 *
76 *
77 * +------+
78 * |reader| RING BUFFER
79 * |page |------------------v
80 * +------+ +---+ +---+ +---+
81 * | |-->| |-->| |
82 * +---+ +---+ +---+
83 * ^ |
84 * | |
85 * +---------------+
86 *
87 *
88 * +------+
89 * |reader| RING BUFFER
90 * |page |------------------v
91 * +------+ +---+ +---+ +---+
92 * ^ | |-->| |-->| |
93 * | +---+ +---+ +---+
94 * | |
95 * | |
96 * +------------------------------+
97 *
98 *
99 * +------+
100 * |buffer| RING BUFFER
101 * |page |------------------v
102 * +------+ +---+ +---+ +---+
103 * ^ | | | |-->| |
104 * | New +---+ +---+ +---+
105 * | Reader------^ |
106 * | page |
107 * +------------------------------+
108 *
109 *
110 * After we make this swap, the reader can hand this page off to the splice
111 * code and be done with it. It can even allocate a new page if it needs to
112 * and swap that into the ring buffer.
113 *
114 * We will be using cmpxchg soon to make all this lockless.
115 *
116 */
117
118/* Used for individual buffers (after the counter) */
119#define RB_BUFFER_OFF (1 << 20)
120
121#define BUF_PAGE_HDR_SIZE offsetof(struct buffer_data_page, data)
122
123#define RB_EVNT_HDR_SIZE (offsetof(struct ring_buffer_event, array))
124#define RB_ALIGNMENT 4U
125#define RB_MAX_SMALL_DATA (RB_ALIGNMENT * RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
126#define RB_EVNT_MIN_SIZE 8U /* two 32bit words */
127
128#ifndef CONFIG_HAVE_64BIT_ALIGNED_ACCESS
129# define RB_FORCE_8BYTE_ALIGNMENT 0
130# define RB_ARCH_ALIGNMENT RB_ALIGNMENT
131#else
132# define RB_FORCE_8BYTE_ALIGNMENT 1
133# define RB_ARCH_ALIGNMENT 8U
134#endif
135
136#define RB_ALIGN_DATA __aligned(RB_ARCH_ALIGNMENT)
137
138/* define RINGBUF_TYPE_DATA for 'case RINGBUF_TYPE_DATA:' */
139#define RINGBUF_TYPE_DATA 0 ... RINGBUF_TYPE_DATA_TYPE_LEN_MAX
140
141enum {
142 RB_LEN_TIME_EXTEND = 8,
143 RB_LEN_TIME_STAMP = 16,
144};
145
146#define skip_time_extend(event) \
147 ((struct ring_buffer_event *)((char *)event + RB_LEN_TIME_EXTEND))
148
149static inline int rb_null_event(struct ring_buffer_event *event)
150{
151 return event->type_len == RINGBUF_TYPE_PADDING && !event->time_delta;
152}
153
154static void rb_event_set_padding(struct ring_buffer_event *event)
155{
156 /* padding has a NULL time_delta */
157 event->type_len = RINGBUF_TYPE_PADDING;
158 event->time_delta = 0;
159}
160
161static unsigned
162rb_event_data_length(struct ring_buffer_event *event)
163{
164 unsigned length;
165
166 if (event->type_len)
167 length = event->type_len * RB_ALIGNMENT;
168 else
169 length = event->array[0];
170 return length + RB_EVNT_HDR_SIZE;
171}
172
173/*
174 * Return the length of the given event. Will return
175 * the length of the time extend if the event is a
176 * time extend.
177 */
178static inline unsigned
179rb_event_length(struct ring_buffer_event *event)
180{
181 switch (event->type_len) {
182 case RINGBUF_TYPE_PADDING:
183 if (rb_null_event(event))
184 /* undefined */
185 return -1;
186 return event->array[0] + RB_EVNT_HDR_SIZE;
187
188 case RINGBUF_TYPE_TIME_EXTEND:
189 return RB_LEN_TIME_EXTEND;
190
191 case RINGBUF_TYPE_TIME_STAMP:
192 return RB_LEN_TIME_STAMP;
193
194 case RINGBUF_TYPE_DATA:
195 return rb_event_data_length(event);
196 default:
197 BUG();
198 }
199 /* not hit */
200 return 0;
201}
202
203/*
204 * Return total length of time extend and data,
205 * or just the event length for all other events.
206 */
207static inline unsigned
208rb_event_ts_length(struct ring_buffer_event *event)
209{
210 unsigned len = 0;
211
212 if (event->type_len == RINGBUF_TYPE_TIME_EXTEND) {
213 /* time extends include the data event after it */
214 len = RB_LEN_TIME_EXTEND;
215 event = skip_time_extend(event);
216 }
217 return len + rb_event_length(event);
218}
219
220/**
221 * ring_buffer_event_length - return the length of the event
222 * @event: the event to get the length of
223 *
224 * Returns the size of the data load of a data event.
225 * If the event is something other than a data event, it
226 * returns the size of the event itself. With the exception
227 * of a TIME EXTEND, where it still returns the size of the
228 * data load of the data event after it.
229 */
230unsigned ring_buffer_event_length(struct ring_buffer_event *event)
231{
232 unsigned length;
233
234 if (event->type_len == RINGBUF_TYPE_TIME_EXTEND)
235 event = skip_time_extend(event);
236
237 length = rb_event_length(event);
238 if (event->type_len > RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
239 return length;
240 length -= RB_EVNT_HDR_SIZE;
241 if (length > RB_MAX_SMALL_DATA + sizeof(event->array[0]))
242 length -= sizeof(event->array[0]);
243 return length;
244}
245EXPORT_SYMBOL_GPL(ring_buffer_event_length);
246
247/* inline for ring buffer fast paths */
248static void *
249rb_event_data(struct ring_buffer_event *event)
250{
251 if (event->type_len == RINGBUF_TYPE_TIME_EXTEND)
252 event = skip_time_extend(event);
253 BUG_ON(event->type_len > RINGBUF_TYPE_DATA_TYPE_LEN_MAX);
254 /* If length is in len field, then array[0] has the data */
255 if (event->type_len)
256 return (void *)&event->array[0];
257 /* Otherwise length is in array[0] and array[1] has the data */
258 return (void *)&event->array[1];
259}
260
261/**
262 * ring_buffer_event_data - return the data of the event
263 * @event: the event to get the data from
264 */
265void *ring_buffer_event_data(struct ring_buffer_event *event)
266{
267 return rb_event_data(event);
268}
269EXPORT_SYMBOL_GPL(ring_buffer_event_data);
270
271#define for_each_buffer_cpu(buffer, cpu) \
272 for_each_cpu(cpu, buffer->cpumask)
273
274#define TS_SHIFT 27
275#define TS_MASK ((1ULL << TS_SHIFT) - 1)
276#define TS_DELTA_TEST (~TS_MASK)
277
278/* Flag when events were overwritten */
279#define RB_MISSED_EVENTS (1 << 31)
280/* Missed count stored at end */
281#define RB_MISSED_STORED (1 << 30)
282
283struct buffer_data_page {
284 u64 time_stamp; /* page time stamp */
285 local_t commit; /* write committed index */
286 unsigned char data[] RB_ALIGN_DATA; /* data of buffer page */
287};
288
289/*
290 * Note, the buffer_page list must be first. The buffer pages
291 * are allocated in cache lines, which means that each buffer
292 * page will be at the beginning of a cache line, and thus
293 * the least significant bits will be zero. We use this to
294 * add flags in the list struct pointers, to make the ring buffer
295 * lockless.
296 */
297struct buffer_page {
298 struct list_head list; /* list of buffer pages */
299 local_t write; /* index for next write */
300 unsigned read; /* index for next read */
301 local_t entries; /* entries on this page */
302 unsigned long real_end; /* real end of data */
303 struct buffer_data_page *page; /* Actual data page */
304};
305
306/*
307 * The buffer page counters, write and entries, must be reset
308 * atomically when crossing page boundaries. To synchronize this
309 * update, two counters are inserted into the number. One is
310 * the actual counter for the write position or count on the page.
311 *
312 * The other is a counter of updaters. Before an update happens
313 * the update partition of the counter is incremented. This will
314 * allow the updater to update the counter atomically.
315 *
316 * The counter is 20 bits, and the state data is 12.
317 */
318#define RB_WRITE_MASK 0xfffff
319#define RB_WRITE_INTCNT (1 << 20)
320
321static void rb_init_page(struct buffer_data_page *bpage)
322{
323 local_set(&bpage->commit, 0);
324}
325
326/**
327 * ring_buffer_page_len - the size of data on the page.
328 * @page: The page to read
329 *
330 * Returns the amount of data on the page, including buffer page header.
331 */
332size_t ring_buffer_page_len(void *page)
333{
334 return local_read(&((struct buffer_data_page *)page)->commit)
335 + BUF_PAGE_HDR_SIZE;
336}
337
338/*
339 * Also stolen from mm/slob.c. Thanks to Mathieu Desnoyers for pointing
340 * this issue out.
341 */
342static void free_buffer_page(struct buffer_page *bpage)
343{
344 free_page((unsigned long)bpage->page);
345 kfree(bpage);
346}
347
348/*
349 * We need to fit the time_stamp delta into 27 bits.
350 */
351static inline int test_time_stamp(u64 delta)
352{
353 if (delta & TS_DELTA_TEST)
354 return 1;
355 return 0;
356}
357
358#define BUF_PAGE_SIZE (PAGE_SIZE - BUF_PAGE_HDR_SIZE)
359
360/* Max payload is BUF_PAGE_SIZE - header (8bytes) */
361#define BUF_MAX_DATA_SIZE (BUF_PAGE_SIZE - (sizeof(u32) * 2))
362
363int ring_buffer_print_page_header(struct trace_seq *s)
364{
365 struct buffer_data_page field;
366
367 trace_seq_printf(s, "\tfield: u64 timestamp;\t"
368 "offset:0;\tsize:%u;\tsigned:%u;\n",
369 (unsigned int)sizeof(field.time_stamp),
370 (unsigned int)is_signed_type(u64));
371
372 trace_seq_printf(s, "\tfield: local_t commit;\t"
373 "offset:%u;\tsize:%u;\tsigned:%u;\n",
374 (unsigned int)offsetof(typeof(field), commit),
375 (unsigned int)sizeof(field.commit),
376 (unsigned int)is_signed_type(long));
377
378 trace_seq_printf(s, "\tfield: int overwrite;\t"
379 "offset:%u;\tsize:%u;\tsigned:%u;\n",
380 (unsigned int)offsetof(typeof(field), commit),
381 1,
382 (unsigned int)is_signed_type(long));
383
384 trace_seq_printf(s, "\tfield: char data;\t"
385 "offset:%u;\tsize:%u;\tsigned:%u;\n",
386 (unsigned int)offsetof(typeof(field), data),
387 (unsigned int)BUF_PAGE_SIZE,
388 (unsigned int)is_signed_type(char));
389
390 return !trace_seq_has_overflowed(s);
391}
392
393struct rb_irq_work {
394 struct irq_work work;
395 wait_queue_head_t waiters;
396 wait_queue_head_t full_waiters;
397 bool waiters_pending;
398 bool full_waiters_pending;
399 bool wakeup_full;
400};
401
402/*
403 * Structure to hold event state and handle nested events.
404 */
405struct rb_event_info {
406 u64 ts;
407 u64 delta;
408 unsigned long length;
409 struct buffer_page *tail_page;
410 int add_timestamp;
411};
412
413/*
414 * Used for which event context the event is in.
415 * NMI = 0
416 * IRQ = 1
417 * SOFTIRQ = 2
418 * NORMAL = 3
419 *
420 * See trace_recursive_lock() comment below for more details.
421 */
422enum {
423 RB_CTX_NMI,
424 RB_CTX_IRQ,
425 RB_CTX_SOFTIRQ,
426 RB_CTX_NORMAL,
427 RB_CTX_MAX
428};
429
430/*
431 * head_page == tail_page && head == tail then buffer is empty.
432 */
433struct ring_buffer_per_cpu {
434 int cpu;
435 atomic_t record_disabled;
436 struct ring_buffer *buffer;
437 raw_spinlock_t reader_lock; /* serialize readers */
438 arch_spinlock_t lock;
439 struct lock_class_key lock_key;
440 unsigned int nr_pages;
441 unsigned int current_context;
442 struct list_head *pages;
443 struct buffer_page *head_page; /* read from head */
444 struct buffer_page *tail_page; /* write to tail */
445 struct buffer_page *commit_page; /* committed pages */
446 struct buffer_page *reader_page;
447 unsigned long lost_events;
448 unsigned long last_overrun;
449 local_t entries_bytes;
450 local_t entries;
451 local_t overrun;
452 local_t commit_overrun;
453 local_t dropped_events;
454 local_t committing;
455 local_t commits;
456 unsigned long read;
457 unsigned long read_bytes;
458 u64 write_stamp;
459 u64 read_stamp;
460 /* ring buffer pages to update, > 0 to add, < 0 to remove */
461 int nr_pages_to_update;
462 struct list_head new_pages; /* new pages to add */
463 struct work_struct update_pages_work;
464 struct completion update_done;
465
466 struct rb_irq_work irq_work;
467};
468
469struct ring_buffer {
470 unsigned flags;
471 int cpus;
472 atomic_t record_disabled;
473 atomic_t resize_disabled;
474 cpumask_var_t cpumask;
475
476 struct lock_class_key *reader_lock_key;
477
478 struct mutex mutex;
479
480 struct ring_buffer_per_cpu **buffers;
481
482#ifdef CONFIG_HOTPLUG_CPU
483 struct notifier_block cpu_notify;
484#endif
485 u64 (*clock)(void);
486
487 struct rb_irq_work irq_work;
488};
489
490struct ring_buffer_iter {
491 struct ring_buffer_per_cpu *cpu_buffer;
492 unsigned long head;
493 struct buffer_page *head_page;
494 struct buffer_page *cache_reader_page;
495 unsigned long cache_read;
496 u64 read_stamp;
497};
498
499/*
500 * rb_wake_up_waiters - wake up tasks waiting for ring buffer input
501 *
502 * Schedules a delayed work to wake up any task that is blocked on the
503 * ring buffer waiters queue.
504 */
505static void rb_wake_up_waiters(struct irq_work *work)
506{
507 struct rb_irq_work *rbwork = container_of(work, struct rb_irq_work, work);
508
509 wake_up_all(&rbwork->waiters);
510 if (rbwork->wakeup_full) {
511 rbwork->wakeup_full = false;
512 wake_up_all(&rbwork->full_waiters);
513 }
514}
515
516/**
517 * ring_buffer_wait - wait for input to the ring buffer
518 * @buffer: buffer to wait on
519 * @cpu: the cpu buffer to wait on
520 * @full: wait until a full page is available, if @cpu != RING_BUFFER_ALL_CPUS
521 *
522 * If @cpu == RING_BUFFER_ALL_CPUS then the task will wake up as soon
523 * as data is added to any of the @buffer's cpu buffers. Otherwise
524 * it will wait for data to be added to a specific cpu buffer.
525 */
526int ring_buffer_wait(struct ring_buffer *buffer, int cpu, bool full)
527{
528 struct ring_buffer_per_cpu *uninitialized_var(cpu_buffer);
529 DEFINE_WAIT(wait);
530 struct rb_irq_work *work;
531 int ret = 0;
532
533 /*
534 * Depending on what the caller is waiting for, either any
535 * data in any cpu buffer, or a specific buffer, put the
536 * caller on the appropriate wait queue.
537 */
538 if (cpu == RING_BUFFER_ALL_CPUS) {
539 work = &buffer->irq_work;
540 /* Full only makes sense on per cpu reads */
541 full = false;
542 } else {
543 if (!cpumask_test_cpu(cpu, buffer->cpumask))
544 return -ENODEV;
545 cpu_buffer = buffer->buffers[cpu];
546 work = &cpu_buffer->irq_work;
547 }
548
549
550 while (true) {
551 if (full)
552 prepare_to_wait(&work->full_waiters, &wait, TASK_INTERRUPTIBLE);
553 else
554 prepare_to_wait(&work->waiters, &wait, TASK_INTERRUPTIBLE);
555
556 /*
557 * The events can happen in critical sections where
558 * checking a work queue can cause deadlocks.
559 * After adding a task to the queue, this flag is set
560 * only to notify events to try to wake up the queue
561 * using irq_work.
562 *
563 * We don't clear it even if the buffer is no longer
564 * empty. The flag only causes the next event to run
565 * irq_work to do the work queue wake up. The worse
566 * that can happen if we race with !trace_empty() is that
567 * an event will cause an irq_work to try to wake up
568 * an empty queue.
569 *
570 * There's no reason to protect this flag either, as
571 * the work queue and irq_work logic will do the necessary
572 * synchronization for the wake ups. The only thing
573 * that is necessary is that the wake up happens after
574 * a task has been queued. It's OK for spurious wake ups.
575 */
576 if (full)
577 work->full_waiters_pending = true;
578 else
579 work->waiters_pending = true;
580
581 if (signal_pending(current)) {
582 ret = -EINTR;
583 break;
584 }
585
586 if (cpu == RING_BUFFER_ALL_CPUS && !ring_buffer_empty(buffer))
587 break;
588
589 if (cpu != RING_BUFFER_ALL_CPUS &&
590 !ring_buffer_empty_cpu(buffer, cpu)) {
591 unsigned long flags;
592 bool pagebusy;
593
594 if (!full)
595 break;
596
597 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
598 pagebusy = cpu_buffer->reader_page == cpu_buffer->commit_page;
599 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
600
601 if (!pagebusy)
602 break;
603 }
604
605 schedule();
606 }
607
608 if (full)
609 finish_wait(&work->full_waiters, &wait);
610 else
611 finish_wait(&work->waiters, &wait);
612
613 return ret;
614}
615
616/**
617 * ring_buffer_poll_wait - poll on buffer input
618 * @buffer: buffer to wait on
619 * @cpu: the cpu buffer to wait on
620 * @filp: the file descriptor
621 * @poll_table: The poll descriptor
622 *
623 * If @cpu == RING_BUFFER_ALL_CPUS then the task will wake up as soon
624 * as data is added to any of the @buffer's cpu buffers. Otherwise
625 * it will wait for data to be added to a specific cpu buffer.
626 *
627 * Returns POLLIN | POLLRDNORM if data exists in the buffers,
628 * zero otherwise.
629 */
630int ring_buffer_poll_wait(struct ring_buffer *buffer, int cpu,
631 struct file *filp, poll_table *poll_table)
632{
633 struct ring_buffer_per_cpu *cpu_buffer;
634 struct rb_irq_work *work;
635
636 if (cpu == RING_BUFFER_ALL_CPUS)
637 work = &buffer->irq_work;
638 else {
639 if (!cpumask_test_cpu(cpu, buffer->cpumask))
640 return -EINVAL;
641
642 cpu_buffer = buffer->buffers[cpu];
643 work = &cpu_buffer->irq_work;
644 }
645
646 poll_wait(filp, &work->waiters, poll_table);
647 work->waiters_pending = true;
648 /*
649 * There's a tight race between setting the waiters_pending and
650 * checking if the ring buffer is empty. Once the waiters_pending bit
651 * is set, the next event will wake the task up, but we can get stuck
652 * if there's only a single event in.
653 *
654 * FIXME: Ideally, we need a memory barrier on the writer side as well,
655 * but adding a memory barrier to all events will cause too much of a
656 * performance hit in the fast path. We only need a memory barrier when
657 * the buffer goes from empty to having content. But as this race is
658 * extremely small, and it's not a problem if another event comes in, we
659 * will fix it later.
660 */
661 smp_mb();
662
663 if ((cpu == RING_BUFFER_ALL_CPUS && !ring_buffer_empty(buffer)) ||
664 (cpu != RING_BUFFER_ALL_CPUS && !ring_buffer_empty_cpu(buffer, cpu)))
665 return POLLIN | POLLRDNORM;
666 return 0;
667}
668
669/* buffer may be either ring_buffer or ring_buffer_per_cpu */
670#define RB_WARN_ON(b, cond) \
671 ({ \
672 int _____ret = unlikely(cond); \
673 if (_____ret) { \
674 if (__same_type(*(b), struct ring_buffer_per_cpu)) { \
675 struct ring_buffer_per_cpu *__b = \
676 (void *)b; \
677 atomic_inc(&__b->buffer->record_disabled); \
678 } else \
679 atomic_inc(&b->record_disabled); \
680 WARN_ON(1); \
681 } \
682 _____ret; \
683 })
684
685/* Up this if you want to test the TIME_EXTENTS and normalization */
686#define DEBUG_SHIFT 0
687
688static inline u64 rb_time_stamp(struct ring_buffer *buffer)
689{
690 /* shift to debug/test normalization and TIME_EXTENTS */
691 return buffer->clock() << DEBUG_SHIFT;
692}
693
694u64 ring_buffer_time_stamp(struct ring_buffer *buffer, int cpu)
695{
696 u64 time;
697
698 preempt_disable_notrace();
699 time = rb_time_stamp(buffer);
700 preempt_enable_no_resched_notrace();
701
702 return time;
703}
704EXPORT_SYMBOL_GPL(ring_buffer_time_stamp);
705
706void ring_buffer_normalize_time_stamp(struct ring_buffer *buffer,
707 int cpu, u64 *ts)
708{
709 /* Just stupid testing the normalize function and deltas */
710 *ts >>= DEBUG_SHIFT;
711}
712EXPORT_SYMBOL_GPL(ring_buffer_normalize_time_stamp);
713
714/*
715 * Making the ring buffer lockless makes things tricky.
716 * Although writes only happen on the CPU that they are on,
717 * and they only need to worry about interrupts. Reads can
718 * happen on any CPU.
719 *
720 * The reader page is always off the ring buffer, but when the
721 * reader finishes with a page, it needs to swap its page with
722 * a new one from the buffer. The reader needs to take from
723 * the head (writes go to the tail). But if a writer is in overwrite
724 * mode and wraps, it must push the head page forward.
725 *
726 * Here lies the problem.
727 *
728 * The reader must be careful to replace only the head page, and
729 * not another one. As described at the top of the file in the
730 * ASCII art, the reader sets its old page to point to the next
731 * page after head. It then sets the page after head to point to
732 * the old reader page. But if the writer moves the head page
733 * during this operation, the reader could end up with the tail.
734 *
735 * We use cmpxchg to help prevent this race. We also do something
736 * special with the page before head. We set the LSB to 1.
737 *
738 * When the writer must push the page forward, it will clear the
739 * bit that points to the head page, move the head, and then set
740 * the bit that points to the new head page.
741 *
742 * We also don't want an interrupt coming in and moving the head
743 * page on another writer. Thus we use the second LSB to catch
744 * that too. Thus:
745 *
746 * head->list->prev->next bit 1 bit 0
747 * ------- -------
748 * Normal page 0 0
749 * Points to head page 0 1
750 * New head page 1 0
751 *
752 * Note we can not trust the prev pointer of the head page, because:
753 *
754 * +----+ +-----+ +-----+
755 * | |------>| T |---X--->| N |
756 * | |<------| | | |
757 * +----+ +-----+ +-----+
758 * ^ ^ |
759 * | +-----+ | |
760 * +----------| R |----------+ |
761 * | |<-----------+
762 * +-----+
763 *
764 * Key: ---X--> HEAD flag set in pointer
765 * T Tail page
766 * R Reader page
767 * N Next page
768 *
769 * (see __rb_reserve_next() to see where this happens)
770 *
771 * What the above shows is that the reader just swapped out
772 * the reader page with a page in the buffer, but before it
773 * could make the new header point back to the new page added
774 * it was preempted by a writer. The writer moved forward onto
775 * the new page added by the reader and is about to move forward
776 * again.
777 *
778 * You can see, it is legitimate for the previous pointer of
779 * the head (or any page) not to point back to itself. But only
780 * temporarially.
781 */
782
783#define RB_PAGE_NORMAL 0UL
784#define RB_PAGE_HEAD 1UL
785#define RB_PAGE_UPDATE 2UL
786
787
788#define RB_FLAG_MASK 3UL
789
790/* PAGE_MOVED is not part of the mask */
791#define RB_PAGE_MOVED 4UL
792
793/*
794 * rb_list_head - remove any bit
795 */
796static struct list_head *rb_list_head(struct list_head *list)
797{
798 unsigned long val = (unsigned long)list;
799
800 return (struct list_head *)(val & ~RB_FLAG_MASK);
801}
802
803/*
804 * rb_is_head_page - test if the given page is the head page
805 *
806 * Because the reader may move the head_page pointer, we can
807 * not trust what the head page is (it may be pointing to
808 * the reader page). But if the next page is a header page,
809 * its flags will be non zero.
810 */
811static inline int
812rb_is_head_page(struct ring_buffer_per_cpu *cpu_buffer,
813 struct buffer_page *page, struct list_head *list)
814{
815 unsigned long val;
816
817 val = (unsigned long)list->next;
818
819 if ((val & ~RB_FLAG_MASK) != (unsigned long)&page->list)
820 return RB_PAGE_MOVED;
821
822 return val & RB_FLAG_MASK;
823}
824
825/*
826 * rb_is_reader_page
827 *
828 * The unique thing about the reader page, is that, if the
829 * writer is ever on it, the previous pointer never points
830 * back to the reader page.
831 */
832static bool rb_is_reader_page(struct buffer_page *page)
833{
834 struct list_head *list = page->list.prev;
835
836 return rb_list_head(list->next) != &page->list;
837}
838
839/*
840 * rb_set_list_to_head - set a list_head to be pointing to head.
841 */
842static void rb_set_list_to_head(struct ring_buffer_per_cpu *cpu_buffer,
843 struct list_head *list)
844{
845 unsigned long *ptr;
846
847 ptr = (unsigned long *)&list->next;
848 *ptr |= RB_PAGE_HEAD;
849 *ptr &= ~RB_PAGE_UPDATE;
850}
851
852/*
853 * rb_head_page_activate - sets up head page
854 */
855static void rb_head_page_activate(struct ring_buffer_per_cpu *cpu_buffer)
856{
857 struct buffer_page *head;
858
859 head = cpu_buffer->head_page;
860 if (!head)
861 return;
862
863 /*
864 * Set the previous list pointer to have the HEAD flag.
865 */
866 rb_set_list_to_head(cpu_buffer, head->list.prev);
867}
868
869static void rb_list_head_clear(struct list_head *list)
870{
871 unsigned long *ptr = (unsigned long *)&list->next;
872
873 *ptr &= ~RB_FLAG_MASK;
874}
875
876/*
877 * rb_head_page_dactivate - clears head page ptr (for free list)
878 */
879static void
880rb_head_page_deactivate(struct ring_buffer_per_cpu *cpu_buffer)
881{
882 struct list_head *hd;
883
884 /* Go through the whole list and clear any pointers found. */
885 rb_list_head_clear(cpu_buffer->pages);
886
887 list_for_each(hd, cpu_buffer->pages)
888 rb_list_head_clear(hd);
889}
890
891static int rb_head_page_set(struct ring_buffer_per_cpu *cpu_buffer,
892 struct buffer_page *head,
893 struct buffer_page *prev,
894 int old_flag, int new_flag)
895{
896 struct list_head *list;
897 unsigned long val = (unsigned long)&head->list;
898 unsigned long ret;
899
900 list = &prev->list;
901
902 val &= ~RB_FLAG_MASK;
903
904 ret = cmpxchg((unsigned long *)&list->next,
905 val | old_flag, val | new_flag);
906
907 /* check if the reader took the page */
908 if ((ret & ~RB_FLAG_MASK) != val)
909 return RB_PAGE_MOVED;
910
911 return ret & RB_FLAG_MASK;
912}
913
914static int rb_head_page_set_update(struct ring_buffer_per_cpu *cpu_buffer,
915 struct buffer_page *head,
916 struct buffer_page *prev,
917 int old_flag)
918{
919 return rb_head_page_set(cpu_buffer, head, prev,
920 old_flag, RB_PAGE_UPDATE);
921}
922
923static int rb_head_page_set_head(struct ring_buffer_per_cpu *cpu_buffer,
924 struct buffer_page *head,
925 struct buffer_page *prev,
926 int old_flag)
927{
928 return rb_head_page_set(cpu_buffer, head, prev,
929 old_flag, RB_PAGE_HEAD);
930}
931
932static int rb_head_page_set_normal(struct ring_buffer_per_cpu *cpu_buffer,
933 struct buffer_page *head,
934 struct buffer_page *prev,
935 int old_flag)
936{
937 return rb_head_page_set(cpu_buffer, head, prev,
938 old_flag, RB_PAGE_NORMAL);
939}
940
941static inline void rb_inc_page(struct ring_buffer_per_cpu *cpu_buffer,
942 struct buffer_page **bpage)
943{
944 struct list_head *p = rb_list_head((*bpage)->list.next);
945
946 *bpage = list_entry(p, struct buffer_page, list);
947}
948
949static struct buffer_page *
950rb_set_head_page(struct ring_buffer_per_cpu *cpu_buffer)
951{
952 struct buffer_page *head;
953 struct buffer_page *page;
954 struct list_head *list;
955 int i;
956
957 if (RB_WARN_ON(cpu_buffer, !cpu_buffer->head_page))
958 return NULL;
959
960 /* sanity check */
961 list = cpu_buffer->pages;
962 if (RB_WARN_ON(cpu_buffer, rb_list_head(list->prev->next) != list))
963 return NULL;
964
965 page = head = cpu_buffer->head_page;
966 /*
967 * It is possible that the writer moves the header behind
968 * where we started, and we miss in one loop.
969 * A second loop should grab the header, but we'll do
970 * three loops just because I'm paranoid.
971 */
972 for (i = 0; i < 3; i++) {
973 do {
974 if (rb_is_head_page(cpu_buffer, page, page->list.prev)) {
975 cpu_buffer->head_page = page;
976 return page;
977 }
978 rb_inc_page(cpu_buffer, &page);
979 } while (page != head);
980 }
981
982 RB_WARN_ON(cpu_buffer, 1);
983
984 return NULL;
985}
986
987static int rb_head_page_replace(struct buffer_page *old,
988 struct buffer_page *new)
989{
990 unsigned long *ptr = (unsigned long *)&old->list.prev->next;
991 unsigned long val;
992 unsigned long ret;
993
994 val = *ptr & ~RB_FLAG_MASK;
995 val |= RB_PAGE_HEAD;
996
997 ret = cmpxchg(ptr, val, (unsigned long)&new->list);
998
999 return ret == val;
1000}
1001
1002/*
1003 * rb_tail_page_update - move the tail page forward
1004 */
1005static void rb_tail_page_update(struct ring_buffer_per_cpu *cpu_buffer,
1006 struct buffer_page *tail_page,
1007 struct buffer_page *next_page)
1008{
1009 unsigned long old_entries;
1010 unsigned long old_write;
1011
1012 /*
1013 * The tail page now needs to be moved forward.
1014 *
1015 * We need to reset the tail page, but without messing
1016 * with possible erasing of data brought in by interrupts
1017 * that have moved the tail page and are currently on it.
1018 *
1019 * We add a counter to the write field to denote this.
1020 */
1021 old_write = local_add_return(RB_WRITE_INTCNT, &next_page->write);
1022 old_entries = local_add_return(RB_WRITE_INTCNT, &next_page->entries);
1023
1024 /*
1025 * Just make sure we have seen our old_write and synchronize
1026 * with any interrupts that come in.
1027 */
1028 barrier();
1029
1030 /*
1031 * If the tail page is still the same as what we think
1032 * it is, then it is up to us to update the tail
1033 * pointer.
1034 */
1035 if (tail_page == READ_ONCE(cpu_buffer->tail_page)) {
1036 /* Zero the write counter */
1037 unsigned long val = old_write & ~RB_WRITE_MASK;
1038 unsigned long eval = old_entries & ~RB_WRITE_MASK;
1039
1040 /*
1041 * This will only succeed if an interrupt did
1042 * not come in and change it. In which case, we
1043 * do not want to modify it.
1044 *
1045 * We add (void) to let the compiler know that we do not care
1046 * about the return value of these functions. We use the
1047 * cmpxchg to only update if an interrupt did not already
1048 * do it for us. If the cmpxchg fails, we don't care.
1049 */
1050 (void)local_cmpxchg(&next_page->write, old_write, val);
1051 (void)local_cmpxchg(&next_page->entries, old_entries, eval);
1052
1053 /*
1054 * No need to worry about races with clearing out the commit.
1055 * it only can increment when a commit takes place. But that
1056 * only happens in the outer most nested commit.
1057 */
1058 local_set(&next_page->page->commit, 0);
1059
1060 /* Again, either we update tail_page or an interrupt does */
1061 (void)cmpxchg(&cpu_buffer->tail_page, tail_page, next_page);
1062 }
1063}
1064
1065static int rb_check_bpage(struct ring_buffer_per_cpu *cpu_buffer,
1066 struct buffer_page *bpage)
1067{
1068 unsigned long val = (unsigned long)bpage;
1069
1070 if (RB_WARN_ON(cpu_buffer, val & RB_FLAG_MASK))
1071 return 1;
1072
1073 return 0;
1074}
1075
1076/**
1077 * rb_check_list - make sure a pointer to a list has the last bits zero
1078 */
1079static int rb_check_list(struct ring_buffer_per_cpu *cpu_buffer,
1080 struct list_head *list)
1081{
1082 if (RB_WARN_ON(cpu_buffer, rb_list_head(list->prev) != list->prev))
1083 return 1;
1084 if (RB_WARN_ON(cpu_buffer, rb_list_head(list->next) != list->next))
1085 return 1;
1086 return 0;
1087}
1088
1089/**
1090 * rb_check_pages - integrity check of buffer pages
1091 * @cpu_buffer: CPU buffer with pages to test
1092 *
1093 * As a safety measure we check to make sure the data pages have not
1094 * been corrupted.
1095 */
1096static int rb_check_pages(struct ring_buffer_per_cpu *cpu_buffer)
1097{
1098 struct list_head *head = cpu_buffer->pages;
1099 struct buffer_page *bpage, *tmp;
1100
1101 /* Reset the head page if it exists */
1102 if (cpu_buffer->head_page)
1103 rb_set_head_page(cpu_buffer);
1104
1105 rb_head_page_deactivate(cpu_buffer);
1106
1107 if (RB_WARN_ON(cpu_buffer, head->next->prev != head))
1108 return -1;
1109 if (RB_WARN_ON(cpu_buffer, head->prev->next != head))
1110 return -1;
1111
1112 if (rb_check_list(cpu_buffer, head))
1113 return -1;
1114
1115 list_for_each_entry_safe(bpage, tmp, head, list) {
1116 if (RB_WARN_ON(cpu_buffer,
1117 bpage->list.next->prev != &bpage->list))
1118 return -1;
1119 if (RB_WARN_ON(cpu_buffer,
1120 bpage->list.prev->next != &bpage->list))
1121 return -1;
1122 if (rb_check_list(cpu_buffer, &bpage->list))
1123 return -1;
1124 }
1125
1126 rb_head_page_activate(cpu_buffer);
1127
1128 return 0;
1129}
1130
1131static int __rb_allocate_pages(int nr_pages, struct list_head *pages, int cpu)
1132{
1133 int i;
1134 struct buffer_page *bpage, *tmp;
1135
1136 for (i = 0; i < nr_pages; i++) {
1137 struct page *page;
1138 /*
1139 * __GFP_NORETRY flag makes sure that the allocation fails
1140 * gracefully without invoking oom-killer and the system is
1141 * not destabilized.
1142 */
1143 bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
1144 GFP_KERNEL | __GFP_NORETRY,
1145 cpu_to_node(cpu));
1146 if (!bpage)
1147 goto free_pages;
1148
1149 list_add(&bpage->list, pages);
1150
1151 page = alloc_pages_node(cpu_to_node(cpu),
1152 GFP_KERNEL | __GFP_NORETRY, 0);
1153 if (!page)
1154 goto free_pages;
1155 bpage->page = page_address(page);
1156 rb_init_page(bpage->page);
1157 }
1158
1159 return 0;
1160
1161free_pages:
1162 list_for_each_entry_safe(bpage, tmp, pages, list) {
1163 list_del_init(&bpage->list);
1164 free_buffer_page(bpage);
1165 }
1166
1167 return -ENOMEM;
1168}
1169
1170static int rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
1171 unsigned nr_pages)
1172{
1173 LIST_HEAD(pages);
1174
1175 WARN_ON(!nr_pages);
1176
1177 if (__rb_allocate_pages(nr_pages, &pages, cpu_buffer->cpu))
1178 return -ENOMEM;
1179
1180 /*
1181 * The ring buffer page list is a circular list that does not
1182 * start and end with a list head. All page list items point to
1183 * other pages.
1184 */
1185 cpu_buffer->pages = pages.next;
1186 list_del(&pages);
1187
1188 cpu_buffer->nr_pages = nr_pages;
1189
1190 rb_check_pages(cpu_buffer);
1191
1192 return 0;
1193}
1194
1195static struct ring_buffer_per_cpu *
1196rb_allocate_cpu_buffer(struct ring_buffer *buffer, int nr_pages, int cpu)
1197{
1198 struct ring_buffer_per_cpu *cpu_buffer;
1199 struct buffer_page *bpage;
1200 struct page *page;
1201 int ret;
1202
1203 cpu_buffer = kzalloc_node(ALIGN(sizeof(*cpu_buffer), cache_line_size()),
1204 GFP_KERNEL, cpu_to_node(cpu));
1205 if (!cpu_buffer)
1206 return NULL;
1207
1208 cpu_buffer->cpu = cpu;
1209 cpu_buffer->buffer = buffer;
1210 raw_spin_lock_init(&cpu_buffer->reader_lock);
1211 lockdep_set_class(&cpu_buffer->reader_lock, buffer->reader_lock_key);
1212 cpu_buffer->lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
1213 INIT_WORK(&cpu_buffer->update_pages_work, update_pages_handler);
1214 init_completion(&cpu_buffer->update_done);
1215 init_irq_work(&cpu_buffer->irq_work.work, rb_wake_up_waiters);
1216 init_waitqueue_head(&cpu_buffer->irq_work.waiters);
1217 init_waitqueue_head(&cpu_buffer->irq_work.full_waiters);
1218
1219 bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
1220 GFP_KERNEL, cpu_to_node(cpu));
1221 if (!bpage)
1222 goto fail_free_buffer;
1223
1224 rb_check_bpage(cpu_buffer, bpage);
1225
1226 cpu_buffer->reader_page = bpage;
1227 page = alloc_pages_node(cpu_to_node(cpu), GFP_KERNEL, 0);
1228 if (!page)
1229 goto fail_free_reader;
1230 bpage->page = page_address(page);
1231 rb_init_page(bpage->page);
1232
1233 INIT_LIST_HEAD(&cpu_buffer->reader_page->list);
1234 INIT_LIST_HEAD(&cpu_buffer->new_pages);
1235
1236 ret = rb_allocate_pages(cpu_buffer, nr_pages);
1237 if (ret < 0)
1238 goto fail_free_reader;
1239
1240 cpu_buffer->head_page
1241 = list_entry(cpu_buffer->pages, struct buffer_page, list);
1242 cpu_buffer->tail_page = cpu_buffer->commit_page = cpu_buffer->head_page;
1243
1244 rb_head_page_activate(cpu_buffer);
1245
1246 return cpu_buffer;
1247
1248 fail_free_reader:
1249 free_buffer_page(cpu_buffer->reader_page);
1250
1251 fail_free_buffer:
1252 kfree(cpu_buffer);
1253 return NULL;
1254}
1255
1256static void rb_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
1257{
1258 struct list_head *head = cpu_buffer->pages;
1259 struct buffer_page *bpage, *tmp;
1260
1261 free_buffer_page(cpu_buffer->reader_page);
1262
1263 rb_head_page_deactivate(cpu_buffer);
1264
1265 if (head) {
1266 list_for_each_entry_safe(bpage, tmp, head, list) {
1267 list_del_init(&bpage->list);
1268 free_buffer_page(bpage);
1269 }
1270 bpage = list_entry(head, struct buffer_page, list);
1271 free_buffer_page(bpage);
1272 }
1273
1274 kfree(cpu_buffer);
1275}
1276
1277#ifdef CONFIG_HOTPLUG_CPU
1278static int rb_cpu_notify(struct notifier_block *self,
1279 unsigned long action, void *hcpu);
1280#endif
1281
1282/**
1283 * __ring_buffer_alloc - allocate a new ring_buffer
1284 * @size: the size in bytes per cpu that is needed.
1285 * @flags: attributes to set for the ring buffer.
1286 *
1287 * Currently the only flag that is available is the RB_FL_OVERWRITE
1288 * flag. This flag means that the buffer will overwrite old data
1289 * when the buffer wraps. If this flag is not set, the buffer will
1290 * drop data when the tail hits the head.
1291 */
1292struct ring_buffer *__ring_buffer_alloc(unsigned long size, unsigned flags,
1293 struct lock_class_key *key)
1294{
1295 struct ring_buffer *buffer;
1296 int bsize;
1297 int cpu, nr_pages;
1298
1299 /* keep it in its own cache line */
1300 buffer = kzalloc(ALIGN(sizeof(*buffer), cache_line_size()),
1301 GFP_KERNEL);
1302 if (!buffer)
1303 return NULL;
1304
1305 if (!alloc_cpumask_var(&buffer->cpumask, GFP_KERNEL))
1306 goto fail_free_buffer;
1307
1308 nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
1309 buffer->flags = flags;
1310 buffer->clock = trace_clock_local;
1311 buffer->reader_lock_key = key;
1312
1313 init_irq_work(&buffer->irq_work.work, rb_wake_up_waiters);
1314 init_waitqueue_head(&buffer->irq_work.waiters);
1315
1316 /* need at least two pages */
1317 if (nr_pages < 2)
1318 nr_pages = 2;
1319
1320 /*
1321 * In case of non-hotplug cpu, if the ring-buffer is allocated
1322 * in early initcall, it will not be notified of secondary cpus.
1323 * In that off case, we need to allocate for all possible cpus.
1324 */
1325#ifdef CONFIG_HOTPLUG_CPU
1326 cpu_notifier_register_begin();
1327 cpumask_copy(buffer->cpumask, cpu_online_mask);
1328#else
1329 cpumask_copy(buffer->cpumask, cpu_possible_mask);
1330#endif
1331 buffer->cpus = nr_cpu_ids;
1332
1333 bsize = sizeof(void *) * nr_cpu_ids;
1334 buffer->buffers = kzalloc(ALIGN(bsize, cache_line_size()),
1335 GFP_KERNEL);
1336 if (!buffer->buffers)
1337 goto fail_free_cpumask;
1338
1339 for_each_buffer_cpu(buffer, cpu) {
1340 buffer->buffers[cpu] =
1341 rb_allocate_cpu_buffer(buffer, nr_pages, cpu);
1342 if (!buffer->buffers[cpu])
1343 goto fail_free_buffers;
1344 }
1345
1346#ifdef CONFIG_HOTPLUG_CPU
1347 buffer->cpu_notify.notifier_call = rb_cpu_notify;
1348 buffer->cpu_notify.priority = 0;
1349 __register_cpu_notifier(&buffer->cpu_notify);
1350 cpu_notifier_register_done();
1351#endif
1352
1353 mutex_init(&buffer->mutex);
1354
1355 return buffer;
1356
1357 fail_free_buffers:
1358 for_each_buffer_cpu(buffer, cpu) {
1359 if (buffer->buffers[cpu])
1360 rb_free_cpu_buffer(buffer->buffers[cpu]);
1361 }
1362 kfree(buffer->buffers);
1363
1364 fail_free_cpumask:
1365 free_cpumask_var(buffer->cpumask);
1366#ifdef CONFIG_HOTPLUG_CPU
1367 cpu_notifier_register_done();
1368#endif
1369
1370 fail_free_buffer:
1371 kfree(buffer);
1372 return NULL;
1373}
1374EXPORT_SYMBOL_GPL(__ring_buffer_alloc);
1375
1376/**
1377 * ring_buffer_free - free a ring buffer.
1378 * @buffer: the buffer to free.
1379 */
1380void
1381ring_buffer_free(struct ring_buffer *buffer)
1382{
1383 int cpu;
1384
1385#ifdef CONFIG_HOTPLUG_CPU
1386 cpu_notifier_register_begin();
1387 __unregister_cpu_notifier(&buffer->cpu_notify);
1388#endif
1389
1390 for_each_buffer_cpu(buffer, cpu)
1391 rb_free_cpu_buffer(buffer->buffers[cpu]);
1392
1393#ifdef CONFIG_HOTPLUG_CPU
1394 cpu_notifier_register_done();
1395#endif
1396
1397 kfree(buffer->buffers);
1398 free_cpumask_var(buffer->cpumask);
1399
1400 kfree(buffer);
1401}
1402EXPORT_SYMBOL_GPL(ring_buffer_free);
1403
1404void ring_buffer_set_clock(struct ring_buffer *buffer,
1405 u64 (*clock)(void))
1406{
1407 buffer->clock = clock;
1408}
1409
1410static void rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer);
1411
1412static inline unsigned long rb_page_entries(struct buffer_page *bpage)
1413{
1414 return local_read(&bpage->entries) & RB_WRITE_MASK;
1415}
1416
1417static inline unsigned long rb_page_write(struct buffer_page *bpage)
1418{
1419 return local_read(&bpage->write) & RB_WRITE_MASK;
1420}
1421
1422static int
1423rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned int nr_pages)
1424{
1425 struct list_head *tail_page, *to_remove, *next_page;
1426 struct buffer_page *to_remove_page, *tmp_iter_page;
1427 struct buffer_page *last_page, *first_page;
1428 unsigned int nr_removed;
1429 unsigned long head_bit;
1430 int page_entries;
1431
1432 head_bit = 0;
1433
1434 raw_spin_lock_irq(&cpu_buffer->reader_lock);
1435 atomic_inc(&cpu_buffer->record_disabled);
1436 /*
1437 * We don't race with the readers since we have acquired the reader
1438 * lock. We also don't race with writers after disabling recording.
1439 * This makes it easy to figure out the first and the last page to be
1440 * removed from the list. We unlink all the pages in between including
1441 * the first and last pages. This is done in a busy loop so that we
1442 * lose the least number of traces.
1443 * The pages are freed after we restart recording and unlock readers.
1444 */
1445 tail_page = &cpu_buffer->tail_page->list;
1446
1447 /*
1448 * tail page might be on reader page, we remove the next page
1449 * from the ring buffer
1450 */
1451 if (cpu_buffer->tail_page == cpu_buffer->reader_page)
1452 tail_page = rb_list_head(tail_page->next);
1453 to_remove = tail_page;
1454
1455 /* start of pages to remove */
1456 first_page = list_entry(rb_list_head(to_remove->next),
1457 struct buffer_page, list);
1458
1459 for (nr_removed = 0; nr_removed < nr_pages; nr_removed++) {
1460 to_remove = rb_list_head(to_remove)->next;
1461 head_bit |= (unsigned long)to_remove & RB_PAGE_HEAD;
1462 }
1463
1464 next_page = rb_list_head(to_remove)->next;
1465
1466 /*
1467 * Now we remove all pages between tail_page and next_page.
1468 * Make sure that we have head_bit value preserved for the
1469 * next page
1470 */
1471 tail_page->next = (struct list_head *)((unsigned long)next_page |
1472 head_bit);
1473 next_page = rb_list_head(next_page);
1474 next_page->prev = tail_page;
1475
1476 /* make sure pages points to a valid page in the ring buffer */
1477 cpu_buffer->pages = next_page;
1478
1479 /* update head page */
1480 if (head_bit)
1481 cpu_buffer->head_page = list_entry(next_page,
1482 struct buffer_page, list);
1483
1484 /*
1485 * change read pointer to make sure any read iterators reset
1486 * themselves
1487 */
1488 cpu_buffer->read = 0;
1489
1490 /* pages are removed, resume tracing and then free the pages */
1491 atomic_dec(&cpu_buffer->record_disabled);
1492 raw_spin_unlock_irq(&cpu_buffer->reader_lock);
1493
1494 RB_WARN_ON(cpu_buffer, list_empty(cpu_buffer->pages));
1495
1496 /* last buffer page to remove */
1497 last_page = list_entry(rb_list_head(to_remove), struct buffer_page,
1498 list);
1499 tmp_iter_page = first_page;
1500
1501 do {
1502 to_remove_page = tmp_iter_page;
1503 rb_inc_page(cpu_buffer, &tmp_iter_page);
1504
1505 /* update the counters */
1506 page_entries = rb_page_entries(to_remove_page);
1507 if (page_entries) {
1508 /*
1509 * If something was added to this page, it was full
1510 * since it is not the tail page. So we deduct the
1511 * bytes consumed in ring buffer from here.
1512 * Increment overrun to account for the lost events.
1513 */
1514 local_add(page_entries, &cpu_buffer->overrun);
1515 local_sub(BUF_PAGE_SIZE, &cpu_buffer->entries_bytes);
1516 }
1517
1518 /*
1519 * We have already removed references to this list item, just
1520 * free up the buffer_page and its page
1521 */
1522 free_buffer_page(to_remove_page);
1523 nr_removed--;
1524
1525 } while (to_remove_page != last_page);
1526
1527 RB_WARN_ON(cpu_buffer, nr_removed);
1528
1529 return nr_removed == 0;
1530}
1531
1532static int
1533rb_insert_pages(struct ring_buffer_per_cpu *cpu_buffer)
1534{
1535 struct list_head *pages = &cpu_buffer->new_pages;
1536 int retries, success;
1537
1538 raw_spin_lock_irq(&cpu_buffer->reader_lock);
1539 /*
1540 * We are holding the reader lock, so the reader page won't be swapped
1541 * in the ring buffer. Now we are racing with the writer trying to
1542 * move head page and the tail page.
1543 * We are going to adapt the reader page update process where:
1544 * 1. We first splice the start and end of list of new pages between
1545 * the head page and its previous page.
1546 * 2. We cmpxchg the prev_page->next to point from head page to the
1547 * start of new pages list.
1548 * 3. Finally, we update the head->prev to the end of new list.
1549 *
1550 * We will try this process 10 times, to make sure that we don't keep
1551 * spinning.
1552 */
1553 retries = 10;
1554 success = 0;
1555 while (retries--) {
1556 struct list_head *head_page, *prev_page, *r;
1557 struct list_head *last_page, *first_page;
1558 struct list_head *head_page_with_bit;
1559
1560 head_page = &rb_set_head_page(cpu_buffer)->list;
1561 if (!head_page)
1562 break;
1563 prev_page = head_page->prev;
1564
1565 first_page = pages->next;
1566 last_page = pages->prev;
1567
1568 head_page_with_bit = (struct list_head *)
1569 ((unsigned long)head_page | RB_PAGE_HEAD);
1570
1571 last_page->next = head_page_with_bit;
1572 first_page->prev = prev_page;
1573
1574 r = cmpxchg(&prev_page->next, head_page_with_bit, first_page);
1575
1576 if (r == head_page_with_bit) {
1577 /*
1578 * yay, we replaced the page pointer to our new list,
1579 * now, we just have to update to head page's prev
1580 * pointer to point to end of list
1581 */
1582 head_page->prev = last_page;
1583 success = 1;
1584 break;
1585 }
1586 }
1587
1588 if (success)
1589 INIT_LIST_HEAD(pages);
1590 /*
1591 * If we weren't successful in adding in new pages, warn and stop
1592 * tracing
1593 */
1594 RB_WARN_ON(cpu_buffer, !success);
1595 raw_spin_unlock_irq(&cpu_buffer->reader_lock);
1596
1597 /* free pages if they weren't inserted */
1598 if (!success) {
1599 struct buffer_page *bpage, *tmp;
1600 list_for_each_entry_safe(bpage, tmp, &cpu_buffer->new_pages,
1601 list) {
1602 list_del_init(&bpage->list);
1603 free_buffer_page(bpage);
1604 }
1605 }
1606 return success;
1607}
1608
1609static void rb_update_pages(struct ring_buffer_per_cpu *cpu_buffer)
1610{
1611 int success;
1612
1613 if (cpu_buffer->nr_pages_to_update > 0)
1614 success = rb_insert_pages(cpu_buffer);
1615 else
1616 success = rb_remove_pages(cpu_buffer,
1617 -cpu_buffer->nr_pages_to_update);
1618
1619 if (success)
1620 cpu_buffer->nr_pages += cpu_buffer->nr_pages_to_update;
1621}
1622
1623static void update_pages_handler(struct work_struct *work)
1624{
1625 struct ring_buffer_per_cpu *cpu_buffer = container_of(work,
1626 struct ring_buffer_per_cpu, update_pages_work);
1627 rb_update_pages(cpu_buffer);
1628 complete(&cpu_buffer->update_done);
1629}
1630
1631/**
1632 * ring_buffer_resize - resize the ring buffer
1633 * @buffer: the buffer to resize.
1634 * @size: the new size.
1635 * @cpu_id: the cpu buffer to resize
1636 *
1637 * Minimum size is 2 * BUF_PAGE_SIZE.
1638 *
1639 * Returns 0 on success and < 0 on failure.
1640 */
1641int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size,
1642 int cpu_id)
1643{
1644 struct ring_buffer_per_cpu *cpu_buffer;
1645 unsigned nr_pages;
1646 int cpu, err = 0;
1647
1648 /*
1649 * Always succeed at resizing a non-existent buffer:
1650 */
1651 if (!buffer)
1652 return size;
1653
1654 /* Make sure the requested buffer exists */
1655 if (cpu_id != RING_BUFFER_ALL_CPUS &&
1656 !cpumask_test_cpu(cpu_id, buffer->cpumask))
1657 return size;
1658
1659 size = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
1660 size *= BUF_PAGE_SIZE;
1661
1662 /* we need a minimum of two pages */
1663 if (size < BUF_PAGE_SIZE * 2)
1664 size = BUF_PAGE_SIZE * 2;
1665
1666 nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
1667
1668 /*
1669 * Don't succeed if resizing is disabled, as a reader might be
1670 * manipulating the ring buffer and is expecting a sane state while
1671 * this is true.
1672 */
1673 if (atomic_read(&buffer->resize_disabled))
1674 return -EBUSY;
1675
1676 /* prevent another thread from changing buffer sizes */
1677 mutex_lock(&buffer->mutex);
1678
1679 if (cpu_id == RING_BUFFER_ALL_CPUS) {
1680 /* calculate the pages to update */
1681 for_each_buffer_cpu(buffer, cpu) {
1682 cpu_buffer = buffer->buffers[cpu];
1683
1684 cpu_buffer->nr_pages_to_update = nr_pages -
1685 cpu_buffer->nr_pages;
1686 /*
1687 * nothing more to do for removing pages or no update
1688 */
1689 if (cpu_buffer->nr_pages_to_update <= 0)
1690 continue;
1691 /*
1692 * to add pages, make sure all new pages can be
1693 * allocated without receiving ENOMEM
1694 */
1695 INIT_LIST_HEAD(&cpu_buffer->new_pages);
1696 if (__rb_allocate_pages(cpu_buffer->nr_pages_to_update,
1697 &cpu_buffer->new_pages, cpu)) {
1698 /* not enough memory for new pages */
1699 err = -ENOMEM;
1700 goto out_err;
1701 }
1702 }
1703
1704 get_online_cpus();
1705 /*
1706 * Fire off all the required work handlers
1707 * We can't schedule on offline CPUs, but it's not necessary
1708 * since we can change their buffer sizes without any race.
1709 */
1710 for_each_buffer_cpu(buffer, cpu) {
1711 cpu_buffer = buffer->buffers[cpu];
1712 if (!cpu_buffer->nr_pages_to_update)
1713 continue;
1714
1715 /* Can't run something on an offline CPU. */
1716 if (!cpu_online(cpu)) {
1717 rb_update_pages(cpu_buffer);
1718 cpu_buffer->nr_pages_to_update = 0;
1719 } else {
1720 schedule_work_on(cpu,
1721 &cpu_buffer->update_pages_work);
1722 }
1723 }
1724
1725 /* wait for all the updates to complete */
1726 for_each_buffer_cpu(buffer, cpu) {
1727 cpu_buffer = buffer->buffers[cpu];
1728 if (!cpu_buffer->nr_pages_to_update)
1729 continue;
1730
1731 if (cpu_online(cpu))
1732 wait_for_completion(&cpu_buffer->update_done);
1733 cpu_buffer->nr_pages_to_update = 0;
1734 }
1735
1736 put_online_cpus();
1737 } else {
1738 /* Make sure this CPU has been intitialized */
1739 if (!cpumask_test_cpu(cpu_id, buffer->cpumask))
1740 goto out;
1741
1742 cpu_buffer = buffer->buffers[cpu_id];
1743
1744 if (nr_pages == cpu_buffer->nr_pages)
1745 goto out;
1746
1747 cpu_buffer->nr_pages_to_update = nr_pages -
1748 cpu_buffer->nr_pages;
1749
1750 INIT_LIST_HEAD(&cpu_buffer->new_pages);
1751 if (cpu_buffer->nr_pages_to_update > 0 &&
1752 __rb_allocate_pages(cpu_buffer->nr_pages_to_update,
1753 &cpu_buffer->new_pages, cpu_id)) {
1754 err = -ENOMEM;
1755 goto out_err;
1756 }
1757
1758 get_online_cpus();
1759
1760 /* Can't run something on an offline CPU. */
1761 if (!cpu_online(cpu_id))
1762 rb_update_pages(cpu_buffer);
1763 else {
1764 schedule_work_on(cpu_id,
1765 &cpu_buffer->update_pages_work);
1766 wait_for_completion(&cpu_buffer->update_done);
1767 }
1768
1769 cpu_buffer->nr_pages_to_update = 0;
1770 put_online_cpus();
1771 }
1772
1773 out:
1774 /*
1775 * The ring buffer resize can happen with the ring buffer
1776 * enabled, so that the update disturbs the tracing as little
1777 * as possible. But if the buffer is disabled, we do not need
1778 * to worry about that, and we can take the time to verify
1779 * that the buffer is not corrupt.
1780 */
1781 if (atomic_read(&buffer->record_disabled)) {
1782 atomic_inc(&buffer->record_disabled);
1783 /*
1784 * Even though the buffer was disabled, we must make sure
1785 * that it is truly disabled before calling rb_check_pages.
1786 * There could have been a race between checking
1787 * record_disable and incrementing it.
1788 */
1789 synchronize_sched();
1790 for_each_buffer_cpu(buffer, cpu) {
1791 cpu_buffer = buffer->buffers[cpu];
1792 rb_check_pages(cpu_buffer);
1793 }
1794 atomic_dec(&buffer->record_disabled);
1795 }
1796
1797 mutex_unlock(&buffer->mutex);
1798 return size;
1799
1800 out_err:
1801 for_each_buffer_cpu(buffer, cpu) {
1802 struct buffer_page *bpage, *tmp;
1803
1804 cpu_buffer = buffer->buffers[cpu];
1805 cpu_buffer->nr_pages_to_update = 0;
1806
1807 if (list_empty(&cpu_buffer->new_pages))
1808 continue;
1809
1810 list_for_each_entry_safe(bpage, tmp, &cpu_buffer->new_pages,
1811 list) {
1812 list_del_init(&bpage->list);
1813 free_buffer_page(bpage);
1814 }
1815 }
1816 mutex_unlock(&buffer->mutex);
1817 return err;
1818}
1819EXPORT_SYMBOL_GPL(ring_buffer_resize);
1820
1821void ring_buffer_change_overwrite(struct ring_buffer *buffer, int val)
1822{
1823 mutex_lock(&buffer->mutex);
1824 if (val)
1825 buffer->flags |= RB_FL_OVERWRITE;
1826 else
1827 buffer->flags &= ~RB_FL_OVERWRITE;
1828 mutex_unlock(&buffer->mutex);
1829}
1830EXPORT_SYMBOL_GPL(ring_buffer_change_overwrite);
1831
1832static inline void *
1833__rb_data_page_index(struct buffer_data_page *bpage, unsigned index)
1834{
1835 return bpage->data + index;
1836}
1837
1838static inline void *__rb_page_index(struct buffer_page *bpage, unsigned index)
1839{
1840 return bpage->page->data + index;
1841}
1842
1843static inline struct ring_buffer_event *
1844rb_reader_event(struct ring_buffer_per_cpu *cpu_buffer)
1845{
1846 return __rb_page_index(cpu_buffer->reader_page,
1847 cpu_buffer->reader_page->read);
1848}
1849
1850static inline struct ring_buffer_event *
1851rb_iter_head_event(struct ring_buffer_iter *iter)
1852{
1853 return __rb_page_index(iter->head_page, iter->head);
1854}
1855
1856static inline unsigned rb_page_commit(struct buffer_page *bpage)
1857{
1858 return local_read(&bpage->page->commit);
1859}
1860
1861/* Size is determined by what has been committed */
1862static inline unsigned rb_page_size(struct buffer_page *bpage)
1863{
1864 return rb_page_commit(bpage);
1865}
1866
1867static inline unsigned
1868rb_commit_index(struct ring_buffer_per_cpu *cpu_buffer)
1869{
1870 return rb_page_commit(cpu_buffer->commit_page);
1871}
1872
1873static inline unsigned
1874rb_event_index(struct ring_buffer_event *event)
1875{
1876 unsigned long addr = (unsigned long)event;
1877
1878 return (addr & ~PAGE_MASK) - BUF_PAGE_HDR_SIZE;
1879}
1880
1881static void rb_inc_iter(struct ring_buffer_iter *iter)
1882{
1883 struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
1884
1885 /*
1886 * The iterator could be on the reader page (it starts there).
1887 * But the head could have moved, since the reader was
1888 * found. Check for this case and assign the iterator
1889 * to the head page instead of next.
1890 */
1891 if (iter->head_page == cpu_buffer->reader_page)
1892 iter->head_page = rb_set_head_page(cpu_buffer);
1893 else
1894 rb_inc_page(cpu_buffer, &iter->head_page);
1895
1896 iter->read_stamp = iter->head_page->page->time_stamp;
1897 iter->head = 0;
1898}
1899
1900/*
1901 * rb_handle_head_page - writer hit the head page
1902 *
1903 * Returns: +1 to retry page
1904 * 0 to continue
1905 * -1 on error
1906 */
1907static int
1908rb_handle_head_page(struct ring_buffer_per_cpu *cpu_buffer,
1909 struct buffer_page *tail_page,
1910 struct buffer_page *next_page)
1911{
1912 struct buffer_page *new_head;
1913 int entries;
1914 int type;
1915 int ret;
1916
1917 entries = rb_page_entries(next_page);
1918
1919 /*
1920 * The hard part is here. We need to move the head
1921 * forward, and protect against both readers on
1922 * other CPUs and writers coming in via interrupts.
1923 */
1924 type = rb_head_page_set_update(cpu_buffer, next_page, tail_page,
1925 RB_PAGE_HEAD);
1926
1927 /*
1928 * type can be one of four:
1929 * NORMAL - an interrupt already moved it for us
1930 * HEAD - we are the first to get here.
1931 * UPDATE - we are the interrupt interrupting
1932 * a current move.
1933 * MOVED - a reader on another CPU moved the next
1934 * pointer to its reader page. Give up
1935 * and try again.
1936 */
1937
1938 switch (type) {
1939 case RB_PAGE_HEAD:
1940 /*
1941 * We changed the head to UPDATE, thus
1942 * it is our responsibility to update
1943 * the counters.
1944 */
1945 local_add(entries, &cpu_buffer->overrun);
1946 local_sub(BUF_PAGE_SIZE, &cpu_buffer->entries_bytes);
1947
1948 /*
1949 * The entries will be zeroed out when we move the
1950 * tail page.
1951 */
1952
1953 /* still more to do */
1954 break;
1955
1956 case RB_PAGE_UPDATE:
1957 /*
1958 * This is an interrupt that interrupt the
1959 * previous update. Still more to do.
1960 */
1961 break;
1962 case RB_PAGE_NORMAL:
1963 /*
1964 * An interrupt came in before the update
1965 * and processed this for us.
1966 * Nothing left to do.
1967 */
1968 return 1;
1969 case RB_PAGE_MOVED:
1970 /*
1971 * The reader is on another CPU and just did
1972 * a swap with our next_page.
1973 * Try again.
1974 */
1975 return 1;
1976 default:
1977 RB_WARN_ON(cpu_buffer, 1); /* WTF??? */
1978 return -1;
1979 }
1980
1981 /*
1982 * Now that we are here, the old head pointer is
1983 * set to UPDATE. This will keep the reader from
1984 * swapping the head page with the reader page.
1985 * The reader (on another CPU) will spin till
1986 * we are finished.
1987 *
1988 * We just need to protect against interrupts
1989 * doing the job. We will set the next pointer
1990 * to HEAD. After that, we set the old pointer
1991 * to NORMAL, but only if it was HEAD before.
1992 * otherwise we are an interrupt, and only
1993 * want the outer most commit to reset it.
1994 */
1995 new_head = next_page;
1996 rb_inc_page(cpu_buffer, &new_head);
1997
1998 ret = rb_head_page_set_head(cpu_buffer, new_head, next_page,
1999 RB_PAGE_NORMAL);
2000
2001 /*
2002 * Valid returns are:
2003 * HEAD - an interrupt came in and already set it.
2004 * NORMAL - One of two things:
2005 * 1) We really set it.
2006 * 2) A bunch of interrupts came in and moved
2007 * the page forward again.
2008 */
2009 switch (ret) {
2010 case RB_PAGE_HEAD:
2011 case RB_PAGE_NORMAL:
2012 /* OK */
2013 break;
2014 default:
2015 RB_WARN_ON(cpu_buffer, 1);
2016 return -1;
2017 }
2018
2019 /*
2020 * It is possible that an interrupt came in,
2021 * set the head up, then more interrupts came in
2022 * and moved it again. When we get back here,
2023 * the page would have been set to NORMAL but we
2024 * just set it back to HEAD.
2025 *
2026 * How do you detect this? Well, if that happened
2027 * the tail page would have moved.
2028 */
2029 if (ret == RB_PAGE_NORMAL) {
2030 struct buffer_page *buffer_tail_page;
2031
2032 buffer_tail_page = READ_ONCE(cpu_buffer->tail_page);
2033 /*
2034 * If the tail had moved passed next, then we need
2035 * to reset the pointer.
2036 */
2037 if (buffer_tail_page != tail_page &&
2038 buffer_tail_page != next_page)
2039 rb_head_page_set_normal(cpu_buffer, new_head,
2040 next_page,
2041 RB_PAGE_HEAD);
2042 }
2043
2044 /*
2045 * If this was the outer most commit (the one that
2046 * changed the original pointer from HEAD to UPDATE),
2047 * then it is up to us to reset it to NORMAL.
2048 */
2049 if (type == RB_PAGE_HEAD) {
2050 ret = rb_head_page_set_normal(cpu_buffer, next_page,
2051 tail_page,
2052 RB_PAGE_UPDATE);
2053 if (RB_WARN_ON(cpu_buffer,
2054 ret != RB_PAGE_UPDATE))
2055 return -1;
2056 }
2057
2058 return 0;
2059}
2060
2061static inline void
2062rb_reset_tail(struct ring_buffer_per_cpu *cpu_buffer,
2063 unsigned long tail, struct rb_event_info *info)
2064{
2065 struct buffer_page *tail_page = info->tail_page;
2066 struct ring_buffer_event *event;
2067 unsigned long length = info->length;
2068
2069 /*
2070 * Only the event that crossed the page boundary
2071 * must fill the old tail_page with padding.
2072 */
2073 if (tail >= BUF_PAGE_SIZE) {
2074 /*
2075 * If the page was filled, then we still need
2076 * to update the real_end. Reset it to zero
2077 * and the reader will ignore it.
2078 */
2079 if (tail == BUF_PAGE_SIZE)
2080 tail_page->real_end = 0;
2081
2082 local_sub(length, &tail_page->write);
2083 return;
2084 }
2085
2086 event = __rb_page_index(tail_page, tail);
2087 kmemcheck_annotate_bitfield(event, bitfield);
2088
2089 /* account for padding bytes */
2090 local_add(BUF_PAGE_SIZE - tail, &cpu_buffer->entries_bytes);
2091
2092 /*
2093 * Save the original length to the meta data.
2094 * This will be used by the reader to add lost event
2095 * counter.
2096 */
2097 tail_page->real_end = tail;
2098
2099 /*
2100 * If this event is bigger than the minimum size, then
2101 * we need to be careful that we don't subtract the
2102 * write counter enough to allow another writer to slip
2103 * in on this page.
2104 * We put in a discarded commit instead, to make sure
2105 * that this space is not used again.
2106 *
2107 * If we are less than the minimum size, we don't need to
2108 * worry about it.
2109 */
2110 if (tail > (BUF_PAGE_SIZE - RB_EVNT_MIN_SIZE)) {
2111 /* No room for any events */
2112
2113 /* Mark the rest of the page with padding */
2114 rb_event_set_padding(event);
2115
2116 /* Set the write back to the previous setting */
2117 local_sub(length, &tail_page->write);
2118 return;
2119 }
2120
2121 /* Put in a discarded event */
2122 event->array[0] = (BUF_PAGE_SIZE - tail) - RB_EVNT_HDR_SIZE;
2123 event->type_len = RINGBUF_TYPE_PADDING;
2124 /* time delta must be non zero */
2125 event->time_delta = 1;
2126
2127 /* Set write to end of buffer */
2128 length = (tail + length) - BUF_PAGE_SIZE;
2129 local_sub(length, &tail_page->write);
2130}
2131
2132static inline void rb_end_commit(struct ring_buffer_per_cpu *cpu_buffer);
2133
2134/*
2135 * This is the slow path, force gcc not to inline it.
2136 */
2137static noinline struct ring_buffer_event *
2138rb_move_tail(struct ring_buffer_per_cpu *cpu_buffer,
2139 unsigned long tail, struct rb_event_info *info)
2140{
2141 struct buffer_page *tail_page = info->tail_page;
2142 struct buffer_page *commit_page = cpu_buffer->commit_page;
2143 struct ring_buffer *buffer = cpu_buffer->buffer;
2144 struct buffer_page *next_page;
2145 int ret;
2146
2147 next_page = tail_page;
2148
2149 rb_inc_page(cpu_buffer, &next_page);
2150
2151 /*
2152 * If for some reason, we had an interrupt storm that made
2153 * it all the way around the buffer, bail, and warn
2154 * about it.
2155 */
2156 if (unlikely(next_page == commit_page)) {
2157 local_inc(&cpu_buffer->commit_overrun);
2158 goto out_reset;
2159 }
2160
2161 /*
2162 * This is where the fun begins!
2163 *
2164 * We are fighting against races between a reader that
2165 * could be on another CPU trying to swap its reader
2166 * page with the buffer head.
2167 *
2168 * We are also fighting against interrupts coming in and
2169 * moving the head or tail on us as well.
2170 *
2171 * If the next page is the head page then we have filled
2172 * the buffer, unless the commit page is still on the
2173 * reader page.
2174 */
2175 if (rb_is_head_page(cpu_buffer, next_page, &tail_page->list)) {
2176
2177 /*
2178 * If the commit is not on the reader page, then
2179 * move the header page.
2180 */
2181 if (!rb_is_reader_page(cpu_buffer->commit_page)) {
2182 /*
2183 * If we are not in overwrite mode,
2184 * this is easy, just stop here.
2185 */
2186 if (!(buffer->flags & RB_FL_OVERWRITE)) {
2187 local_inc(&cpu_buffer->dropped_events);
2188 goto out_reset;
2189 }
2190
2191 ret = rb_handle_head_page(cpu_buffer,
2192 tail_page,
2193 next_page);
2194 if (ret < 0)
2195 goto out_reset;
2196 if (ret)
2197 goto out_again;
2198 } else {
2199 /*
2200 * We need to be careful here too. The
2201 * commit page could still be on the reader
2202 * page. We could have a small buffer, and
2203 * have filled up the buffer with events
2204 * from interrupts and such, and wrapped.
2205 *
2206 * Note, if the tail page is also the on the
2207 * reader_page, we let it move out.
2208 */
2209 if (unlikely((cpu_buffer->commit_page !=
2210 cpu_buffer->tail_page) &&
2211 (cpu_buffer->commit_page ==
2212 cpu_buffer->reader_page))) {
2213 local_inc(&cpu_buffer->commit_overrun);
2214 goto out_reset;
2215 }
2216 }
2217 }
2218
2219 rb_tail_page_update(cpu_buffer, tail_page, next_page);
2220
2221 out_again:
2222
2223 rb_reset_tail(cpu_buffer, tail, info);
2224
2225 /* Commit what we have for now. */
2226 rb_end_commit(cpu_buffer);
2227 /* rb_end_commit() decs committing */
2228 local_inc(&cpu_buffer->committing);
2229
2230 /* fail and let the caller try again */
2231 return ERR_PTR(-EAGAIN);
2232
2233 out_reset:
2234 /* reset write */
2235 rb_reset_tail(cpu_buffer, tail, info);
2236
2237 return NULL;
2238}
2239
2240/* Slow path, do not inline */
2241static noinline struct ring_buffer_event *
2242rb_add_time_stamp(struct ring_buffer_event *event, u64 delta)
2243{
2244 event->type_len = RINGBUF_TYPE_TIME_EXTEND;
2245
2246 /* Not the first event on the page? */
2247 if (rb_event_index(event)) {
2248 event->time_delta = delta & TS_MASK;
2249 event->array[0] = delta >> TS_SHIFT;
2250 } else {
2251 /* nope, just zero it */
2252 event->time_delta = 0;
2253 event->array[0] = 0;
2254 }
2255
2256 return skip_time_extend(event);
2257}
2258
2259static inline bool rb_event_is_commit(struct ring_buffer_per_cpu *cpu_buffer,
2260 struct ring_buffer_event *event);
2261
2262/**
2263 * rb_update_event - update event type and data
2264 * @event: the event to update
2265 * @type: the type of event
2266 * @length: the size of the event field in the ring buffer
2267 *
2268 * Update the type and data fields of the event. The length
2269 * is the actual size that is written to the ring buffer,
2270 * and with this, we can determine what to place into the
2271 * data field.
2272 */
2273static void
2274rb_update_event(struct ring_buffer_per_cpu *cpu_buffer,
2275 struct ring_buffer_event *event,
2276 struct rb_event_info *info)
2277{
2278 unsigned length = info->length;
2279 u64 delta = info->delta;
2280
2281 /* Only a commit updates the timestamp */
2282 if (unlikely(!rb_event_is_commit(cpu_buffer, event)))
2283 delta = 0;
2284
2285 /*
2286 * If we need to add a timestamp, then we
2287 * add it to the start of the resevered space.
2288 */
2289 if (unlikely(info->add_timestamp)) {
2290 event = rb_add_time_stamp(event, delta);
2291 length -= RB_LEN_TIME_EXTEND;
2292 delta = 0;
2293 }
2294
2295 event->time_delta = delta;
2296 length -= RB_EVNT_HDR_SIZE;
2297 if (length > RB_MAX_SMALL_DATA || RB_FORCE_8BYTE_ALIGNMENT) {
2298 event->type_len = 0;
2299 event->array[0] = length;
2300 } else
2301 event->type_len = DIV_ROUND_UP(length, RB_ALIGNMENT);
2302}
2303
2304static unsigned rb_calculate_event_length(unsigned length)
2305{
2306 struct ring_buffer_event event; /* Used only for sizeof array */
2307
2308 /* zero length can cause confusions */
2309 if (!length)
2310 length++;
2311
2312 if (length > RB_MAX_SMALL_DATA || RB_FORCE_8BYTE_ALIGNMENT)
2313 length += sizeof(event.array[0]);
2314
2315 length += RB_EVNT_HDR_SIZE;
2316 length = ALIGN(length, RB_ARCH_ALIGNMENT);
2317
2318 /*
2319 * In case the time delta is larger than the 27 bits for it
2320 * in the header, we need to add a timestamp. If another
2321 * event comes in when trying to discard this one to increase
2322 * the length, then the timestamp will be added in the allocated
2323 * space of this event. If length is bigger than the size needed
2324 * for the TIME_EXTEND, then padding has to be used. The events
2325 * length must be either RB_LEN_TIME_EXTEND, or greater than or equal
2326 * to RB_LEN_TIME_EXTEND + 8, as 8 is the minimum size for padding.
2327 * As length is a multiple of 4, we only need to worry if it
2328 * is 12 (RB_LEN_TIME_EXTEND + 4).
2329 */
2330 if (length == RB_LEN_TIME_EXTEND + RB_ALIGNMENT)
2331 length += RB_ALIGNMENT;
2332
2333 return length;
2334}
2335
2336#ifndef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
2337static inline bool sched_clock_stable(void)
2338{
2339 return true;
2340}
2341#endif
2342
2343static inline int
2344rb_try_to_discard(struct ring_buffer_per_cpu *cpu_buffer,
2345 struct ring_buffer_event *event)
2346{
2347 unsigned long new_index, old_index;
2348 struct buffer_page *bpage;
2349 unsigned long index;
2350 unsigned long addr;
2351
2352 new_index = rb_event_index(event);
2353 old_index = new_index + rb_event_ts_length(event);
2354 addr = (unsigned long)event;
2355 addr &= PAGE_MASK;
2356
2357 bpage = READ_ONCE(cpu_buffer->tail_page);
2358
2359 if (bpage->page == (void *)addr && rb_page_write(bpage) == old_index) {
2360 unsigned long write_mask =
2361 local_read(&bpage->write) & ~RB_WRITE_MASK;
2362 unsigned long event_length = rb_event_length(event);
2363 /*
2364 * This is on the tail page. It is possible that
2365 * a write could come in and move the tail page
2366 * and write to the next page. That is fine
2367 * because we just shorten what is on this page.
2368 */
2369 old_index += write_mask;
2370 new_index += write_mask;
2371 index = local_cmpxchg(&bpage->write, old_index, new_index);
2372 if (index == old_index) {
2373 /* update counters */
2374 local_sub(event_length, &cpu_buffer->entries_bytes);
2375 return 1;
2376 }
2377 }
2378
2379 /* could not discard */
2380 return 0;
2381}
2382
2383static void rb_start_commit(struct ring_buffer_per_cpu *cpu_buffer)
2384{
2385 local_inc(&cpu_buffer->committing);
2386 local_inc(&cpu_buffer->commits);
2387}
2388
2389static void
2390rb_set_commit_to_write(struct ring_buffer_per_cpu *cpu_buffer)
2391{
2392 unsigned long max_count;
2393
2394 /*
2395 * We only race with interrupts and NMIs on this CPU.
2396 * If we own the commit event, then we can commit
2397 * all others that interrupted us, since the interruptions
2398 * are in stack format (they finish before they come
2399 * back to us). This allows us to do a simple loop to
2400 * assign the commit to the tail.
2401 */
2402 again:
2403 max_count = cpu_buffer->nr_pages * 100;
2404
2405 while (cpu_buffer->commit_page != READ_ONCE(cpu_buffer->tail_page)) {
2406 if (RB_WARN_ON(cpu_buffer, !(--max_count)))
2407 return;
2408 if (RB_WARN_ON(cpu_buffer,
2409 rb_is_reader_page(cpu_buffer->tail_page)))
2410 return;
2411 local_set(&cpu_buffer->commit_page->page->commit,
2412 rb_page_write(cpu_buffer->commit_page));
2413 rb_inc_page(cpu_buffer, &cpu_buffer->commit_page);
2414 /* Only update the write stamp if the page has an event */
2415 if (rb_page_write(cpu_buffer->commit_page))
2416 cpu_buffer->write_stamp =
2417 cpu_buffer->commit_page->page->time_stamp;
2418 /* add barrier to keep gcc from optimizing too much */
2419 barrier();
2420 }
2421 while (rb_commit_index(cpu_buffer) !=
2422 rb_page_write(cpu_buffer->commit_page)) {
2423
2424 local_set(&cpu_buffer->commit_page->page->commit,
2425 rb_page_write(cpu_buffer->commit_page));
2426 RB_WARN_ON(cpu_buffer,
2427 local_read(&cpu_buffer->commit_page->page->commit) &
2428 ~RB_WRITE_MASK);
2429 barrier();
2430 }
2431
2432 /* again, keep gcc from optimizing */
2433 barrier();
2434
2435 /*
2436 * If an interrupt came in just after the first while loop
2437 * and pushed the tail page forward, we will be left with
2438 * a dangling commit that will never go forward.
2439 */
2440 if (unlikely(cpu_buffer->commit_page != READ_ONCE(cpu_buffer->tail_page)))
2441 goto again;
2442}
2443
2444static inline void rb_end_commit(struct ring_buffer_per_cpu *cpu_buffer)
2445{
2446 unsigned long commits;
2447
2448 if (RB_WARN_ON(cpu_buffer,
2449 !local_read(&cpu_buffer->committing)))
2450 return;
2451
2452 again:
2453 commits = local_read(&cpu_buffer->commits);
2454 /* synchronize with interrupts */
2455 barrier();
2456 if (local_read(&cpu_buffer->committing) == 1)
2457 rb_set_commit_to_write(cpu_buffer);
2458
2459 local_dec(&cpu_buffer->committing);
2460
2461 /* synchronize with interrupts */
2462 barrier();
2463
2464 /*
2465 * Need to account for interrupts coming in between the
2466 * updating of the commit page and the clearing of the
2467 * committing counter.
2468 */
2469 if (unlikely(local_read(&cpu_buffer->commits) != commits) &&
2470 !local_read(&cpu_buffer->committing)) {
2471 local_inc(&cpu_buffer->committing);
2472 goto again;
2473 }
2474}
2475
2476static inline void rb_event_discard(struct ring_buffer_event *event)
2477{
2478 if (event->type_len == RINGBUF_TYPE_TIME_EXTEND)
2479 event = skip_time_extend(event);
2480
2481 /* array[0] holds the actual length for the discarded event */
2482 event->array[0] = rb_event_data_length(event) - RB_EVNT_HDR_SIZE;
2483 event->type_len = RINGBUF_TYPE_PADDING;
2484 /* time delta must be non zero */
2485 if (!event->time_delta)
2486 event->time_delta = 1;
2487}
2488
2489static inline bool
2490rb_event_is_commit(struct ring_buffer_per_cpu *cpu_buffer,
2491 struct ring_buffer_event *event)
2492{
2493 unsigned long addr = (unsigned long)event;
2494 unsigned long index;
2495
2496 index = rb_event_index(event);
2497 addr &= PAGE_MASK;
2498
2499 return cpu_buffer->commit_page->page == (void *)addr &&
2500 rb_commit_index(cpu_buffer) == index;
2501}
2502
2503static void
2504rb_update_write_stamp(struct ring_buffer_per_cpu *cpu_buffer,
2505 struct ring_buffer_event *event)
2506{
2507 u64 delta;
2508
2509 /*
2510 * The event first in the commit queue updates the
2511 * time stamp.
2512 */
2513 if (rb_event_is_commit(cpu_buffer, event)) {
2514 /*
2515 * A commit event that is first on a page
2516 * updates the write timestamp with the page stamp
2517 */
2518 if (!rb_event_index(event))
2519 cpu_buffer->write_stamp =
2520 cpu_buffer->commit_page->page->time_stamp;
2521 else if (event->type_len == RINGBUF_TYPE_TIME_EXTEND) {
2522 delta = event->array[0];
2523 delta <<= TS_SHIFT;
2524 delta += event->time_delta;
2525 cpu_buffer->write_stamp += delta;
2526 } else
2527 cpu_buffer->write_stamp += event->time_delta;
2528 }
2529}
2530
2531static void rb_commit(struct ring_buffer_per_cpu *cpu_buffer,
2532 struct ring_buffer_event *event)
2533{
2534 local_inc(&cpu_buffer->entries);
2535 rb_update_write_stamp(cpu_buffer, event);
2536 rb_end_commit(cpu_buffer);
2537}
2538
2539static __always_inline void
2540rb_wakeups(struct ring_buffer *buffer, struct ring_buffer_per_cpu *cpu_buffer)
2541{
2542 bool pagebusy;
2543
2544 if (buffer->irq_work.waiters_pending) {
2545 buffer->irq_work.waiters_pending = false;
2546 /* irq_work_queue() supplies it's own memory barriers */
2547 irq_work_queue(&buffer->irq_work.work);
2548 }
2549
2550 if (cpu_buffer->irq_work.waiters_pending) {
2551 cpu_buffer->irq_work.waiters_pending = false;
2552 /* irq_work_queue() supplies it's own memory barriers */
2553 irq_work_queue(&cpu_buffer->irq_work.work);
2554 }
2555
2556 pagebusy = cpu_buffer->reader_page == cpu_buffer->commit_page;
2557
2558 if (!pagebusy && cpu_buffer->irq_work.full_waiters_pending) {
2559 cpu_buffer->irq_work.wakeup_full = true;
2560 cpu_buffer->irq_work.full_waiters_pending = false;
2561 /* irq_work_queue() supplies it's own memory barriers */
2562 irq_work_queue(&cpu_buffer->irq_work.work);
2563 }
2564}
2565
2566/*
2567 * The lock and unlock are done within a preempt disable section.
2568 * The current_context per_cpu variable can only be modified
2569 * by the current task between lock and unlock. But it can
2570 * be modified more than once via an interrupt. To pass this
2571 * information from the lock to the unlock without having to
2572 * access the 'in_interrupt()' functions again (which do show
2573 * a bit of overhead in something as critical as function tracing,
2574 * we use a bitmask trick.
2575 *
2576 * bit 0 = NMI context
2577 * bit 1 = IRQ context
2578 * bit 2 = SoftIRQ context
2579 * bit 3 = normal context.
2580 *
2581 * This works because this is the order of contexts that can
2582 * preempt other contexts. A SoftIRQ never preempts an IRQ
2583 * context.
2584 *
2585 * When the context is determined, the corresponding bit is
2586 * checked and set (if it was set, then a recursion of that context
2587 * happened).
2588 *
2589 * On unlock, we need to clear this bit. To do so, just subtract
2590 * 1 from the current_context and AND it to itself.
2591 *
2592 * (binary)
2593 * 101 - 1 = 100
2594 * 101 & 100 = 100 (clearing bit zero)
2595 *
2596 * 1010 - 1 = 1001
2597 * 1010 & 1001 = 1000 (clearing bit 1)
2598 *
2599 * The least significant bit can be cleared this way, and it
2600 * just so happens that it is the same bit corresponding to
2601 * the current context.
2602 */
2603
2604static __always_inline int
2605trace_recursive_lock(struct ring_buffer_per_cpu *cpu_buffer)
2606{
2607 unsigned int val = cpu_buffer->current_context;
2608 int bit;
2609
2610 if (in_interrupt()) {
2611 if (in_nmi())
2612 bit = RB_CTX_NMI;
2613 else if (in_irq())
2614 bit = RB_CTX_IRQ;
2615 else
2616 bit = RB_CTX_SOFTIRQ;
2617 } else
2618 bit = RB_CTX_NORMAL;
2619
2620 if (unlikely(val & (1 << bit)))
2621 return 1;
2622
2623 val |= (1 << bit);
2624 cpu_buffer->current_context = val;
2625
2626 return 0;
2627}
2628
2629static __always_inline void
2630trace_recursive_unlock(struct ring_buffer_per_cpu *cpu_buffer)
2631{
2632 cpu_buffer->current_context &= cpu_buffer->current_context - 1;
2633}
2634
2635/**
2636 * ring_buffer_unlock_commit - commit a reserved
2637 * @buffer: The buffer to commit to
2638 * @event: The event pointer to commit.
2639 *
2640 * This commits the data to the ring buffer, and releases any locks held.
2641 *
2642 * Must be paired with ring_buffer_lock_reserve.
2643 */
2644int ring_buffer_unlock_commit(struct ring_buffer *buffer,
2645 struct ring_buffer_event *event)
2646{
2647 struct ring_buffer_per_cpu *cpu_buffer;
2648 int cpu = raw_smp_processor_id();
2649
2650 cpu_buffer = buffer->buffers[cpu];
2651
2652 rb_commit(cpu_buffer, event);
2653
2654 rb_wakeups(buffer, cpu_buffer);
2655
2656 trace_recursive_unlock(cpu_buffer);
2657
2658 preempt_enable_notrace();
2659
2660 return 0;
2661}
2662EXPORT_SYMBOL_GPL(ring_buffer_unlock_commit);
2663
2664static noinline void
2665rb_handle_timestamp(struct ring_buffer_per_cpu *cpu_buffer,
2666 struct rb_event_info *info)
2667{
2668 WARN_ONCE(info->delta > (1ULL << 59),
2669 KERN_WARNING "Delta way too big! %llu ts=%llu write stamp = %llu\n%s",
2670 (unsigned long long)info->delta,
2671 (unsigned long long)info->ts,
2672 (unsigned long long)cpu_buffer->write_stamp,
2673 sched_clock_stable() ? "" :
2674 "If you just came from a suspend/resume,\n"
2675 "please switch to the trace global clock:\n"
2676 " echo global > /sys/kernel/debug/tracing/trace_clock\n");
2677 info->add_timestamp = 1;
2678}
2679
2680static struct ring_buffer_event *
2681__rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
2682 struct rb_event_info *info)
2683{
2684 struct ring_buffer_event *event;
2685 struct buffer_page *tail_page;
2686 unsigned long tail, write;
2687
2688 /*
2689 * If the time delta since the last event is too big to
2690 * hold in the time field of the event, then we append a
2691 * TIME EXTEND event ahead of the data event.
2692 */
2693 if (unlikely(info->add_timestamp))
2694 info->length += RB_LEN_TIME_EXTEND;
2695
2696 /* Don't let the compiler play games with cpu_buffer->tail_page */
2697 tail_page = info->tail_page = READ_ONCE(cpu_buffer->tail_page);
2698 write = local_add_return(info->length, &tail_page->write);
2699
2700 /* set write to only the index of the write */
2701 write &= RB_WRITE_MASK;
2702 tail = write - info->length;
2703
2704 /*
2705 * If this is the first commit on the page, then it has the same
2706 * timestamp as the page itself.
2707 */
2708 if (!tail)
2709 info->delta = 0;
2710
2711 /* See if we shot pass the end of this buffer page */
2712 if (unlikely(write > BUF_PAGE_SIZE))
2713 return rb_move_tail(cpu_buffer, tail, info);
2714
2715 /* We reserved something on the buffer */
2716
2717 event = __rb_page_index(tail_page, tail);
2718 kmemcheck_annotate_bitfield(event, bitfield);
2719 rb_update_event(cpu_buffer, event, info);
2720
2721 local_inc(&tail_page->entries);
2722
2723 /*
2724 * If this is the first commit on the page, then update
2725 * its timestamp.
2726 */
2727 if (!tail)
2728 tail_page->page->time_stamp = info->ts;
2729
2730 /* account for these added bytes */
2731 local_add(info->length, &cpu_buffer->entries_bytes);
2732
2733 return event;
2734}
2735
2736static struct ring_buffer_event *
2737rb_reserve_next_event(struct ring_buffer *buffer,
2738 struct ring_buffer_per_cpu *cpu_buffer,
2739 unsigned long length)
2740{
2741 struct ring_buffer_event *event;
2742 struct rb_event_info info;
2743 int nr_loops = 0;
2744 u64 diff;
2745
2746 rb_start_commit(cpu_buffer);
2747
2748#ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
2749 /*
2750 * Due to the ability to swap a cpu buffer from a buffer
2751 * it is possible it was swapped before we committed.
2752 * (committing stops a swap). We check for it here and
2753 * if it happened, we have to fail the write.
2754 */
2755 barrier();
2756 if (unlikely(ACCESS_ONCE(cpu_buffer->buffer) != buffer)) {
2757 local_dec(&cpu_buffer->committing);
2758 local_dec(&cpu_buffer->commits);
2759 return NULL;
2760 }
2761#endif
2762
2763 info.length = rb_calculate_event_length(length);
2764 again:
2765 info.add_timestamp = 0;
2766 info.delta = 0;
2767
2768 /*
2769 * We allow for interrupts to reenter here and do a trace.
2770 * If one does, it will cause this original code to loop
2771 * back here. Even with heavy interrupts happening, this
2772 * should only happen a few times in a row. If this happens
2773 * 1000 times in a row, there must be either an interrupt
2774 * storm or we have something buggy.
2775 * Bail!
2776 */
2777 if (RB_WARN_ON(cpu_buffer, ++nr_loops > 1000))
2778 goto out_fail;
2779
2780 info.ts = rb_time_stamp(cpu_buffer->buffer);
2781 diff = info.ts - cpu_buffer->write_stamp;
2782
2783 /* make sure this diff is calculated here */
2784 barrier();
2785
2786 /* Did the write stamp get updated already? */
2787 if (likely(info.ts >= cpu_buffer->write_stamp)) {
2788 info.delta = diff;
2789 if (unlikely(test_time_stamp(info.delta)))
2790 rb_handle_timestamp(cpu_buffer, &info);
2791 }
2792
2793 event = __rb_reserve_next(cpu_buffer, &info);
2794
2795 if (unlikely(PTR_ERR(event) == -EAGAIN)) {
2796 if (info.add_timestamp)
2797 info.length -= RB_LEN_TIME_EXTEND;
2798 goto again;
2799 }
2800
2801 if (!event)
2802 goto out_fail;
2803
2804 return event;
2805
2806 out_fail:
2807 rb_end_commit(cpu_buffer);
2808 return NULL;
2809}
2810
2811/**
2812 * ring_buffer_lock_reserve - reserve a part of the buffer
2813 * @buffer: the ring buffer to reserve from
2814 * @length: the length of the data to reserve (excluding event header)
2815 *
2816 * Returns a reseverd event on the ring buffer to copy directly to.
2817 * The user of this interface will need to get the body to write into
2818 * and can use the ring_buffer_event_data() interface.
2819 *
2820 * The length is the length of the data needed, not the event length
2821 * which also includes the event header.
2822 *
2823 * Must be paired with ring_buffer_unlock_commit, unless NULL is returned.
2824 * If NULL is returned, then nothing has been allocated or locked.
2825 */
2826struct ring_buffer_event *
2827ring_buffer_lock_reserve(struct ring_buffer *buffer, unsigned long length)
2828{
2829 struct ring_buffer_per_cpu *cpu_buffer;
2830 struct ring_buffer_event *event;
2831 int cpu;
2832
2833 /* If we are tracing schedule, we don't want to recurse */
2834 preempt_disable_notrace();
2835
2836 if (unlikely(atomic_read(&buffer->record_disabled)))
2837 goto out;
2838
2839 cpu = raw_smp_processor_id();
2840
2841 if (unlikely(!cpumask_test_cpu(cpu, buffer->cpumask)))
2842 goto out;
2843
2844 cpu_buffer = buffer->buffers[cpu];
2845
2846 if (unlikely(atomic_read(&cpu_buffer->record_disabled)))
2847 goto out;
2848
2849 if (unlikely(length > BUF_MAX_DATA_SIZE))
2850 goto out;
2851
2852 if (unlikely(trace_recursive_lock(cpu_buffer)))
2853 goto out;
2854
2855 event = rb_reserve_next_event(buffer, cpu_buffer, length);
2856 if (!event)
2857 goto out_unlock;
2858
2859 return event;
2860
2861 out_unlock:
2862 trace_recursive_unlock(cpu_buffer);
2863 out:
2864 preempt_enable_notrace();
2865 return NULL;
2866}
2867EXPORT_SYMBOL_GPL(ring_buffer_lock_reserve);
2868
2869/*
2870 * Decrement the entries to the page that an event is on.
2871 * The event does not even need to exist, only the pointer
2872 * to the page it is on. This may only be called before the commit
2873 * takes place.
2874 */
2875static inline void
2876rb_decrement_entry(struct ring_buffer_per_cpu *cpu_buffer,
2877 struct ring_buffer_event *event)
2878{
2879 unsigned long addr = (unsigned long)event;
2880 struct buffer_page *bpage = cpu_buffer->commit_page;
2881 struct buffer_page *start;
2882
2883 addr &= PAGE_MASK;
2884
2885 /* Do the likely case first */
2886 if (likely(bpage->page == (void *)addr)) {
2887 local_dec(&bpage->entries);
2888 return;
2889 }
2890
2891 /*
2892 * Because the commit page may be on the reader page we
2893 * start with the next page and check the end loop there.
2894 */
2895 rb_inc_page(cpu_buffer, &bpage);
2896 start = bpage;
2897 do {
2898 if (bpage->page == (void *)addr) {
2899 local_dec(&bpage->entries);
2900 return;
2901 }
2902 rb_inc_page(cpu_buffer, &bpage);
2903 } while (bpage != start);
2904
2905 /* commit not part of this buffer?? */
2906 RB_WARN_ON(cpu_buffer, 1);
2907}
2908
2909/**
2910 * ring_buffer_commit_discard - discard an event that has not been committed
2911 * @buffer: the ring buffer
2912 * @event: non committed event to discard
2913 *
2914 * Sometimes an event that is in the ring buffer needs to be ignored.
2915 * This function lets the user discard an event in the ring buffer
2916 * and then that event will not be read later.
2917 *
2918 * This function only works if it is called before the the item has been
2919 * committed. It will try to free the event from the ring buffer
2920 * if another event has not been added behind it.
2921 *
2922 * If another event has been added behind it, it will set the event
2923 * up as discarded, and perform the commit.
2924 *
2925 * If this function is called, do not call ring_buffer_unlock_commit on
2926 * the event.
2927 */
2928void ring_buffer_discard_commit(struct ring_buffer *buffer,
2929 struct ring_buffer_event *event)
2930{
2931 struct ring_buffer_per_cpu *cpu_buffer;
2932 int cpu;
2933
2934 /* The event is discarded regardless */
2935 rb_event_discard(event);
2936
2937 cpu = smp_processor_id();
2938 cpu_buffer = buffer->buffers[cpu];
2939
2940 /*
2941 * This must only be called if the event has not been
2942 * committed yet. Thus we can assume that preemption
2943 * is still disabled.
2944 */
2945 RB_WARN_ON(buffer, !local_read(&cpu_buffer->committing));
2946
2947 rb_decrement_entry(cpu_buffer, event);
2948 if (rb_try_to_discard(cpu_buffer, event))
2949 goto out;
2950
2951 /*
2952 * The commit is still visible by the reader, so we
2953 * must still update the timestamp.
2954 */
2955 rb_update_write_stamp(cpu_buffer, event);
2956 out:
2957 rb_end_commit(cpu_buffer);
2958
2959 trace_recursive_unlock(cpu_buffer);
2960
2961 preempt_enable_notrace();
2962
2963}
2964EXPORT_SYMBOL_GPL(ring_buffer_discard_commit);
2965
2966/**
2967 * ring_buffer_write - write data to the buffer without reserving
2968 * @buffer: The ring buffer to write to.
2969 * @length: The length of the data being written (excluding the event header)
2970 * @data: The data to write to the buffer.
2971 *
2972 * This is like ring_buffer_lock_reserve and ring_buffer_unlock_commit as
2973 * one function. If you already have the data to write to the buffer, it
2974 * may be easier to simply call this function.
2975 *
2976 * Note, like ring_buffer_lock_reserve, the length is the length of the data
2977 * and not the length of the event which would hold the header.
2978 */
2979int ring_buffer_write(struct ring_buffer *buffer,
2980 unsigned long length,
2981 void *data)
2982{
2983 struct ring_buffer_per_cpu *cpu_buffer;
2984 struct ring_buffer_event *event;
2985 void *body;
2986 int ret = -EBUSY;
2987 int cpu;
2988
2989 preempt_disable_notrace();
2990
2991 if (atomic_read(&buffer->record_disabled))
2992 goto out;
2993
2994 cpu = raw_smp_processor_id();
2995
2996 if (!cpumask_test_cpu(cpu, buffer->cpumask))
2997 goto out;
2998
2999 cpu_buffer = buffer->buffers[cpu];
3000
3001 if (atomic_read(&cpu_buffer->record_disabled))
3002 goto out;
3003
3004 if (length > BUF_MAX_DATA_SIZE)
3005 goto out;
3006
3007 if (unlikely(trace_recursive_lock(cpu_buffer)))
3008 goto out;
3009
3010 event = rb_reserve_next_event(buffer, cpu_buffer, length);
3011 if (!event)
3012 goto out_unlock;
3013
3014 body = rb_event_data(event);
3015
3016 memcpy(body, data, length);
3017
3018 rb_commit(cpu_buffer, event);
3019
3020 rb_wakeups(buffer, cpu_buffer);
3021
3022 ret = 0;
3023
3024 out_unlock:
3025 trace_recursive_unlock(cpu_buffer);
3026
3027 out:
3028 preempt_enable_notrace();
3029
3030 return ret;
3031}
3032EXPORT_SYMBOL_GPL(ring_buffer_write);
3033
3034static bool rb_per_cpu_empty(struct ring_buffer_per_cpu *cpu_buffer)
3035{
3036 struct buffer_page *reader = cpu_buffer->reader_page;
3037 struct buffer_page *head = rb_set_head_page(cpu_buffer);
3038 struct buffer_page *commit = cpu_buffer->commit_page;
3039
3040 /* In case of error, head will be NULL */
3041 if (unlikely(!head))
3042 return true;
3043
3044 return reader->read == rb_page_commit(reader) &&
3045 (commit == reader ||
3046 (commit == head &&
3047 head->read == rb_page_commit(commit)));
3048}
3049
3050/**
3051 * ring_buffer_record_disable - stop all writes into the buffer
3052 * @buffer: The ring buffer to stop writes to.
3053 *
3054 * This prevents all writes to the buffer. Any attempt to write
3055 * to the buffer after this will fail and return NULL.
3056 *
3057 * The caller should call synchronize_sched() after this.
3058 */
3059void ring_buffer_record_disable(struct ring_buffer *buffer)
3060{
3061 atomic_inc(&buffer->record_disabled);
3062}
3063EXPORT_SYMBOL_GPL(ring_buffer_record_disable);
3064
3065/**
3066 * ring_buffer_record_enable - enable writes to the buffer
3067 * @buffer: The ring buffer to enable writes
3068 *
3069 * Note, multiple disables will need the same number of enables
3070 * to truly enable the writing (much like preempt_disable).
3071 */
3072void ring_buffer_record_enable(struct ring_buffer *buffer)
3073{
3074 atomic_dec(&buffer->record_disabled);
3075}
3076EXPORT_SYMBOL_GPL(ring_buffer_record_enable);
3077
3078/**
3079 * ring_buffer_record_off - stop all writes into the buffer
3080 * @buffer: The ring buffer to stop writes to.
3081 *
3082 * This prevents all writes to the buffer. Any attempt to write
3083 * to the buffer after this will fail and return NULL.
3084 *
3085 * This is different than ring_buffer_record_disable() as
3086 * it works like an on/off switch, where as the disable() version
3087 * must be paired with a enable().
3088 */
3089void ring_buffer_record_off(struct ring_buffer *buffer)
3090{
3091 unsigned int rd;
3092 unsigned int new_rd;
3093
3094 do {
3095 rd = atomic_read(&buffer->record_disabled);
3096 new_rd = rd | RB_BUFFER_OFF;
3097 } while (atomic_cmpxchg(&buffer->record_disabled, rd, new_rd) != rd);
3098}
3099EXPORT_SYMBOL_GPL(ring_buffer_record_off);
3100
3101/**
3102 * ring_buffer_record_on - restart writes into the buffer
3103 * @buffer: The ring buffer to start writes to.
3104 *
3105 * This enables all writes to the buffer that was disabled by
3106 * ring_buffer_record_off().
3107 *
3108 * This is different than ring_buffer_record_enable() as
3109 * it works like an on/off switch, where as the enable() version
3110 * must be paired with a disable().
3111 */
3112void ring_buffer_record_on(struct ring_buffer *buffer)
3113{
3114 unsigned int rd;
3115 unsigned int new_rd;
3116
3117 do {
3118 rd = atomic_read(&buffer->record_disabled);
3119 new_rd = rd & ~RB_BUFFER_OFF;
3120 } while (atomic_cmpxchg(&buffer->record_disabled, rd, new_rd) != rd);
3121}
3122EXPORT_SYMBOL_GPL(ring_buffer_record_on);
3123
3124/**
3125 * ring_buffer_record_is_on - return true if the ring buffer can write
3126 * @buffer: The ring buffer to see if write is enabled
3127 *
3128 * Returns true if the ring buffer is in a state that it accepts writes.
3129 */
3130int ring_buffer_record_is_on(struct ring_buffer *buffer)
3131{
3132 return !atomic_read(&buffer->record_disabled);
3133}
3134
3135/**
3136 * ring_buffer_record_disable_cpu - stop all writes into the cpu_buffer
3137 * @buffer: The ring buffer to stop writes to.
3138 * @cpu: The CPU buffer to stop
3139 *
3140 * This prevents all writes to the buffer. Any attempt to write
3141 * to the buffer after this will fail and return NULL.
3142 *
3143 * The caller should call synchronize_sched() after this.
3144 */
3145void ring_buffer_record_disable_cpu(struct ring_buffer *buffer, int cpu)
3146{
3147 struct ring_buffer_per_cpu *cpu_buffer;
3148
3149 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3150 return;
3151
3152 cpu_buffer = buffer->buffers[cpu];
3153 atomic_inc(&cpu_buffer->record_disabled);
3154}
3155EXPORT_SYMBOL_GPL(ring_buffer_record_disable_cpu);
3156
3157/**
3158 * ring_buffer_record_enable_cpu - enable writes to the buffer
3159 * @buffer: The ring buffer to enable writes
3160 * @cpu: The CPU to enable.
3161 *
3162 * Note, multiple disables will need the same number of enables
3163 * to truly enable the writing (much like preempt_disable).
3164 */
3165void ring_buffer_record_enable_cpu(struct ring_buffer *buffer, int cpu)
3166{
3167 struct ring_buffer_per_cpu *cpu_buffer;
3168
3169 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3170 return;
3171
3172 cpu_buffer = buffer->buffers[cpu];
3173 atomic_dec(&cpu_buffer->record_disabled);
3174}
3175EXPORT_SYMBOL_GPL(ring_buffer_record_enable_cpu);
3176
3177/*
3178 * The total entries in the ring buffer is the running counter
3179 * of entries entered into the ring buffer, minus the sum of
3180 * the entries read from the ring buffer and the number of
3181 * entries that were overwritten.
3182 */
3183static inline unsigned long
3184rb_num_of_entries(struct ring_buffer_per_cpu *cpu_buffer)
3185{
3186 return local_read(&cpu_buffer->entries) -
3187 (local_read(&cpu_buffer->overrun) + cpu_buffer->read);
3188}
3189
3190/**
3191 * ring_buffer_oldest_event_ts - get the oldest event timestamp from the buffer
3192 * @buffer: The ring buffer
3193 * @cpu: The per CPU buffer to read from.
3194 */
3195u64 ring_buffer_oldest_event_ts(struct ring_buffer *buffer, int cpu)
3196{
3197 unsigned long flags;
3198 struct ring_buffer_per_cpu *cpu_buffer;
3199 struct buffer_page *bpage;
3200 u64 ret = 0;
3201
3202 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3203 return 0;
3204
3205 cpu_buffer = buffer->buffers[cpu];
3206 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
3207 /*
3208 * if the tail is on reader_page, oldest time stamp is on the reader
3209 * page
3210 */
3211 if (cpu_buffer->tail_page == cpu_buffer->reader_page)
3212 bpage = cpu_buffer->reader_page;
3213 else
3214 bpage = rb_set_head_page(cpu_buffer);
3215 if (bpage)
3216 ret = bpage->page->time_stamp;
3217 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
3218
3219 return ret;
3220}
3221EXPORT_SYMBOL_GPL(ring_buffer_oldest_event_ts);
3222
3223/**
3224 * ring_buffer_bytes_cpu - get the number of bytes consumed in a cpu buffer
3225 * @buffer: The ring buffer
3226 * @cpu: The per CPU buffer to read from.
3227 */
3228unsigned long ring_buffer_bytes_cpu(struct ring_buffer *buffer, int cpu)
3229{
3230 struct ring_buffer_per_cpu *cpu_buffer;
3231 unsigned long ret;
3232
3233 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3234 return 0;
3235
3236 cpu_buffer = buffer->buffers[cpu];
3237 ret = local_read(&cpu_buffer->entries_bytes) - cpu_buffer->read_bytes;
3238
3239 return ret;
3240}
3241EXPORT_SYMBOL_GPL(ring_buffer_bytes_cpu);
3242
3243/**
3244 * ring_buffer_entries_cpu - get the number of entries in a cpu buffer
3245 * @buffer: The ring buffer
3246 * @cpu: The per CPU buffer to get the entries from.
3247 */
3248unsigned long ring_buffer_entries_cpu(struct ring_buffer *buffer, int cpu)
3249{
3250 struct ring_buffer_per_cpu *cpu_buffer;
3251
3252 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3253 return 0;
3254
3255 cpu_buffer = buffer->buffers[cpu];
3256
3257 return rb_num_of_entries(cpu_buffer);
3258}
3259EXPORT_SYMBOL_GPL(ring_buffer_entries_cpu);
3260
3261/**
3262 * ring_buffer_overrun_cpu - get the number of overruns caused by the ring
3263 * buffer wrapping around (only if RB_FL_OVERWRITE is on).
3264 * @buffer: The ring buffer
3265 * @cpu: The per CPU buffer to get the number of overruns from
3266 */
3267unsigned long ring_buffer_overrun_cpu(struct ring_buffer *buffer, int cpu)
3268{
3269 struct ring_buffer_per_cpu *cpu_buffer;
3270 unsigned long ret;
3271
3272 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3273 return 0;
3274
3275 cpu_buffer = buffer->buffers[cpu];
3276 ret = local_read(&cpu_buffer->overrun);
3277
3278 return ret;
3279}
3280EXPORT_SYMBOL_GPL(ring_buffer_overrun_cpu);
3281
3282/**
3283 * ring_buffer_commit_overrun_cpu - get the number of overruns caused by
3284 * commits failing due to the buffer wrapping around while there are uncommitted
3285 * events, such as during an interrupt storm.
3286 * @buffer: The ring buffer
3287 * @cpu: The per CPU buffer to get the number of overruns from
3288 */
3289unsigned long
3290ring_buffer_commit_overrun_cpu(struct ring_buffer *buffer, int cpu)
3291{
3292 struct ring_buffer_per_cpu *cpu_buffer;
3293 unsigned long ret;
3294
3295 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3296 return 0;
3297
3298 cpu_buffer = buffer->buffers[cpu];
3299 ret = local_read(&cpu_buffer->commit_overrun);
3300
3301 return ret;
3302}
3303EXPORT_SYMBOL_GPL(ring_buffer_commit_overrun_cpu);
3304
3305/**
3306 * ring_buffer_dropped_events_cpu - get the number of dropped events caused by
3307 * the ring buffer filling up (only if RB_FL_OVERWRITE is off).
3308 * @buffer: The ring buffer
3309 * @cpu: The per CPU buffer to get the number of overruns from
3310 */
3311unsigned long
3312ring_buffer_dropped_events_cpu(struct ring_buffer *buffer, int cpu)
3313{
3314 struct ring_buffer_per_cpu *cpu_buffer;
3315 unsigned long ret;
3316
3317 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3318 return 0;
3319
3320 cpu_buffer = buffer->buffers[cpu];
3321 ret = local_read(&cpu_buffer->dropped_events);
3322
3323 return ret;
3324}
3325EXPORT_SYMBOL_GPL(ring_buffer_dropped_events_cpu);
3326
3327/**
3328 * ring_buffer_read_events_cpu - get the number of events successfully read
3329 * @buffer: The ring buffer
3330 * @cpu: The per CPU buffer to get the number of events read
3331 */
3332unsigned long
3333ring_buffer_read_events_cpu(struct ring_buffer *buffer, int cpu)
3334{
3335 struct ring_buffer_per_cpu *cpu_buffer;
3336
3337 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3338 return 0;
3339
3340 cpu_buffer = buffer->buffers[cpu];
3341 return cpu_buffer->read;
3342}
3343EXPORT_SYMBOL_GPL(ring_buffer_read_events_cpu);
3344
3345/**
3346 * ring_buffer_entries - get the number of entries in a buffer
3347 * @buffer: The ring buffer
3348 *
3349 * Returns the total number of entries in the ring buffer
3350 * (all CPU entries)
3351 */
3352unsigned long ring_buffer_entries(struct ring_buffer *buffer)
3353{
3354 struct ring_buffer_per_cpu *cpu_buffer;
3355 unsigned long entries = 0;
3356 int cpu;
3357
3358 /* if you care about this being correct, lock the buffer */
3359 for_each_buffer_cpu(buffer, cpu) {
3360 cpu_buffer = buffer->buffers[cpu];
3361 entries += rb_num_of_entries(cpu_buffer);
3362 }
3363
3364 return entries;
3365}
3366EXPORT_SYMBOL_GPL(ring_buffer_entries);
3367
3368/**
3369 * ring_buffer_overruns - get the number of overruns in buffer
3370 * @buffer: The ring buffer
3371 *
3372 * Returns the total number of overruns in the ring buffer
3373 * (all CPU entries)
3374 */
3375unsigned long ring_buffer_overruns(struct ring_buffer *buffer)
3376{
3377 struct ring_buffer_per_cpu *cpu_buffer;
3378 unsigned long overruns = 0;
3379 int cpu;
3380
3381 /* if you care about this being correct, lock the buffer */
3382 for_each_buffer_cpu(buffer, cpu) {
3383 cpu_buffer = buffer->buffers[cpu];
3384 overruns += local_read(&cpu_buffer->overrun);
3385 }
3386
3387 return overruns;
3388}
3389EXPORT_SYMBOL_GPL(ring_buffer_overruns);
3390
3391static void rb_iter_reset(struct ring_buffer_iter *iter)
3392{
3393 struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
3394
3395 /* Iterator usage is expected to have record disabled */
3396 iter->head_page = cpu_buffer->reader_page;
3397 iter->head = cpu_buffer->reader_page->read;
3398
3399 iter->cache_reader_page = iter->head_page;
3400 iter->cache_read = cpu_buffer->read;
3401
3402 if (iter->head)
3403 iter->read_stamp = cpu_buffer->read_stamp;
3404 else
3405 iter->read_stamp = iter->head_page->page->time_stamp;
3406}
3407
3408/**
3409 * ring_buffer_iter_reset - reset an iterator
3410 * @iter: The iterator to reset
3411 *
3412 * Resets the iterator, so that it will start from the beginning
3413 * again.
3414 */
3415void ring_buffer_iter_reset(struct ring_buffer_iter *iter)
3416{
3417 struct ring_buffer_per_cpu *cpu_buffer;
3418 unsigned long flags;
3419
3420 if (!iter)
3421 return;
3422
3423 cpu_buffer = iter->cpu_buffer;
3424
3425 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
3426 rb_iter_reset(iter);
3427 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
3428}
3429EXPORT_SYMBOL_GPL(ring_buffer_iter_reset);
3430
3431/**
3432 * ring_buffer_iter_empty - check if an iterator has no more to read
3433 * @iter: The iterator to check
3434 */
3435int ring_buffer_iter_empty(struct ring_buffer_iter *iter)
3436{
3437 struct ring_buffer_per_cpu *cpu_buffer;
3438
3439 cpu_buffer = iter->cpu_buffer;
3440
3441 return iter->head_page == cpu_buffer->commit_page &&
3442 iter->head == rb_commit_index(cpu_buffer);
3443}
3444EXPORT_SYMBOL_GPL(ring_buffer_iter_empty);
3445
3446static void
3447rb_update_read_stamp(struct ring_buffer_per_cpu *cpu_buffer,
3448 struct ring_buffer_event *event)
3449{
3450 u64 delta;
3451
3452 switch (event->type_len) {
3453 case RINGBUF_TYPE_PADDING:
3454 return;
3455
3456 case RINGBUF_TYPE_TIME_EXTEND:
3457 delta = event->array[0];
3458 delta <<= TS_SHIFT;
3459 delta += event->time_delta;
3460 cpu_buffer->read_stamp += delta;
3461 return;
3462
3463 case RINGBUF_TYPE_TIME_STAMP:
3464 /* FIXME: not implemented */
3465 return;
3466
3467 case RINGBUF_TYPE_DATA:
3468 cpu_buffer->read_stamp += event->time_delta;
3469 return;
3470
3471 default:
3472 BUG();
3473 }
3474 return;
3475}
3476
3477static void
3478rb_update_iter_read_stamp(struct ring_buffer_iter *iter,
3479 struct ring_buffer_event *event)
3480{
3481 u64 delta;
3482
3483 switch (event->type_len) {
3484 case RINGBUF_TYPE_PADDING:
3485 return;
3486
3487 case RINGBUF_TYPE_TIME_EXTEND:
3488 delta = event->array[0];
3489 delta <<= TS_SHIFT;
3490 delta += event->time_delta;
3491 iter->read_stamp += delta;
3492 return;
3493
3494 case RINGBUF_TYPE_TIME_STAMP:
3495 /* FIXME: not implemented */
3496 return;
3497
3498 case RINGBUF_TYPE_DATA:
3499 iter->read_stamp += event->time_delta;
3500 return;
3501
3502 default:
3503 BUG();
3504 }
3505 return;
3506}
3507
3508static struct buffer_page *
3509rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
3510{
3511 struct buffer_page *reader = NULL;
3512 unsigned long overwrite;
3513 unsigned long flags;
3514 int nr_loops = 0;
3515 int ret;
3516
3517 local_irq_save(flags);
3518 arch_spin_lock(&cpu_buffer->lock);
3519
3520 again:
3521 /*
3522 * This should normally only loop twice. But because the
3523 * start of the reader inserts an empty page, it causes
3524 * a case where we will loop three times. There should be no
3525 * reason to loop four times (that I know of).
3526 */
3527 if (RB_WARN_ON(cpu_buffer, ++nr_loops > 3)) {
3528 reader = NULL;
3529 goto out;
3530 }
3531
3532 reader = cpu_buffer->reader_page;
3533
3534 /* If there's more to read, return this page */
3535 if (cpu_buffer->reader_page->read < rb_page_size(reader))
3536 goto out;
3537
3538 /* Never should we have an index greater than the size */
3539 if (RB_WARN_ON(cpu_buffer,
3540 cpu_buffer->reader_page->read > rb_page_size(reader)))
3541 goto out;
3542
3543 /* check if we caught up to the tail */
3544 reader = NULL;
3545 if (cpu_buffer->commit_page == cpu_buffer->reader_page)
3546 goto out;
3547
3548 /* Don't bother swapping if the ring buffer is empty */
3549 if (rb_num_of_entries(cpu_buffer) == 0)
3550 goto out;
3551
3552 /*
3553 * Reset the reader page to size zero.
3554 */
3555 local_set(&cpu_buffer->reader_page->write, 0);
3556 local_set(&cpu_buffer->reader_page->entries, 0);
3557 local_set(&cpu_buffer->reader_page->page->commit, 0);
3558 cpu_buffer->reader_page->real_end = 0;
3559
3560 spin:
3561 /*
3562 * Splice the empty reader page into the list around the head.
3563 */
3564 reader = rb_set_head_page(cpu_buffer);
3565 if (!reader)
3566 goto out;
3567 cpu_buffer->reader_page->list.next = rb_list_head(reader->list.next);
3568 cpu_buffer->reader_page->list.prev = reader->list.prev;
3569
3570 /*
3571 * cpu_buffer->pages just needs to point to the buffer, it
3572 * has no specific buffer page to point to. Lets move it out
3573 * of our way so we don't accidentally swap it.
3574 */
3575 cpu_buffer->pages = reader->list.prev;
3576
3577 /* The reader page will be pointing to the new head */
3578 rb_set_list_to_head(cpu_buffer, &cpu_buffer->reader_page->list);
3579
3580 /*
3581 * We want to make sure we read the overruns after we set up our
3582 * pointers to the next object. The writer side does a
3583 * cmpxchg to cross pages which acts as the mb on the writer
3584 * side. Note, the reader will constantly fail the swap
3585 * while the writer is updating the pointers, so this
3586 * guarantees that the overwrite recorded here is the one we
3587 * want to compare with the last_overrun.
3588 */
3589 smp_mb();
3590 overwrite = local_read(&(cpu_buffer->overrun));
3591
3592 /*
3593 * Here's the tricky part.
3594 *
3595 * We need to move the pointer past the header page.
3596 * But we can only do that if a writer is not currently
3597 * moving it. The page before the header page has the
3598 * flag bit '1' set if it is pointing to the page we want.
3599 * but if the writer is in the process of moving it
3600 * than it will be '2' or already moved '0'.
3601 */
3602
3603 ret = rb_head_page_replace(reader, cpu_buffer->reader_page);
3604
3605 /*
3606 * If we did not convert it, then we must try again.
3607 */
3608 if (!ret)
3609 goto spin;
3610
3611 /*
3612 * Yeah! We succeeded in replacing the page.
3613 *
3614 * Now make the new head point back to the reader page.
3615 */
3616 rb_list_head(reader->list.next)->prev = &cpu_buffer->reader_page->list;
3617 rb_inc_page(cpu_buffer, &cpu_buffer->head_page);
3618
3619 /* Finally update the reader page to the new head */
3620 cpu_buffer->reader_page = reader;
3621 cpu_buffer->reader_page->read = 0;
3622
3623 if (overwrite != cpu_buffer->last_overrun) {
3624 cpu_buffer->lost_events = overwrite - cpu_buffer->last_overrun;
3625 cpu_buffer->last_overrun = overwrite;
3626 }
3627
3628 goto again;
3629
3630 out:
3631 /* Update the read_stamp on the first event */
3632 if (reader && reader->read == 0)
3633 cpu_buffer->read_stamp = reader->page->time_stamp;
3634
3635 arch_spin_unlock(&cpu_buffer->lock);
3636 local_irq_restore(flags);
3637
3638 return reader;
3639}
3640
3641static void rb_advance_reader(struct ring_buffer_per_cpu *cpu_buffer)
3642{
3643 struct ring_buffer_event *event;
3644 struct buffer_page *reader;
3645 unsigned length;
3646
3647 reader = rb_get_reader_page(cpu_buffer);
3648
3649 /* This function should not be called when buffer is empty */
3650 if (RB_WARN_ON(cpu_buffer, !reader))
3651 return;
3652
3653 event = rb_reader_event(cpu_buffer);
3654
3655 if (event->type_len <= RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
3656 cpu_buffer->read++;
3657
3658 rb_update_read_stamp(cpu_buffer, event);
3659
3660 length = rb_event_length(event);
3661 cpu_buffer->reader_page->read += length;
3662}
3663
3664static void rb_advance_iter(struct ring_buffer_iter *iter)
3665{
3666 struct ring_buffer_per_cpu *cpu_buffer;
3667 struct ring_buffer_event *event;
3668 unsigned length;
3669
3670 cpu_buffer = iter->cpu_buffer;
3671
3672 /*
3673 * Check if we are at the end of the buffer.
3674 */
3675 if (iter->head >= rb_page_size(iter->head_page)) {
3676 /* discarded commits can make the page empty */
3677 if (iter->head_page == cpu_buffer->commit_page)
3678 return;
3679 rb_inc_iter(iter);
3680 return;
3681 }
3682
3683 event = rb_iter_head_event(iter);
3684
3685 length = rb_event_length(event);
3686
3687 /*
3688 * This should not be called to advance the header if we are
3689 * at the tail of the buffer.
3690 */
3691 if (RB_WARN_ON(cpu_buffer,
3692 (iter->head_page == cpu_buffer->commit_page) &&
3693 (iter->head + length > rb_commit_index(cpu_buffer))))
3694 return;
3695
3696 rb_update_iter_read_stamp(iter, event);
3697
3698 iter->head += length;
3699
3700 /* check for end of page padding */
3701 if ((iter->head >= rb_page_size(iter->head_page)) &&
3702 (iter->head_page != cpu_buffer->commit_page))
3703 rb_inc_iter(iter);
3704}
3705
3706static int rb_lost_events(struct ring_buffer_per_cpu *cpu_buffer)
3707{
3708 return cpu_buffer->lost_events;
3709}
3710
3711static struct ring_buffer_event *
3712rb_buffer_peek(struct ring_buffer_per_cpu *cpu_buffer, u64 *ts,
3713 unsigned long *lost_events)
3714{
3715 struct ring_buffer_event *event;
3716 struct buffer_page *reader;
3717 int nr_loops = 0;
3718
3719 again:
3720 /*
3721 * We repeat when a time extend is encountered.
3722 * Since the time extend is always attached to a data event,
3723 * we should never loop more than once.
3724 * (We never hit the following condition more than twice).
3725 */
3726 if (RB_WARN_ON(cpu_buffer, ++nr_loops > 2))
3727 return NULL;
3728
3729 reader = rb_get_reader_page(cpu_buffer);
3730 if (!reader)
3731 return NULL;
3732
3733 event = rb_reader_event(cpu_buffer);
3734
3735 switch (event->type_len) {
3736 case RINGBUF_TYPE_PADDING:
3737 if (rb_null_event(event))
3738 RB_WARN_ON(cpu_buffer, 1);
3739 /*
3740 * Because the writer could be discarding every
3741 * event it creates (which would probably be bad)
3742 * if we were to go back to "again" then we may never
3743 * catch up, and will trigger the warn on, or lock
3744 * the box. Return the padding, and we will release
3745 * the current locks, and try again.
3746 */
3747 return event;
3748
3749 case RINGBUF_TYPE_TIME_EXTEND:
3750 /* Internal data, OK to advance */
3751 rb_advance_reader(cpu_buffer);
3752 goto again;
3753
3754 case RINGBUF_TYPE_TIME_STAMP:
3755 /* FIXME: not implemented */
3756 rb_advance_reader(cpu_buffer);
3757 goto again;
3758
3759 case RINGBUF_TYPE_DATA:
3760 if (ts) {
3761 *ts = cpu_buffer->read_stamp + event->time_delta;
3762 ring_buffer_normalize_time_stamp(cpu_buffer->buffer,
3763 cpu_buffer->cpu, ts);
3764 }
3765 if (lost_events)
3766 *lost_events = rb_lost_events(cpu_buffer);
3767 return event;
3768
3769 default:
3770 BUG();
3771 }
3772
3773 return NULL;
3774}
3775EXPORT_SYMBOL_GPL(ring_buffer_peek);
3776
3777static struct ring_buffer_event *
3778rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
3779{
3780 struct ring_buffer *buffer;
3781 struct ring_buffer_per_cpu *cpu_buffer;
3782 struct ring_buffer_event *event;
3783 int nr_loops = 0;
3784
3785 cpu_buffer = iter->cpu_buffer;
3786 buffer = cpu_buffer->buffer;
3787
3788 /*
3789 * Check if someone performed a consuming read to
3790 * the buffer. A consuming read invalidates the iterator
3791 * and we need to reset the iterator in this case.
3792 */
3793 if (unlikely(iter->cache_read != cpu_buffer->read ||
3794 iter->cache_reader_page != cpu_buffer->reader_page))
3795 rb_iter_reset(iter);
3796
3797 again:
3798 if (ring_buffer_iter_empty(iter))
3799 return NULL;
3800
3801 /*
3802 * We repeat when a time extend is encountered or we hit
3803 * the end of the page. Since the time extend is always attached
3804 * to a data event, we should never loop more than three times.
3805 * Once for going to next page, once on time extend, and
3806 * finally once to get the event.
3807 * (We never hit the following condition more than thrice).
3808 */
3809 if (RB_WARN_ON(cpu_buffer, ++nr_loops > 3))
3810 return NULL;
3811
3812 if (rb_per_cpu_empty(cpu_buffer))
3813 return NULL;
3814
3815 if (iter->head >= rb_page_size(iter->head_page)) {
3816 rb_inc_iter(iter);
3817 goto again;
3818 }
3819
3820 event = rb_iter_head_event(iter);
3821
3822 switch (event->type_len) {
3823 case RINGBUF_TYPE_PADDING:
3824 if (rb_null_event(event)) {
3825 rb_inc_iter(iter);
3826 goto again;
3827 }
3828 rb_advance_iter(iter);
3829 return event;
3830
3831 case RINGBUF_TYPE_TIME_EXTEND:
3832 /* Internal data, OK to advance */
3833 rb_advance_iter(iter);
3834 goto again;
3835
3836 case RINGBUF_TYPE_TIME_STAMP:
3837 /* FIXME: not implemented */
3838 rb_advance_iter(iter);
3839 goto again;
3840
3841 case RINGBUF_TYPE_DATA:
3842 if (ts) {
3843 *ts = iter->read_stamp + event->time_delta;
3844 ring_buffer_normalize_time_stamp(buffer,
3845 cpu_buffer->cpu, ts);
3846 }
3847 return event;
3848
3849 default:
3850 BUG();
3851 }
3852
3853 return NULL;
3854}
3855EXPORT_SYMBOL_GPL(ring_buffer_iter_peek);
3856
3857static inline bool rb_reader_lock(struct ring_buffer_per_cpu *cpu_buffer)
3858{
3859 if (likely(!in_nmi())) {
3860 raw_spin_lock(&cpu_buffer->reader_lock);
3861 return true;
3862 }
3863
3864 /*
3865 * If an NMI die dumps out the content of the ring buffer
3866 * trylock must be used to prevent a deadlock if the NMI
3867 * preempted a task that holds the ring buffer locks. If
3868 * we get the lock then all is fine, if not, then continue
3869 * to do the read, but this can corrupt the ring buffer,
3870 * so it must be permanently disabled from future writes.
3871 * Reading from NMI is a oneshot deal.
3872 */
3873 if (raw_spin_trylock(&cpu_buffer->reader_lock))
3874 return true;
3875
3876 /* Continue without locking, but disable the ring buffer */
3877 atomic_inc(&cpu_buffer->record_disabled);
3878 return false;
3879}
3880
3881static inline void
3882rb_reader_unlock(struct ring_buffer_per_cpu *cpu_buffer, bool locked)
3883{
3884 if (likely(locked))
3885 raw_spin_unlock(&cpu_buffer->reader_lock);
3886 return;
3887}
3888
3889/**
3890 * ring_buffer_peek - peek at the next event to be read
3891 * @buffer: The ring buffer to read
3892 * @cpu: The cpu to peak at
3893 * @ts: The timestamp counter of this event.
3894 * @lost_events: a variable to store if events were lost (may be NULL)
3895 *
3896 * This will return the event that will be read next, but does
3897 * not consume the data.
3898 */
3899struct ring_buffer_event *
3900ring_buffer_peek(struct ring_buffer *buffer, int cpu, u64 *ts,
3901 unsigned long *lost_events)
3902{
3903 struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
3904 struct ring_buffer_event *event;
3905 unsigned long flags;
3906 bool dolock;
3907
3908 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3909 return NULL;
3910
3911 again:
3912 local_irq_save(flags);
3913 dolock = rb_reader_lock(cpu_buffer);
3914 event = rb_buffer_peek(cpu_buffer, ts, lost_events);
3915 if (event && event->type_len == RINGBUF_TYPE_PADDING)
3916 rb_advance_reader(cpu_buffer);
3917 rb_reader_unlock(cpu_buffer, dolock);
3918 local_irq_restore(flags);
3919
3920 if (event && event->type_len == RINGBUF_TYPE_PADDING)
3921 goto again;
3922
3923 return event;
3924}
3925
3926/**
3927 * ring_buffer_iter_peek - peek at the next event to be read
3928 * @iter: The ring buffer iterator
3929 * @ts: The timestamp counter of this event.
3930 *
3931 * This will return the event that will be read next, but does
3932 * not increment the iterator.
3933 */
3934struct ring_buffer_event *
3935ring_buffer_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
3936{
3937 struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
3938 struct ring_buffer_event *event;
3939 unsigned long flags;
3940
3941 again:
3942 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
3943 event = rb_iter_peek(iter, ts);
3944 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
3945
3946 if (event && event->type_len == RINGBUF_TYPE_PADDING)
3947 goto again;
3948
3949 return event;
3950}
3951
3952/**
3953 * ring_buffer_consume - return an event and consume it
3954 * @buffer: The ring buffer to get the next event from
3955 * @cpu: the cpu to read the buffer from
3956 * @ts: a variable to store the timestamp (may be NULL)
3957 * @lost_events: a variable to store if events were lost (may be NULL)
3958 *
3959 * Returns the next event in the ring buffer, and that event is consumed.
3960 * Meaning, that sequential reads will keep returning a different event,
3961 * and eventually empty the ring buffer if the producer is slower.
3962 */
3963struct ring_buffer_event *
3964ring_buffer_consume(struct ring_buffer *buffer, int cpu, u64 *ts,
3965 unsigned long *lost_events)
3966{
3967 struct ring_buffer_per_cpu *cpu_buffer;
3968 struct ring_buffer_event *event = NULL;
3969 unsigned long flags;
3970 bool dolock;
3971
3972 again:
3973 /* might be called in atomic */
3974 preempt_disable();
3975
3976 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3977 goto out;
3978
3979 cpu_buffer = buffer->buffers[cpu];
3980 local_irq_save(flags);
3981 dolock = rb_reader_lock(cpu_buffer);
3982
3983 event = rb_buffer_peek(cpu_buffer, ts, lost_events);
3984 if (event) {
3985 cpu_buffer->lost_events = 0;
3986 rb_advance_reader(cpu_buffer);
3987 }
3988
3989 rb_reader_unlock(cpu_buffer, dolock);
3990 local_irq_restore(flags);
3991
3992 out:
3993 preempt_enable();
3994
3995 if (event && event->type_len == RINGBUF_TYPE_PADDING)
3996 goto again;
3997
3998 return event;
3999}
4000EXPORT_SYMBOL_GPL(ring_buffer_consume);
4001
4002/**
4003 * ring_buffer_read_prepare - Prepare for a non consuming read of the buffer
4004 * @buffer: The ring buffer to read from
4005 * @cpu: The cpu buffer to iterate over
4006 *
4007 * This performs the initial preparations necessary to iterate
4008 * through the buffer. Memory is allocated, buffer recording
4009 * is disabled, and the iterator pointer is returned to the caller.
4010 *
4011 * Disabling buffer recordng prevents the reading from being
4012 * corrupted. This is not a consuming read, so a producer is not
4013 * expected.
4014 *
4015 * After a sequence of ring_buffer_read_prepare calls, the user is
4016 * expected to make at least one call to ring_buffer_read_prepare_sync.
4017 * Afterwards, ring_buffer_read_start is invoked to get things going
4018 * for real.
4019 *
4020 * This overall must be paired with ring_buffer_read_finish.
4021 */
4022struct ring_buffer_iter *
4023ring_buffer_read_prepare(struct ring_buffer *buffer, int cpu)
4024{
4025 struct ring_buffer_per_cpu *cpu_buffer;
4026 struct ring_buffer_iter *iter;
4027
4028 if (!cpumask_test_cpu(cpu, buffer->cpumask))
4029 return NULL;
4030
4031 iter = kmalloc(sizeof(*iter), GFP_KERNEL);
4032 if (!iter)
4033 return NULL;
4034
4035 cpu_buffer = buffer->buffers[cpu];
4036
4037 iter->cpu_buffer = cpu_buffer;
4038
4039 atomic_inc(&buffer->resize_disabled);
4040 atomic_inc(&cpu_buffer->record_disabled);
4041
4042 return iter;
4043}
4044EXPORT_SYMBOL_GPL(ring_buffer_read_prepare);
4045
4046/**
4047 * ring_buffer_read_prepare_sync - Synchronize a set of prepare calls
4048 *
4049 * All previously invoked ring_buffer_read_prepare calls to prepare
4050 * iterators will be synchronized. Afterwards, read_buffer_read_start
4051 * calls on those iterators are allowed.
4052 */
4053void
4054ring_buffer_read_prepare_sync(void)
4055{
4056 synchronize_sched();
4057}
4058EXPORT_SYMBOL_GPL(ring_buffer_read_prepare_sync);
4059
4060/**
4061 * ring_buffer_read_start - start a non consuming read of the buffer
4062 * @iter: The iterator returned by ring_buffer_read_prepare
4063 *
4064 * This finalizes the startup of an iteration through the buffer.
4065 * The iterator comes from a call to ring_buffer_read_prepare and
4066 * an intervening ring_buffer_read_prepare_sync must have been
4067 * performed.
4068 *
4069 * Must be paired with ring_buffer_read_finish.
4070 */
4071void
4072ring_buffer_read_start(struct ring_buffer_iter *iter)
4073{
4074 struct ring_buffer_per_cpu *cpu_buffer;
4075 unsigned long flags;
4076
4077 if (!iter)
4078 return;
4079
4080 cpu_buffer = iter->cpu_buffer;
4081
4082 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
4083 arch_spin_lock(&cpu_buffer->lock);
4084 rb_iter_reset(iter);
4085 arch_spin_unlock(&cpu_buffer->lock);
4086 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
4087}
4088EXPORT_SYMBOL_GPL(ring_buffer_read_start);
4089
4090/**
4091 * ring_buffer_read_finish - finish reading the iterator of the buffer
4092 * @iter: The iterator retrieved by ring_buffer_start
4093 *
4094 * This re-enables the recording to the buffer, and frees the
4095 * iterator.
4096 */
4097void
4098ring_buffer_read_finish(struct ring_buffer_iter *iter)
4099{
4100 struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
4101 unsigned long flags;
4102
4103 /*
4104 * Ring buffer is disabled from recording, here's a good place
4105 * to check the integrity of the ring buffer.
4106 * Must prevent readers from trying to read, as the check
4107 * clears the HEAD page and readers require it.
4108 */
4109 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
4110 rb_check_pages(cpu_buffer);
4111 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
4112
4113 atomic_dec(&cpu_buffer->record_disabled);
4114 atomic_dec(&cpu_buffer->buffer->resize_disabled);
4115 kfree(iter);
4116}
4117EXPORT_SYMBOL_GPL(ring_buffer_read_finish);
4118
4119/**
4120 * ring_buffer_read - read the next item in the ring buffer by the iterator
4121 * @iter: The ring buffer iterator
4122 * @ts: The time stamp of the event read.
4123 *
4124 * This reads the next event in the ring buffer and increments the iterator.
4125 */
4126struct ring_buffer_event *
4127ring_buffer_read(struct ring_buffer_iter *iter, u64 *ts)
4128{
4129 struct ring_buffer_event *event;
4130 struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
4131 unsigned long flags;
4132
4133 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
4134 again:
4135 event = rb_iter_peek(iter, ts);
4136 if (!event)
4137 goto out;
4138
4139 if (event->type_len == RINGBUF_TYPE_PADDING)
4140 goto again;
4141
4142 rb_advance_iter(iter);
4143 out:
4144 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
4145
4146 return event;
4147}
4148EXPORT_SYMBOL_GPL(ring_buffer_read);
4149
4150/**
4151 * ring_buffer_size - return the size of the ring buffer (in bytes)
4152 * @buffer: The ring buffer.
4153 */
4154unsigned long ring_buffer_size(struct ring_buffer *buffer, int cpu)
4155{
4156 /*
4157 * Earlier, this method returned
4158 * BUF_PAGE_SIZE * buffer->nr_pages
4159 * Since the nr_pages field is now removed, we have converted this to
4160 * return the per cpu buffer value.
4161 */
4162 if (!cpumask_test_cpu(cpu, buffer->cpumask))
4163 return 0;
4164
4165 return BUF_PAGE_SIZE * buffer->buffers[cpu]->nr_pages;
4166}
4167EXPORT_SYMBOL_GPL(ring_buffer_size);
4168
4169static void
4170rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
4171{
4172 rb_head_page_deactivate(cpu_buffer);
4173
4174 cpu_buffer->head_page
4175 = list_entry(cpu_buffer->pages, struct buffer_page, list);
4176 local_set(&cpu_buffer->head_page->write, 0);
4177 local_set(&cpu_buffer->head_page->entries, 0);
4178 local_set(&cpu_buffer->head_page->page->commit, 0);
4179
4180 cpu_buffer->head_page->read = 0;
4181
4182 cpu_buffer->tail_page = cpu_buffer->head_page;
4183 cpu_buffer->commit_page = cpu_buffer->head_page;
4184
4185 INIT_LIST_HEAD(&cpu_buffer->reader_page->list);
4186 INIT_LIST_HEAD(&cpu_buffer->new_pages);
4187 local_set(&cpu_buffer->reader_page->write, 0);
4188 local_set(&cpu_buffer->reader_page->entries, 0);
4189 local_set(&cpu_buffer->reader_page->page->commit, 0);
4190 cpu_buffer->reader_page->read = 0;
4191
4192 local_set(&cpu_buffer->entries_bytes, 0);
4193 local_set(&cpu_buffer->overrun, 0);
4194 local_set(&cpu_buffer->commit_overrun, 0);
4195 local_set(&cpu_buffer->dropped_events, 0);
4196 local_set(&cpu_buffer->entries, 0);
4197 local_set(&cpu_buffer->committing, 0);
4198 local_set(&cpu_buffer->commits, 0);
4199 cpu_buffer->read = 0;
4200 cpu_buffer->read_bytes = 0;
4201
4202 cpu_buffer->write_stamp = 0;
4203 cpu_buffer->read_stamp = 0;
4204
4205 cpu_buffer->lost_events = 0;
4206 cpu_buffer->last_overrun = 0;
4207
4208 rb_head_page_activate(cpu_buffer);
4209}
4210
4211/**
4212 * ring_buffer_reset_cpu - reset a ring buffer per CPU buffer
4213 * @buffer: The ring buffer to reset a per cpu buffer of
4214 * @cpu: The CPU buffer to be reset
4215 */
4216void ring_buffer_reset_cpu(struct ring_buffer *buffer, int cpu)
4217{
4218 struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
4219 unsigned long flags;
4220
4221 if (!cpumask_test_cpu(cpu, buffer->cpumask))
4222 return;
4223
4224 atomic_inc(&buffer->resize_disabled);
4225 atomic_inc(&cpu_buffer->record_disabled);
4226
4227 /* Make sure all commits have finished */
4228 synchronize_sched();
4229
4230 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
4231
4232 if (RB_WARN_ON(cpu_buffer, local_read(&cpu_buffer->committing)))
4233 goto out;
4234
4235 arch_spin_lock(&cpu_buffer->lock);
4236
4237 rb_reset_cpu(cpu_buffer);
4238
4239 arch_spin_unlock(&cpu_buffer->lock);
4240
4241 out:
4242 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
4243
4244 atomic_dec(&cpu_buffer->record_disabled);
4245 atomic_dec(&buffer->resize_disabled);
4246}
4247EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu);
4248
4249/**
4250 * ring_buffer_reset - reset a ring buffer
4251 * @buffer: The ring buffer to reset all cpu buffers
4252 */
4253void ring_buffer_reset(struct ring_buffer *buffer)
4254{
4255 int cpu;
4256
4257 for_each_buffer_cpu(buffer, cpu)
4258 ring_buffer_reset_cpu(buffer, cpu);
4259}
4260EXPORT_SYMBOL_GPL(ring_buffer_reset);
4261
4262/**
4263 * rind_buffer_empty - is the ring buffer empty?
4264 * @buffer: The ring buffer to test
4265 */
4266bool ring_buffer_empty(struct ring_buffer *buffer)
4267{
4268 struct ring_buffer_per_cpu *cpu_buffer;
4269 unsigned long flags;
4270 bool dolock;
4271 int cpu;
4272 int ret;
4273
4274 /* yes this is racy, but if you don't like the race, lock the buffer */
4275 for_each_buffer_cpu(buffer, cpu) {
4276 cpu_buffer = buffer->buffers[cpu];
4277 local_irq_save(flags);
4278 dolock = rb_reader_lock(cpu_buffer);
4279 ret = rb_per_cpu_empty(cpu_buffer);
4280 rb_reader_unlock(cpu_buffer, dolock);
4281 local_irq_restore(flags);
4282
4283 if (!ret)
4284 return false;
4285 }
4286
4287 return true;
4288}
4289EXPORT_SYMBOL_GPL(ring_buffer_empty);
4290
4291/**
4292 * ring_buffer_empty_cpu - is a cpu buffer of a ring buffer empty?
4293 * @buffer: The ring buffer
4294 * @cpu: The CPU buffer to test
4295 */
4296bool ring_buffer_empty_cpu(struct ring_buffer *buffer, int cpu)
4297{
4298 struct ring_buffer_per_cpu *cpu_buffer;
4299 unsigned long flags;
4300 bool dolock;
4301 int ret;
4302
4303 if (!cpumask_test_cpu(cpu, buffer->cpumask))
4304 return true;
4305
4306 cpu_buffer = buffer->buffers[cpu];
4307 local_irq_save(flags);
4308 dolock = rb_reader_lock(cpu_buffer);
4309 ret = rb_per_cpu_empty(cpu_buffer);
4310 rb_reader_unlock(cpu_buffer, dolock);
4311 local_irq_restore(flags);
4312
4313 return ret;
4314}
4315EXPORT_SYMBOL_GPL(ring_buffer_empty_cpu);
4316
4317#ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
4318/**
4319 * ring_buffer_swap_cpu - swap a CPU buffer between two ring buffers
4320 * @buffer_a: One buffer to swap with
4321 * @buffer_b: The other buffer to swap with
4322 *
4323 * This function is useful for tracers that want to take a "snapshot"
4324 * of a CPU buffer and has another back up buffer lying around.
4325 * it is expected that the tracer handles the cpu buffer not being
4326 * used at the moment.
4327 */
4328int ring_buffer_swap_cpu(struct ring_buffer *buffer_a,
4329 struct ring_buffer *buffer_b, int cpu)
4330{
4331 struct ring_buffer_per_cpu *cpu_buffer_a;
4332 struct ring_buffer_per_cpu *cpu_buffer_b;
4333 int ret = -EINVAL;
4334
4335 if (!cpumask_test_cpu(cpu, buffer_a->cpumask) ||
4336 !cpumask_test_cpu(cpu, buffer_b->cpumask))
4337 goto out;
4338
4339 cpu_buffer_a = buffer_a->buffers[cpu];
4340 cpu_buffer_b = buffer_b->buffers[cpu];
4341
4342 /* At least make sure the two buffers are somewhat the same */
4343 if (cpu_buffer_a->nr_pages != cpu_buffer_b->nr_pages)
4344 goto out;
4345
4346 ret = -EAGAIN;
4347
4348 if (atomic_read(&buffer_a->record_disabled))
4349 goto out;
4350
4351 if (atomic_read(&buffer_b->record_disabled))
4352 goto out;
4353
4354 if (atomic_read(&cpu_buffer_a->record_disabled))
4355 goto out;
4356
4357 if (atomic_read(&cpu_buffer_b->record_disabled))
4358 goto out;
4359
4360 /*
4361 * We can't do a synchronize_sched here because this
4362 * function can be called in atomic context.
4363 * Normally this will be called from the same CPU as cpu.
4364 * If not it's up to the caller to protect this.
4365 */
4366 atomic_inc(&cpu_buffer_a->record_disabled);
4367 atomic_inc(&cpu_buffer_b->record_disabled);
4368
4369 ret = -EBUSY;
4370 if (local_read(&cpu_buffer_a->committing))
4371 goto out_dec;
4372 if (local_read(&cpu_buffer_b->committing))
4373 goto out_dec;
4374
4375 buffer_a->buffers[cpu] = cpu_buffer_b;
4376 buffer_b->buffers[cpu] = cpu_buffer_a;
4377
4378 cpu_buffer_b->buffer = buffer_a;
4379 cpu_buffer_a->buffer = buffer_b;
4380
4381 ret = 0;
4382
4383out_dec:
4384 atomic_dec(&cpu_buffer_a->record_disabled);
4385 atomic_dec(&cpu_buffer_b->record_disabled);
4386out:
4387 return ret;
4388}
4389EXPORT_SYMBOL_GPL(ring_buffer_swap_cpu);
4390#endif /* CONFIG_RING_BUFFER_ALLOW_SWAP */
4391
4392/**
4393 * ring_buffer_alloc_read_page - allocate a page to read from buffer
4394 * @buffer: the buffer to allocate for.
4395 * @cpu: the cpu buffer to allocate.
4396 *
4397 * This function is used in conjunction with ring_buffer_read_page.
4398 * When reading a full page from the ring buffer, these functions
4399 * can be used to speed up the process. The calling function should
4400 * allocate a few pages first with this function. Then when it
4401 * needs to get pages from the ring buffer, it passes the result
4402 * of this function into ring_buffer_read_page, which will swap
4403 * the page that was allocated, with the read page of the buffer.
4404 *
4405 * Returns:
4406 * The page allocated, or NULL on error.
4407 */
4408void *ring_buffer_alloc_read_page(struct ring_buffer *buffer, int cpu)
4409{
4410 struct buffer_data_page *bpage;
4411 struct page *page;
4412
4413 page = alloc_pages_node(cpu_to_node(cpu),
4414 GFP_KERNEL | __GFP_NORETRY, 0);
4415 if (!page)
4416 return NULL;
4417
4418 bpage = page_address(page);
4419
4420 rb_init_page(bpage);
4421
4422 return bpage;
4423}
4424EXPORT_SYMBOL_GPL(ring_buffer_alloc_read_page);
4425
4426/**
4427 * ring_buffer_free_read_page - free an allocated read page
4428 * @buffer: the buffer the page was allocate for
4429 * @data: the page to free
4430 *
4431 * Free a page allocated from ring_buffer_alloc_read_page.
4432 */
4433void ring_buffer_free_read_page(struct ring_buffer *buffer, void *data)
4434{
4435 free_page((unsigned long)data);
4436}
4437EXPORT_SYMBOL_GPL(ring_buffer_free_read_page);
4438
4439/**
4440 * ring_buffer_read_page - extract a page from the ring buffer
4441 * @buffer: buffer to extract from
4442 * @data_page: the page to use allocated from ring_buffer_alloc_read_page
4443 * @len: amount to extract
4444 * @cpu: the cpu of the buffer to extract
4445 * @full: should the extraction only happen when the page is full.
4446 *
4447 * This function will pull out a page from the ring buffer and consume it.
4448 * @data_page must be the address of the variable that was returned
4449 * from ring_buffer_alloc_read_page. This is because the page might be used
4450 * to swap with a page in the ring buffer.
4451 *
4452 * for example:
4453 * rpage = ring_buffer_alloc_read_page(buffer, cpu);
4454 * if (!rpage)
4455 * return error;
4456 * ret = ring_buffer_read_page(buffer, &rpage, len, cpu, 0);
4457 * if (ret >= 0)
4458 * process_page(rpage, ret);
4459 *
4460 * When @full is set, the function will not return true unless
4461 * the writer is off the reader page.
4462 *
4463 * Note: it is up to the calling functions to handle sleeps and wakeups.
4464 * The ring buffer can be used anywhere in the kernel and can not
4465 * blindly call wake_up. The layer that uses the ring buffer must be
4466 * responsible for that.
4467 *
4468 * Returns:
4469 * >=0 if data has been transferred, returns the offset of consumed data.
4470 * <0 if no data has been transferred.
4471 */
4472int ring_buffer_read_page(struct ring_buffer *buffer,
4473 void **data_page, size_t len, int cpu, int full)
4474{
4475 struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
4476 struct ring_buffer_event *event;
4477 struct buffer_data_page *bpage;
4478 struct buffer_page *reader;
4479 unsigned long missed_events;
4480 unsigned long flags;
4481 unsigned int commit;
4482 unsigned int read;
4483 u64 save_timestamp;
4484 int ret = -1;
4485
4486 if (!cpumask_test_cpu(cpu, buffer->cpumask))
4487 goto out;
4488
4489 /*
4490 * If len is not big enough to hold the page header, then
4491 * we can not copy anything.
4492 */
4493 if (len <= BUF_PAGE_HDR_SIZE)
4494 goto out;
4495
4496 len -= BUF_PAGE_HDR_SIZE;
4497
4498 if (!data_page)
4499 goto out;
4500
4501 bpage = *data_page;
4502 if (!bpage)
4503 goto out;
4504
4505 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
4506
4507 reader = rb_get_reader_page(cpu_buffer);
4508 if (!reader)
4509 goto out_unlock;
4510
4511 event = rb_reader_event(cpu_buffer);
4512
4513 read = reader->read;
4514 commit = rb_page_commit(reader);
4515
4516 /* Check if any events were dropped */
4517 missed_events = cpu_buffer->lost_events;
4518
4519 /*
4520 * If this page has been partially read or
4521 * if len is not big enough to read the rest of the page or
4522 * a writer is still on the page, then
4523 * we must copy the data from the page to the buffer.
4524 * Otherwise, we can simply swap the page with the one passed in.
4525 */
4526 if (read || (len < (commit - read)) ||
4527 cpu_buffer->reader_page == cpu_buffer->commit_page) {
4528 struct buffer_data_page *rpage = cpu_buffer->reader_page->page;
4529 unsigned int rpos = read;
4530 unsigned int pos = 0;
4531 unsigned int size;
4532
4533 if (full)
4534 goto out_unlock;
4535
4536 if (len > (commit - read))
4537 len = (commit - read);
4538
4539 /* Always keep the time extend and data together */
4540 size = rb_event_ts_length(event);
4541
4542 if (len < size)
4543 goto out_unlock;
4544
4545 /* save the current timestamp, since the user will need it */
4546 save_timestamp = cpu_buffer->read_stamp;
4547
4548 /* Need to copy one event at a time */
4549 do {
4550 /* We need the size of one event, because
4551 * rb_advance_reader only advances by one event,
4552 * whereas rb_event_ts_length may include the size of
4553 * one or two events.
4554 * We have already ensured there's enough space if this
4555 * is a time extend. */
4556 size = rb_event_length(event);
4557 memcpy(bpage->data + pos, rpage->data + rpos, size);
4558
4559 len -= size;
4560
4561 rb_advance_reader(cpu_buffer);
4562 rpos = reader->read;
4563 pos += size;
4564
4565 if (rpos >= commit)
4566 break;
4567
4568 event = rb_reader_event(cpu_buffer);
4569 /* Always keep the time extend and data together */
4570 size = rb_event_ts_length(event);
4571 } while (len >= size);
4572
4573 /* update bpage */
4574 local_set(&bpage->commit, pos);
4575 bpage->time_stamp = save_timestamp;
4576
4577 /* we copied everything to the beginning */
4578 read = 0;
4579 } else {
4580 /* update the entry counter */
4581 cpu_buffer->read += rb_page_entries(reader);
4582 cpu_buffer->read_bytes += BUF_PAGE_SIZE;
4583
4584 /* swap the pages */
4585 rb_init_page(bpage);
4586 bpage = reader->page;
4587 reader->page = *data_page;
4588 local_set(&reader->write, 0);
4589 local_set(&reader->entries, 0);
4590 reader->read = 0;
4591 *data_page = bpage;
4592
4593 /*
4594 * Use the real_end for the data size,
4595 * This gives us a chance to store the lost events
4596 * on the page.
4597 */
4598 if (reader->real_end)
4599 local_set(&bpage->commit, reader->real_end);
4600 }
4601 ret = read;
4602
4603 cpu_buffer->lost_events = 0;
4604
4605 commit = local_read(&bpage->commit);
4606 /*
4607 * Set a flag in the commit field if we lost events
4608 */
4609 if (missed_events) {
4610 /* If there is room at the end of the page to save the
4611 * missed events, then record it there.
4612 */
4613 if (BUF_PAGE_SIZE - commit >= sizeof(missed_events)) {
4614 memcpy(&bpage->data[commit], &missed_events,
4615 sizeof(missed_events));
4616 local_add(RB_MISSED_STORED, &bpage->commit);
4617 commit += sizeof(missed_events);
4618 }
4619 local_add(RB_MISSED_EVENTS, &bpage->commit);
4620 }
4621
4622 /*
4623 * This page may be off to user land. Zero it out here.
4624 */
4625 if (commit < BUF_PAGE_SIZE)
4626 memset(&bpage->data[commit], 0, BUF_PAGE_SIZE - commit);
4627
4628 out_unlock:
4629 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
4630
4631 out:
4632 return ret;
4633}
4634EXPORT_SYMBOL_GPL(ring_buffer_read_page);
4635
4636#ifdef CONFIG_HOTPLUG_CPU
4637static int rb_cpu_notify(struct notifier_block *self,
4638 unsigned long action, void *hcpu)
4639{
4640 struct ring_buffer *buffer =
4641 container_of(self, struct ring_buffer, cpu_notify);
4642 long cpu = (long)hcpu;
4643 int cpu_i, nr_pages_same;
4644 unsigned int nr_pages;
4645
4646 switch (action) {
4647 case CPU_UP_PREPARE:
4648 case CPU_UP_PREPARE_FROZEN:
4649 if (cpumask_test_cpu(cpu, buffer->cpumask))
4650 return NOTIFY_OK;
4651
4652 nr_pages = 0;
4653 nr_pages_same = 1;
4654 /* check if all cpu sizes are same */
4655 for_each_buffer_cpu(buffer, cpu_i) {
4656 /* fill in the size from first enabled cpu */
4657 if (nr_pages == 0)
4658 nr_pages = buffer->buffers[cpu_i]->nr_pages;
4659 if (nr_pages != buffer->buffers[cpu_i]->nr_pages) {
4660 nr_pages_same = 0;
4661 break;
4662 }
4663 }
4664 /* allocate minimum pages, user can later expand it */
4665 if (!nr_pages_same)
4666 nr_pages = 2;
4667 buffer->buffers[cpu] =
4668 rb_allocate_cpu_buffer(buffer, nr_pages, cpu);
4669 if (!buffer->buffers[cpu]) {
4670 WARN(1, "failed to allocate ring buffer on CPU %ld\n",
4671 cpu);
4672 return NOTIFY_OK;
4673 }
4674 smp_wmb();
4675 cpumask_set_cpu(cpu, buffer->cpumask);
4676 break;
4677 case CPU_DOWN_PREPARE:
4678 case CPU_DOWN_PREPARE_FROZEN:
4679 /*
4680 * Do nothing.
4681 * If we were to free the buffer, then the user would
4682 * lose any trace that was in the buffer.
4683 */
4684 break;
4685 default:
4686 break;
4687 }
4688 return NOTIFY_OK;
4689}
4690#endif
4691
4692#ifdef CONFIG_RING_BUFFER_STARTUP_TEST
4693/*
4694 * This is a basic integrity check of the ring buffer.
4695 * Late in the boot cycle this test will run when configured in.
4696 * It will kick off a thread per CPU that will go into a loop
4697 * writing to the per cpu ring buffer various sizes of data.
4698 * Some of the data will be large items, some small.
4699 *
4700 * Another thread is created that goes into a spin, sending out
4701 * IPIs to the other CPUs to also write into the ring buffer.
4702 * this is to test the nesting ability of the buffer.
4703 *
4704 * Basic stats are recorded and reported. If something in the
4705 * ring buffer should happen that's not expected, a big warning
4706 * is displayed and all ring buffers are disabled.
4707 */
4708static struct task_struct *rb_threads[NR_CPUS] __initdata;
4709
4710struct rb_test_data {
4711 struct ring_buffer *buffer;
4712 unsigned long events;
4713 unsigned long bytes_written;
4714 unsigned long bytes_alloc;
4715 unsigned long bytes_dropped;
4716 unsigned long events_nested;
4717 unsigned long bytes_written_nested;
4718 unsigned long bytes_alloc_nested;
4719 unsigned long bytes_dropped_nested;
4720 int min_size_nested;
4721 int max_size_nested;
4722 int max_size;
4723 int min_size;
4724 int cpu;
4725 int cnt;
4726};
4727
4728static struct rb_test_data rb_data[NR_CPUS] __initdata;
4729
4730/* 1 meg per cpu */
4731#define RB_TEST_BUFFER_SIZE 1048576
4732
4733static char rb_string[] __initdata =
4734 "abcdefghijklmnopqrstuvwxyz1234567890!@#$%^&*()?+\\"
4735 "?+|:';\",.<>/?abcdefghijklmnopqrstuvwxyz1234567890"
4736 "!@#$%^&*()?+\\?+|:';\",.<>/?abcdefghijklmnopqrstuv";
4737
4738static bool rb_test_started __initdata;
4739
4740struct rb_item {
4741 int size;
4742 char str[];
4743};
4744
4745static __init int rb_write_something(struct rb_test_data *data, bool nested)
4746{
4747 struct ring_buffer_event *event;
4748 struct rb_item *item;
4749 bool started;
4750 int event_len;
4751 int size;
4752 int len;
4753 int cnt;
4754
4755 /* Have nested writes different that what is written */
4756 cnt = data->cnt + (nested ? 27 : 0);
4757
4758 /* Multiply cnt by ~e, to make some unique increment */
4759 size = (data->cnt * 68 / 25) % (sizeof(rb_string) - 1);
4760
4761 len = size + sizeof(struct rb_item);
4762
4763 started = rb_test_started;
4764 /* read rb_test_started before checking buffer enabled */
4765 smp_rmb();
4766
4767 event = ring_buffer_lock_reserve(data->buffer, len);
4768 if (!event) {
4769 /* Ignore dropped events before test starts. */
4770 if (started) {
4771 if (nested)
4772 data->bytes_dropped += len;
4773 else
4774 data->bytes_dropped_nested += len;
4775 }
4776 return len;
4777 }
4778
4779 event_len = ring_buffer_event_length(event);
4780
4781 if (RB_WARN_ON(data->buffer, event_len < len))
4782 goto out;
4783
4784 item = ring_buffer_event_data(event);
4785 item->size = size;
4786 memcpy(item->str, rb_string, size);
4787
4788 if (nested) {
4789 data->bytes_alloc_nested += event_len;
4790 data->bytes_written_nested += len;
4791 data->events_nested++;
4792 if (!data->min_size_nested || len < data->min_size_nested)
4793 data->min_size_nested = len;
4794 if (len > data->max_size_nested)
4795 data->max_size_nested = len;
4796 } else {
4797 data->bytes_alloc += event_len;
4798 data->bytes_written += len;
4799 data->events++;
4800 if (!data->min_size || len < data->min_size)
4801 data->max_size = len;
4802 if (len > data->max_size)
4803 data->max_size = len;
4804 }
4805
4806 out:
4807 ring_buffer_unlock_commit(data->buffer, event);
4808
4809 return 0;
4810}
4811
4812static __init int rb_test(void *arg)
4813{
4814 struct rb_test_data *data = arg;
4815
4816 while (!kthread_should_stop()) {
4817 rb_write_something(data, false);
4818 data->cnt++;
4819
4820 set_current_state(TASK_INTERRUPTIBLE);
4821 /* Now sleep between a min of 100-300us and a max of 1ms */
4822 usleep_range(((data->cnt % 3) + 1) * 100, 1000);
4823 }
4824
4825 return 0;
4826}
4827
4828static __init void rb_ipi(void *ignore)
4829{
4830 struct rb_test_data *data;
4831 int cpu = smp_processor_id();
4832
4833 data = &rb_data[cpu];
4834 rb_write_something(data, true);
4835}
4836
4837static __init int rb_hammer_test(void *arg)
4838{
4839 while (!kthread_should_stop()) {
4840
4841 /* Send an IPI to all cpus to write data! */
4842 smp_call_function(rb_ipi, NULL, 1);
4843 /* No sleep, but for non preempt, let others run */
4844 schedule();
4845 }
4846
4847 return 0;
4848}
4849
4850static __init int test_ringbuffer(void)
4851{
4852 struct task_struct *rb_hammer;
4853 struct ring_buffer *buffer;
4854 int cpu;
4855 int ret = 0;
4856
4857 pr_info("Running ring buffer tests...\n");
4858
4859 buffer = ring_buffer_alloc(RB_TEST_BUFFER_SIZE, RB_FL_OVERWRITE);
4860 if (WARN_ON(!buffer))
4861 return 0;
4862
4863 /* Disable buffer so that threads can't write to it yet */
4864 ring_buffer_record_off(buffer);
4865
4866 for_each_online_cpu(cpu) {
4867 rb_data[cpu].buffer = buffer;
4868 rb_data[cpu].cpu = cpu;
4869 rb_data[cpu].cnt = cpu;
4870 rb_threads[cpu] = kthread_create(rb_test, &rb_data[cpu],
4871 "rbtester/%d", cpu);
4872 if (WARN_ON(!rb_threads[cpu])) {
4873 pr_cont("FAILED\n");
4874 ret = -1;
4875 goto out_free;
4876 }
4877
4878 kthread_bind(rb_threads[cpu], cpu);
4879 wake_up_process(rb_threads[cpu]);
4880 }
4881
4882 /* Now create the rb hammer! */
4883 rb_hammer = kthread_run(rb_hammer_test, NULL, "rbhammer");
4884 if (WARN_ON(!rb_hammer)) {
4885 pr_cont("FAILED\n");
4886 ret = -1;
4887 goto out_free;
4888 }
4889
4890 ring_buffer_record_on(buffer);
4891 /*
4892 * Show buffer is enabled before setting rb_test_started.
4893 * Yes there's a small race window where events could be
4894 * dropped and the thread wont catch it. But when a ring
4895 * buffer gets enabled, there will always be some kind of
4896 * delay before other CPUs see it. Thus, we don't care about
4897 * those dropped events. We care about events dropped after
4898 * the threads see that the buffer is active.
4899 */
4900 smp_wmb();
4901 rb_test_started = true;
4902
4903 set_current_state(TASK_INTERRUPTIBLE);
4904 /* Just run for 10 seconds */;
4905 schedule_timeout(10 * HZ);
4906
4907 kthread_stop(rb_hammer);
4908
4909 out_free:
4910 for_each_online_cpu(cpu) {
4911 if (!rb_threads[cpu])
4912 break;
4913 kthread_stop(rb_threads[cpu]);
4914 }
4915 if (ret) {
4916 ring_buffer_free(buffer);
4917 return ret;
4918 }
4919
4920 /* Report! */
4921 pr_info("finished\n");
4922 for_each_online_cpu(cpu) {
4923 struct ring_buffer_event *event;
4924 struct rb_test_data *data = &rb_data[cpu];
4925 struct rb_item *item;
4926 unsigned long total_events;
4927 unsigned long total_dropped;
4928 unsigned long total_written;
4929 unsigned long total_alloc;
4930 unsigned long total_read = 0;
4931 unsigned long total_size = 0;
4932 unsigned long total_len = 0;
4933 unsigned long total_lost = 0;
4934 unsigned long lost;
4935 int big_event_size;
4936 int small_event_size;
4937
4938 ret = -1;
4939
4940 total_events = data->events + data->events_nested;
4941 total_written = data->bytes_written + data->bytes_written_nested;
4942 total_alloc = data->bytes_alloc + data->bytes_alloc_nested;
4943 total_dropped = data->bytes_dropped + data->bytes_dropped_nested;
4944
4945 big_event_size = data->max_size + data->max_size_nested;
4946 small_event_size = data->min_size + data->min_size_nested;
4947
4948 pr_info("CPU %d:\n", cpu);
4949 pr_info(" events: %ld\n", total_events);
4950 pr_info(" dropped bytes: %ld\n", total_dropped);
4951 pr_info(" alloced bytes: %ld\n", total_alloc);
4952 pr_info(" written bytes: %ld\n", total_written);
4953 pr_info(" biggest event: %d\n", big_event_size);
4954 pr_info(" smallest event: %d\n", small_event_size);
4955
4956 if (RB_WARN_ON(buffer, total_dropped))
4957 break;
4958
4959 ret = 0;
4960
4961 while ((event = ring_buffer_consume(buffer, cpu, NULL, &lost))) {
4962 total_lost += lost;
4963 item = ring_buffer_event_data(event);
4964 total_len += ring_buffer_event_length(event);
4965 total_size += item->size + sizeof(struct rb_item);
4966 if (memcmp(&item->str[0], rb_string, item->size) != 0) {
4967 pr_info("FAILED!\n");
4968 pr_info("buffer had: %.*s\n", item->size, item->str);
4969 pr_info("expected: %.*s\n", item->size, rb_string);
4970 RB_WARN_ON(buffer, 1);
4971 ret = -1;
4972 break;
4973 }
4974 total_read++;
4975 }
4976 if (ret)
4977 break;
4978
4979 ret = -1;
4980
4981 pr_info(" read events: %ld\n", total_read);
4982 pr_info(" lost events: %ld\n", total_lost);
4983 pr_info(" total events: %ld\n", total_lost + total_read);
4984 pr_info(" recorded len bytes: %ld\n", total_len);
4985 pr_info(" recorded size bytes: %ld\n", total_size);
4986 if (total_lost)
4987 pr_info(" With dropped events, record len and size may not match\n"
4988 " alloced and written from above\n");
4989 if (!total_lost) {
4990 if (RB_WARN_ON(buffer, total_len != total_alloc ||
4991 total_size != total_written))
4992 break;
4993 }
4994 if (RB_WARN_ON(buffer, total_lost + total_read != total_events))
4995 break;
4996
4997 ret = 0;
4998 }
4999 if (!ret)
5000 pr_info("Ring buffer PASSED!\n");
5001
5002 ring_buffer_free(buffer);
5003 return 0;
5004}
5005
5006late_initcall(test_ringbuffer);
5007#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/ring_buffer.h>
7#include <linux/trace_clock.h>
8#include <linux/spinlock.h>
9#include <linux/debugfs.h>
10#include <linux/uaccess.h>
11#include <linux/hardirq.h>
12#include <linux/kmemcheck.h>
13#include <linux/module.h>
14#include <linux/percpu.h>
15#include <linux/mutex.h>
16#include <linux/slab.h>
17#include <linux/init.h>
18#include <linux/hash.h>
19#include <linux/list.h>
20#include <linux/cpu.h>
21#include <linux/fs.h>
22
23#include <asm/local.h>
24#include "trace.h"
25
26static void update_pages_handler(struct work_struct *work);
27
28/*
29 * The ring buffer header is special. We must manually up keep it.
30 */
31int ring_buffer_print_entry_header(struct trace_seq *s)
32{
33 int ret;
34
35 ret = trace_seq_printf(s, "# compressed entry header\n");
36 ret = trace_seq_printf(s, "\ttype_len : 5 bits\n");
37 ret = trace_seq_printf(s, "\ttime_delta : 27 bits\n");
38 ret = trace_seq_printf(s, "\tarray : 32 bits\n");
39 ret = trace_seq_printf(s, "\n");
40 ret = trace_seq_printf(s, "\tpadding : type == %d\n",
41 RINGBUF_TYPE_PADDING);
42 ret = trace_seq_printf(s, "\ttime_extend : type == %d\n",
43 RINGBUF_TYPE_TIME_EXTEND);
44 ret = trace_seq_printf(s, "\tdata max type_len == %d\n",
45 RINGBUF_TYPE_DATA_TYPE_LEN_MAX);
46
47 return ret;
48}
49
50/*
51 * The ring buffer is made up of a list of pages. A separate list of pages is
52 * allocated for each CPU. A writer may only write to a buffer that is
53 * associated with the CPU it is currently executing on. A reader may read
54 * from any per cpu buffer.
55 *
56 * The reader is special. For each per cpu buffer, the reader has its own
57 * reader page. When a reader has read the entire reader page, this reader
58 * page is swapped with another page in the ring buffer.
59 *
60 * Now, as long as the writer is off the reader page, the reader can do what
61 * ever it wants with that page. The writer will never write to that page
62 * again (as long as it is out of the ring buffer).
63 *
64 * Here's some silly ASCII art.
65 *
66 * +------+
67 * |reader| RING BUFFER
68 * |page |
69 * +------+ +---+ +---+ +---+
70 * | |-->| |-->| |
71 * +---+ +---+ +---+
72 * ^ |
73 * | |
74 * +---------------+
75 *
76 *
77 * +------+
78 * |reader| RING BUFFER
79 * |page |------------------v
80 * +------+ +---+ +---+ +---+
81 * | |-->| |-->| |
82 * +---+ +---+ +---+
83 * ^ |
84 * | |
85 * +---------------+
86 *
87 *
88 * +------+
89 * |reader| RING BUFFER
90 * |page |------------------v
91 * +------+ +---+ +---+ +---+
92 * ^ | |-->| |-->| |
93 * | +---+ +---+ +---+
94 * | |
95 * | |
96 * +------------------------------+
97 *
98 *
99 * +------+
100 * |buffer| RING BUFFER
101 * |page |------------------v
102 * +------+ +---+ +---+ +---+
103 * ^ | | | |-->| |
104 * | New +---+ +---+ +---+
105 * | Reader------^ |
106 * | page |
107 * +------------------------------+
108 *
109 *
110 * After we make this swap, the reader can hand this page off to the splice
111 * code and be done with it. It can even allocate a new page if it needs to
112 * and swap that into the ring buffer.
113 *
114 * We will be using cmpxchg soon to make all this lockless.
115 *
116 */
117
118/*
119 * A fast way to enable or disable all ring buffers is to
120 * call tracing_on or tracing_off. Turning off the ring buffers
121 * prevents all ring buffers from being recorded to.
122 * Turning this switch on, makes it OK to write to the
123 * ring buffer, if the ring buffer is enabled itself.
124 *
125 * There's three layers that must be on in order to write
126 * to the ring buffer.
127 *
128 * 1) This global flag must be set.
129 * 2) The ring buffer must be enabled for recording.
130 * 3) The per cpu buffer must be enabled for recording.
131 *
132 * In case of an anomaly, this global flag has a bit set that
133 * will permantly disable all ring buffers.
134 */
135
136/*
137 * Global flag to disable all recording to ring buffers
138 * This has two bits: ON, DISABLED
139 *
140 * ON DISABLED
141 * ---- ----------
142 * 0 0 : ring buffers are off
143 * 1 0 : ring buffers are on
144 * X 1 : ring buffers are permanently disabled
145 */
146
147enum {
148 RB_BUFFERS_ON_BIT = 0,
149 RB_BUFFERS_DISABLED_BIT = 1,
150};
151
152enum {
153 RB_BUFFERS_ON = 1 << RB_BUFFERS_ON_BIT,
154 RB_BUFFERS_DISABLED = 1 << RB_BUFFERS_DISABLED_BIT,
155};
156
157static unsigned long ring_buffer_flags __read_mostly = RB_BUFFERS_ON;
158
159/* Used for individual buffers (after the counter) */
160#define RB_BUFFER_OFF (1 << 20)
161
162#define BUF_PAGE_HDR_SIZE offsetof(struct buffer_data_page, data)
163
164/**
165 * tracing_off_permanent - permanently disable ring buffers
166 *
167 * This function, once called, will disable all ring buffers
168 * permanently.
169 */
170void tracing_off_permanent(void)
171{
172 set_bit(RB_BUFFERS_DISABLED_BIT, &ring_buffer_flags);
173}
174
175#define RB_EVNT_HDR_SIZE (offsetof(struct ring_buffer_event, array))
176#define RB_ALIGNMENT 4U
177#define RB_MAX_SMALL_DATA (RB_ALIGNMENT * RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
178#define RB_EVNT_MIN_SIZE 8U /* two 32bit words */
179
180#if !defined(CONFIG_64BIT) || defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
181# define RB_FORCE_8BYTE_ALIGNMENT 0
182# define RB_ARCH_ALIGNMENT RB_ALIGNMENT
183#else
184# define RB_FORCE_8BYTE_ALIGNMENT 1
185# define RB_ARCH_ALIGNMENT 8U
186#endif
187
188/* define RINGBUF_TYPE_DATA for 'case RINGBUF_TYPE_DATA:' */
189#define RINGBUF_TYPE_DATA 0 ... RINGBUF_TYPE_DATA_TYPE_LEN_MAX
190
191enum {
192 RB_LEN_TIME_EXTEND = 8,
193 RB_LEN_TIME_STAMP = 16,
194};
195
196#define skip_time_extend(event) \
197 ((struct ring_buffer_event *)((char *)event + RB_LEN_TIME_EXTEND))
198
199static inline int rb_null_event(struct ring_buffer_event *event)
200{
201 return event->type_len == RINGBUF_TYPE_PADDING && !event->time_delta;
202}
203
204static void rb_event_set_padding(struct ring_buffer_event *event)
205{
206 /* padding has a NULL time_delta */
207 event->type_len = RINGBUF_TYPE_PADDING;
208 event->time_delta = 0;
209}
210
211static unsigned
212rb_event_data_length(struct ring_buffer_event *event)
213{
214 unsigned length;
215
216 if (event->type_len)
217 length = event->type_len * RB_ALIGNMENT;
218 else
219 length = event->array[0];
220 return length + RB_EVNT_HDR_SIZE;
221}
222
223/*
224 * Return the length of the given event. Will return
225 * the length of the time extend if the event is a
226 * time extend.
227 */
228static inline unsigned
229rb_event_length(struct ring_buffer_event *event)
230{
231 switch (event->type_len) {
232 case RINGBUF_TYPE_PADDING:
233 if (rb_null_event(event))
234 /* undefined */
235 return -1;
236 return event->array[0] + RB_EVNT_HDR_SIZE;
237
238 case RINGBUF_TYPE_TIME_EXTEND:
239 return RB_LEN_TIME_EXTEND;
240
241 case RINGBUF_TYPE_TIME_STAMP:
242 return RB_LEN_TIME_STAMP;
243
244 case RINGBUF_TYPE_DATA:
245 return rb_event_data_length(event);
246 default:
247 BUG();
248 }
249 /* not hit */
250 return 0;
251}
252
253/*
254 * Return total length of time extend and data,
255 * or just the event length for all other events.
256 */
257static inline unsigned
258rb_event_ts_length(struct ring_buffer_event *event)
259{
260 unsigned len = 0;
261
262 if (event->type_len == RINGBUF_TYPE_TIME_EXTEND) {
263 /* time extends include the data event after it */
264 len = RB_LEN_TIME_EXTEND;
265 event = skip_time_extend(event);
266 }
267 return len + rb_event_length(event);
268}
269
270/**
271 * ring_buffer_event_length - return the length of the event
272 * @event: the event to get the length of
273 *
274 * Returns the size of the data load of a data event.
275 * If the event is something other than a data event, it
276 * returns the size of the event itself. With the exception
277 * of a TIME EXTEND, where it still returns the size of the
278 * data load of the data event after it.
279 */
280unsigned ring_buffer_event_length(struct ring_buffer_event *event)
281{
282 unsigned length;
283
284 if (event->type_len == RINGBUF_TYPE_TIME_EXTEND)
285 event = skip_time_extend(event);
286
287 length = rb_event_length(event);
288 if (event->type_len > RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
289 return length;
290 length -= RB_EVNT_HDR_SIZE;
291 if (length > RB_MAX_SMALL_DATA + sizeof(event->array[0]))
292 length -= sizeof(event->array[0]);
293 return length;
294}
295EXPORT_SYMBOL_GPL(ring_buffer_event_length);
296
297/* inline for ring buffer fast paths */
298static void *
299rb_event_data(struct ring_buffer_event *event)
300{
301 if (event->type_len == RINGBUF_TYPE_TIME_EXTEND)
302 event = skip_time_extend(event);
303 BUG_ON(event->type_len > RINGBUF_TYPE_DATA_TYPE_LEN_MAX);
304 /* If length is in len field, then array[0] has the data */
305 if (event->type_len)
306 return (void *)&event->array[0];
307 /* Otherwise length is in array[0] and array[1] has the data */
308 return (void *)&event->array[1];
309}
310
311/**
312 * ring_buffer_event_data - return the data of the event
313 * @event: the event to get the data from
314 */
315void *ring_buffer_event_data(struct ring_buffer_event *event)
316{
317 return rb_event_data(event);
318}
319EXPORT_SYMBOL_GPL(ring_buffer_event_data);
320
321#define for_each_buffer_cpu(buffer, cpu) \
322 for_each_cpu(cpu, buffer->cpumask)
323
324#define TS_SHIFT 27
325#define TS_MASK ((1ULL << TS_SHIFT) - 1)
326#define TS_DELTA_TEST (~TS_MASK)
327
328/* Flag when events were overwritten */
329#define RB_MISSED_EVENTS (1 << 31)
330/* Missed count stored at end */
331#define RB_MISSED_STORED (1 << 30)
332
333struct buffer_data_page {
334 u64 time_stamp; /* page time stamp */
335 local_t commit; /* write committed index */
336 unsigned char data[]; /* data of buffer page */
337};
338
339/*
340 * Note, the buffer_page list must be first. The buffer pages
341 * are allocated in cache lines, which means that each buffer
342 * page will be at the beginning of a cache line, and thus
343 * the least significant bits will be zero. We use this to
344 * add flags in the list struct pointers, to make the ring buffer
345 * lockless.
346 */
347struct buffer_page {
348 struct list_head list; /* list of buffer pages */
349 local_t write; /* index for next write */
350 unsigned read; /* index for next read */
351 local_t entries; /* entries on this page */
352 unsigned long real_end; /* real end of data */
353 struct buffer_data_page *page; /* Actual data page */
354};
355
356/*
357 * The buffer page counters, write and entries, must be reset
358 * atomically when crossing page boundaries. To synchronize this
359 * update, two counters are inserted into the number. One is
360 * the actual counter for the write position or count on the page.
361 *
362 * The other is a counter of updaters. Before an update happens
363 * the update partition of the counter is incremented. This will
364 * allow the updater to update the counter atomically.
365 *
366 * The counter is 20 bits, and the state data is 12.
367 */
368#define RB_WRITE_MASK 0xfffff
369#define RB_WRITE_INTCNT (1 << 20)
370
371static void rb_init_page(struct buffer_data_page *bpage)
372{
373 local_set(&bpage->commit, 0);
374}
375
376/**
377 * ring_buffer_page_len - the size of data on the page.
378 * @page: The page to read
379 *
380 * Returns the amount of data on the page, including buffer page header.
381 */
382size_t ring_buffer_page_len(void *page)
383{
384 return local_read(&((struct buffer_data_page *)page)->commit)
385 + BUF_PAGE_HDR_SIZE;
386}
387
388/*
389 * Also stolen from mm/slob.c. Thanks to Mathieu Desnoyers for pointing
390 * this issue out.
391 */
392static void free_buffer_page(struct buffer_page *bpage)
393{
394 free_page((unsigned long)bpage->page);
395 kfree(bpage);
396}
397
398/*
399 * We need to fit the time_stamp delta into 27 bits.
400 */
401static inline int test_time_stamp(u64 delta)
402{
403 if (delta & TS_DELTA_TEST)
404 return 1;
405 return 0;
406}
407
408#define BUF_PAGE_SIZE (PAGE_SIZE - BUF_PAGE_HDR_SIZE)
409
410/* Max payload is BUF_PAGE_SIZE - header (8bytes) */
411#define BUF_MAX_DATA_SIZE (BUF_PAGE_SIZE - (sizeof(u32) * 2))
412
413int ring_buffer_print_page_header(struct trace_seq *s)
414{
415 struct buffer_data_page field;
416 int ret;
417
418 ret = trace_seq_printf(s, "\tfield: u64 timestamp;\t"
419 "offset:0;\tsize:%u;\tsigned:%u;\n",
420 (unsigned int)sizeof(field.time_stamp),
421 (unsigned int)is_signed_type(u64));
422
423 ret = trace_seq_printf(s, "\tfield: local_t commit;\t"
424 "offset:%u;\tsize:%u;\tsigned:%u;\n",
425 (unsigned int)offsetof(typeof(field), commit),
426 (unsigned int)sizeof(field.commit),
427 (unsigned int)is_signed_type(long));
428
429 ret = trace_seq_printf(s, "\tfield: int overwrite;\t"
430 "offset:%u;\tsize:%u;\tsigned:%u;\n",
431 (unsigned int)offsetof(typeof(field), commit),
432 1,
433 (unsigned int)is_signed_type(long));
434
435 ret = trace_seq_printf(s, "\tfield: char data;\t"
436 "offset:%u;\tsize:%u;\tsigned:%u;\n",
437 (unsigned int)offsetof(typeof(field), data),
438 (unsigned int)BUF_PAGE_SIZE,
439 (unsigned int)is_signed_type(char));
440
441 return ret;
442}
443
444/*
445 * head_page == tail_page && head == tail then buffer is empty.
446 */
447struct ring_buffer_per_cpu {
448 int cpu;
449 atomic_t record_disabled;
450 struct ring_buffer *buffer;
451 raw_spinlock_t reader_lock; /* serialize readers */
452 arch_spinlock_t lock;
453 struct lock_class_key lock_key;
454 unsigned int nr_pages;
455 struct list_head *pages;
456 struct buffer_page *head_page; /* read from head */
457 struct buffer_page *tail_page; /* write to tail */
458 struct buffer_page *commit_page; /* committed pages */
459 struct buffer_page *reader_page;
460 unsigned long lost_events;
461 unsigned long last_overrun;
462 local_t entries_bytes;
463 local_t commit_overrun;
464 local_t overrun;
465 local_t entries;
466 local_t committing;
467 local_t commits;
468 unsigned long read;
469 unsigned long read_bytes;
470 u64 write_stamp;
471 u64 read_stamp;
472 /* ring buffer pages to update, > 0 to add, < 0 to remove */
473 int nr_pages_to_update;
474 struct list_head new_pages; /* new pages to add */
475 struct work_struct update_pages_work;
476 struct completion update_done;
477};
478
479struct ring_buffer {
480 unsigned flags;
481 int cpus;
482 atomic_t record_disabled;
483 atomic_t resize_disabled;
484 cpumask_var_t cpumask;
485
486 struct lock_class_key *reader_lock_key;
487
488 struct mutex mutex;
489
490 struct ring_buffer_per_cpu **buffers;
491
492#ifdef CONFIG_HOTPLUG_CPU
493 struct notifier_block cpu_notify;
494#endif
495 u64 (*clock)(void);
496};
497
498struct ring_buffer_iter {
499 struct ring_buffer_per_cpu *cpu_buffer;
500 unsigned long head;
501 struct buffer_page *head_page;
502 struct buffer_page *cache_reader_page;
503 unsigned long cache_read;
504 u64 read_stamp;
505};
506
507/* buffer may be either ring_buffer or ring_buffer_per_cpu */
508#define RB_WARN_ON(b, cond) \
509 ({ \
510 int _____ret = unlikely(cond); \
511 if (_____ret) { \
512 if (__same_type(*(b), struct ring_buffer_per_cpu)) { \
513 struct ring_buffer_per_cpu *__b = \
514 (void *)b; \
515 atomic_inc(&__b->buffer->record_disabled); \
516 } else \
517 atomic_inc(&b->record_disabled); \
518 WARN_ON(1); \
519 } \
520 _____ret; \
521 })
522
523/* Up this if you want to test the TIME_EXTENTS and normalization */
524#define DEBUG_SHIFT 0
525
526static inline u64 rb_time_stamp(struct ring_buffer *buffer)
527{
528 /* shift to debug/test normalization and TIME_EXTENTS */
529 return buffer->clock() << DEBUG_SHIFT;
530}
531
532u64 ring_buffer_time_stamp(struct ring_buffer *buffer, int cpu)
533{
534 u64 time;
535
536 preempt_disable_notrace();
537 time = rb_time_stamp(buffer);
538 preempt_enable_no_resched_notrace();
539
540 return time;
541}
542EXPORT_SYMBOL_GPL(ring_buffer_time_stamp);
543
544void ring_buffer_normalize_time_stamp(struct ring_buffer *buffer,
545 int cpu, u64 *ts)
546{
547 /* Just stupid testing the normalize function and deltas */
548 *ts >>= DEBUG_SHIFT;
549}
550EXPORT_SYMBOL_GPL(ring_buffer_normalize_time_stamp);
551
552/*
553 * Making the ring buffer lockless makes things tricky.
554 * Although writes only happen on the CPU that they are on,
555 * and they only need to worry about interrupts. Reads can
556 * happen on any CPU.
557 *
558 * The reader page is always off the ring buffer, but when the
559 * reader finishes with a page, it needs to swap its page with
560 * a new one from the buffer. The reader needs to take from
561 * the head (writes go to the tail). But if a writer is in overwrite
562 * mode and wraps, it must push the head page forward.
563 *
564 * Here lies the problem.
565 *
566 * The reader must be careful to replace only the head page, and
567 * not another one. As described at the top of the file in the
568 * ASCII art, the reader sets its old page to point to the next
569 * page after head. It then sets the page after head to point to
570 * the old reader page. But if the writer moves the head page
571 * during this operation, the reader could end up with the tail.
572 *
573 * We use cmpxchg to help prevent this race. We also do something
574 * special with the page before head. We set the LSB to 1.
575 *
576 * When the writer must push the page forward, it will clear the
577 * bit that points to the head page, move the head, and then set
578 * the bit that points to the new head page.
579 *
580 * We also don't want an interrupt coming in and moving the head
581 * page on another writer. Thus we use the second LSB to catch
582 * that too. Thus:
583 *
584 * head->list->prev->next bit 1 bit 0
585 * ------- -------
586 * Normal page 0 0
587 * Points to head page 0 1
588 * New head page 1 0
589 *
590 * Note we can not trust the prev pointer of the head page, because:
591 *
592 * +----+ +-----+ +-----+
593 * | |------>| T |---X--->| N |
594 * | |<------| | | |
595 * +----+ +-----+ +-----+
596 * ^ ^ |
597 * | +-----+ | |
598 * +----------| R |----------+ |
599 * | |<-----------+
600 * +-----+
601 *
602 * Key: ---X--> HEAD flag set in pointer
603 * T Tail page
604 * R Reader page
605 * N Next page
606 *
607 * (see __rb_reserve_next() to see where this happens)
608 *
609 * What the above shows is that the reader just swapped out
610 * the reader page with a page in the buffer, but before it
611 * could make the new header point back to the new page added
612 * it was preempted by a writer. The writer moved forward onto
613 * the new page added by the reader and is about to move forward
614 * again.
615 *
616 * You can see, it is legitimate for the previous pointer of
617 * the head (or any page) not to point back to itself. But only
618 * temporarially.
619 */
620
621#define RB_PAGE_NORMAL 0UL
622#define RB_PAGE_HEAD 1UL
623#define RB_PAGE_UPDATE 2UL
624
625
626#define RB_FLAG_MASK 3UL
627
628/* PAGE_MOVED is not part of the mask */
629#define RB_PAGE_MOVED 4UL
630
631/*
632 * rb_list_head - remove any bit
633 */
634static struct list_head *rb_list_head(struct list_head *list)
635{
636 unsigned long val = (unsigned long)list;
637
638 return (struct list_head *)(val & ~RB_FLAG_MASK);
639}
640
641/*
642 * rb_is_head_page - test if the given page is the head page
643 *
644 * Because the reader may move the head_page pointer, we can
645 * not trust what the head page is (it may be pointing to
646 * the reader page). But if the next page is a header page,
647 * its flags will be non zero.
648 */
649static inline int
650rb_is_head_page(struct ring_buffer_per_cpu *cpu_buffer,
651 struct buffer_page *page, struct list_head *list)
652{
653 unsigned long val;
654
655 val = (unsigned long)list->next;
656
657 if ((val & ~RB_FLAG_MASK) != (unsigned long)&page->list)
658 return RB_PAGE_MOVED;
659
660 return val & RB_FLAG_MASK;
661}
662
663/*
664 * rb_is_reader_page
665 *
666 * The unique thing about the reader page, is that, if the
667 * writer is ever on it, the previous pointer never points
668 * back to the reader page.
669 */
670static int rb_is_reader_page(struct buffer_page *page)
671{
672 struct list_head *list = page->list.prev;
673
674 return rb_list_head(list->next) != &page->list;
675}
676
677/*
678 * rb_set_list_to_head - set a list_head to be pointing to head.
679 */
680static void rb_set_list_to_head(struct ring_buffer_per_cpu *cpu_buffer,
681 struct list_head *list)
682{
683 unsigned long *ptr;
684
685 ptr = (unsigned long *)&list->next;
686 *ptr |= RB_PAGE_HEAD;
687 *ptr &= ~RB_PAGE_UPDATE;
688}
689
690/*
691 * rb_head_page_activate - sets up head page
692 */
693static void rb_head_page_activate(struct ring_buffer_per_cpu *cpu_buffer)
694{
695 struct buffer_page *head;
696
697 head = cpu_buffer->head_page;
698 if (!head)
699 return;
700
701 /*
702 * Set the previous list pointer to have the HEAD flag.
703 */
704 rb_set_list_to_head(cpu_buffer, head->list.prev);
705}
706
707static void rb_list_head_clear(struct list_head *list)
708{
709 unsigned long *ptr = (unsigned long *)&list->next;
710
711 *ptr &= ~RB_FLAG_MASK;
712}
713
714/*
715 * rb_head_page_dactivate - clears head page ptr (for free list)
716 */
717static void
718rb_head_page_deactivate(struct ring_buffer_per_cpu *cpu_buffer)
719{
720 struct list_head *hd;
721
722 /* Go through the whole list and clear any pointers found. */
723 rb_list_head_clear(cpu_buffer->pages);
724
725 list_for_each(hd, cpu_buffer->pages)
726 rb_list_head_clear(hd);
727}
728
729static int rb_head_page_set(struct ring_buffer_per_cpu *cpu_buffer,
730 struct buffer_page *head,
731 struct buffer_page *prev,
732 int old_flag, int new_flag)
733{
734 struct list_head *list;
735 unsigned long val = (unsigned long)&head->list;
736 unsigned long ret;
737
738 list = &prev->list;
739
740 val &= ~RB_FLAG_MASK;
741
742 ret = cmpxchg((unsigned long *)&list->next,
743 val | old_flag, val | new_flag);
744
745 /* check if the reader took the page */
746 if ((ret & ~RB_FLAG_MASK) != val)
747 return RB_PAGE_MOVED;
748
749 return ret & RB_FLAG_MASK;
750}
751
752static int rb_head_page_set_update(struct ring_buffer_per_cpu *cpu_buffer,
753 struct buffer_page *head,
754 struct buffer_page *prev,
755 int old_flag)
756{
757 return rb_head_page_set(cpu_buffer, head, prev,
758 old_flag, RB_PAGE_UPDATE);
759}
760
761static int rb_head_page_set_head(struct ring_buffer_per_cpu *cpu_buffer,
762 struct buffer_page *head,
763 struct buffer_page *prev,
764 int old_flag)
765{
766 return rb_head_page_set(cpu_buffer, head, prev,
767 old_flag, RB_PAGE_HEAD);
768}
769
770static int rb_head_page_set_normal(struct ring_buffer_per_cpu *cpu_buffer,
771 struct buffer_page *head,
772 struct buffer_page *prev,
773 int old_flag)
774{
775 return rb_head_page_set(cpu_buffer, head, prev,
776 old_flag, RB_PAGE_NORMAL);
777}
778
779static inline void rb_inc_page(struct ring_buffer_per_cpu *cpu_buffer,
780 struct buffer_page **bpage)
781{
782 struct list_head *p = rb_list_head((*bpage)->list.next);
783
784 *bpage = list_entry(p, struct buffer_page, list);
785}
786
787static struct buffer_page *
788rb_set_head_page(struct ring_buffer_per_cpu *cpu_buffer)
789{
790 struct buffer_page *head;
791 struct buffer_page *page;
792 struct list_head *list;
793 int i;
794
795 if (RB_WARN_ON(cpu_buffer, !cpu_buffer->head_page))
796 return NULL;
797
798 /* sanity check */
799 list = cpu_buffer->pages;
800 if (RB_WARN_ON(cpu_buffer, rb_list_head(list->prev->next) != list))
801 return NULL;
802
803 page = head = cpu_buffer->head_page;
804 /*
805 * It is possible that the writer moves the header behind
806 * where we started, and we miss in one loop.
807 * A second loop should grab the header, but we'll do
808 * three loops just because I'm paranoid.
809 */
810 for (i = 0; i < 3; i++) {
811 do {
812 if (rb_is_head_page(cpu_buffer, page, page->list.prev)) {
813 cpu_buffer->head_page = page;
814 return page;
815 }
816 rb_inc_page(cpu_buffer, &page);
817 } while (page != head);
818 }
819
820 RB_WARN_ON(cpu_buffer, 1);
821
822 return NULL;
823}
824
825static int rb_head_page_replace(struct buffer_page *old,
826 struct buffer_page *new)
827{
828 unsigned long *ptr = (unsigned long *)&old->list.prev->next;
829 unsigned long val;
830 unsigned long ret;
831
832 val = *ptr & ~RB_FLAG_MASK;
833 val |= RB_PAGE_HEAD;
834
835 ret = cmpxchg(ptr, val, (unsigned long)&new->list);
836
837 return ret == val;
838}
839
840/*
841 * rb_tail_page_update - move the tail page forward
842 *
843 * Returns 1 if moved tail page, 0 if someone else did.
844 */
845static int rb_tail_page_update(struct ring_buffer_per_cpu *cpu_buffer,
846 struct buffer_page *tail_page,
847 struct buffer_page *next_page)
848{
849 struct buffer_page *old_tail;
850 unsigned long old_entries;
851 unsigned long old_write;
852 int ret = 0;
853
854 /*
855 * The tail page now needs to be moved forward.
856 *
857 * We need to reset the tail page, but without messing
858 * with possible erasing of data brought in by interrupts
859 * that have moved the tail page and are currently on it.
860 *
861 * We add a counter to the write field to denote this.
862 */
863 old_write = local_add_return(RB_WRITE_INTCNT, &next_page->write);
864 old_entries = local_add_return(RB_WRITE_INTCNT, &next_page->entries);
865
866 /*
867 * Just make sure we have seen our old_write and synchronize
868 * with any interrupts that come in.
869 */
870 barrier();
871
872 /*
873 * If the tail page is still the same as what we think
874 * it is, then it is up to us to update the tail
875 * pointer.
876 */
877 if (tail_page == cpu_buffer->tail_page) {
878 /* Zero the write counter */
879 unsigned long val = old_write & ~RB_WRITE_MASK;
880 unsigned long eval = old_entries & ~RB_WRITE_MASK;
881
882 /*
883 * This will only succeed if an interrupt did
884 * not come in and change it. In which case, we
885 * do not want to modify it.
886 *
887 * We add (void) to let the compiler know that we do not care
888 * about the return value of these functions. We use the
889 * cmpxchg to only update if an interrupt did not already
890 * do it for us. If the cmpxchg fails, we don't care.
891 */
892 (void)local_cmpxchg(&next_page->write, old_write, val);
893 (void)local_cmpxchg(&next_page->entries, old_entries, eval);
894
895 /*
896 * No need to worry about races with clearing out the commit.
897 * it only can increment when a commit takes place. But that
898 * only happens in the outer most nested commit.
899 */
900 local_set(&next_page->page->commit, 0);
901
902 old_tail = cmpxchg(&cpu_buffer->tail_page,
903 tail_page, next_page);
904
905 if (old_tail == tail_page)
906 ret = 1;
907 }
908
909 return ret;
910}
911
912static int rb_check_bpage(struct ring_buffer_per_cpu *cpu_buffer,
913 struct buffer_page *bpage)
914{
915 unsigned long val = (unsigned long)bpage;
916
917 if (RB_WARN_ON(cpu_buffer, val & RB_FLAG_MASK))
918 return 1;
919
920 return 0;
921}
922
923/**
924 * rb_check_list - make sure a pointer to a list has the last bits zero
925 */
926static int rb_check_list(struct ring_buffer_per_cpu *cpu_buffer,
927 struct list_head *list)
928{
929 if (RB_WARN_ON(cpu_buffer, rb_list_head(list->prev) != list->prev))
930 return 1;
931 if (RB_WARN_ON(cpu_buffer, rb_list_head(list->next) != list->next))
932 return 1;
933 return 0;
934}
935
936/**
937 * check_pages - integrity check of buffer pages
938 * @cpu_buffer: CPU buffer with pages to test
939 *
940 * As a safety measure we check to make sure the data pages have not
941 * been corrupted.
942 */
943static int rb_check_pages(struct ring_buffer_per_cpu *cpu_buffer)
944{
945 struct list_head *head = cpu_buffer->pages;
946 struct buffer_page *bpage, *tmp;
947
948 /* Reset the head page if it exists */
949 if (cpu_buffer->head_page)
950 rb_set_head_page(cpu_buffer);
951
952 rb_head_page_deactivate(cpu_buffer);
953
954 if (RB_WARN_ON(cpu_buffer, head->next->prev != head))
955 return -1;
956 if (RB_WARN_ON(cpu_buffer, head->prev->next != head))
957 return -1;
958
959 if (rb_check_list(cpu_buffer, head))
960 return -1;
961
962 list_for_each_entry_safe(bpage, tmp, head, list) {
963 if (RB_WARN_ON(cpu_buffer,
964 bpage->list.next->prev != &bpage->list))
965 return -1;
966 if (RB_WARN_ON(cpu_buffer,
967 bpage->list.prev->next != &bpage->list))
968 return -1;
969 if (rb_check_list(cpu_buffer, &bpage->list))
970 return -1;
971 }
972
973 rb_head_page_activate(cpu_buffer);
974
975 return 0;
976}
977
978static int __rb_allocate_pages(int nr_pages, struct list_head *pages, int cpu)
979{
980 int i;
981 struct buffer_page *bpage, *tmp;
982
983 for (i = 0; i < nr_pages; i++) {
984 struct page *page;
985 /*
986 * __GFP_NORETRY flag makes sure that the allocation fails
987 * gracefully without invoking oom-killer and the system is
988 * not destabilized.
989 */
990 bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
991 GFP_KERNEL | __GFP_NORETRY,
992 cpu_to_node(cpu));
993 if (!bpage)
994 goto free_pages;
995
996 list_add(&bpage->list, pages);
997
998 page = alloc_pages_node(cpu_to_node(cpu),
999 GFP_KERNEL | __GFP_NORETRY, 0);
1000 if (!page)
1001 goto free_pages;
1002 bpage->page = page_address(page);
1003 rb_init_page(bpage->page);
1004 }
1005
1006 return 0;
1007
1008free_pages:
1009 list_for_each_entry_safe(bpage, tmp, pages, list) {
1010 list_del_init(&bpage->list);
1011 free_buffer_page(bpage);
1012 }
1013
1014 return -ENOMEM;
1015}
1016
1017static int rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
1018 unsigned nr_pages)
1019{
1020 LIST_HEAD(pages);
1021
1022 WARN_ON(!nr_pages);
1023
1024 if (__rb_allocate_pages(nr_pages, &pages, cpu_buffer->cpu))
1025 return -ENOMEM;
1026
1027 /*
1028 * The ring buffer page list is a circular list that does not
1029 * start and end with a list head. All page list items point to
1030 * other pages.
1031 */
1032 cpu_buffer->pages = pages.next;
1033 list_del(&pages);
1034
1035 cpu_buffer->nr_pages = nr_pages;
1036
1037 rb_check_pages(cpu_buffer);
1038
1039 return 0;
1040}
1041
1042static struct ring_buffer_per_cpu *
1043rb_allocate_cpu_buffer(struct ring_buffer *buffer, int nr_pages, int cpu)
1044{
1045 struct ring_buffer_per_cpu *cpu_buffer;
1046 struct buffer_page *bpage;
1047 struct page *page;
1048 int ret;
1049
1050 cpu_buffer = kzalloc_node(ALIGN(sizeof(*cpu_buffer), cache_line_size()),
1051 GFP_KERNEL, cpu_to_node(cpu));
1052 if (!cpu_buffer)
1053 return NULL;
1054
1055 cpu_buffer->cpu = cpu;
1056 cpu_buffer->buffer = buffer;
1057 raw_spin_lock_init(&cpu_buffer->reader_lock);
1058 lockdep_set_class(&cpu_buffer->reader_lock, buffer->reader_lock_key);
1059 cpu_buffer->lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
1060 INIT_WORK(&cpu_buffer->update_pages_work, update_pages_handler);
1061 init_completion(&cpu_buffer->update_done);
1062
1063 bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
1064 GFP_KERNEL, cpu_to_node(cpu));
1065 if (!bpage)
1066 goto fail_free_buffer;
1067
1068 rb_check_bpage(cpu_buffer, bpage);
1069
1070 cpu_buffer->reader_page = bpage;
1071 page = alloc_pages_node(cpu_to_node(cpu), GFP_KERNEL, 0);
1072 if (!page)
1073 goto fail_free_reader;
1074 bpage->page = page_address(page);
1075 rb_init_page(bpage->page);
1076
1077 INIT_LIST_HEAD(&cpu_buffer->reader_page->list);
1078 INIT_LIST_HEAD(&cpu_buffer->new_pages);
1079
1080 ret = rb_allocate_pages(cpu_buffer, nr_pages);
1081 if (ret < 0)
1082 goto fail_free_reader;
1083
1084 cpu_buffer->head_page
1085 = list_entry(cpu_buffer->pages, struct buffer_page, list);
1086 cpu_buffer->tail_page = cpu_buffer->commit_page = cpu_buffer->head_page;
1087
1088 rb_head_page_activate(cpu_buffer);
1089
1090 return cpu_buffer;
1091
1092 fail_free_reader:
1093 free_buffer_page(cpu_buffer->reader_page);
1094
1095 fail_free_buffer:
1096 kfree(cpu_buffer);
1097 return NULL;
1098}
1099
1100static void rb_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
1101{
1102 struct list_head *head = cpu_buffer->pages;
1103 struct buffer_page *bpage, *tmp;
1104
1105 free_buffer_page(cpu_buffer->reader_page);
1106
1107 rb_head_page_deactivate(cpu_buffer);
1108
1109 if (head) {
1110 list_for_each_entry_safe(bpage, tmp, head, list) {
1111 list_del_init(&bpage->list);
1112 free_buffer_page(bpage);
1113 }
1114 bpage = list_entry(head, struct buffer_page, list);
1115 free_buffer_page(bpage);
1116 }
1117
1118 kfree(cpu_buffer);
1119}
1120
1121#ifdef CONFIG_HOTPLUG_CPU
1122static int rb_cpu_notify(struct notifier_block *self,
1123 unsigned long action, void *hcpu);
1124#endif
1125
1126/**
1127 * ring_buffer_alloc - allocate a new ring_buffer
1128 * @size: the size in bytes per cpu that is needed.
1129 * @flags: attributes to set for the ring buffer.
1130 *
1131 * Currently the only flag that is available is the RB_FL_OVERWRITE
1132 * flag. This flag means that the buffer will overwrite old data
1133 * when the buffer wraps. If this flag is not set, the buffer will
1134 * drop data when the tail hits the head.
1135 */
1136struct ring_buffer *__ring_buffer_alloc(unsigned long size, unsigned flags,
1137 struct lock_class_key *key)
1138{
1139 struct ring_buffer *buffer;
1140 int bsize;
1141 int cpu, nr_pages;
1142
1143 /* keep it in its own cache line */
1144 buffer = kzalloc(ALIGN(sizeof(*buffer), cache_line_size()),
1145 GFP_KERNEL);
1146 if (!buffer)
1147 return NULL;
1148
1149 if (!alloc_cpumask_var(&buffer->cpumask, GFP_KERNEL))
1150 goto fail_free_buffer;
1151
1152 nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
1153 buffer->flags = flags;
1154 buffer->clock = trace_clock_local;
1155 buffer->reader_lock_key = key;
1156
1157 /* need at least two pages */
1158 if (nr_pages < 2)
1159 nr_pages = 2;
1160
1161 /*
1162 * In case of non-hotplug cpu, if the ring-buffer is allocated
1163 * in early initcall, it will not be notified of secondary cpus.
1164 * In that off case, we need to allocate for all possible cpus.
1165 */
1166#ifdef CONFIG_HOTPLUG_CPU
1167 get_online_cpus();
1168 cpumask_copy(buffer->cpumask, cpu_online_mask);
1169#else
1170 cpumask_copy(buffer->cpumask, cpu_possible_mask);
1171#endif
1172 buffer->cpus = nr_cpu_ids;
1173
1174 bsize = sizeof(void *) * nr_cpu_ids;
1175 buffer->buffers = kzalloc(ALIGN(bsize, cache_line_size()),
1176 GFP_KERNEL);
1177 if (!buffer->buffers)
1178 goto fail_free_cpumask;
1179
1180 for_each_buffer_cpu(buffer, cpu) {
1181 buffer->buffers[cpu] =
1182 rb_allocate_cpu_buffer(buffer, nr_pages, cpu);
1183 if (!buffer->buffers[cpu])
1184 goto fail_free_buffers;
1185 }
1186
1187#ifdef CONFIG_HOTPLUG_CPU
1188 buffer->cpu_notify.notifier_call = rb_cpu_notify;
1189 buffer->cpu_notify.priority = 0;
1190 register_cpu_notifier(&buffer->cpu_notify);
1191#endif
1192
1193 put_online_cpus();
1194 mutex_init(&buffer->mutex);
1195
1196 return buffer;
1197
1198 fail_free_buffers:
1199 for_each_buffer_cpu(buffer, cpu) {
1200 if (buffer->buffers[cpu])
1201 rb_free_cpu_buffer(buffer->buffers[cpu]);
1202 }
1203 kfree(buffer->buffers);
1204
1205 fail_free_cpumask:
1206 free_cpumask_var(buffer->cpumask);
1207 put_online_cpus();
1208
1209 fail_free_buffer:
1210 kfree(buffer);
1211 return NULL;
1212}
1213EXPORT_SYMBOL_GPL(__ring_buffer_alloc);
1214
1215/**
1216 * ring_buffer_free - free a ring buffer.
1217 * @buffer: the buffer to free.
1218 */
1219void
1220ring_buffer_free(struct ring_buffer *buffer)
1221{
1222 int cpu;
1223
1224 get_online_cpus();
1225
1226#ifdef CONFIG_HOTPLUG_CPU
1227 unregister_cpu_notifier(&buffer->cpu_notify);
1228#endif
1229
1230 for_each_buffer_cpu(buffer, cpu)
1231 rb_free_cpu_buffer(buffer->buffers[cpu]);
1232
1233 put_online_cpus();
1234
1235 kfree(buffer->buffers);
1236 free_cpumask_var(buffer->cpumask);
1237
1238 kfree(buffer);
1239}
1240EXPORT_SYMBOL_GPL(ring_buffer_free);
1241
1242void ring_buffer_set_clock(struct ring_buffer *buffer,
1243 u64 (*clock)(void))
1244{
1245 buffer->clock = clock;
1246}
1247
1248static void rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer);
1249
1250static inline unsigned long rb_page_entries(struct buffer_page *bpage)
1251{
1252 return local_read(&bpage->entries) & RB_WRITE_MASK;
1253}
1254
1255static inline unsigned long rb_page_write(struct buffer_page *bpage)
1256{
1257 return local_read(&bpage->write) & RB_WRITE_MASK;
1258}
1259
1260static int
1261rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned int nr_pages)
1262{
1263 struct list_head *tail_page, *to_remove, *next_page;
1264 struct buffer_page *to_remove_page, *tmp_iter_page;
1265 struct buffer_page *last_page, *first_page;
1266 unsigned int nr_removed;
1267 unsigned long head_bit;
1268 int page_entries;
1269
1270 head_bit = 0;
1271
1272 raw_spin_lock_irq(&cpu_buffer->reader_lock);
1273 atomic_inc(&cpu_buffer->record_disabled);
1274 /*
1275 * We don't race with the readers since we have acquired the reader
1276 * lock. We also don't race with writers after disabling recording.
1277 * This makes it easy to figure out the first and the last page to be
1278 * removed from the list. We unlink all the pages in between including
1279 * the first and last pages. This is done in a busy loop so that we
1280 * lose the least number of traces.
1281 * The pages are freed after we restart recording and unlock readers.
1282 */
1283 tail_page = &cpu_buffer->tail_page->list;
1284
1285 /*
1286 * tail page might be on reader page, we remove the next page
1287 * from the ring buffer
1288 */
1289 if (cpu_buffer->tail_page == cpu_buffer->reader_page)
1290 tail_page = rb_list_head(tail_page->next);
1291 to_remove = tail_page;
1292
1293 /* start of pages to remove */
1294 first_page = list_entry(rb_list_head(to_remove->next),
1295 struct buffer_page, list);
1296
1297 for (nr_removed = 0; nr_removed < nr_pages; nr_removed++) {
1298 to_remove = rb_list_head(to_remove)->next;
1299 head_bit |= (unsigned long)to_remove & RB_PAGE_HEAD;
1300 }
1301
1302 next_page = rb_list_head(to_remove)->next;
1303
1304 /*
1305 * Now we remove all pages between tail_page and next_page.
1306 * Make sure that we have head_bit value preserved for the
1307 * next page
1308 */
1309 tail_page->next = (struct list_head *)((unsigned long)next_page |
1310 head_bit);
1311 next_page = rb_list_head(next_page);
1312 next_page->prev = tail_page;
1313
1314 /* make sure pages points to a valid page in the ring buffer */
1315 cpu_buffer->pages = next_page;
1316
1317 /* update head page */
1318 if (head_bit)
1319 cpu_buffer->head_page = list_entry(next_page,
1320 struct buffer_page, list);
1321
1322 /*
1323 * change read pointer to make sure any read iterators reset
1324 * themselves
1325 */
1326 cpu_buffer->read = 0;
1327
1328 /* pages are removed, resume tracing and then free the pages */
1329 atomic_dec(&cpu_buffer->record_disabled);
1330 raw_spin_unlock_irq(&cpu_buffer->reader_lock);
1331
1332 RB_WARN_ON(cpu_buffer, list_empty(cpu_buffer->pages));
1333
1334 /* last buffer page to remove */
1335 last_page = list_entry(rb_list_head(to_remove), struct buffer_page,
1336 list);
1337 tmp_iter_page = first_page;
1338
1339 do {
1340 to_remove_page = tmp_iter_page;
1341 rb_inc_page(cpu_buffer, &tmp_iter_page);
1342
1343 /* update the counters */
1344 page_entries = rb_page_entries(to_remove_page);
1345 if (page_entries) {
1346 /*
1347 * If something was added to this page, it was full
1348 * since it is not the tail page. So we deduct the
1349 * bytes consumed in ring buffer from here.
1350 * Increment overrun to account for the lost events.
1351 */
1352 local_add(page_entries, &cpu_buffer->overrun);
1353 local_sub(BUF_PAGE_SIZE, &cpu_buffer->entries_bytes);
1354 }
1355
1356 /*
1357 * We have already removed references to this list item, just
1358 * free up the buffer_page and its page
1359 */
1360 free_buffer_page(to_remove_page);
1361 nr_removed--;
1362
1363 } while (to_remove_page != last_page);
1364
1365 RB_WARN_ON(cpu_buffer, nr_removed);
1366
1367 return nr_removed == 0;
1368}
1369
1370static int
1371rb_insert_pages(struct ring_buffer_per_cpu *cpu_buffer)
1372{
1373 struct list_head *pages = &cpu_buffer->new_pages;
1374 int retries, success;
1375
1376 raw_spin_lock_irq(&cpu_buffer->reader_lock);
1377 /*
1378 * We are holding the reader lock, so the reader page won't be swapped
1379 * in the ring buffer. Now we are racing with the writer trying to
1380 * move head page and the tail page.
1381 * We are going to adapt the reader page update process where:
1382 * 1. We first splice the start and end of list of new pages between
1383 * the head page and its previous page.
1384 * 2. We cmpxchg the prev_page->next to point from head page to the
1385 * start of new pages list.
1386 * 3. Finally, we update the head->prev to the end of new list.
1387 *
1388 * We will try this process 10 times, to make sure that we don't keep
1389 * spinning.
1390 */
1391 retries = 10;
1392 success = 0;
1393 while (retries--) {
1394 struct list_head *head_page, *prev_page, *r;
1395 struct list_head *last_page, *first_page;
1396 struct list_head *head_page_with_bit;
1397
1398 head_page = &rb_set_head_page(cpu_buffer)->list;
1399 prev_page = head_page->prev;
1400
1401 first_page = pages->next;
1402 last_page = pages->prev;
1403
1404 head_page_with_bit = (struct list_head *)
1405 ((unsigned long)head_page | RB_PAGE_HEAD);
1406
1407 last_page->next = head_page_with_bit;
1408 first_page->prev = prev_page;
1409
1410 r = cmpxchg(&prev_page->next, head_page_with_bit, first_page);
1411
1412 if (r == head_page_with_bit) {
1413 /*
1414 * yay, we replaced the page pointer to our new list,
1415 * now, we just have to update to head page's prev
1416 * pointer to point to end of list
1417 */
1418 head_page->prev = last_page;
1419 success = 1;
1420 break;
1421 }
1422 }
1423
1424 if (success)
1425 INIT_LIST_HEAD(pages);
1426 /*
1427 * If we weren't successful in adding in new pages, warn and stop
1428 * tracing
1429 */
1430 RB_WARN_ON(cpu_buffer, !success);
1431 raw_spin_unlock_irq(&cpu_buffer->reader_lock);
1432
1433 /* free pages if they weren't inserted */
1434 if (!success) {
1435 struct buffer_page *bpage, *tmp;
1436 list_for_each_entry_safe(bpage, tmp, &cpu_buffer->new_pages,
1437 list) {
1438 list_del_init(&bpage->list);
1439 free_buffer_page(bpage);
1440 }
1441 }
1442 return success;
1443}
1444
1445static void rb_update_pages(struct ring_buffer_per_cpu *cpu_buffer)
1446{
1447 int success;
1448
1449 if (cpu_buffer->nr_pages_to_update > 0)
1450 success = rb_insert_pages(cpu_buffer);
1451 else
1452 success = rb_remove_pages(cpu_buffer,
1453 -cpu_buffer->nr_pages_to_update);
1454
1455 if (success)
1456 cpu_buffer->nr_pages += cpu_buffer->nr_pages_to_update;
1457}
1458
1459static void update_pages_handler(struct work_struct *work)
1460{
1461 struct ring_buffer_per_cpu *cpu_buffer = container_of(work,
1462 struct ring_buffer_per_cpu, update_pages_work);
1463 rb_update_pages(cpu_buffer);
1464 complete(&cpu_buffer->update_done);
1465}
1466
1467/**
1468 * ring_buffer_resize - resize the ring buffer
1469 * @buffer: the buffer to resize.
1470 * @size: the new size.
1471 *
1472 * Minimum size is 2 * BUF_PAGE_SIZE.
1473 *
1474 * Returns 0 on success and < 0 on failure.
1475 */
1476int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size,
1477 int cpu_id)
1478{
1479 struct ring_buffer_per_cpu *cpu_buffer;
1480 unsigned nr_pages;
1481 int cpu, err = 0;
1482
1483 /*
1484 * Always succeed at resizing a non-existent buffer:
1485 */
1486 if (!buffer)
1487 return size;
1488
1489 /* Make sure the requested buffer exists */
1490 if (cpu_id != RING_BUFFER_ALL_CPUS &&
1491 !cpumask_test_cpu(cpu_id, buffer->cpumask))
1492 return size;
1493
1494 size = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
1495 size *= BUF_PAGE_SIZE;
1496
1497 /* we need a minimum of two pages */
1498 if (size < BUF_PAGE_SIZE * 2)
1499 size = BUF_PAGE_SIZE * 2;
1500
1501 nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
1502
1503 /*
1504 * Don't succeed if resizing is disabled, as a reader might be
1505 * manipulating the ring buffer and is expecting a sane state while
1506 * this is true.
1507 */
1508 if (atomic_read(&buffer->resize_disabled))
1509 return -EBUSY;
1510
1511 /* prevent another thread from changing buffer sizes */
1512 mutex_lock(&buffer->mutex);
1513
1514 if (cpu_id == RING_BUFFER_ALL_CPUS) {
1515 /* calculate the pages to update */
1516 for_each_buffer_cpu(buffer, cpu) {
1517 cpu_buffer = buffer->buffers[cpu];
1518
1519 cpu_buffer->nr_pages_to_update = nr_pages -
1520 cpu_buffer->nr_pages;
1521 /*
1522 * nothing more to do for removing pages or no update
1523 */
1524 if (cpu_buffer->nr_pages_to_update <= 0)
1525 continue;
1526 /*
1527 * to add pages, make sure all new pages can be
1528 * allocated without receiving ENOMEM
1529 */
1530 INIT_LIST_HEAD(&cpu_buffer->new_pages);
1531 if (__rb_allocate_pages(cpu_buffer->nr_pages_to_update,
1532 &cpu_buffer->new_pages, cpu)) {
1533 /* not enough memory for new pages */
1534 err = -ENOMEM;
1535 goto out_err;
1536 }
1537 }
1538
1539 get_online_cpus();
1540 /*
1541 * Fire off all the required work handlers
1542 * We can't schedule on offline CPUs, but it's not necessary
1543 * since we can change their buffer sizes without any race.
1544 */
1545 for_each_buffer_cpu(buffer, cpu) {
1546 cpu_buffer = buffer->buffers[cpu];
1547 if (!cpu_buffer->nr_pages_to_update)
1548 continue;
1549
1550 if (cpu_online(cpu))
1551 schedule_work_on(cpu,
1552 &cpu_buffer->update_pages_work);
1553 else
1554 rb_update_pages(cpu_buffer);
1555 }
1556
1557 /* wait for all the updates to complete */
1558 for_each_buffer_cpu(buffer, cpu) {
1559 cpu_buffer = buffer->buffers[cpu];
1560 if (!cpu_buffer->nr_pages_to_update)
1561 continue;
1562
1563 if (cpu_online(cpu))
1564 wait_for_completion(&cpu_buffer->update_done);
1565 cpu_buffer->nr_pages_to_update = 0;
1566 }
1567
1568 put_online_cpus();
1569 } else {
1570 cpu_buffer = buffer->buffers[cpu_id];
1571
1572 if (nr_pages == cpu_buffer->nr_pages)
1573 goto out;
1574
1575 cpu_buffer->nr_pages_to_update = nr_pages -
1576 cpu_buffer->nr_pages;
1577
1578 INIT_LIST_HEAD(&cpu_buffer->new_pages);
1579 if (cpu_buffer->nr_pages_to_update > 0 &&
1580 __rb_allocate_pages(cpu_buffer->nr_pages_to_update,
1581 &cpu_buffer->new_pages, cpu_id)) {
1582 err = -ENOMEM;
1583 goto out_err;
1584 }
1585
1586 get_online_cpus();
1587
1588 if (cpu_online(cpu_id)) {
1589 schedule_work_on(cpu_id,
1590 &cpu_buffer->update_pages_work);
1591 wait_for_completion(&cpu_buffer->update_done);
1592 } else
1593 rb_update_pages(cpu_buffer);
1594
1595 cpu_buffer->nr_pages_to_update = 0;
1596 put_online_cpus();
1597 }
1598
1599 out:
1600 /*
1601 * The ring buffer resize can happen with the ring buffer
1602 * enabled, so that the update disturbs the tracing as little
1603 * as possible. But if the buffer is disabled, we do not need
1604 * to worry about that, and we can take the time to verify
1605 * that the buffer is not corrupt.
1606 */
1607 if (atomic_read(&buffer->record_disabled)) {
1608 atomic_inc(&buffer->record_disabled);
1609 /*
1610 * Even though the buffer was disabled, we must make sure
1611 * that it is truly disabled before calling rb_check_pages.
1612 * There could have been a race between checking
1613 * record_disable and incrementing it.
1614 */
1615 synchronize_sched();
1616 for_each_buffer_cpu(buffer, cpu) {
1617 cpu_buffer = buffer->buffers[cpu];
1618 rb_check_pages(cpu_buffer);
1619 }
1620 atomic_dec(&buffer->record_disabled);
1621 }
1622
1623 mutex_unlock(&buffer->mutex);
1624 return size;
1625
1626 out_err:
1627 for_each_buffer_cpu(buffer, cpu) {
1628 struct buffer_page *bpage, *tmp;
1629
1630 cpu_buffer = buffer->buffers[cpu];
1631 cpu_buffer->nr_pages_to_update = 0;
1632
1633 if (list_empty(&cpu_buffer->new_pages))
1634 continue;
1635
1636 list_for_each_entry_safe(bpage, tmp, &cpu_buffer->new_pages,
1637 list) {
1638 list_del_init(&bpage->list);
1639 free_buffer_page(bpage);
1640 }
1641 }
1642 mutex_unlock(&buffer->mutex);
1643 return err;
1644}
1645EXPORT_SYMBOL_GPL(ring_buffer_resize);
1646
1647void ring_buffer_change_overwrite(struct ring_buffer *buffer, int val)
1648{
1649 mutex_lock(&buffer->mutex);
1650 if (val)
1651 buffer->flags |= RB_FL_OVERWRITE;
1652 else
1653 buffer->flags &= ~RB_FL_OVERWRITE;
1654 mutex_unlock(&buffer->mutex);
1655}
1656EXPORT_SYMBOL_GPL(ring_buffer_change_overwrite);
1657
1658static inline void *
1659__rb_data_page_index(struct buffer_data_page *bpage, unsigned index)
1660{
1661 return bpage->data + index;
1662}
1663
1664static inline void *__rb_page_index(struct buffer_page *bpage, unsigned index)
1665{
1666 return bpage->page->data + index;
1667}
1668
1669static inline struct ring_buffer_event *
1670rb_reader_event(struct ring_buffer_per_cpu *cpu_buffer)
1671{
1672 return __rb_page_index(cpu_buffer->reader_page,
1673 cpu_buffer->reader_page->read);
1674}
1675
1676static inline struct ring_buffer_event *
1677rb_iter_head_event(struct ring_buffer_iter *iter)
1678{
1679 return __rb_page_index(iter->head_page, iter->head);
1680}
1681
1682static inline unsigned rb_page_commit(struct buffer_page *bpage)
1683{
1684 return local_read(&bpage->page->commit);
1685}
1686
1687/* Size is determined by what has been committed */
1688static inline unsigned rb_page_size(struct buffer_page *bpage)
1689{
1690 return rb_page_commit(bpage);
1691}
1692
1693static inline unsigned
1694rb_commit_index(struct ring_buffer_per_cpu *cpu_buffer)
1695{
1696 return rb_page_commit(cpu_buffer->commit_page);
1697}
1698
1699static inline unsigned
1700rb_event_index(struct ring_buffer_event *event)
1701{
1702 unsigned long addr = (unsigned long)event;
1703
1704 return (addr & ~PAGE_MASK) - BUF_PAGE_HDR_SIZE;
1705}
1706
1707static inline int
1708rb_event_is_commit(struct ring_buffer_per_cpu *cpu_buffer,
1709 struct ring_buffer_event *event)
1710{
1711 unsigned long addr = (unsigned long)event;
1712 unsigned long index;
1713
1714 index = rb_event_index(event);
1715 addr &= PAGE_MASK;
1716
1717 return cpu_buffer->commit_page->page == (void *)addr &&
1718 rb_commit_index(cpu_buffer) == index;
1719}
1720
1721static void
1722rb_set_commit_to_write(struct ring_buffer_per_cpu *cpu_buffer)
1723{
1724 unsigned long max_count;
1725
1726 /*
1727 * We only race with interrupts and NMIs on this CPU.
1728 * If we own the commit event, then we can commit
1729 * all others that interrupted us, since the interruptions
1730 * are in stack format (they finish before they come
1731 * back to us). This allows us to do a simple loop to
1732 * assign the commit to the tail.
1733 */
1734 again:
1735 max_count = cpu_buffer->nr_pages * 100;
1736
1737 while (cpu_buffer->commit_page != cpu_buffer->tail_page) {
1738 if (RB_WARN_ON(cpu_buffer, !(--max_count)))
1739 return;
1740 if (RB_WARN_ON(cpu_buffer,
1741 rb_is_reader_page(cpu_buffer->tail_page)))
1742 return;
1743 local_set(&cpu_buffer->commit_page->page->commit,
1744 rb_page_write(cpu_buffer->commit_page));
1745 rb_inc_page(cpu_buffer, &cpu_buffer->commit_page);
1746 cpu_buffer->write_stamp =
1747 cpu_buffer->commit_page->page->time_stamp;
1748 /* add barrier to keep gcc from optimizing too much */
1749 barrier();
1750 }
1751 while (rb_commit_index(cpu_buffer) !=
1752 rb_page_write(cpu_buffer->commit_page)) {
1753
1754 local_set(&cpu_buffer->commit_page->page->commit,
1755 rb_page_write(cpu_buffer->commit_page));
1756 RB_WARN_ON(cpu_buffer,
1757 local_read(&cpu_buffer->commit_page->page->commit) &
1758 ~RB_WRITE_MASK);
1759 barrier();
1760 }
1761
1762 /* again, keep gcc from optimizing */
1763 barrier();
1764
1765 /*
1766 * If an interrupt came in just after the first while loop
1767 * and pushed the tail page forward, we will be left with
1768 * a dangling commit that will never go forward.
1769 */
1770 if (unlikely(cpu_buffer->commit_page != cpu_buffer->tail_page))
1771 goto again;
1772}
1773
1774static void rb_reset_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
1775{
1776 cpu_buffer->read_stamp = cpu_buffer->reader_page->page->time_stamp;
1777 cpu_buffer->reader_page->read = 0;
1778}
1779
1780static void rb_inc_iter(struct ring_buffer_iter *iter)
1781{
1782 struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
1783
1784 /*
1785 * The iterator could be on the reader page (it starts there).
1786 * But the head could have moved, since the reader was
1787 * found. Check for this case and assign the iterator
1788 * to the head page instead of next.
1789 */
1790 if (iter->head_page == cpu_buffer->reader_page)
1791 iter->head_page = rb_set_head_page(cpu_buffer);
1792 else
1793 rb_inc_page(cpu_buffer, &iter->head_page);
1794
1795 iter->read_stamp = iter->head_page->page->time_stamp;
1796 iter->head = 0;
1797}
1798
1799/* Slow path, do not inline */
1800static noinline struct ring_buffer_event *
1801rb_add_time_stamp(struct ring_buffer_event *event, u64 delta)
1802{
1803 event->type_len = RINGBUF_TYPE_TIME_EXTEND;
1804
1805 /* Not the first event on the page? */
1806 if (rb_event_index(event)) {
1807 event->time_delta = delta & TS_MASK;
1808 event->array[0] = delta >> TS_SHIFT;
1809 } else {
1810 /* nope, just zero it */
1811 event->time_delta = 0;
1812 event->array[0] = 0;
1813 }
1814
1815 return skip_time_extend(event);
1816}
1817
1818/**
1819 * ring_buffer_update_event - update event type and data
1820 * @event: the even to update
1821 * @type: the type of event
1822 * @length: the size of the event field in the ring buffer
1823 *
1824 * Update the type and data fields of the event. The length
1825 * is the actual size that is written to the ring buffer,
1826 * and with this, we can determine what to place into the
1827 * data field.
1828 */
1829static void
1830rb_update_event(struct ring_buffer_per_cpu *cpu_buffer,
1831 struct ring_buffer_event *event, unsigned length,
1832 int add_timestamp, u64 delta)
1833{
1834 /* Only a commit updates the timestamp */
1835 if (unlikely(!rb_event_is_commit(cpu_buffer, event)))
1836 delta = 0;
1837
1838 /*
1839 * If we need to add a timestamp, then we
1840 * add it to the start of the resevered space.
1841 */
1842 if (unlikely(add_timestamp)) {
1843 event = rb_add_time_stamp(event, delta);
1844 length -= RB_LEN_TIME_EXTEND;
1845 delta = 0;
1846 }
1847
1848 event->time_delta = delta;
1849 length -= RB_EVNT_HDR_SIZE;
1850 if (length > RB_MAX_SMALL_DATA || RB_FORCE_8BYTE_ALIGNMENT) {
1851 event->type_len = 0;
1852 event->array[0] = length;
1853 } else
1854 event->type_len = DIV_ROUND_UP(length, RB_ALIGNMENT);
1855}
1856
1857/*
1858 * rb_handle_head_page - writer hit the head page
1859 *
1860 * Returns: +1 to retry page
1861 * 0 to continue
1862 * -1 on error
1863 */
1864static int
1865rb_handle_head_page(struct ring_buffer_per_cpu *cpu_buffer,
1866 struct buffer_page *tail_page,
1867 struct buffer_page *next_page)
1868{
1869 struct buffer_page *new_head;
1870 int entries;
1871 int type;
1872 int ret;
1873
1874 entries = rb_page_entries(next_page);
1875
1876 /*
1877 * The hard part is here. We need to move the head
1878 * forward, and protect against both readers on
1879 * other CPUs and writers coming in via interrupts.
1880 */
1881 type = rb_head_page_set_update(cpu_buffer, next_page, tail_page,
1882 RB_PAGE_HEAD);
1883
1884 /*
1885 * type can be one of four:
1886 * NORMAL - an interrupt already moved it for us
1887 * HEAD - we are the first to get here.
1888 * UPDATE - we are the interrupt interrupting
1889 * a current move.
1890 * MOVED - a reader on another CPU moved the next
1891 * pointer to its reader page. Give up
1892 * and try again.
1893 */
1894
1895 switch (type) {
1896 case RB_PAGE_HEAD:
1897 /*
1898 * We changed the head to UPDATE, thus
1899 * it is our responsibility to update
1900 * the counters.
1901 */
1902 local_add(entries, &cpu_buffer->overrun);
1903 local_sub(BUF_PAGE_SIZE, &cpu_buffer->entries_bytes);
1904
1905 /*
1906 * The entries will be zeroed out when we move the
1907 * tail page.
1908 */
1909
1910 /* still more to do */
1911 break;
1912
1913 case RB_PAGE_UPDATE:
1914 /*
1915 * This is an interrupt that interrupt the
1916 * previous update. Still more to do.
1917 */
1918 break;
1919 case RB_PAGE_NORMAL:
1920 /*
1921 * An interrupt came in before the update
1922 * and processed this for us.
1923 * Nothing left to do.
1924 */
1925 return 1;
1926 case RB_PAGE_MOVED:
1927 /*
1928 * The reader is on another CPU and just did
1929 * a swap with our next_page.
1930 * Try again.
1931 */
1932 return 1;
1933 default:
1934 RB_WARN_ON(cpu_buffer, 1); /* WTF??? */
1935 return -1;
1936 }
1937
1938 /*
1939 * Now that we are here, the old head pointer is
1940 * set to UPDATE. This will keep the reader from
1941 * swapping the head page with the reader page.
1942 * The reader (on another CPU) will spin till
1943 * we are finished.
1944 *
1945 * We just need to protect against interrupts
1946 * doing the job. We will set the next pointer
1947 * to HEAD. After that, we set the old pointer
1948 * to NORMAL, but only if it was HEAD before.
1949 * otherwise we are an interrupt, and only
1950 * want the outer most commit to reset it.
1951 */
1952 new_head = next_page;
1953 rb_inc_page(cpu_buffer, &new_head);
1954
1955 ret = rb_head_page_set_head(cpu_buffer, new_head, next_page,
1956 RB_PAGE_NORMAL);
1957
1958 /*
1959 * Valid returns are:
1960 * HEAD - an interrupt came in and already set it.
1961 * NORMAL - One of two things:
1962 * 1) We really set it.
1963 * 2) A bunch of interrupts came in and moved
1964 * the page forward again.
1965 */
1966 switch (ret) {
1967 case RB_PAGE_HEAD:
1968 case RB_PAGE_NORMAL:
1969 /* OK */
1970 break;
1971 default:
1972 RB_WARN_ON(cpu_buffer, 1);
1973 return -1;
1974 }
1975
1976 /*
1977 * It is possible that an interrupt came in,
1978 * set the head up, then more interrupts came in
1979 * and moved it again. When we get back here,
1980 * the page would have been set to NORMAL but we
1981 * just set it back to HEAD.
1982 *
1983 * How do you detect this? Well, if that happened
1984 * the tail page would have moved.
1985 */
1986 if (ret == RB_PAGE_NORMAL) {
1987 /*
1988 * If the tail had moved passed next, then we need
1989 * to reset the pointer.
1990 */
1991 if (cpu_buffer->tail_page != tail_page &&
1992 cpu_buffer->tail_page != next_page)
1993 rb_head_page_set_normal(cpu_buffer, new_head,
1994 next_page,
1995 RB_PAGE_HEAD);
1996 }
1997
1998 /*
1999 * If this was the outer most commit (the one that
2000 * changed the original pointer from HEAD to UPDATE),
2001 * then it is up to us to reset it to NORMAL.
2002 */
2003 if (type == RB_PAGE_HEAD) {
2004 ret = rb_head_page_set_normal(cpu_buffer, next_page,
2005 tail_page,
2006 RB_PAGE_UPDATE);
2007 if (RB_WARN_ON(cpu_buffer,
2008 ret != RB_PAGE_UPDATE))
2009 return -1;
2010 }
2011
2012 return 0;
2013}
2014
2015static unsigned rb_calculate_event_length(unsigned length)
2016{
2017 struct ring_buffer_event event; /* Used only for sizeof array */
2018
2019 /* zero length can cause confusions */
2020 if (!length)
2021 length = 1;
2022
2023 if (length > RB_MAX_SMALL_DATA || RB_FORCE_8BYTE_ALIGNMENT)
2024 length += sizeof(event.array[0]);
2025
2026 length += RB_EVNT_HDR_SIZE;
2027 length = ALIGN(length, RB_ARCH_ALIGNMENT);
2028
2029 return length;
2030}
2031
2032static inline void
2033rb_reset_tail(struct ring_buffer_per_cpu *cpu_buffer,
2034 struct buffer_page *tail_page,
2035 unsigned long tail, unsigned long length)
2036{
2037 struct ring_buffer_event *event;
2038
2039 /*
2040 * Only the event that crossed the page boundary
2041 * must fill the old tail_page with padding.
2042 */
2043 if (tail >= BUF_PAGE_SIZE) {
2044 /*
2045 * If the page was filled, then we still need
2046 * to update the real_end. Reset it to zero
2047 * and the reader will ignore it.
2048 */
2049 if (tail == BUF_PAGE_SIZE)
2050 tail_page->real_end = 0;
2051
2052 local_sub(length, &tail_page->write);
2053 return;
2054 }
2055
2056 event = __rb_page_index(tail_page, tail);
2057 kmemcheck_annotate_bitfield(event, bitfield);
2058
2059 /* account for padding bytes */
2060 local_add(BUF_PAGE_SIZE - tail, &cpu_buffer->entries_bytes);
2061
2062 /*
2063 * Save the original length to the meta data.
2064 * This will be used by the reader to add lost event
2065 * counter.
2066 */
2067 tail_page->real_end = tail;
2068
2069 /*
2070 * If this event is bigger than the minimum size, then
2071 * we need to be careful that we don't subtract the
2072 * write counter enough to allow another writer to slip
2073 * in on this page.
2074 * We put in a discarded commit instead, to make sure
2075 * that this space is not used again.
2076 *
2077 * If we are less than the minimum size, we don't need to
2078 * worry about it.
2079 */
2080 if (tail > (BUF_PAGE_SIZE - RB_EVNT_MIN_SIZE)) {
2081 /* No room for any events */
2082
2083 /* Mark the rest of the page with padding */
2084 rb_event_set_padding(event);
2085
2086 /* Set the write back to the previous setting */
2087 local_sub(length, &tail_page->write);
2088 return;
2089 }
2090
2091 /* Put in a discarded event */
2092 event->array[0] = (BUF_PAGE_SIZE - tail) - RB_EVNT_HDR_SIZE;
2093 event->type_len = RINGBUF_TYPE_PADDING;
2094 /* time delta must be non zero */
2095 event->time_delta = 1;
2096
2097 /* Set write to end of buffer */
2098 length = (tail + length) - BUF_PAGE_SIZE;
2099 local_sub(length, &tail_page->write);
2100}
2101
2102/*
2103 * This is the slow path, force gcc not to inline it.
2104 */
2105static noinline struct ring_buffer_event *
2106rb_move_tail(struct ring_buffer_per_cpu *cpu_buffer,
2107 unsigned long length, unsigned long tail,
2108 struct buffer_page *tail_page, u64 ts)
2109{
2110 struct buffer_page *commit_page = cpu_buffer->commit_page;
2111 struct ring_buffer *buffer = cpu_buffer->buffer;
2112 struct buffer_page *next_page;
2113 int ret;
2114
2115 next_page = tail_page;
2116
2117 rb_inc_page(cpu_buffer, &next_page);
2118
2119 /*
2120 * If for some reason, we had an interrupt storm that made
2121 * it all the way around the buffer, bail, and warn
2122 * about it.
2123 */
2124 if (unlikely(next_page == commit_page)) {
2125 local_inc(&cpu_buffer->commit_overrun);
2126 goto out_reset;
2127 }
2128
2129 /*
2130 * This is where the fun begins!
2131 *
2132 * We are fighting against races between a reader that
2133 * could be on another CPU trying to swap its reader
2134 * page with the buffer head.
2135 *
2136 * We are also fighting against interrupts coming in and
2137 * moving the head or tail on us as well.
2138 *
2139 * If the next page is the head page then we have filled
2140 * the buffer, unless the commit page is still on the
2141 * reader page.
2142 */
2143 if (rb_is_head_page(cpu_buffer, next_page, &tail_page->list)) {
2144
2145 /*
2146 * If the commit is not on the reader page, then
2147 * move the header page.
2148 */
2149 if (!rb_is_reader_page(cpu_buffer->commit_page)) {
2150 /*
2151 * If we are not in overwrite mode,
2152 * this is easy, just stop here.
2153 */
2154 if (!(buffer->flags & RB_FL_OVERWRITE))
2155 goto out_reset;
2156
2157 ret = rb_handle_head_page(cpu_buffer,
2158 tail_page,
2159 next_page);
2160 if (ret < 0)
2161 goto out_reset;
2162 if (ret)
2163 goto out_again;
2164 } else {
2165 /*
2166 * We need to be careful here too. The
2167 * commit page could still be on the reader
2168 * page. We could have a small buffer, and
2169 * have filled up the buffer with events
2170 * from interrupts and such, and wrapped.
2171 *
2172 * Note, if the tail page is also the on the
2173 * reader_page, we let it move out.
2174 */
2175 if (unlikely((cpu_buffer->commit_page !=
2176 cpu_buffer->tail_page) &&
2177 (cpu_buffer->commit_page ==
2178 cpu_buffer->reader_page))) {
2179 local_inc(&cpu_buffer->commit_overrun);
2180 goto out_reset;
2181 }
2182 }
2183 }
2184
2185 ret = rb_tail_page_update(cpu_buffer, tail_page, next_page);
2186 if (ret) {
2187 /*
2188 * Nested commits always have zero deltas, so
2189 * just reread the time stamp
2190 */
2191 ts = rb_time_stamp(buffer);
2192 next_page->page->time_stamp = ts;
2193 }
2194
2195 out_again:
2196
2197 rb_reset_tail(cpu_buffer, tail_page, tail, length);
2198
2199 /* fail and let the caller try again */
2200 return ERR_PTR(-EAGAIN);
2201
2202 out_reset:
2203 /* reset write */
2204 rb_reset_tail(cpu_buffer, tail_page, tail, length);
2205
2206 return NULL;
2207}
2208
2209static struct ring_buffer_event *
2210__rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
2211 unsigned long length, u64 ts,
2212 u64 delta, int add_timestamp)
2213{
2214 struct buffer_page *tail_page;
2215 struct ring_buffer_event *event;
2216 unsigned long tail, write;
2217
2218 /*
2219 * If the time delta since the last event is too big to
2220 * hold in the time field of the event, then we append a
2221 * TIME EXTEND event ahead of the data event.
2222 */
2223 if (unlikely(add_timestamp))
2224 length += RB_LEN_TIME_EXTEND;
2225
2226 tail_page = cpu_buffer->tail_page;
2227 write = local_add_return(length, &tail_page->write);
2228
2229 /* set write to only the index of the write */
2230 write &= RB_WRITE_MASK;
2231 tail = write - length;
2232
2233 /* See if we shot pass the end of this buffer page */
2234 if (unlikely(write > BUF_PAGE_SIZE))
2235 return rb_move_tail(cpu_buffer, length, tail,
2236 tail_page, ts);
2237
2238 /* We reserved something on the buffer */
2239
2240 event = __rb_page_index(tail_page, tail);
2241 kmemcheck_annotate_bitfield(event, bitfield);
2242 rb_update_event(cpu_buffer, event, length, add_timestamp, delta);
2243
2244 local_inc(&tail_page->entries);
2245
2246 /*
2247 * If this is the first commit on the page, then update
2248 * its timestamp.
2249 */
2250 if (!tail)
2251 tail_page->page->time_stamp = ts;
2252
2253 /* account for these added bytes */
2254 local_add(length, &cpu_buffer->entries_bytes);
2255
2256 return event;
2257}
2258
2259static inline int
2260rb_try_to_discard(struct ring_buffer_per_cpu *cpu_buffer,
2261 struct ring_buffer_event *event)
2262{
2263 unsigned long new_index, old_index;
2264 struct buffer_page *bpage;
2265 unsigned long index;
2266 unsigned long addr;
2267
2268 new_index = rb_event_index(event);
2269 old_index = new_index + rb_event_ts_length(event);
2270 addr = (unsigned long)event;
2271 addr &= PAGE_MASK;
2272
2273 bpage = cpu_buffer->tail_page;
2274
2275 if (bpage->page == (void *)addr && rb_page_write(bpage) == old_index) {
2276 unsigned long write_mask =
2277 local_read(&bpage->write) & ~RB_WRITE_MASK;
2278 unsigned long event_length = rb_event_length(event);
2279 /*
2280 * This is on the tail page. It is possible that
2281 * a write could come in and move the tail page
2282 * and write to the next page. That is fine
2283 * because we just shorten what is on this page.
2284 */
2285 old_index += write_mask;
2286 new_index += write_mask;
2287 index = local_cmpxchg(&bpage->write, old_index, new_index);
2288 if (index == old_index) {
2289 /* update counters */
2290 local_sub(event_length, &cpu_buffer->entries_bytes);
2291 return 1;
2292 }
2293 }
2294
2295 /* could not discard */
2296 return 0;
2297}
2298
2299static void rb_start_commit(struct ring_buffer_per_cpu *cpu_buffer)
2300{
2301 local_inc(&cpu_buffer->committing);
2302 local_inc(&cpu_buffer->commits);
2303}
2304
2305static inline void rb_end_commit(struct ring_buffer_per_cpu *cpu_buffer)
2306{
2307 unsigned long commits;
2308
2309 if (RB_WARN_ON(cpu_buffer,
2310 !local_read(&cpu_buffer->committing)))
2311 return;
2312
2313 again:
2314 commits = local_read(&cpu_buffer->commits);
2315 /* synchronize with interrupts */
2316 barrier();
2317 if (local_read(&cpu_buffer->committing) == 1)
2318 rb_set_commit_to_write(cpu_buffer);
2319
2320 local_dec(&cpu_buffer->committing);
2321
2322 /* synchronize with interrupts */
2323 barrier();
2324
2325 /*
2326 * Need to account for interrupts coming in between the
2327 * updating of the commit page and the clearing of the
2328 * committing counter.
2329 */
2330 if (unlikely(local_read(&cpu_buffer->commits) != commits) &&
2331 !local_read(&cpu_buffer->committing)) {
2332 local_inc(&cpu_buffer->committing);
2333 goto again;
2334 }
2335}
2336
2337static struct ring_buffer_event *
2338rb_reserve_next_event(struct ring_buffer *buffer,
2339 struct ring_buffer_per_cpu *cpu_buffer,
2340 unsigned long length)
2341{
2342 struct ring_buffer_event *event;
2343 u64 ts, delta;
2344 int nr_loops = 0;
2345 int add_timestamp;
2346 u64 diff;
2347
2348 rb_start_commit(cpu_buffer);
2349
2350#ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
2351 /*
2352 * Due to the ability to swap a cpu buffer from a buffer
2353 * it is possible it was swapped before we committed.
2354 * (committing stops a swap). We check for it here and
2355 * if it happened, we have to fail the write.
2356 */
2357 barrier();
2358 if (unlikely(ACCESS_ONCE(cpu_buffer->buffer) != buffer)) {
2359 local_dec(&cpu_buffer->committing);
2360 local_dec(&cpu_buffer->commits);
2361 return NULL;
2362 }
2363#endif
2364
2365 length = rb_calculate_event_length(length);
2366 again:
2367 add_timestamp = 0;
2368 delta = 0;
2369
2370 /*
2371 * We allow for interrupts to reenter here and do a trace.
2372 * If one does, it will cause this original code to loop
2373 * back here. Even with heavy interrupts happening, this
2374 * should only happen a few times in a row. If this happens
2375 * 1000 times in a row, there must be either an interrupt
2376 * storm or we have something buggy.
2377 * Bail!
2378 */
2379 if (RB_WARN_ON(cpu_buffer, ++nr_loops > 1000))
2380 goto out_fail;
2381
2382 ts = rb_time_stamp(cpu_buffer->buffer);
2383 diff = ts - cpu_buffer->write_stamp;
2384
2385 /* make sure this diff is calculated here */
2386 barrier();
2387
2388 /* Did the write stamp get updated already? */
2389 if (likely(ts >= cpu_buffer->write_stamp)) {
2390 delta = diff;
2391 if (unlikely(test_time_stamp(delta))) {
2392 int local_clock_stable = 1;
2393#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
2394 local_clock_stable = sched_clock_stable;
2395#endif
2396 WARN_ONCE(delta > (1ULL << 59),
2397 KERN_WARNING "Delta way too big! %llu ts=%llu write stamp = %llu\n%s",
2398 (unsigned long long)delta,
2399 (unsigned long long)ts,
2400 (unsigned long long)cpu_buffer->write_stamp,
2401 local_clock_stable ? "" :
2402 "If you just came from a suspend/resume,\n"
2403 "please switch to the trace global clock:\n"
2404 " echo global > /sys/kernel/debug/tracing/trace_clock\n");
2405 add_timestamp = 1;
2406 }
2407 }
2408
2409 event = __rb_reserve_next(cpu_buffer, length, ts,
2410 delta, add_timestamp);
2411 if (unlikely(PTR_ERR(event) == -EAGAIN))
2412 goto again;
2413
2414 if (!event)
2415 goto out_fail;
2416
2417 return event;
2418
2419 out_fail:
2420 rb_end_commit(cpu_buffer);
2421 return NULL;
2422}
2423
2424#ifdef CONFIG_TRACING
2425
2426#define TRACE_RECURSIVE_DEPTH 16
2427
2428/* Keep this code out of the fast path cache */
2429static noinline void trace_recursive_fail(void)
2430{
2431 /* Disable all tracing before we do anything else */
2432 tracing_off_permanent();
2433
2434 printk_once(KERN_WARNING "Tracing recursion: depth[%ld]:"
2435 "HC[%lu]:SC[%lu]:NMI[%lu]\n",
2436 trace_recursion_buffer(),
2437 hardirq_count() >> HARDIRQ_SHIFT,
2438 softirq_count() >> SOFTIRQ_SHIFT,
2439 in_nmi());
2440
2441 WARN_ON_ONCE(1);
2442}
2443
2444static inline int trace_recursive_lock(void)
2445{
2446 trace_recursion_inc();
2447
2448 if (likely(trace_recursion_buffer() < TRACE_RECURSIVE_DEPTH))
2449 return 0;
2450
2451 trace_recursive_fail();
2452
2453 return -1;
2454}
2455
2456static inline void trace_recursive_unlock(void)
2457{
2458 WARN_ON_ONCE(!trace_recursion_buffer());
2459
2460 trace_recursion_dec();
2461}
2462
2463#else
2464
2465#define trace_recursive_lock() (0)
2466#define trace_recursive_unlock() do { } while (0)
2467
2468#endif
2469
2470/**
2471 * ring_buffer_lock_reserve - reserve a part of the buffer
2472 * @buffer: the ring buffer to reserve from
2473 * @length: the length of the data to reserve (excluding event header)
2474 *
2475 * Returns a reseverd event on the ring buffer to copy directly to.
2476 * The user of this interface will need to get the body to write into
2477 * and can use the ring_buffer_event_data() interface.
2478 *
2479 * The length is the length of the data needed, not the event length
2480 * which also includes the event header.
2481 *
2482 * Must be paired with ring_buffer_unlock_commit, unless NULL is returned.
2483 * If NULL is returned, then nothing has been allocated or locked.
2484 */
2485struct ring_buffer_event *
2486ring_buffer_lock_reserve(struct ring_buffer *buffer, unsigned long length)
2487{
2488 struct ring_buffer_per_cpu *cpu_buffer;
2489 struct ring_buffer_event *event;
2490 int cpu;
2491
2492 if (ring_buffer_flags != RB_BUFFERS_ON)
2493 return NULL;
2494
2495 /* If we are tracing schedule, we don't want to recurse */
2496 preempt_disable_notrace();
2497
2498 if (atomic_read(&buffer->record_disabled))
2499 goto out_nocheck;
2500
2501 if (trace_recursive_lock())
2502 goto out_nocheck;
2503
2504 cpu = raw_smp_processor_id();
2505
2506 if (!cpumask_test_cpu(cpu, buffer->cpumask))
2507 goto out;
2508
2509 cpu_buffer = buffer->buffers[cpu];
2510
2511 if (atomic_read(&cpu_buffer->record_disabled))
2512 goto out;
2513
2514 if (length > BUF_MAX_DATA_SIZE)
2515 goto out;
2516
2517 event = rb_reserve_next_event(buffer, cpu_buffer, length);
2518 if (!event)
2519 goto out;
2520
2521 return event;
2522
2523 out:
2524 trace_recursive_unlock();
2525
2526 out_nocheck:
2527 preempt_enable_notrace();
2528 return NULL;
2529}
2530EXPORT_SYMBOL_GPL(ring_buffer_lock_reserve);
2531
2532static void
2533rb_update_write_stamp(struct ring_buffer_per_cpu *cpu_buffer,
2534 struct ring_buffer_event *event)
2535{
2536 u64 delta;
2537
2538 /*
2539 * The event first in the commit queue updates the
2540 * time stamp.
2541 */
2542 if (rb_event_is_commit(cpu_buffer, event)) {
2543 /*
2544 * A commit event that is first on a page
2545 * updates the write timestamp with the page stamp
2546 */
2547 if (!rb_event_index(event))
2548 cpu_buffer->write_stamp =
2549 cpu_buffer->commit_page->page->time_stamp;
2550 else if (event->type_len == RINGBUF_TYPE_TIME_EXTEND) {
2551 delta = event->array[0];
2552 delta <<= TS_SHIFT;
2553 delta += event->time_delta;
2554 cpu_buffer->write_stamp += delta;
2555 } else
2556 cpu_buffer->write_stamp += event->time_delta;
2557 }
2558}
2559
2560static void rb_commit(struct ring_buffer_per_cpu *cpu_buffer,
2561 struct ring_buffer_event *event)
2562{
2563 local_inc(&cpu_buffer->entries);
2564 rb_update_write_stamp(cpu_buffer, event);
2565 rb_end_commit(cpu_buffer);
2566}
2567
2568/**
2569 * ring_buffer_unlock_commit - commit a reserved
2570 * @buffer: The buffer to commit to
2571 * @event: The event pointer to commit.
2572 *
2573 * This commits the data to the ring buffer, and releases any locks held.
2574 *
2575 * Must be paired with ring_buffer_lock_reserve.
2576 */
2577int ring_buffer_unlock_commit(struct ring_buffer *buffer,
2578 struct ring_buffer_event *event)
2579{
2580 struct ring_buffer_per_cpu *cpu_buffer;
2581 int cpu = raw_smp_processor_id();
2582
2583 cpu_buffer = buffer->buffers[cpu];
2584
2585 rb_commit(cpu_buffer, event);
2586
2587 trace_recursive_unlock();
2588
2589 preempt_enable_notrace();
2590
2591 return 0;
2592}
2593EXPORT_SYMBOL_GPL(ring_buffer_unlock_commit);
2594
2595static inline void rb_event_discard(struct ring_buffer_event *event)
2596{
2597 if (event->type_len == RINGBUF_TYPE_TIME_EXTEND)
2598 event = skip_time_extend(event);
2599
2600 /* array[0] holds the actual length for the discarded event */
2601 event->array[0] = rb_event_data_length(event) - RB_EVNT_HDR_SIZE;
2602 event->type_len = RINGBUF_TYPE_PADDING;
2603 /* time delta must be non zero */
2604 if (!event->time_delta)
2605 event->time_delta = 1;
2606}
2607
2608/*
2609 * Decrement the entries to the page that an event is on.
2610 * The event does not even need to exist, only the pointer
2611 * to the page it is on. This may only be called before the commit
2612 * takes place.
2613 */
2614static inline void
2615rb_decrement_entry(struct ring_buffer_per_cpu *cpu_buffer,
2616 struct ring_buffer_event *event)
2617{
2618 unsigned long addr = (unsigned long)event;
2619 struct buffer_page *bpage = cpu_buffer->commit_page;
2620 struct buffer_page *start;
2621
2622 addr &= PAGE_MASK;
2623
2624 /* Do the likely case first */
2625 if (likely(bpage->page == (void *)addr)) {
2626 local_dec(&bpage->entries);
2627 return;
2628 }
2629
2630 /*
2631 * Because the commit page may be on the reader page we
2632 * start with the next page and check the end loop there.
2633 */
2634 rb_inc_page(cpu_buffer, &bpage);
2635 start = bpage;
2636 do {
2637 if (bpage->page == (void *)addr) {
2638 local_dec(&bpage->entries);
2639 return;
2640 }
2641 rb_inc_page(cpu_buffer, &bpage);
2642 } while (bpage != start);
2643
2644 /* commit not part of this buffer?? */
2645 RB_WARN_ON(cpu_buffer, 1);
2646}
2647
2648/**
2649 * ring_buffer_commit_discard - discard an event that has not been committed
2650 * @buffer: the ring buffer
2651 * @event: non committed event to discard
2652 *
2653 * Sometimes an event that is in the ring buffer needs to be ignored.
2654 * This function lets the user discard an event in the ring buffer
2655 * and then that event will not be read later.
2656 *
2657 * This function only works if it is called before the the item has been
2658 * committed. It will try to free the event from the ring buffer
2659 * if another event has not been added behind it.
2660 *
2661 * If another event has been added behind it, it will set the event
2662 * up as discarded, and perform the commit.
2663 *
2664 * If this function is called, do not call ring_buffer_unlock_commit on
2665 * the event.
2666 */
2667void ring_buffer_discard_commit(struct ring_buffer *buffer,
2668 struct ring_buffer_event *event)
2669{
2670 struct ring_buffer_per_cpu *cpu_buffer;
2671 int cpu;
2672
2673 /* The event is discarded regardless */
2674 rb_event_discard(event);
2675
2676 cpu = smp_processor_id();
2677 cpu_buffer = buffer->buffers[cpu];
2678
2679 /*
2680 * This must only be called if the event has not been
2681 * committed yet. Thus we can assume that preemption
2682 * is still disabled.
2683 */
2684 RB_WARN_ON(buffer, !local_read(&cpu_buffer->committing));
2685
2686 rb_decrement_entry(cpu_buffer, event);
2687 if (rb_try_to_discard(cpu_buffer, event))
2688 goto out;
2689
2690 /*
2691 * The commit is still visible by the reader, so we
2692 * must still update the timestamp.
2693 */
2694 rb_update_write_stamp(cpu_buffer, event);
2695 out:
2696 rb_end_commit(cpu_buffer);
2697
2698 trace_recursive_unlock();
2699
2700 preempt_enable_notrace();
2701
2702}
2703EXPORT_SYMBOL_GPL(ring_buffer_discard_commit);
2704
2705/**
2706 * ring_buffer_write - write data to the buffer without reserving
2707 * @buffer: The ring buffer to write to.
2708 * @length: The length of the data being written (excluding the event header)
2709 * @data: The data to write to the buffer.
2710 *
2711 * This is like ring_buffer_lock_reserve and ring_buffer_unlock_commit as
2712 * one function. If you already have the data to write to the buffer, it
2713 * may be easier to simply call this function.
2714 *
2715 * Note, like ring_buffer_lock_reserve, the length is the length of the data
2716 * and not the length of the event which would hold the header.
2717 */
2718int ring_buffer_write(struct ring_buffer *buffer,
2719 unsigned long length,
2720 void *data)
2721{
2722 struct ring_buffer_per_cpu *cpu_buffer;
2723 struct ring_buffer_event *event;
2724 void *body;
2725 int ret = -EBUSY;
2726 int cpu;
2727
2728 if (ring_buffer_flags != RB_BUFFERS_ON)
2729 return -EBUSY;
2730
2731 preempt_disable_notrace();
2732
2733 if (atomic_read(&buffer->record_disabled))
2734 goto out;
2735
2736 cpu = raw_smp_processor_id();
2737
2738 if (!cpumask_test_cpu(cpu, buffer->cpumask))
2739 goto out;
2740
2741 cpu_buffer = buffer->buffers[cpu];
2742
2743 if (atomic_read(&cpu_buffer->record_disabled))
2744 goto out;
2745
2746 if (length > BUF_MAX_DATA_SIZE)
2747 goto out;
2748
2749 event = rb_reserve_next_event(buffer, cpu_buffer, length);
2750 if (!event)
2751 goto out;
2752
2753 body = rb_event_data(event);
2754
2755 memcpy(body, data, length);
2756
2757 rb_commit(cpu_buffer, event);
2758
2759 ret = 0;
2760 out:
2761 preempt_enable_notrace();
2762
2763 return ret;
2764}
2765EXPORT_SYMBOL_GPL(ring_buffer_write);
2766
2767static int rb_per_cpu_empty(struct ring_buffer_per_cpu *cpu_buffer)
2768{
2769 struct buffer_page *reader = cpu_buffer->reader_page;
2770 struct buffer_page *head = rb_set_head_page(cpu_buffer);
2771 struct buffer_page *commit = cpu_buffer->commit_page;
2772
2773 /* In case of error, head will be NULL */
2774 if (unlikely(!head))
2775 return 1;
2776
2777 return reader->read == rb_page_commit(reader) &&
2778 (commit == reader ||
2779 (commit == head &&
2780 head->read == rb_page_commit(commit)));
2781}
2782
2783/**
2784 * ring_buffer_record_disable - stop all writes into the buffer
2785 * @buffer: The ring buffer to stop writes to.
2786 *
2787 * This prevents all writes to the buffer. Any attempt to write
2788 * to the buffer after this will fail and return NULL.
2789 *
2790 * The caller should call synchronize_sched() after this.
2791 */
2792void ring_buffer_record_disable(struct ring_buffer *buffer)
2793{
2794 atomic_inc(&buffer->record_disabled);
2795}
2796EXPORT_SYMBOL_GPL(ring_buffer_record_disable);
2797
2798/**
2799 * ring_buffer_record_enable - enable writes to the buffer
2800 * @buffer: The ring buffer to enable writes
2801 *
2802 * Note, multiple disables will need the same number of enables
2803 * to truly enable the writing (much like preempt_disable).
2804 */
2805void ring_buffer_record_enable(struct ring_buffer *buffer)
2806{
2807 atomic_dec(&buffer->record_disabled);
2808}
2809EXPORT_SYMBOL_GPL(ring_buffer_record_enable);
2810
2811/**
2812 * ring_buffer_record_off - stop all writes into the buffer
2813 * @buffer: The ring buffer to stop writes to.
2814 *
2815 * This prevents all writes to the buffer. Any attempt to write
2816 * to the buffer after this will fail and return NULL.
2817 *
2818 * This is different than ring_buffer_record_disable() as
2819 * it works like an on/off switch, where as the disable() verison
2820 * must be paired with a enable().
2821 */
2822void ring_buffer_record_off(struct ring_buffer *buffer)
2823{
2824 unsigned int rd;
2825 unsigned int new_rd;
2826
2827 do {
2828 rd = atomic_read(&buffer->record_disabled);
2829 new_rd = rd | RB_BUFFER_OFF;
2830 } while (atomic_cmpxchg(&buffer->record_disabled, rd, new_rd) != rd);
2831}
2832EXPORT_SYMBOL_GPL(ring_buffer_record_off);
2833
2834/**
2835 * ring_buffer_record_on - restart writes into the buffer
2836 * @buffer: The ring buffer to start writes to.
2837 *
2838 * This enables all writes to the buffer that was disabled by
2839 * ring_buffer_record_off().
2840 *
2841 * This is different than ring_buffer_record_enable() as
2842 * it works like an on/off switch, where as the enable() verison
2843 * must be paired with a disable().
2844 */
2845void ring_buffer_record_on(struct ring_buffer *buffer)
2846{
2847 unsigned int rd;
2848 unsigned int new_rd;
2849
2850 do {
2851 rd = atomic_read(&buffer->record_disabled);
2852 new_rd = rd & ~RB_BUFFER_OFF;
2853 } while (atomic_cmpxchg(&buffer->record_disabled, rd, new_rd) != rd);
2854}
2855EXPORT_SYMBOL_GPL(ring_buffer_record_on);
2856
2857/**
2858 * ring_buffer_record_is_on - return true if the ring buffer can write
2859 * @buffer: The ring buffer to see if write is enabled
2860 *
2861 * Returns true if the ring buffer is in a state that it accepts writes.
2862 */
2863int ring_buffer_record_is_on(struct ring_buffer *buffer)
2864{
2865 return !atomic_read(&buffer->record_disabled);
2866}
2867
2868/**
2869 * ring_buffer_record_disable_cpu - stop all writes into the cpu_buffer
2870 * @buffer: The ring buffer to stop writes to.
2871 * @cpu: The CPU buffer to stop
2872 *
2873 * This prevents all writes to the buffer. Any attempt to write
2874 * to the buffer after this will fail and return NULL.
2875 *
2876 * The caller should call synchronize_sched() after this.
2877 */
2878void ring_buffer_record_disable_cpu(struct ring_buffer *buffer, int cpu)
2879{
2880 struct ring_buffer_per_cpu *cpu_buffer;
2881
2882 if (!cpumask_test_cpu(cpu, buffer->cpumask))
2883 return;
2884
2885 cpu_buffer = buffer->buffers[cpu];
2886 atomic_inc(&cpu_buffer->record_disabled);
2887}
2888EXPORT_SYMBOL_GPL(ring_buffer_record_disable_cpu);
2889
2890/**
2891 * ring_buffer_record_enable_cpu - enable writes to the buffer
2892 * @buffer: The ring buffer to enable writes
2893 * @cpu: The CPU to enable.
2894 *
2895 * Note, multiple disables will need the same number of enables
2896 * to truly enable the writing (much like preempt_disable).
2897 */
2898void ring_buffer_record_enable_cpu(struct ring_buffer *buffer, int cpu)
2899{
2900 struct ring_buffer_per_cpu *cpu_buffer;
2901
2902 if (!cpumask_test_cpu(cpu, buffer->cpumask))
2903 return;
2904
2905 cpu_buffer = buffer->buffers[cpu];
2906 atomic_dec(&cpu_buffer->record_disabled);
2907}
2908EXPORT_SYMBOL_GPL(ring_buffer_record_enable_cpu);
2909
2910/*
2911 * The total entries in the ring buffer is the running counter
2912 * of entries entered into the ring buffer, minus the sum of
2913 * the entries read from the ring buffer and the number of
2914 * entries that were overwritten.
2915 */
2916static inline unsigned long
2917rb_num_of_entries(struct ring_buffer_per_cpu *cpu_buffer)
2918{
2919 return local_read(&cpu_buffer->entries) -
2920 (local_read(&cpu_buffer->overrun) + cpu_buffer->read);
2921}
2922
2923/**
2924 * ring_buffer_oldest_event_ts - get the oldest event timestamp from the buffer
2925 * @buffer: The ring buffer
2926 * @cpu: The per CPU buffer to read from.
2927 */
2928unsigned long ring_buffer_oldest_event_ts(struct ring_buffer *buffer, int cpu)
2929{
2930 unsigned long flags;
2931 struct ring_buffer_per_cpu *cpu_buffer;
2932 struct buffer_page *bpage;
2933 unsigned long ret;
2934
2935 if (!cpumask_test_cpu(cpu, buffer->cpumask))
2936 return 0;
2937
2938 cpu_buffer = buffer->buffers[cpu];
2939 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
2940 /*
2941 * if the tail is on reader_page, oldest time stamp is on the reader
2942 * page
2943 */
2944 if (cpu_buffer->tail_page == cpu_buffer->reader_page)
2945 bpage = cpu_buffer->reader_page;
2946 else
2947 bpage = rb_set_head_page(cpu_buffer);
2948 ret = bpage->page->time_stamp;
2949 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
2950
2951 return ret;
2952}
2953EXPORT_SYMBOL_GPL(ring_buffer_oldest_event_ts);
2954
2955/**
2956 * ring_buffer_bytes_cpu - get the number of bytes consumed in a cpu buffer
2957 * @buffer: The ring buffer
2958 * @cpu: The per CPU buffer to read from.
2959 */
2960unsigned long ring_buffer_bytes_cpu(struct ring_buffer *buffer, int cpu)
2961{
2962 struct ring_buffer_per_cpu *cpu_buffer;
2963 unsigned long ret;
2964
2965 if (!cpumask_test_cpu(cpu, buffer->cpumask))
2966 return 0;
2967
2968 cpu_buffer = buffer->buffers[cpu];
2969 ret = local_read(&cpu_buffer->entries_bytes) - cpu_buffer->read_bytes;
2970
2971 return ret;
2972}
2973EXPORT_SYMBOL_GPL(ring_buffer_bytes_cpu);
2974
2975/**
2976 * ring_buffer_entries_cpu - get the number of entries in a cpu buffer
2977 * @buffer: The ring buffer
2978 * @cpu: The per CPU buffer to get the entries from.
2979 */
2980unsigned long ring_buffer_entries_cpu(struct ring_buffer *buffer, int cpu)
2981{
2982 struct ring_buffer_per_cpu *cpu_buffer;
2983
2984 if (!cpumask_test_cpu(cpu, buffer->cpumask))
2985 return 0;
2986
2987 cpu_buffer = buffer->buffers[cpu];
2988
2989 return rb_num_of_entries(cpu_buffer);
2990}
2991EXPORT_SYMBOL_GPL(ring_buffer_entries_cpu);
2992
2993/**
2994 * ring_buffer_overrun_cpu - get the number of overruns in a cpu_buffer
2995 * @buffer: The ring buffer
2996 * @cpu: The per CPU buffer to get the number of overruns from
2997 */
2998unsigned long ring_buffer_overrun_cpu(struct ring_buffer *buffer, int cpu)
2999{
3000 struct ring_buffer_per_cpu *cpu_buffer;
3001 unsigned long ret;
3002
3003 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3004 return 0;
3005
3006 cpu_buffer = buffer->buffers[cpu];
3007 ret = local_read(&cpu_buffer->overrun);
3008
3009 return ret;
3010}
3011EXPORT_SYMBOL_GPL(ring_buffer_overrun_cpu);
3012
3013/**
3014 * ring_buffer_commit_overrun_cpu - get the number of overruns caused by commits
3015 * @buffer: The ring buffer
3016 * @cpu: The per CPU buffer to get the number of overruns from
3017 */
3018unsigned long
3019ring_buffer_commit_overrun_cpu(struct ring_buffer *buffer, int cpu)
3020{
3021 struct ring_buffer_per_cpu *cpu_buffer;
3022 unsigned long ret;
3023
3024 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3025 return 0;
3026
3027 cpu_buffer = buffer->buffers[cpu];
3028 ret = local_read(&cpu_buffer->commit_overrun);
3029
3030 return ret;
3031}
3032EXPORT_SYMBOL_GPL(ring_buffer_commit_overrun_cpu);
3033
3034/**
3035 * ring_buffer_entries - get the number of entries in a buffer
3036 * @buffer: The ring buffer
3037 *
3038 * Returns the total number of entries in the ring buffer
3039 * (all CPU entries)
3040 */
3041unsigned long ring_buffer_entries(struct ring_buffer *buffer)
3042{
3043 struct ring_buffer_per_cpu *cpu_buffer;
3044 unsigned long entries = 0;
3045 int cpu;
3046
3047 /* if you care about this being correct, lock the buffer */
3048 for_each_buffer_cpu(buffer, cpu) {
3049 cpu_buffer = buffer->buffers[cpu];
3050 entries += rb_num_of_entries(cpu_buffer);
3051 }
3052
3053 return entries;
3054}
3055EXPORT_SYMBOL_GPL(ring_buffer_entries);
3056
3057/**
3058 * ring_buffer_overruns - get the number of overruns in buffer
3059 * @buffer: The ring buffer
3060 *
3061 * Returns the total number of overruns in the ring buffer
3062 * (all CPU entries)
3063 */
3064unsigned long ring_buffer_overruns(struct ring_buffer *buffer)
3065{
3066 struct ring_buffer_per_cpu *cpu_buffer;
3067 unsigned long overruns = 0;
3068 int cpu;
3069
3070 /* if you care about this being correct, lock the buffer */
3071 for_each_buffer_cpu(buffer, cpu) {
3072 cpu_buffer = buffer->buffers[cpu];
3073 overruns += local_read(&cpu_buffer->overrun);
3074 }
3075
3076 return overruns;
3077}
3078EXPORT_SYMBOL_GPL(ring_buffer_overruns);
3079
3080static void rb_iter_reset(struct ring_buffer_iter *iter)
3081{
3082 struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
3083
3084 /* Iterator usage is expected to have record disabled */
3085 if (list_empty(&cpu_buffer->reader_page->list)) {
3086 iter->head_page = rb_set_head_page(cpu_buffer);
3087 if (unlikely(!iter->head_page))
3088 return;
3089 iter->head = iter->head_page->read;
3090 } else {
3091 iter->head_page = cpu_buffer->reader_page;
3092 iter->head = cpu_buffer->reader_page->read;
3093 }
3094 if (iter->head)
3095 iter->read_stamp = cpu_buffer->read_stamp;
3096 else
3097 iter->read_stamp = iter->head_page->page->time_stamp;
3098 iter->cache_reader_page = cpu_buffer->reader_page;
3099 iter->cache_read = cpu_buffer->read;
3100}
3101
3102/**
3103 * ring_buffer_iter_reset - reset an iterator
3104 * @iter: The iterator to reset
3105 *
3106 * Resets the iterator, so that it will start from the beginning
3107 * again.
3108 */
3109void ring_buffer_iter_reset(struct ring_buffer_iter *iter)
3110{
3111 struct ring_buffer_per_cpu *cpu_buffer;
3112 unsigned long flags;
3113
3114 if (!iter)
3115 return;
3116
3117 cpu_buffer = iter->cpu_buffer;
3118
3119 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
3120 rb_iter_reset(iter);
3121 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
3122}
3123EXPORT_SYMBOL_GPL(ring_buffer_iter_reset);
3124
3125/**
3126 * ring_buffer_iter_empty - check if an iterator has no more to read
3127 * @iter: The iterator to check
3128 */
3129int ring_buffer_iter_empty(struct ring_buffer_iter *iter)
3130{
3131 struct ring_buffer_per_cpu *cpu_buffer;
3132
3133 cpu_buffer = iter->cpu_buffer;
3134
3135 return iter->head_page == cpu_buffer->commit_page &&
3136 iter->head == rb_commit_index(cpu_buffer);
3137}
3138EXPORT_SYMBOL_GPL(ring_buffer_iter_empty);
3139
3140static void
3141rb_update_read_stamp(struct ring_buffer_per_cpu *cpu_buffer,
3142 struct ring_buffer_event *event)
3143{
3144 u64 delta;
3145
3146 switch (event->type_len) {
3147 case RINGBUF_TYPE_PADDING:
3148 return;
3149
3150 case RINGBUF_TYPE_TIME_EXTEND:
3151 delta = event->array[0];
3152 delta <<= TS_SHIFT;
3153 delta += event->time_delta;
3154 cpu_buffer->read_stamp += delta;
3155 return;
3156
3157 case RINGBUF_TYPE_TIME_STAMP:
3158 /* FIXME: not implemented */
3159 return;
3160
3161 case RINGBUF_TYPE_DATA:
3162 cpu_buffer->read_stamp += event->time_delta;
3163 return;
3164
3165 default:
3166 BUG();
3167 }
3168 return;
3169}
3170
3171static void
3172rb_update_iter_read_stamp(struct ring_buffer_iter *iter,
3173 struct ring_buffer_event *event)
3174{
3175 u64 delta;
3176
3177 switch (event->type_len) {
3178 case RINGBUF_TYPE_PADDING:
3179 return;
3180
3181 case RINGBUF_TYPE_TIME_EXTEND:
3182 delta = event->array[0];
3183 delta <<= TS_SHIFT;
3184 delta += event->time_delta;
3185 iter->read_stamp += delta;
3186 return;
3187
3188 case RINGBUF_TYPE_TIME_STAMP:
3189 /* FIXME: not implemented */
3190 return;
3191
3192 case RINGBUF_TYPE_DATA:
3193 iter->read_stamp += event->time_delta;
3194 return;
3195
3196 default:
3197 BUG();
3198 }
3199 return;
3200}
3201
3202static struct buffer_page *
3203rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
3204{
3205 struct buffer_page *reader = NULL;
3206 unsigned long overwrite;
3207 unsigned long flags;
3208 int nr_loops = 0;
3209 int ret;
3210
3211 local_irq_save(flags);
3212 arch_spin_lock(&cpu_buffer->lock);
3213
3214 again:
3215 /*
3216 * This should normally only loop twice. But because the
3217 * start of the reader inserts an empty page, it causes
3218 * a case where we will loop three times. There should be no
3219 * reason to loop four times (that I know of).
3220 */
3221 if (RB_WARN_ON(cpu_buffer, ++nr_loops > 3)) {
3222 reader = NULL;
3223 goto out;
3224 }
3225
3226 reader = cpu_buffer->reader_page;
3227
3228 /* If there's more to read, return this page */
3229 if (cpu_buffer->reader_page->read < rb_page_size(reader))
3230 goto out;
3231
3232 /* Never should we have an index greater than the size */
3233 if (RB_WARN_ON(cpu_buffer,
3234 cpu_buffer->reader_page->read > rb_page_size(reader)))
3235 goto out;
3236
3237 /* check if we caught up to the tail */
3238 reader = NULL;
3239 if (cpu_buffer->commit_page == cpu_buffer->reader_page)
3240 goto out;
3241
3242 /*
3243 * Reset the reader page to size zero.
3244 */
3245 local_set(&cpu_buffer->reader_page->write, 0);
3246 local_set(&cpu_buffer->reader_page->entries, 0);
3247 local_set(&cpu_buffer->reader_page->page->commit, 0);
3248 cpu_buffer->reader_page->real_end = 0;
3249
3250 spin:
3251 /*
3252 * Splice the empty reader page into the list around the head.
3253 */
3254 reader = rb_set_head_page(cpu_buffer);
3255 cpu_buffer->reader_page->list.next = rb_list_head(reader->list.next);
3256 cpu_buffer->reader_page->list.prev = reader->list.prev;
3257
3258 /*
3259 * cpu_buffer->pages just needs to point to the buffer, it
3260 * has no specific buffer page to point to. Lets move it out
3261 * of our way so we don't accidentally swap it.
3262 */
3263 cpu_buffer->pages = reader->list.prev;
3264
3265 /* The reader page will be pointing to the new head */
3266 rb_set_list_to_head(cpu_buffer, &cpu_buffer->reader_page->list);
3267
3268 /*
3269 * We want to make sure we read the overruns after we set up our
3270 * pointers to the next object. The writer side does a
3271 * cmpxchg to cross pages which acts as the mb on the writer
3272 * side. Note, the reader will constantly fail the swap
3273 * while the writer is updating the pointers, so this
3274 * guarantees that the overwrite recorded here is the one we
3275 * want to compare with the last_overrun.
3276 */
3277 smp_mb();
3278 overwrite = local_read(&(cpu_buffer->overrun));
3279
3280 /*
3281 * Here's the tricky part.
3282 *
3283 * We need to move the pointer past the header page.
3284 * But we can only do that if a writer is not currently
3285 * moving it. The page before the header page has the
3286 * flag bit '1' set if it is pointing to the page we want.
3287 * but if the writer is in the process of moving it
3288 * than it will be '2' or already moved '0'.
3289 */
3290
3291 ret = rb_head_page_replace(reader, cpu_buffer->reader_page);
3292
3293 /*
3294 * If we did not convert it, then we must try again.
3295 */
3296 if (!ret)
3297 goto spin;
3298
3299 /*
3300 * Yeah! We succeeded in replacing the page.
3301 *
3302 * Now make the new head point back to the reader page.
3303 */
3304 rb_list_head(reader->list.next)->prev = &cpu_buffer->reader_page->list;
3305 rb_inc_page(cpu_buffer, &cpu_buffer->head_page);
3306
3307 /* Finally update the reader page to the new head */
3308 cpu_buffer->reader_page = reader;
3309 rb_reset_reader_page(cpu_buffer);
3310
3311 if (overwrite != cpu_buffer->last_overrun) {
3312 cpu_buffer->lost_events = overwrite - cpu_buffer->last_overrun;
3313 cpu_buffer->last_overrun = overwrite;
3314 }
3315
3316 goto again;
3317
3318 out:
3319 arch_spin_unlock(&cpu_buffer->lock);
3320 local_irq_restore(flags);
3321
3322 return reader;
3323}
3324
3325static void rb_advance_reader(struct ring_buffer_per_cpu *cpu_buffer)
3326{
3327 struct ring_buffer_event *event;
3328 struct buffer_page *reader;
3329 unsigned length;
3330
3331 reader = rb_get_reader_page(cpu_buffer);
3332
3333 /* This function should not be called when buffer is empty */
3334 if (RB_WARN_ON(cpu_buffer, !reader))
3335 return;
3336
3337 event = rb_reader_event(cpu_buffer);
3338
3339 if (event->type_len <= RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
3340 cpu_buffer->read++;
3341
3342 rb_update_read_stamp(cpu_buffer, event);
3343
3344 length = rb_event_length(event);
3345 cpu_buffer->reader_page->read += length;
3346}
3347
3348static void rb_advance_iter(struct ring_buffer_iter *iter)
3349{
3350 struct ring_buffer_per_cpu *cpu_buffer;
3351 struct ring_buffer_event *event;
3352 unsigned length;
3353
3354 cpu_buffer = iter->cpu_buffer;
3355
3356 /*
3357 * Check if we are at the end of the buffer.
3358 */
3359 if (iter->head >= rb_page_size(iter->head_page)) {
3360 /* discarded commits can make the page empty */
3361 if (iter->head_page == cpu_buffer->commit_page)
3362 return;
3363 rb_inc_iter(iter);
3364 return;
3365 }
3366
3367 event = rb_iter_head_event(iter);
3368
3369 length = rb_event_length(event);
3370
3371 /*
3372 * This should not be called to advance the header if we are
3373 * at the tail of the buffer.
3374 */
3375 if (RB_WARN_ON(cpu_buffer,
3376 (iter->head_page == cpu_buffer->commit_page) &&
3377 (iter->head + length > rb_commit_index(cpu_buffer))))
3378 return;
3379
3380 rb_update_iter_read_stamp(iter, event);
3381
3382 iter->head += length;
3383
3384 /* check for end of page padding */
3385 if ((iter->head >= rb_page_size(iter->head_page)) &&
3386 (iter->head_page != cpu_buffer->commit_page))
3387 rb_advance_iter(iter);
3388}
3389
3390static int rb_lost_events(struct ring_buffer_per_cpu *cpu_buffer)
3391{
3392 return cpu_buffer->lost_events;
3393}
3394
3395static struct ring_buffer_event *
3396rb_buffer_peek(struct ring_buffer_per_cpu *cpu_buffer, u64 *ts,
3397 unsigned long *lost_events)
3398{
3399 struct ring_buffer_event *event;
3400 struct buffer_page *reader;
3401 int nr_loops = 0;
3402
3403 again:
3404 /*
3405 * We repeat when a time extend is encountered.
3406 * Since the time extend is always attached to a data event,
3407 * we should never loop more than once.
3408 * (We never hit the following condition more than twice).
3409 */
3410 if (RB_WARN_ON(cpu_buffer, ++nr_loops > 2))
3411 return NULL;
3412
3413 reader = rb_get_reader_page(cpu_buffer);
3414 if (!reader)
3415 return NULL;
3416
3417 event = rb_reader_event(cpu_buffer);
3418
3419 switch (event->type_len) {
3420 case RINGBUF_TYPE_PADDING:
3421 if (rb_null_event(event))
3422 RB_WARN_ON(cpu_buffer, 1);
3423 /*
3424 * Because the writer could be discarding every
3425 * event it creates (which would probably be bad)
3426 * if we were to go back to "again" then we may never
3427 * catch up, and will trigger the warn on, or lock
3428 * the box. Return the padding, and we will release
3429 * the current locks, and try again.
3430 */
3431 return event;
3432
3433 case RINGBUF_TYPE_TIME_EXTEND:
3434 /* Internal data, OK to advance */
3435 rb_advance_reader(cpu_buffer);
3436 goto again;
3437
3438 case RINGBUF_TYPE_TIME_STAMP:
3439 /* FIXME: not implemented */
3440 rb_advance_reader(cpu_buffer);
3441 goto again;
3442
3443 case RINGBUF_TYPE_DATA:
3444 if (ts) {
3445 *ts = cpu_buffer->read_stamp + event->time_delta;
3446 ring_buffer_normalize_time_stamp(cpu_buffer->buffer,
3447 cpu_buffer->cpu, ts);
3448 }
3449 if (lost_events)
3450 *lost_events = rb_lost_events(cpu_buffer);
3451 return event;
3452
3453 default:
3454 BUG();
3455 }
3456
3457 return NULL;
3458}
3459EXPORT_SYMBOL_GPL(ring_buffer_peek);
3460
3461static struct ring_buffer_event *
3462rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
3463{
3464 struct ring_buffer *buffer;
3465 struct ring_buffer_per_cpu *cpu_buffer;
3466 struct ring_buffer_event *event;
3467 int nr_loops = 0;
3468
3469 cpu_buffer = iter->cpu_buffer;
3470 buffer = cpu_buffer->buffer;
3471
3472 /*
3473 * Check if someone performed a consuming read to
3474 * the buffer. A consuming read invalidates the iterator
3475 * and we need to reset the iterator in this case.
3476 */
3477 if (unlikely(iter->cache_read != cpu_buffer->read ||
3478 iter->cache_reader_page != cpu_buffer->reader_page))
3479 rb_iter_reset(iter);
3480
3481 again:
3482 if (ring_buffer_iter_empty(iter))
3483 return NULL;
3484
3485 /*
3486 * We repeat when a time extend is encountered.
3487 * Since the time extend is always attached to a data event,
3488 * we should never loop more than once.
3489 * (We never hit the following condition more than twice).
3490 */
3491 if (RB_WARN_ON(cpu_buffer, ++nr_loops > 2))
3492 return NULL;
3493
3494 if (rb_per_cpu_empty(cpu_buffer))
3495 return NULL;
3496
3497 if (iter->head >= local_read(&iter->head_page->page->commit)) {
3498 rb_inc_iter(iter);
3499 goto again;
3500 }
3501
3502 event = rb_iter_head_event(iter);
3503
3504 switch (event->type_len) {
3505 case RINGBUF_TYPE_PADDING:
3506 if (rb_null_event(event)) {
3507 rb_inc_iter(iter);
3508 goto again;
3509 }
3510 rb_advance_iter(iter);
3511 return event;
3512
3513 case RINGBUF_TYPE_TIME_EXTEND:
3514 /* Internal data, OK to advance */
3515 rb_advance_iter(iter);
3516 goto again;
3517
3518 case RINGBUF_TYPE_TIME_STAMP:
3519 /* FIXME: not implemented */
3520 rb_advance_iter(iter);
3521 goto again;
3522
3523 case RINGBUF_TYPE_DATA:
3524 if (ts) {
3525 *ts = iter->read_stamp + event->time_delta;
3526 ring_buffer_normalize_time_stamp(buffer,
3527 cpu_buffer->cpu, ts);
3528 }
3529 return event;
3530
3531 default:
3532 BUG();
3533 }
3534
3535 return NULL;
3536}
3537EXPORT_SYMBOL_GPL(ring_buffer_iter_peek);
3538
3539static inline int rb_ok_to_lock(void)
3540{
3541 /*
3542 * If an NMI die dumps out the content of the ring buffer
3543 * do not grab locks. We also permanently disable the ring
3544 * buffer too. A one time deal is all you get from reading
3545 * the ring buffer from an NMI.
3546 */
3547 if (likely(!in_nmi()))
3548 return 1;
3549
3550 tracing_off_permanent();
3551 return 0;
3552}
3553
3554/**
3555 * ring_buffer_peek - peek at the next event to be read
3556 * @buffer: The ring buffer to read
3557 * @cpu: The cpu to peak at
3558 * @ts: The timestamp counter of this event.
3559 * @lost_events: a variable to store if events were lost (may be NULL)
3560 *
3561 * This will return the event that will be read next, but does
3562 * not consume the data.
3563 */
3564struct ring_buffer_event *
3565ring_buffer_peek(struct ring_buffer *buffer, int cpu, u64 *ts,
3566 unsigned long *lost_events)
3567{
3568 struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
3569 struct ring_buffer_event *event;
3570 unsigned long flags;
3571 int dolock;
3572
3573 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3574 return NULL;
3575
3576 dolock = rb_ok_to_lock();
3577 again:
3578 local_irq_save(flags);
3579 if (dolock)
3580 raw_spin_lock(&cpu_buffer->reader_lock);
3581 event = rb_buffer_peek(cpu_buffer, ts, lost_events);
3582 if (event && event->type_len == RINGBUF_TYPE_PADDING)
3583 rb_advance_reader(cpu_buffer);
3584 if (dolock)
3585 raw_spin_unlock(&cpu_buffer->reader_lock);
3586 local_irq_restore(flags);
3587
3588 if (event && event->type_len == RINGBUF_TYPE_PADDING)
3589 goto again;
3590
3591 return event;
3592}
3593
3594/**
3595 * ring_buffer_iter_peek - peek at the next event to be read
3596 * @iter: The ring buffer iterator
3597 * @ts: The timestamp counter of this event.
3598 *
3599 * This will return the event that will be read next, but does
3600 * not increment the iterator.
3601 */
3602struct ring_buffer_event *
3603ring_buffer_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
3604{
3605 struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
3606 struct ring_buffer_event *event;
3607 unsigned long flags;
3608
3609 again:
3610 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
3611 event = rb_iter_peek(iter, ts);
3612 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
3613
3614 if (event && event->type_len == RINGBUF_TYPE_PADDING)
3615 goto again;
3616
3617 return event;
3618}
3619
3620/**
3621 * ring_buffer_consume - return an event and consume it
3622 * @buffer: The ring buffer to get the next event from
3623 * @cpu: the cpu to read the buffer from
3624 * @ts: a variable to store the timestamp (may be NULL)
3625 * @lost_events: a variable to store if events were lost (may be NULL)
3626 *
3627 * Returns the next event in the ring buffer, and that event is consumed.
3628 * Meaning, that sequential reads will keep returning a different event,
3629 * and eventually empty the ring buffer if the producer is slower.
3630 */
3631struct ring_buffer_event *
3632ring_buffer_consume(struct ring_buffer *buffer, int cpu, u64 *ts,
3633 unsigned long *lost_events)
3634{
3635 struct ring_buffer_per_cpu *cpu_buffer;
3636 struct ring_buffer_event *event = NULL;
3637 unsigned long flags;
3638 int dolock;
3639
3640 dolock = rb_ok_to_lock();
3641
3642 again:
3643 /* might be called in atomic */
3644 preempt_disable();
3645
3646 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3647 goto out;
3648
3649 cpu_buffer = buffer->buffers[cpu];
3650 local_irq_save(flags);
3651 if (dolock)
3652 raw_spin_lock(&cpu_buffer->reader_lock);
3653
3654 event = rb_buffer_peek(cpu_buffer, ts, lost_events);
3655 if (event) {
3656 cpu_buffer->lost_events = 0;
3657 rb_advance_reader(cpu_buffer);
3658 }
3659
3660 if (dolock)
3661 raw_spin_unlock(&cpu_buffer->reader_lock);
3662 local_irq_restore(flags);
3663
3664 out:
3665 preempt_enable();
3666
3667 if (event && event->type_len == RINGBUF_TYPE_PADDING)
3668 goto again;
3669
3670 return event;
3671}
3672EXPORT_SYMBOL_GPL(ring_buffer_consume);
3673
3674/**
3675 * ring_buffer_read_prepare - Prepare for a non consuming read of the buffer
3676 * @buffer: The ring buffer to read from
3677 * @cpu: The cpu buffer to iterate over
3678 *
3679 * This performs the initial preparations necessary to iterate
3680 * through the buffer. Memory is allocated, buffer recording
3681 * is disabled, and the iterator pointer is returned to the caller.
3682 *
3683 * Disabling buffer recordng prevents the reading from being
3684 * corrupted. This is not a consuming read, so a producer is not
3685 * expected.
3686 *
3687 * After a sequence of ring_buffer_read_prepare calls, the user is
3688 * expected to make at least one call to ring_buffer_prepare_sync.
3689 * Afterwards, ring_buffer_read_start is invoked to get things going
3690 * for real.
3691 *
3692 * This overall must be paired with ring_buffer_finish.
3693 */
3694struct ring_buffer_iter *
3695ring_buffer_read_prepare(struct ring_buffer *buffer, int cpu)
3696{
3697 struct ring_buffer_per_cpu *cpu_buffer;
3698 struct ring_buffer_iter *iter;
3699
3700 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3701 return NULL;
3702
3703 iter = kmalloc(sizeof(*iter), GFP_KERNEL);
3704 if (!iter)
3705 return NULL;
3706
3707 cpu_buffer = buffer->buffers[cpu];
3708
3709 iter->cpu_buffer = cpu_buffer;
3710
3711 atomic_inc(&buffer->resize_disabled);
3712 atomic_inc(&cpu_buffer->record_disabled);
3713
3714 return iter;
3715}
3716EXPORT_SYMBOL_GPL(ring_buffer_read_prepare);
3717
3718/**
3719 * ring_buffer_read_prepare_sync - Synchronize a set of prepare calls
3720 *
3721 * All previously invoked ring_buffer_read_prepare calls to prepare
3722 * iterators will be synchronized. Afterwards, read_buffer_read_start
3723 * calls on those iterators are allowed.
3724 */
3725void
3726ring_buffer_read_prepare_sync(void)
3727{
3728 synchronize_sched();
3729}
3730EXPORT_SYMBOL_GPL(ring_buffer_read_prepare_sync);
3731
3732/**
3733 * ring_buffer_read_start - start a non consuming read of the buffer
3734 * @iter: The iterator returned by ring_buffer_read_prepare
3735 *
3736 * This finalizes the startup of an iteration through the buffer.
3737 * The iterator comes from a call to ring_buffer_read_prepare and
3738 * an intervening ring_buffer_read_prepare_sync must have been
3739 * performed.
3740 *
3741 * Must be paired with ring_buffer_finish.
3742 */
3743void
3744ring_buffer_read_start(struct ring_buffer_iter *iter)
3745{
3746 struct ring_buffer_per_cpu *cpu_buffer;
3747 unsigned long flags;
3748
3749 if (!iter)
3750 return;
3751
3752 cpu_buffer = iter->cpu_buffer;
3753
3754 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
3755 arch_spin_lock(&cpu_buffer->lock);
3756 rb_iter_reset(iter);
3757 arch_spin_unlock(&cpu_buffer->lock);
3758 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
3759}
3760EXPORT_SYMBOL_GPL(ring_buffer_read_start);
3761
3762/**
3763 * ring_buffer_finish - finish reading the iterator of the buffer
3764 * @iter: The iterator retrieved by ring_buffer_start
3765 *
3766 * This re-enables the recording to the buffer, and frees the
3767 * iterator.
3768 */
3769void
3770ring_buffer_read_finish(struct ring_buffer_iter *iter)
3771{
3772 struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
3773
3774 /*
3775 * Ring buffer is disabled from recording, here's a good place
3776 * to check the integrity of the ring buffer.
3777 */
3778 rb_check_pages(cpu_buffer);
3779
3780 atomic_dec(&cpu_buffer->record_disabled);
3781 atomic_dec(&cpu_buffer->buffer->resize_disabled);
3782 kfree(iter);
3783}
3784EXPORT_SYMBOL_GPL(ring_buffer_read_finish);
3785
3786/**
3787 * ring_buffer_read - read the next item in the ring buffer by the iterator
3788 * @iter: The ring buffer iterator
3789 * @ts: The time stamp of the event read.
3790 *
3791 * This reads the next event in the ring buffer and increments the iterator.
3792 */
3793struct ring_buffer_event *
3794ring_buffer_read(struct ring_buffer_iter *iter, u64 *ts)
3795{
3796 struct ring_buffer_event *event;
3797 struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
3798 unsigned long flags;
3799
3800 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
3801 again:
3802 event = rb_iter_peek(iter, ts);
3803 if (!event)
3804 goto out;
3805
3806 if (event->type_len == RINGBUF_TYPE_PADDING)
3807 goto again;
3808
3809 rb_advance_iter(iter);
3810 out:
3811 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
3812
3813 return event;
3814}
3815EXPORT_SYMBOL_GPL(ring_buffer_read);
3816
3817/**
3818 * ring_buffer_size - return the size of the ring buffer (in bytes)
3819 * @buffer: The ring buffer.
3820 */
3821unsigned long ring_buffer_size(struct ring_buffer *buffer, int cpu)
3822{
3823 /*
3824 * Earlier, this method returned
3825 * BUF_PAGE_SIZE * buffer->nr_pages
3826 * Since the nr_pages field is now removed, we have converted this to
3827 * return the per cpu buffer value.
3828 */
3829 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3830 return 0;
3831
3832 return BUF_PAGE_SIZE * buffer->buffers[cpu]->nr_pages;
3833}
3834EXPORT_SYMBOL_GPL(ring_buffer_size);
3835
3836static void
3837rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
3838{
3839 rb_head_page_deactivate(cpu_buffer);
3840
3841 cpu_buffer->head_page
3842 = list_entry(cpu_buffer->pages, struct buffer_page, list);
3843 local_set(&cpu_buffer->head_page->write, 0);
3844 local_set(&cpu_buffer->head_page->entries, 0);
3845 local_set(&cpu_buffer->head_page->page->commit, 0);
3846
3847 cpu_buffer->head_page->read = 0;
3848
3849 cpu_buffer->tail_page = cpu_buffer->head_page;
3850 cpu_buffer->commit_page = cpu_buffer->head_page;
3851
3852 INIT_LIST_HEAD(&cpu_buffer->reader_page->list);
3853 INIT_LIST_HEAD(&cpu_buffer->new_pages);
3854 local_set(&cpu_buffer->reader_page->write, 0);
3855 local_set(&cpu_buffer->reader_page->entries, 0);
3856 local_set(&cpu_buffer->reader_page->page->commit, 0);
3857 cpu_buffer->reader_page->read = 0;
3858
3859 local_set(&cpu_buffer->commit_overrun, 0);
3860 local_set(&cpu_buffer->entries_bytes, 0);
3861 local_set(&cpu_buffer->overrun, 0);
3862 local_set(&cpu_buffer->entries, 0);
3863 local_set(&cpu_buffer->committing, 0);
3864 local_set(&cpu_buffer->commits, 0);
3865 cpu_buffer->read = 0;
3866 cpu_buffer->read_bytes = 0;
3867
3868 cpu_buffer->write_stamp = 0;
3869 cpu_buffer->read_stamp = 0;
3870
3871 cpu_buffer->lost_events = 0;
3872 cpu_buffer->last_overrun = 0;
3873
3874 rb_head_page_activate(cpu_buffer);
3875}
3876
3877/**
3878 * ring_buffer_reset_cpu - reset a ring buffer per CPU buffer
3879 * @buffer: The ring buffer to reset a per cpu buffer of
3880 * @cpu: The CPU buffer to be reset
3881 */
3882void ring_buffer_reset_cpu(struct ring_buffer *buffer, int cpu)
3883{
3884 struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
3885 unsigned long flags;
3886
3887 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3888 return;
3889
3890 atomic_inc(&buffer->resize_disabled);
3891 atomic_inc(&cpu_buffer->record_disabled);
3892
3893 /* Make sure all commits have finished */
3894 synchronize_sched();
3895
3896 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
3897
3898 if (RB_WARN_ON(cpu_buffer, local_read(&cpu_buffer->committing)))
3899 goto out;
3900
3901 arch_spin_lock(&cpu_buffer->lock);
3902
3903 rb_reset_cpu(cpu_buffer);
3904
3905 arch_spin_unlock(&cpu_buffer->lock);
3906
3907 out:
3908 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
3909
3910 atomic_dec(&cpu_buffer->record_disabled);
3911 atomic_dec(&buffer->resize_disabled);
3912}
3913EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu);
3914
3915/**
3916 * ring_buffer_reset - reset a ring buffer
3917 * @buffer: The ring buffer to reset all cpu buffers
3918 */
3919void ring_buffer_reset(struct ring_buffer *buffer)
3920{
3921 int cpu;
3922
3923 for_each_buffer_cpu(buffer, cpu)
3924 ring_buffer_reset_cpu(buffer, cpu);
3925}
3926EXPORT_SYMBOL_GPL(ring_buffer_reset);
3927
3928/**
3929 * rind_buffer_empty - is the ring buffer empty?
3930 * @buffer: The ring buffer to test
3931 */
3932int ring_buffer_empty(struct ring_buffer *buffer)
3933{
3934 struct ring_buffer_per_cpu *cpu_buffer;
3935 unsigned long flags;
3936 int dolock;
3937 int cpu;
3938 int ret;
3939
3940 dolock = rb_ok_to_lock();
3941
3942 /* yes this is racy, but if you don't like the race, lock the buffer */
3943 for_each_buffer_cpu(buffer, cpu) {
3944 cpu_buffer = buffer->buffers[cpu];
3945 local_irq_save(flags);
3946 if (dolock)
3947 raw_spin_lock(&cpu_buffer->reader_lock);
3948 ret = rb_per_cpu_empty(cpu_buffer);
3949 if (dolock)
3950 raw_spin_unlock(&cpu_buffer->reader_lock);
3951 local_irq_restore(flags);
3952
3953 if (!ret)
3954 return 0;
3955 }
3956
3957 return 1;
3958}
3959EXPORT_SYMBOL_GPL(ring_buffer_empty);
3960
3961/**
3962 * ring_buffer_empty_cpu - is a cpu buffer of a ring buffer empty?
3963 * @buffer: The ring buffer
3964 * @cpu: The CPU buffer to test
3965 */
3966int ring_buffer_empty_cpu(struct ring_buffer *buffer, int cpu)
3967{
3968 struct ring_buffer_per_cpu *cpu_buffer;
3969 unsigned long flags;
3970 int dolock;
3971 int ret;
3972
3973 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3974 return 1;
3975
3976 dolock = rb_ok_to_lock();
3977
3978 cpu_buffer = buffer->buffers[cpu];
3979 local_irq_save(flags);
3980 if (dolock)
3981 raw_spin_lock(&cpu_buffer->reader_lock);
3982 ret = rb_per_cpu_empty(cpu_buffer);
3983 if (dolock)
3984 raw_spin_unlock(&cpu_buffer->reader_lock);
3985 local_irq_restore(flags);
3986
3987 return ret;
3988}
3989EXPORT_SYMBOL_GPL(ring_buffer_empty_cpu);
3990
3991#ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
3992/**
3993 * ring_buffer_swap_cpu - swap a CPU buffer between two ring buffers
3994 * @buffer_a: One buffer to swap with
3995 * @buffer_b: The other buffer to swap with
3996 *
3997 * This function is useful for tracers that want to take a "snapshot"
3998 * of a CPU buffer and has another back up buffer lying around.
3999 * it is expected that the tracer handles the cpu buffer not being
4000 * used at the moment.
4001 */
4002int ring_buffer_swap_cpu(struct ring_buffer *buffer_a,
4003 struct ring_buffer *buffer_b, int cpu)
4004{
4005 struct ring_buffer_per_cpu *cpu_buffer_a;
4006 struct ring_buffer_per_cpu *cpu_buffer_b;
4007 int ret = -EINVAL;
4008
4009 if (!cpumask_test_cpu(cpu, buffer_a->cpumask) ||
4010 !cpumask_test_cpu(cpu, buffer_b->cpumask))
4011 goto out;
4012
4013 cpu_buffer_a = buffer_a->buffers[cpu];
4014 cpu_buffer_b = buffer_b->buffers[cpu];
4015
4016 /* At least make sure the two buffers are somewhat the same */
4017 if (cpu_buffer_a->nr_pages != cpu_buffer_b->nr_pages)
4018 goto out;
4019
4020 ret = -EAGAIN;
4021
4022 if (ring_buffer_flags != RB_BUFFERS_ON)
4023 goto out;
4024
4025 if (atomic_read(&buffer_a->record_disabled))
4026 goto out;
4027
4028 if (atomic_read(&buffer_b->record_disabled))
4029 goto out;
4030
4031 if (atomic_read(&cpu_buffer_a->record_disabled))
4032 goto out;
4033
4034 if (atomic_read(&cpu_buffer_b->record_disabled))
4035 goto out;
4036
4037 /*
4038 * We can't do a synchronize_sched here because this
4039 * function can be called in atomic context.
4040 * Normally this will be called from the same CPU as cpu.
4041 * If not it's up to the caller to protect this.
4042 */
4043 atomic_inc(&cpu_buffer_a->record_disabled);
4044 atomic_inc(&cpu_buffer_b->record_disabled);
4045
4046 ret = -EBUSY;
4047 if (local_read(&cpu_buffer_a->committing))
4048 goto out_dec;
4049 if (local_read(&cpu_buffer_b->committing))
4050 goto out_dec;
4051
4052 buffer_a->buffers[cpu] = cpu_buffer_b;
4053 buffer_b->buffers[cpu] = cpu_buffer_a;
4054
4055 cpu_buffer_b->buffer = buffer_a;
4056 cpu_buffer_a->buffer = buffer_b;
4057
4058 ret = 0;
4059
4060out_dec:
4061 atomic_dec(&cpu_buffer_a->record_disabled);
4062 atomic_dec(&cpu_buffer_b->record_disabled);
4063out:
4064 return ret;
4065}
4066EXPORT_SYMBOL_GPL(ring_buffer_swap_cpu);
4067#endif /* CONFIG_RING_BUFFER_ALLOW_SWAP */
4068
4069/**
4070 * ring_buffer_alloc_read_page - allocate a page to read from buffer
4071 * @buffer: the buffer to allocate for.
4072 *
4073 * This function is used in conjunction with ring_buffer_read_page.
4074 * When reading a full page from the ring buffer, these functions
4075 * can be used to speed up the process. The calling function should
4076 * allocate a few pages first with this function. Then when it
4077 * needs to get pages from the ring buffer, it passes the result
4078 * of this function into ring_buffer_read_page, which will swap
4079 * the page that was allocated, with the read page of the buffer.
4080 *
4081 * Returns:
4082 * The page allocated, or NULL on error.
4083 */
4084void *ring_buffer_alloc_read_page(struct ring_buffer *buffer, int cpu)
4085{
4086 struct buffer_data_page *bpage;
4087 struct page *page;
4088
4089 page = alloc_pages_node(cpu_to_node(cpu),
4090 GFP_KERNEL | __GFP_NORETRY, 0);
4091 if (!page)
4092 return NULL;
4093
4094 bpage = page_address(page);
4095
4096 rb_init_page(bpage);
4097
4098 return bpage;
4099}
4100EXPORT_SYMBOL_GPL(ring_buffer_alloc_read_page);
4101
4102/**
4103 * ring_buffer_free_read_page - free an allocated read page
4104 * @buffer: the buffer the page was allocate for
4105 * @data: the page to free
4106 *
4107 * Free a page allocated from ring_buffer_alloc_read_page.
4108 */
4109void ring_buffer_free_read_page(struct ring_buffer *buffer, void *data)
4110{
4111 free_page((unsigned long)data);
4112}
4113EXPORT_SYMBOL_GPL(ring_buffer_free_read_page);
4114
4115/**
4116 * ring_buffer_read_page - extract a page from the ring buffer
4117 * @buffer: buffer to extract from
4118 * @data_page: the page to use allocated from ring_buffer_alloc_read_page
4119 * @len: amount to extract
4120 * @cpu: the cpu of the buffer to extract
4121 * @full: should the extraction only happen when the page is full.
4122 *
4123 * This function will pull out a page from the ring buffer and consume it.
4124 * @data_page must be the address of the variable that was returned
4125 * from ring_buffer_alloc_read_page. This is because the page might be used
4126 * to swap with a page in the ring buffer.
4127 *
4128 * for example:
4129 * rpage = ring_buffer_alloc_read_page(buffer);
4130 * if (!rpage)
4131 * return error;
4132 * ret = ring_buffer_read_page(buffer, &rpage, len, cpu, 0);
4133 * if (ret >= 0)
4134 * process_page(rpage, ret);
4135 *
4136 * When @full is set, the function will not return true unless
4137 * the writer is off the reader page.
4138 *
4139 * Note: it is up to the calling functions to handle sleeps and wakeups.
4140 * The ring buffer can be used anywhere in the kernel and can not
4141 * blindly call wake_up. The layer that uses the ring buffer must be
4142 * responsible for that.
4143 *
4144 * Returns:
4145 * >=0 if data has been transferred, returns the offset of consumed data.
4146 * <0 if no data has been transferred.
4147 */
4148int ring_buffer_read_page(struct ring_buffer *buffer,
4149 void **data_page, size_t len, int cpu, int full)
4150{
4151 struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
4152 struct ring_buffer_event *event;
4153 struct buffer_data_page *bpage;
4154 struct buffer_page *reader;
4155 unsigned long missed_events;
4156 unsigned long flags;
4157 unsigned int commit;
4158 unsigned int read;
4159 u64 save_timestamp;
4160 int ret = -1;
4161
4162 if (!cpumask_test_cpu(cpu, buffer->cpumask))
4163 goto out;
4164
4165 /*
4166 * If len is not big enough to hold the page header, then
4167 * we can not copy anything.
4168 */
4169 if (len <= BUF_PAGE_HDR_SIZE)
4170 goto out;
4171
4172 len -= BUF_PAGE_HDR_SIZE;
4173
4174 if (!data_page)
4175 goto out;
4176
4177 bpage = *data_page;
4178 if (!bpage)
4179 goto out;
4180
4181 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
4182
4183 reader = rb_get_reader_page(cpu_buffer);
4184 if (!reader)
4185 goto out_unlock;
4186
4187 event = rb_reader_event(cpu_buffer);
4188
4189 read = reader->read;
4190 commit = rb_page_commit(reader);
4191
4192 /* Check if any events were dropped */
4193 missed_events = cpu_buffer->lost_events;
4194
4195 /*
4196 * If this page has been partially read or
4197 * if len is not big enough to read the rest of the page or
4198 * a writer is still on the page, then
4199 * we must copy the data from the page to the buffer.
4200 * Otherwise, we can simply swap the page with the one passed in.
4201 */
4202 if (read || (len < (commit - read)) ||
4203 cpu_buffer->reader_page == cpu_buffer->commit_page) {
4204 struct buffer_data_page *rpage = cpu_buffer->reader_page->page;
4205 unsigned int rpos = read;
4206 unsigned int pos = 0;
4207 unsigned int size;
4208
4209 if (full)
4210 goto out_unlock;
4211
4212 if (len > (commit - read))
4213 len = (commit - read);
4214
4215 /* Always keep the time extend and data together */
4216 size = rb_event_ts_length(event);
4217
4218 if (len < size)
4219 goto out_unlock;
4220
4221 /* save the current timestamp, since the user will need it */
4222 save_timestamp = cpu_buffer->read_stamp;
4223
4224 /* Need to copy one event at a time */
4225 do {
4226 /* We need the size of one event, because
4227 * rb_advance_reader only advances by one event,
4228 * whereas rb_event_ts_length may include the size of
4229 * one or two events.
4230 * We have already ensured there's enough space if this
4231 * is a time extend. */
4232 size = rb_event_length(event);
4233 memcpy(bpage->data + pos, rpage->data + rpos, size);
4234
4235 len -= size;
4236
4237 rb_advance_reader(cpu_buffer);
4238 rpos = reader->read;
4239 pos += size;
4240
4241 if (rpos >= commit)
4242 break;
4243
4244 event = rb_reader_event(cpu_buffer);
4245 /* Always keep the time extend and data together */
4246 size = rb_event_ts_length(event);
4247 } while (len >= size);
4248
4249 /* update bpage */
4250 local_set(&bpage->commit, pos);
4251 bpage->time_stamp = save_timestamp;
4252
4253 /* we copied everything to the beginning */
4254 read = 0;
4255 } else {
4256 /* update the entry counter */
4257 cpu_buffer->read += rb_page_entries(reader);
4258 cpu_buffer->read_bytes += BUF_PAGE_SIZE;
4259
4260 /* swap the pages */
4261 rb_init_page(bpage);
4262 bpage = reader->page;
4263 reader->page = *data_page;
4264 local_set(&reader->write, 0);
4265 local_set(&reader->entries, 0);
4266 reader->read = 0;
4267 *data_page = bpage;
4268
4269 /*
4270 * Use the real_end for the data size,
4271 * This gives us a chance to store the lost events
4272 * on the page.
4273 */
4274 if (reader->real_end)
4275 local_set(&bpage->commit, reader->real_end);
4276 }
4277 ret = read;
4278
4279 cpu_buffer->lost_events = 0;
4280
4281 commit = local_read(&bpage->commit);
4282 /*
4283 * Set a flag in the commit field if we lost events
4284 */
4285 if (missed_events) {
4286 /* If there is room at the end of the page to save the
4287 * missed events, then record it there.
4288 */
4289 if (BUF_PAGE_SIZE - commit >= sizeof(missed_events)) {
4290 memcpy(&bpage->data[commit], &missed_events,
4291 sizeof(missed_events));
4292 local_add(RB_MISSED_STORED, &bpage->commit);
4293 commit += sizeof(missed_events);
4294 }
4295 local_add(RB_MISSED_EVENTS, &bpage->commit);
4296 }
4297
4298 /*
4299 * This page may be off to user land. Zero it out here.
4300 */
4301 if (commit < BUF_PAGE_SIZE)
4302 memset(&bpage->data[commit], 0, BUF_PAGE_SIZE - commit);
4303
4304 out_unlock:
4305 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
4306
4307 out:
4308 return ret;
4309}
4310EXPORT_SYMBOL_GPL(ring_buffer_read_page);
4311
4312#ifdef CONFIG_HOTPLUG_CPU
4313static int rb_cpu_notify(struct notifier_block *self,
4314 unsigned long action, void *hcpu)
4315{
4316 struct ring_buffer *buffer =
4317 container_of(self, struct ring_buffer, cpu_notify);
4318 long cpu = (long)hcpu;
4319 int cpu_i, nr_pages_same;
4320 unsigned int nr_pages;
4321
4322 switch (action) {
4323 case CPU_UP_PREPARE:
4324 case CPU_UP_PREPARE_FROZEN:
4325 if (cpumask_test_cpu(cpu, buffer->cpumask))
4326 return NOTIFY_OK;
4327
4328 nr_pages = 0;
4329 nr_pages_same = 1;
4330 /* check if all cpu sizes are same */
4331 for_each_buffer_cpu(buffer, cpu_i) {
4332 /* fill in the size from first enabled cpu */
4333 if (nr_pages == 0)
4334 nr_pages = buffer->buffers[cpu_i]->nr_pages;
4335 if (nr_pages != buffer->buffers[cpu_i]->nr_pages) {
4336 nr_pages_same = 0;
4337 break;
4338 }
4339 }
4340 /* allocate minimum pages, user can later expand it */
4341 if (!nr_pages_same)
4342 nr_pages = 2;
4343 buffer->buffers[cpu] =
4344 rb_allocate_cpu_buffer(buffer, nr_pages, cpu);
4345 if (!buffer->buffers[cpu]) {
4346 WARN(1, "failed to allocate ring buffer on CPU %ld\n",
4347 cpu);
4348 return NOTIFY_OK;
4349 }
4350 smp_wmb();
4351 cpumask_set_cpu(cpu, buffer->cpumask);
4352 break;
4353 case CPU_DOWN_PREPARE:
4354 case CPU_DOWN_PREPARE_FROZEN:
4355 /*
4356 * Do nothing.
4357 * If we were to free the buffer, then the user would
4358 * lose any trace that was in the buffer.
4359 */
4360 break;
4361 default:
4362 break;
4363 }
4364 return NOTIFY_OK;
4365}
4366#endif