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1/*
2 * Generic ring buffer
3 *
4 * Copyright (C) 2008 Steven Rostedt <srostedt@redhat.com>
5 */
6#include <linux/ftrace_event.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/debugfs.h>
13#include <linux/uaccess.h>
14#include <linux/hardirq.h>
15#include <linux/kthread.h> /* for self test */
16#include <linux/kmemcheck.h>
17#include <linux/module.h>
18#include <linux/percpu.h>
19#include <linux/mutex.h>
20#include <linux/delay.h>
21#include <linux/slab.h>
22#include <linux/init.h>
23#include <linux/hash.h>
24#include <linux/list.h>
25#include <linux/cpu.h>
26#include <linux/fs.h>
27
28#include <asm/local.h>
29
30static void update_pages_handler(struct work_struct *work);
31
32/*
33 * The ring buffer header is special. We must manually up keep it.
34 */
35int ring_buffer_print_entry_header(struct trace_seq *s)
36{
37 int ret;
38
39 ret = trace_seq_puts(s, "# compressed entry header\n");
40 ret = trace_seq_puts(s, "\ttype_len : 5 bits\n");
41 ret = trace_seq_puts(s, "\ttime_delta : 27 bits\n");
42 ret = trace_seq_puts(s, "\tarray : 32 bits\n");
43 ret = trace_seq_putc(s, '\n');
44 ret = trace_seq_printf(s, "\tpadding : type == %d\n",
45 RINGBUF_TYPE_PADDING);
46 ret = trace_seq_printf(s, "\ttime_extend : type == %d\n",
47 RINGBUF_TYPE_TIME_EXTEND);
48 ret = trace_seq_printf(s, "\tdata max type_len == %d\n",
49 RINGBUF_TYPE_DATA_TYPE_LEN_MAX);
50
51 return ret;
52}
53
54/*
55 * The ring buffer is made up of a list of pages. A separate list of pages is
56 * allocated for each CPU. A writer may only write to a buffer that is
57 * associated with the CPU it is currently executing on. A reader may read
58 * from any per cpu buffer.
59 *
60 * The reader is special. For each per cpu buffer, the reader has its own
61 * reader page. When a reader has read the entire reader page, this reader
62 * page is swapped with another page in the ring buffer.
63 *
64 * Now, as long as the writer is off the reader page, the reader can do what
65 * ever it wants with that page. The writer will never write to that page
66 * again (as long as it is out of the ring buffer).
67 *
68 * Here's some silly ASCII art.
69 *
70 * +------+
71 * |reader| RING BUFFER
72 * |page |
73 * +------+ +---+ +---+ +---+
74 * | |-->| |-->| |
75 * +---+ +---+ +---+
76 * ^ |
77 * | |
78 * +---------------+
79 *
80 *
81 * +------+
82 * |reader| RING BUFFER
83 * |page |------------------v
84 * +------+ +---+ +---+ +---+
85 * | |-->| |-->| |
86 * +---+ +---+ +---+
87 * ^ |
88 * | |
89 * +---------------+
90 *
91 *
92 * +------+
93 * |reader| RING BUFFER
94 * |page |------------------v
95 * +------+ +---+ +---+ +---+
96 * ^ | |-->| |-->| |
97 * | +---+ +---+ +---+
98 * | |
99 * | |
100 * +------------------------------+
101 *
102 *
103 * +------+
104 * |buffer| RING BUFFER
105 * |page |------------------v
106 * +------+ +---+ +---+ +---+
107 * ^ | | | |-->| |
108 * | New +---+ +---+ +---+
109 * | Reader------^ |
110 * | page |
111 * +------------------------------+
112 *
113 *
114 * After we make this swap, the reader can hand this page off to the splice
115 * code and be done with it. It can even allocate a new page if it needs to
116 * and swap that into the ring buffer.
117 *
118 * We will be using cmpxchg soon to make all this lockless.
119 *
120 */
121
122/*
123 * A fast way to enable or disable all ring buffers is to
124 * call tracing_on or tracing_off. Turning off the ring buffers
125 * prevents all ring buffers from being recorded to.
126 * Turning this switch on, makes it OK to write to the
127 * ring buffer, if the ring buffer is enabled itself.
128 *
129 * There's three layers that must be on in order to write
130 * to the ring buffer.
131 *
132 * 1) This global flag must be set.
133 * 2) The ring buffer must be enabled for recording.
134 * 3) The per cpu buffer must be enabled for recording.
135 *
136 * In case of an anomaly, this global flag has a bit set that
137 * will permantly disable all ring buffers.
138 */
139
140/*
141 * Global flag to disable all recording to ring buffers
142 * This has two bits: ON, DISABLED
143 *
144 * ON DISABLED
145 * ---- ----------
146 * 0 0 : ring buffers are off
147 * 1 0 : ring buffers are on
148 * X 1 : ring buffers are permanently disabled
149 */
150
151enum {
152 RB_BUFFERS_ON_BIT = 0,
153 RB_BUFFERS_DISABLED_BIT = 1,
154};
155
156enum {
157 RB_BUFFERS_ON = 1 << RB_BUFFERS_ON_BIT,
158 RB_BUFFERS_DISABLED = 1 << RB_BUFFERS_DISABLED_BIT,
159};
160
161static unsigned long ring_buffer_flags __read_mostly = RB_BUFFERS_ON;
162
163/* Used for individual buffers (after the counter) */
164#define RB_BUFFER_OFF (1 << 20)
165
166#define BUF_PAGE_HDR_SIZE offsetof(struct buffer_data_page, data)
167
168/**
169 * tracing_off_permanent - permanently disable ring buffers
170 *
171 * This function, once called, will disable all ring buffers
172 * permanently.
173 */
174void tracing_off_permanent(void)
175{
176 set_bit(RB_BUFFERS_DISABLED_BIT, &ring_buffer_flags);
177}
178
179#define RB_EVNT_HDR_SIZE (offsetof(struct ring_buffer_event, array))
180#define RB_ALIGNMENT 4U
181#define RB_MAX_SMALL_DATA (RB_ALIGNMENT * RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
182#define RB_EVNT_MIN_SIZE 8U /* two 32bit words */
183
184#ifndef CONFIG_HAVE_64BIT_ALIGNED_ACCESS
185# define RB_FORCE_8BYTE_ALIGNMENT 0
186# define RB_ARCH_ALIGNMENT RB_ALIGNMENT
187#else
188# define RB_FORCE_8BYTE_ALIGNMENT 1
189# define RB_ARCH_ALIGNMENT 8U
190#endif
191
192#define RB_ALIGN_DATA __aligned(RB_ARCH_ALIGNMENT)
193
194/* define RINGBUF_TYPE_DATA for 'case RINGBUF_TYPE_DATA:' */
195#define RINGBUF_TYPE_DATA 0 ... RINGBUF_TYPE_DATA_TYPE_LEN_MAX
196
197enum {
198 RB_LEN_TIME_EXTEND = 8,
199 RB_LEN_TIME_STAMP = 16,
200};
201
202#define skip_time_extend(event) \
203 ((struct ring_buffer_event *)((char *)event + RB_LEN_TIME_EXTEND))
204
205static inline int rb_null_event(struct ring_buffer_event *event)
206{
207 return event->type_len == RINGBUF_TYPE_PADDING && !event->time_delta;
208}
209
210static void rb_event_set_padding(struct ring_buffer_event *event)
211{
212 /* padding has a NULL time_delta */
213 event->type_len = RINGBUF_TYPE_PADDING;
214 event->time_delta = 0;
215}
216
217static unsigned
218rb_event_data_length(struct ring_buffer_event *event)
219{
220 unsigned length;
221
222 if (event->type_len)
223 length = event->type_len * RB_ALIGNMENT;
224 else
225 length = event->array[0];
226 return length + RB_EVNT_HDR_SIZE;
227}
228
229/*
230 * Return the length of the given event. Will return
231 * the length of the time extend if the event is a
232 * time extend.
233 */
234static inline unsigned
235rb_event_length(struct ring_buffer_event *event)
236{
237 switch (event->type_len) {
238 case RINGBUF_TYPE_PADDING:
239 if (rb_null_event(event))
240 /* undefined */
241 return -1;
242 return event->array[0] + RB_EVNT_HDR_SIZE;
243
244 case RINGBUF_TYPE_TIME_EXTEND:
245 return RB_LEN_TIME_EXTEND;
246
247 case RINGBUF_TYPE_TIME_STAMP:
248 return RB_LEN_TIME_STAMP;
249
250 case RINGBUF_TYPE_DATA:
251 return rb_event_data_length(event);
252 default:
253 BUG();
254 }
255 /* not hit */
256 return 0;
257}
258
259/*
260 * Return total length of time extend and data,
261 * or just the event length for all other events.
262 */
263static inline unsigned
264rb_event_ts_length(struct ring_buffer_event *event)
265{
266 unsigned len = 0;
267
268 if (event->type_len == RINGBUF_TYPE_TIME_EXTEND) {
269 /* time extends include the data event after it */
270 len = RB_LEN_TIME_EXTEND;
271 event = skip_time_extend(event);
272 }
273 return len + rb_event_length(event);
274}
275
276/**
277 * ring_buffer_event_length - return the length of the event
278 * @event: the event to get the length of
279 *
280 * Returns the size of the data load of a data event.
281 * If the event is something other than a data event, it
282 * returns the size of the event itself. With the exception
283 * of a TIME EXTEND, where it still returns the size of the
284 * data load of the data event after it.
285 */
286unsigned ring_buffer_event_length(struct ring_buffer_event *event)
287{
288 unsigned length;
289
290 if (event->type_len == RINGBUF_TYPE_TIME_EXTEND)
291 event = skip_time_extend(event);
292
293 length = rb_event_length(event);
294 if (event->type_len > RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
295 return length;
296 length -= RB_EVNT_HDR_SIZE;
297 if (length > RB_MAX_SMALL_DATA + sizeof(event->array[0]))
298 length -= sizeof(event->array[0]);
299 return length;
300}
301EXPORT_SYMBOL_GPL(ring_buffer_event_length);
302
303/* inline for ring buffer fast paths */
304static void *
305rb_event_data(struct ring_buffer_event *event)
306{
307 if (event->type_len == RINGBUF_TYPE_TIME_EXTEND)
308 event = skip_time_extend(event);
309 BUG_ON(event->type_len > RINGBUF_TYPE_DATA_TYPE_LEN_MAX);
310 /* If length is in len field, then array[0] has the data */
311 if (event->type_len)
312 return (void *)&event->array[0];
313 /* Otherwise length is in array[0] and array[1] has the data */
314 return (void *)&event->array[1];
315}
316
317/**
318 * ring_buffer_event_data - return the data of the event
319 * @event: the event to get the data from
320 */
321void *ring_buffer_event_data(struct ring_buffer_event *event)
322{
323 return rb_event_data(event);
324}
325EXPORT_SYMBOL_GPL(ring_buffer_event_data);
326
327#define for_each_buffer_cpu(buffer, cpu) \
328 for_each_cpu(cpu, buffer->cpumask)
329
330#define TS_SHIFT 27
331#define TS_MASK ((1ULL << TS_SHIFT) - 1)
332#define TS_DELTA_TEST (~TS_MASK)
333
334/* Flag when events were overwritten */
335#define RB_MISSED_EVENTS (1 << 31)
336/* Missed count stored at end */
337#define RB_MISSED_STORED (1 << 30)
338
339struct buffer_data_page {
340 u64 time_stamp; /* page time stamp */
341 local_t commit; /* write committed index */
342 unsigned char data[] RB_ALIGN_DATA; /* data of buffer page */
343};
344
345/*
346 * Note, the buffer_page list must be first. The buffer pages
347 * are allocated in cache lines, which means that each buffer
348 * page will be at the beginning of a cache line, and thus
349 * the least significant bits will be zero. We use this to
350 * add flags in the list struct pointers, to make the ring buffer
351 * lockless.
352 */
353struct buffer_page {
354 struct list_head list; /* list of buffer pages */
355 local_t write; /* index for next write */
356 unsigned read; /* index for next read */
357 local_t entries; /* entries on this page */
358 unsigned long real_end; /* real end of data */
359 struct buffer_data_page *page; /* Actual data page */
360};
361
362/*
363 * The buffer page counters, write and entries, must be reset
364 * atomically when crossing page boundaries. To synchronize this
365 * update, two counters are inserted into the number. One is
366 * the actual counter for the write position or count on the page.
367 *
368 * The other is a counter of updaters. Before an update happens
369 * the update partition of the counter is incremented. This will
370 * allow the updater to update the counter atomically.
371 *
372 * The counter is 20 bits, and the state data is 12.
373 */
374#define RB_WRITE_MASK 0xfffff
375#define RB_WRITE_INTCNT (1 << 20)
376
377static void rb_init_page(struct buffer_data_page *bpage)
378{
379 local_set(&bpage->commit, 0);
380}
381
382/**
383 * ring_buffer_page_len - the size of data on the page.
384 * @page: The page to read
385 *
386 * Returns the amount of data on the page, including buffer page header.
387 */
388size_t ring_buffer_page_len(void *page)
389{
390 return local_read(&((struct buffer_data_page *)page)->commit)
391 + BUF_PAGE_HDR_SIZE;
392}
393
394/*
395 * Also stolen from mm/slob.c. Thanks to Mathieu Desnoyers for pointing
396 * this issue out.
397 */
398static void free_buffer_page(struct buffer_page *bpage)
399{
400 free_page((unsigned long)bpage->page);
401 kfree(bpage);
402}
403
404/*
405 * We need to fit the time_stamp delta into 27 bits.
406 */
407static inline int test_time_stamp(u64 delta)
408{
409 if (delta & TS_DELTA_TEST)
410 return 1;
411 return 0;
412}
413
414#define BUF_PAGE_SIZE (PAGE_SIZE - BUF_PAGE_HDR_SIZE)
415
416/* Max payload is BUF_PAGE_SIZE - header (8bytes) */
417#define BUF_MAX_DATA_SIZE (BUF_PAGE_SIZE - (sizeof(u32) * 2))
418
419int ring_buffer_print_page_header(struct trace_seq *s)
420{
421 struct buffer_data_page field;
422 int ret;
423
424 ret = trace_seq_printf(s, "\tfield: u64 timestamp;\t"
425 "offset:0;\tsize:%u;\tsigned:%u;\n",
426 (unsigned int)sizeof(field.time_stamp),
427 (unsigned int)is_signed_type(u64));
428
429 ret = trace_seq_printf(s, "\tfield: local_t commit;\t"
430 "offset:%u;\tsize:%u;\tsigned:%u;\n",
431 (unsigned int)offsetof(typeof(field), commit),
432 (unsigned int)sizeof(field.commit),
433 (unsigned int)is_signed_type(long));
434
435 ret = trace_seq_printf(s, "\tfield: int overwrite;\t"
436 "offset:%u;\tsize:%u;\tsigned:%u;\n",
437 (unsigned int)offsetof(typeof(field), commit),
438 1,
439 (unsigned int)is_signed_type(long));
440
441 ret = trace_seq_printf(s, "\tfield: char data;\t"
442 "offset:%u;\tsize:%u;\tsigned:%u;\n",
443 (unsigned int)offsetof(typeof(field), data),
444 (unsigned int)BUF_PAGE_SIZE,
445 (unsigned int)is_signed_type(char));
446
447 return ret;
448}
449
450struct rb_irq_work {
451 struct irq_work work;
452 wait_queue_head_t waiters;
453 bool waiters_pending;
454};
455
456/*
457 * head_page == tail_page && head == tail then buffer is empty.
458 */
459struct ring_buffer_per_cpu {
460 int cpu;
461 atomic_t record_disabled;
462 struct ring_buffer *buffer;
463 raw_spinlock_t reader_lock; /* serialize readers */
464 arch_spinlock_t lock;
465 struct lock_class_key lock_key;
466 unsigned int nr_pages;
467 struct list_head *pages;
468 struct buffer_page *head_page; /* read from head */
469 struct buffer_page *tail_page; /* write to tail */
470 struct buffer_page *commit_page; /* committed pages */
471 struct buffer_page *reader_page;
472 unsigned long lost_events;
473 unsigned long last_overrun;
474 local_t entries_bytes;
475 local_t entries;
476 local_t overrun;
477 local_t commit_overrun;
478 local_t dropped_events;
479 local_t committing;
480 local_t commits;
481 unsigned long read;
482 unsigned long read_bytes;
483 u64 write_stamp;
484 u64 read_stamp;
485 /* ring buffer pages to update, > 0 to add, < 0 to remove */
486 int nr_pages_to_update;
487 struct list_head new_pages; /* new pages to add */
488 struct work_struct update_pages_work;
489 struct completion update_done;
490
491 struct rb_irq_work irq_work;
492};
493
494struct ring_buffer {
495 unsigned flags;
496 int cpus;
497 atomic_t record_disabled;
498 atomic_t resize_disabled;
499 cpumask_var_t cpumask;
500
501 struct lock_class_key *reader_lock_key;
502
503 struct mutex mutex;
504
505 struct ring_buffer_per_cpu **buffers;
506
507#ifdef CONFIG_HOTPLUG_CPU
508 struct notifier_block cpu_notify;
509#endif
510 u64 (*clock)(void);
511
512 struct rb_irq_work irq_work;
513};
514
515struct ring_buffer_iter {
516 struct ring_buffer_per_cpu *cpu_buffer;
517 unsigned long head;
518 struct buffer_page *head_page;
519 struct buffer_page *cache_reader_page;
520 unsigned long cache_read;
521 u64 read_stamp;
522};
523
524/*
525 * rb_wake_up_waiters - wake up tasks waiting for ring buffer input
526 *
527 * Schedules a delayed work to wake up any task that is blocked on the
528 * ring buffer waiters queue.
529 */
530static void rb_wake_up_waiters(struct irq_work *work)
531{
532 struct rb_irq_work *rbwork = container_of(work, struct rb_irq_work, work);
533
534 wake_up_all(&rbwork->waiters);
535}
536
537/**
538 * ring_buffer_wait - wait for input to the ring buffer
539 * @buffer: buffer to wait on
540 * @cpu: the cpu buffer to wait on
541 *
542 * If @cpu == RING_BUFFER_ALL_CPUS then the task will wake up as soon
543 * as data is added to any of the @buffer's cpu buffers. Otherwise
544 * it will wait for data to be added to a specific cpu buffer.
545 */
546void ring_buffer_wait(struct ring_buffer *buffer, int cpu)
547{
548 struct ring_buffer_per_cpu *cpu_buffer;
549 DEFINE_WAIT(wait);
550 struct rb_irq_work *work;
551
552 /*
553 * Depending on what the caller is waiting for, either any
554 * data in any cpu buffer, or a specific buffer, put the
555 * caller on the appropriate wait queue.
556 */
557 if (cpu == RING_BUFFER_ALL_CPUS)
558 work = &buffer->irq_work;
559 else {
560 cpu_buffer = buffer->buffers[cpu];
561 work = &cpu_buffer->irq_work;
562 }
563
564
565 prepare_to_wait(&work->waiters, &wait, TASK_INTERRUPTIBLE);
566
567 /*
568 * The events can happen in critical sections where
569 * checking a work queue can cause deadlocks.
570 * After adding a task to the queue, this flag is set
571 * only to notify events to try to wake up the queue
572 * using irq_work.
573 *
574 * We don't clear it even if the buffer is no longer
575 * empty. The flag only causes the next event to run
576 * irq_work to do the work queue wake up. The worse
577 * that can happen if we race with !trace_empty() is that
578 * an event will cause an irq_work to try to wake up
579 * an empty queue.
580 *
581 * There's no reason to protect this flag either, as
582 * the work queue and irq_work logic will do the necessary
583 * synchronization for the wake ups. The only thing
584 * that is necessary is that the wake up happens after
585 * a task has been queued. It's OK for spurious wake ups.
586 */
587 work->waiters_pending = true;
588
589 if ((cpu == RING_BUFFER_ALL_CPUS && ring_buffer_empty(buffer)) ||
590 (cpu != RING_BUFFER_ALL_CPUS && ring_buffer_empty_cpu(buffer, cpu)))
591 schedule();
592
593 finish_wait(&work->waiters, &wait);
594}
595
596/**
597 * ring_buffer_poll_wait - poll on buffer input
598 * @buffer: buffer to wait on
599 * @cpu: the cpu buffer to wait on
600 * @filp: the file descriptor
601 * @poll_table: The poll descriptor
602 *
603 * If @cpu == RING_BUFFER_ALL_CPUS then the task will wake up as soon
604 * as data is added to any of the @buffer's cpu buffers. Otherwise
605 * it will wait for data to be added to a specific cpu buffer.
606 *
607 * Returns POLLIN | POLLRDNORM if data exists in the buffers,
608 * zero otherwise.
609 */
610int ring_buffer_poll_wait(struct ring_buffer *buffer, int cpu,
611 struct file *filp, poll_table *poll_table)
612{
613 struct ring_buffer_per_cpu *cpu_buffer;
614 struct rb_irq_work *work;
615
616 if ((cpu == RING_BUFFER_ALL_CPUS && !ring_buffer_empty(buffer)) ||
617 (cpu != RING_BUFFER_ALL_CPUS && !ring_buffer_empty_cpu(buffer, cpu)))
618 return POLLIN | POLLRDNORM;
619
620 if (cpu == RING_BUFFER_ALL_CPUS)
621 work = &buffer->irq_work;
622 else {
623 if (!cpumask_test_cpu(cpu, buffer->cpumask))
624 return -EINVAL;
625
626 cpu_buffer = buffer->buffers[cpu];
627 work = &cpu_buffer->irq_work;
628 }
629
630 work->waiters_pending = true;
631 poll_wait(filp, &work->waiters, poll_table);
632
633 if ((cpu == RING_BUFFER_ALL_CPUS && !ring_buffer_empty(buffer)) ||
634 (cpu != RING_BUFFER_ALL_CPUS && !ring_buffer_empty_cpu(buffer, cpu)))
635 return POLLIN | POLLRDNORM;
636 return 0;
637}
638
639/* buffer may be either ring_buffer or ring_buffer_per_cpu */
640#define RB_WARN_ON(b, cond) \
641 ({ \
642 int _____ret = unlikely(cond); \
643 if (_____ret) { \
644 if (__same_type(*(b), struct ring_buffer_per_cpu)) { \
645 struct ring_buffer_per_cpu *__b = \
646 (void *)b; \
647 atomic_inc(&__b->buffer->record_disabled); \
648 } else \
649 atomic_inc(&b->record_disabled); \
650 WARN_ON(1); \
651 } \
652 _____ret; \
653 })
654
655/* Up this if you want to test the TIME_EXTENTS and normalization */
656#define DEBUG_SHIFT 0
657
658static inline u64 rb_time_stamp(struct ring_buffer *buffer)
659{
660 /* shift to debug/test normalization and TIME_EXTENTS */
661 return buffer->clock() << DEBUG_SHIFT;
662}
663
664u64 ring_buffer_time_stamp(struct ring_buffer *buffer, int cpu)
665{
666 u64 time;
667
668 preempt_disable_notrace();
669 time = rb_time_stamp(buffer);
670 preempt_enable_no_resched_notrace();
671
672 return time;
673}
674EXPORT_SYMBOL_GPL(ring_buffer_time_stamp);
675
676void ring_buffer_normalize_time_stamp(struct ring_buffer *buffer,
677 int cpu, u64 *ts)
678{
679 /* Just stupid testing the normalize function and deltas */
680 *ts >>= DEBUG_SHIFT;
681}
682EXPORT_SYMBOL_GPL(ring_buffer_normalize_time_stamp);
683
684/*
685 * Making the ring buffer lockless makes things tricky.
686 * Although writes only happen on the CPU that they are on,
687 * and they only need to worry about interrupts. Reads can
688 * happen on any CPU.
689 *
690 * The reader page is always off the ring buffer, but when the
691 * reader finishes with a page, it needs to swap its page with
692 * a new one from the buffer. The reader needs to take from
693 * the head (writes go to the tail). But if a writer is in overwrite
694 * mode and wraps, it must push the head page forward.
695 *
696 * Here lies the problem.
697 *
698 * The reader must be careful to replace only the head page, and
699 * not another one. As described at the top of the file in the
700 * ASCII art, the reader sets its old page to point to the next
701 * page after head. It then sets the page after head to point to
702 * the old reader page. But if the writer moves the head page
703 * during this operation, the reader could end up with the tail.
704 *
705 * We use cmpxchg to help prevent this race. We also do something
706 * special with the page before head. We set the LSB to 1.
707 *
708 * When the writer must push the page forward, it will clear the
709 * bit that points to the head page, move the head, and then set
710 * the bit that points to the new head page.
711 *
712 * We also don't want an interrupt coming in and moving the head
713 * page on another writer. Thus we use the second LSB to catch
714 * that too. Thus:
715 *
716 * head->list->prev->next bit 1 bit 0
717 * ------- -------
718 * Normal page 0 0
719 * Points to head page 0 1
720 * New head page 1 0
721 *
722 * Note we can not trust the prev pointer of the head page, because:
723 *
724 * +----+ +-----+ +-----+
725 * | |------>| T |---X--->| N |
726 * | |<------| | | |
727 * +----+ +-----+ +-----+
728 * ^ ^ |
729 * | +-----+ | |
730 * +----------| R |----------+ |
731 * | |<-----------+
732 * +-----+
733 *
734 * Key: ---X--> HEAD flag set in pointer
735 * T Tail page
736 * R Reader page
737 * N Next page
738 *
739 * (see __rb_reserve_next() to see where this happens)
740 *
741 * What the above shows is that the reader just swapped out
742 * the reader page with a page in the buffer, but before it
743 * could make the new header point back to the new page added
744 * it was preempted by a writer. The writer moved forward onto
745 * the new page added by the reader and is about to move forward
746 * again.
747 *
748 * You can see, it is legitimate for the previous pointer of
749 * the head (or any page) not to point back to itself. But only
750 * temporarially.
751 */
752
753#define RB_PAGE_NORMAL 0UL
754#define RB_PAGE_HEAD 1UL
755#define RB_PAGE_UPDATE 2UL
756
757
758#define RB_FLAG_MASK 3UL
759
760/* PAGE_MOVED is not part of the mask */
761#define RB_PAGE_MOVED 4UL
762
763/*
764 * rb_list_head - remove any bit
765 */
766static struct list_head *rb_list_head(struct list_head *list)
767{
768 unsigned long val = (unsigned long)list;
769
770 return (struct list_head *)(val & ~RB_FLAG_MASK);
771}
772
773/*
774 * rb_is_head_page - test if the given page is the head page
775 *
776 * Because the reader may move the head_page pointer, we can
777 * not trust what the head page is (it may be pointing to
778 * the reader page). But if the next page is a header page,
779 * its flags will be non zero.
780 */
781static inline int
782rb_is_head_page(struct ring_buffer_per_cpu *cpu_buffer,
783 struct buffer_page *page, struct list_head *list)
784{
785 unsigned long val;
786
787 val = (unsigned long)list->next;
788
789 if ((val & ~RB_FLAG_MASK) != (unsigned long)&page->list)
790 return RB_PAGE_MOVED;
791
792 return val & RB_FLAG_MASK;
793}
794
795/*
796 * rb_is_reader_page
797 *
798 * The unique thing about the reader page, is that, if the
799 * writer is ever on it, the previous pointer never points
800 * back to the reader page.
801 */
802static int rb_is_reader_page(struct buffer_page *page)
803{
804 struct list_head *list = page->list.prev;
805
806 return rb_list_head(list->next) != &page->list;
807}
808
809/*
810 * rb_set_list_to_head - set a list_head to be pointing to head.
811 */
812static void rb_set_list_to_head(struct ring_buffer_per_cpu *cpu_buffer,
813 struct list_head *list)
814{
815 unsigned long *ptr;
816
817 ptr = (unsigned long *)&list->next;
818 *ptr |= RB_PAGE_HEAD;
819 *ptr &= ~RB_PAGE_UPDATE;
820}
821
822/*
823 * rb_head_page_activate - sets up head page
824 */
825static void rb_head_page_activate(struct ring_buffer_per_cpu *cpu_buffer)
826{
827 struct buffer_page *head;
828
829 head = cpu_buffer->head_page;
830 if (!head)
831 return;
832
833 /*
834 * Set the previous list pointer to have the HEAD flag.
835 */
836 rb_set_list_to_head(cpu_buffer, head->list.prev);
837}
838
839static void rb_list_head_clear(struct list_head *list)
840{
841 unsigned long *ptr = (unsigned long *)&list->next;
842
843 *ptr &= ~RB_FLAG_MASK;
844}
845
846/*
847 * rb_head_page_dactivate - clears head page ptr (for free list)
848 */
849static void
850rb_head_page_deactivate(struct ring_buffer_per_cpu *cpu_buffer)
851{
852 struct list_head *hd;
853
854 /* Go through the whole list and clear any pointers found. */
855 rb_list_head_clear(cpu_buffer->pages);
856
857 list_for_each(hd, cpu_buffer->pages)
858 rb_list_head_clear(hd);
859}
860
861static int rb_head_page_set(struct ring_buffer_per_cpu *cpu_buffer,
862 struct buffer_page *head,
863 struct buffer_page *prev,
864 int old_flag, int new_flag)
865{
866 struct list_head *list;
867 unsigned long val = (unsigned long)&head->list;
868 unsigned long ret;
869
870 list = &prev->list;
871
872 val &= ~RB_FLAG_MASK;
873
874 ret = cmpxchg((unsigned long *)&list->next,
875 val | old_flag, val | new_flag);
876
877 /* check if the reader took the page */
878 if ((ret & ~RB_FLAG_MASK) != val)
879 return RB_PAGE_MOVED;
880
881 return ret & RB_FLAG_MASK;
882}
883
884static int rb_head_page_set_update(struct ring_buffer_per_cpu *cpu_buffer,
885 struct buffer_page *head,
886 struct buffer_page *prev,
887 int old_flag)
888{
889 return rb_head_page_set(cpu_buffer, head, prev,
890 old_flag, RB_PAGE_UPDATE);
891}
892
893static int rb_head_page_set_head(struct ring_buffer_per_cpu *cpu_buffer,
894 struct buffer_page *head,
895 struct buffer_page *prev,
896 int old_flag)
897{
898 return rb_head_page_set(cpu_buffer, head, prev,
899 old_flag, RB_PAGE_HEAD);
900}
901
902static int rb_head_page_set_normal(struct ring_buffer_per_cpu *cpu_buffer,
903 struct buffer_page *head,
904 struct buffer_page *prev,
905 int old_flag)
906{
907 return rb_head_page_set(cpu_buffer, head, prev,
908 old_flag, RB_PAGE_NORMAL);
909}
910
911static inline void rb_inc_page(struct ring_buffer_per_cpu *cpu_buffer,
912 struct buffer_page **bpage)
913{
914 struct list_head *p = rb_list_head((*bpage)->list.next);
915
916 *bpage = list_entry(p, struct buffer_page, list);
917}
918
919static struct buffer_page *
920rb_set_head_page(struct ring_buffer_per_cpu *cpu_buffer)
921{
922 struct buffer_page *head;
923 struct buffer_page *page;
924 struct list_head *list;
925 int i;
926
927 if (RB_WARN_ON(cpu_buffer, !cpu_buffer->head_page))
928 return NULL;
929
930 /* sanity check */
931 list = cpu_buffer->pages;
932 if (RB_WARN_ON(cpu_buffer, rb_list_head(list->prev->next) != list))
933 return NULL;
934
935 page = head = cpu_buffer->head_page;
936 /*
937 * It is possible that the writer moves the header behind
938 * where we started, and we miss in one loop.
939 * A second loop should grab the header, but we'll do
940 * three loops just because I'm paranoid.
941 */
942 for (i = 0; i < 3; i++) {
943 do {
944 if (rb_is_head_page(cpu_buffer, page, page->list.prev)) {
945 cpu_buffer->head_page = page;
946 return page;
947 }
948 rb_inc_page(cpu_buffer, &page);
949 } while (page != head);
950 }
951
952 RB_WARN_ON(cpu_buffer, 1);
953
954 return NULL;
955}
956
957static int rb_head_page_replace(struct buffer_page *old,
958 struct buffer_page *new)
959{
960 unsigned long *ptr = (unsigned long *)&old->list.prev->next;
961 unsigned long val;
962 unsigned long ret;
963
964 val = *ptr & ~RB_FLAG_MASK;
965 val |= RB_PAGE_HEAD;
966
967 ret = cmpxchg(ptr, val, (unsigned long)&new->list);
968
969 return ret == val;
970}
971
972/*
973 * rb_tail_page_update - move the tail page forward
974 *
975 * Returns 1 if moved tail page, 0 if someone else did.
976 */
977static int rb_tail_page_update(struct ring_buffer_per_cpu *cpu_buffer,
978 struct buffer_page *tail_page,
979 struct buffer_page *next_page)
980{
981 struct buffer_page *old_tail;
982 unsigned long old_entries;
983 unsigned long old_write;
984 int ret = 0;
985
986 /*
987 * The tail page now needs to be moved forward.
988 *
989 * We need to reset the tail page, but without messing
990 * with possible erasing of data brought in by interrupts
991 * that have moved the tail page and are currently on it.
992 *
993 * We add a counter to the write field to denote this.
994 */
995 old_write = local_add_return(RB_WRITE_INTCNT, &next_page->write);
996 old_entries = local_add_return(RB_WRITE_INTCNT, &next_page->entries);
997
998 /*
999 * Just make sure we have seen our old_write and synchronize
1000 * with any interrupts that come in.
1001 */
1002 barrier();
1003
1004 /*
1005 * If the tail page is still the same as what we think
1006 * it is, then it is up to us to update the tail
1007 * pointer.
1008 */
1009 if (tail_page == cpu_buffer->tail_page) {
1010 /* Zero the write counter */
1011 unsigned long val = old_write & ~RB_WRITE_MASK;
1012 unsigned long eval = old_entries & ~RB_WRITE_MASK;
1013
1014 /*
1015 * This will only succeed if an interrupt did
1016 * not come in and change it. In which case, we
1017 * do not want to modify it.
1018 *
1019 * We add (void) to let the compiler know that we do not care
1020 * about the return value of these functions. We use the
1021 * cmpxchg to only update if an interrupt did not already
1022 * do it for us. If the cmpxchg fails, we don't care.
1023 */
1024 (void)local_cmpxchg(&next_page->write, old_write, val);
1025 (void)local_cmpxchg(&next_page->entries, old_entries, eval);
1026
1027 /*
1028 * No need to worry about races with clearing out the commit.
1029 * it only can increment when a commit takes place. But that
1030 * only happens in the outer most nested commit.
1031 */
1032 local_set(&next_page->page->commit, 0);
1033
1034 old_tail = cmpxchg(&cpu_buffer->tail_page,
1035 tail_page, next_page);
1036
1037 if (old_tail == tail_page)
1038 ret = 1;
1039 }
1040
1041 return ret;
1042}
1043
1044static int rb_check_bpage(struct ring_buffer_per_cpu *cpu_buffer,
1045 struct buffer_page *bpage)
1046{
1047 unsigned long val = (unsigned long)bpage;
1048
1049 if (RB_WARN_ON(cpu_buffer, val & RB_FLAG_MASK))
1050 return 1;
1051
1052 return 0;
1053}
1054
1055/**
1056 * rb_check_list - make sure a pointer to a list has the last bits zero
1057 */
1058static int rb_check_list(struct ring_buffer_per_cpu *cpu_buffer,
1059 struct list_head *list)
1060{
1061 if (RB_WARN_ON(cpu_buffer, rb_list_head(list->prev) != list->prev))
1062 return 1;
1063 if (RB_WARN_ON(cpu_buffer, rb_list_head(list->next) != list->next))
1064 return 1;
1065 return 0;
1066}
1067
1068/**
1069 * rb_check_pages - integrity check of buffer pages
1070 * @cpu_buffer: CPU buffer with pages to test
1071 *
1072 * As a safety measure we check to make sure the data pages have not
1073 * been corrupted.
1074 */
1075static int rb_check_pages(struct ring_buffer_per_cpu *cpu_buffer)
1076{
1077 struct list_head *head = cpu_buffer->pages;
1078 struct buffer_page *bpage, *tmp;
1079
1080 /* Reset the head page if it exists */
1081 if (cpu_buffer->head_page)
1082 rb_set_head_page(cpu_buffer);
1083
1084 rb_head_page_deactivate(cpu_buffer);
1085
1086 if (RB_WARN_ON(cpu_buffer, head->next->prev != head))
1087 return -1;
1088 if (RB_WARN_ON(cpu_buffer, head->prev->next != head))
1089 return -1;
1090
1091 if (rb_check_list(cpu_buffer, head))
1092 return -1;
1093
1094 list_for_each_entry_safe(bpage, tmp, head, list) {
1095 if (RB_WARN_ON(cpu_buffer,
1096 bpage->list.next->prev != &bpage->list))
1097 return -1;
1098 if (RB_WARN_ON(cpu_buffer,
1099 bpage->list.prev->next != &bpage->list))
1100 return -1;
1101 if (rb_check_list(cpu_buffer, &bpage->list))
1102 return -1;
1103 }
1104
1105 rb_head_page_activate(cpu_buffer);
1106
1107 return 0;
1108}
1109
1110static int __rb_allocate_pages(int nr_pages, struct list_head *pages, int cpu)
1111{
1112 int i;
1113 struct buffer_page *bpage, *tmp;
1114
1115 for (i = 0; i < nr_pages; i++) {
1116 struct page *page;
1117 /*
1118 * __GFP_NORETRY flag makes sure that the allocation fails
1119 * gracefully without invoking oom-killer and the system is
1120 * not destabilized.
1121 */
1122 bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
1123 GFP_KERNEL | __GFP_NORETRY,
1124 cpu_to_node(cpu));
1125 if (!bpage)
1126 goto free_pages;
1127
1128 list_add(&bpage->list, pages);
1129
1130 page = alloc_pages_node(cpu_to_node(cpu),
1131 GFP_KERNEL | __GFP_NORETRY, 0);
1132 if (!page)
1133 goto free_pages;
1134 bpage->page = page_address(page);
1135 rb_init_page(bpage->page);
1136 }
1137
1138 return 0;
1139
1140free_pages:
1141 list_for_each_entry_safe(bpage, tmp, pages, list) {
1142 list_del_init(&bpage->list);
1143 free_buffer_page(bpage);
1144 }
1145
1146 return -ENOMEM;
1147}
1148
1149static int rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
1150 unsigned nr_pages)
1151{
1152 LIST_HEAD(pages);
1153
1154 WARN_ON(!nr_pages);
1155
1156 if (__rb_allocate_pages(nr_pages, &pages, cpu_buffer->cpu))
1157 return -ENOMEM;
1158
1159 /*
1160 * The ring buffer page list is a circular list that does not
1161 * start and end with a list head. All page list items point to
1162 * other pages.
1163 */
1164 cpu_buffer->pages = pages.next;
1165 list_del(&pages);
1166
1167 cpu_buffer->nr_pages = nr_pages;
1168
1169 rb_check_pages(cpu_buffer);
1170
1171 return 0;
1172}
1173
1174static struct ring_buffer_per_cpu *
1175rb_allocate_cpu_buffer(struct ring_buffer *buffer, int nr_pages, int cpu)
1176{
1177 struct ring_buffer_per_cpu *cpu_buffer;
1178 struct buffer_page *bpage;
1179 struct page *page;
1180 int ret;
1181
1182 cpu_buffer = kzalloc_node(ALIGN(sizeof(*cpu_buffer), cache_line_size()),
1183 GFP_KERNEL, cpu_to_node(cpu));
1184 if (!cpu_buffer)
1185 return NULL;
1186
1187 cpu_buffer->cpu = cpu;
1188 cpu_buffer->buffer = buffer;
1189 raw_spin_lock_init(&cpu_buffer->reader_lock);
1190 lockdep_set_class(&cpu_buffer->reader_lock, buffer->reader_lock_key);
1191 cpu_buffer->lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
1192 INIT_WORK(&cpu_buffer->update_pages_work, update_pages_handler);
1193 init_completion(&cpu_buffer->update_done);
1194 init_irq_work(&cpu_buffer->irq_work.work, rb_wake_up_waiters);
1195 init_waitqueue_head(&cpu_buffer->irq_work.waiters);
1196
1197 bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
1198 GFP_KERNEL, cpu_to_node(cpu));
1199 if (!bpage)
1200 goto fail_free_buffer;
1201
1202 rb_check_bpage(cpu_buffer, bpage);
1203
1204 cpu_buffer->reader_page = bpage;
1205 page = alloc_pages_node(cpu_to_node(cpu), GFP_KERNEL, 0);
1206 if (!page)
1207 goto fail_free_reader;
1208 bpage->page = page_address(page);
1209 rb_init_page(bpage->page);
1210
1211 INIT_LIST_HEAD(&cpu_buffer->reader_page->list);
1212 INIT_LIST_HEAD(&cpu_buffer->new_pages);
1213
1214 ret = rb_allocate_pages(cpu_buffer, nr_pages);
1215 if (ret < 0)
1216 goto fail_free_reader;
1217
1218 cpu_buffer->head_page
1219 = list_entry(cpu_buffer->pages, struct buffer_page, list);
1220 cpu_buffer->tail_page = cpu_buffer->commit_page = cpu_buffer->head_page;
1221
1222 rb_head_page_activate(cpu_buffer);
1223
1224 return cpu_buffer;
1225
1226 fail_free_reader:
1227 free_buffer_page(cpu_buffer->reader_page);
1228
1229 fail_free_buffer:
1230 kfree(cpu_buffer);
1231 return NULL;
1232}
1233
1234static void rb_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
1235{
1236 struct list_head *head = cpu_buffer->pages;
1237 struct buffer_page *bpage, *tmp;
1238
1239 free_buffer_page(cpu_buffer->reader_page);
1240
1241 rb_head_page_deactivate(cpu_buffer);
1242
1243 if (head) {
1244 list_for_each_entry_safe(bpage, tmp, head, list) {
1245 list_del_init(&bpage->list);
1246 free_buffer_page(bpage);
1247 }
1248 bpage = list_entry(head, struct buffer_page, list);
1249 free_buffer_page(bpage);
1250 }
1251
1252 kfree(cpu_buffer);
1253}
1254
1255#ifdef CONFIG_HOTPLUG_CPU
1256static int rb_cpu_notify(struct notifier_block *self,
1257 unsigned long action, void *hcpu);
1258#endif
1259
1260/**
1261 * __ring_buffer_alloc - allocate a new ring_buffer
1262 * @size: the size in bytes per cpu that is needed.
1263 * @flags: attributes to set for the ring buffer.
1264 *
1265 * Currently the only flag that is available is the RB_FL_OVERWRITE
1266 * flag. This flag means that the buffer will overwrite old data
1267 * when the buffer wraps. If this flag is not set, the buffer will
1268 * drop data when the tail hits the head.
1269 */
1270struct ring_buffer *__ring_buffer_alloc(unsigned long size, unsigned flags,
1271 struct lock_class_key *key)
1272{
1273 struct ring_buffer *buffer;
1274 int bsize;
1275 int cpu, nr_pages;
1276
1277 /* keep it in its own cache line */
1278 buffer = kzalloc(ALIGN(sizeof(*buffer), cache_line_size()),
1279 GFP_KERNEL);
1280 if (!buffer)
1281 return NULL;
1282
1283 if (!alloc_cpumask_var(&buffer->cpumask, GFP_KERNEL))
1284 goto fail_free_buffer;
1285
1286 nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
1287 buffer->flags = flags;
1288 buffer->clock = trace_clock_local;
1289 buffer->reader_lock_key = key;
1290
1291 init_irq_work(&buffer->irq_work.work, rb_wake_up_waiters);
1292 init_waitqueue_head(&buffer->irq_work.waiters);
1293
1294 /* need at least two pages */
1295 if (nr_pages < 2)
1296 nr_pages = 2;
1297
1298 /*
1299 * In case of non-hotplug cpu, if the ring-buffer is allocated
1300 * in early initcall, it will not be notified of secondary cpus.
1301 * In that off case, we need to allocate for all possible cpus.
1302 */
1303#ifdef CONFIG_HOTPLUG_CPU
1304 cpu_notifier_register_begin();
1305 cpumask_copy(buffer->cpumask, cpu_online_mask);
1306#else
1307 cpumask_copy(buffer->cpumask, cpu_possible_mask);
1308#endif
1309 buffer->cpus = nr_cpu_ids;
1310
1311 bsize = sizeof(void *) * nr_cpu_ids;
1312 buffer->buffers = kzalloc(ALIGN(bsize, cache_line_size()),
1313 GFP_KERNEL);
1314 if (!buffer->buffers)
1315 goto fail_free_cpumask;
1316
1317 for_each_buffer_cpu(buffer, cpu) {
1318 buffer->buffers[cpu] =
1319 rb_allocate_cpu_buffer(buffer, nr_pages, cpu);
1320 if (!buffer->buffers[cpu])
1321 goto fail_free_buffers;
1322 }
1323
1324#ifdef CONFIG_HOTPLUG_CPU
1325 buffer->cpu_notify.notifier_call = rb_cpu_notify;
1326 buffer->cpu_notify.priority = 0;
1327 __register_cpu_notifier(&buffer->cpu_notify);
1328 cpu_notifier_register_done();
1329#endif
1330
1331 mutex_init(&buffer->mutex);
1332
1333 return buffer;
1334
1335 fail_free_buffers:
1336 for_each_buffer_cpu(buffer, cpu) {
1337 if (buffer->buffers[cpu])
1338 rb_free_cpu_buffer(buffer->buffers[cpu]);
1339 }
1340 kfree(buffer->buffers);
1341
1342 fail_free_cpumask:
1343 free_cpumask_var(buffer->cpumask);
1344#ifdef CONFIG_HOTPLUG_CPU
1345 cpu_notifier_register_done();
1346#endif
1347
1348 fail_free_buffer:
1349 kfree(buffer);
1350 return NULL;
1351}
1352EXPORT_SYMBOL_GPL(__ring_buffer_alloc);
1353
1354/**
1355 * ring_buffer_free - free a ring buffer.
1356 * @buffer: the buffer to free.
1357 */
1358void
1359ring_buffer_free(struct ring_buffer *buffer)
1360{
1361 int cpu;
1362
1363#ifdef CONFIG_HOTPLUG_CPU
1364 cpu_notifier_register_begin();
1365 __unregister_cpu_notifier(&buffer->cpu_notify);
1366#endif
1367
1368 for_each_buffer_cpu(buffer, cpu)
1369 rb_free_cpu_buffer(buffer->buffers[cpu]);
1370
1371#ifdef CONFIG_HOTPLUG_CPU
1372 cpu_notifier_register_done();
1373#endif
1374
1375 kfree(buffer->buffers);
1376 free_cpumask_var(buffer->cpumask);
1377
1378 kfree(buffer);
1379}
1380EXPORT_SYMBOL_GPL(ring_buffer_free);
1381
1382void ring_buffer_set_clock(struct ring_buffer *buffer,
1383 u64 (*clock)(void))
1384{
1385 buffer->clock = clock;
1386}
1387
1388static void rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer);
1389
1390static inline unsigned long rb_page_entries(struct buffer_page *bpage)
1391{
1392 return local_read(&bpage->entries) & RB_WRITE_MASK;
1393}
1394
1395static inline unsigned long rb_page_write(struct buffer_page *bpage)
1396{
1397 return local_read(&bpage->write) & RB_WRITE_MASK;
1398}
1399
1400static int
1401rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned int nr_pages)
1402{
1403 struct list_head *tail_page, *to_remove, *next_page;
1404 struct buffer_page *to_remove_page, *tmp_iter_page;
1405 struct buffer_page *last_page, *first_page;
1406 unsigned int nr_removed;
1407 unsigned long head_bit;
1408 int page_entries;
1409
1410 head_bit = 0;
1411
1412 raw_spin_lock_irq(&cpu_buffer->reader_lock);
1413 atomic_inc(&cpu_buffer->record_disabled);
1414 /*
1415 * We don't race with the readers since we have acquired the reader
1416 * lock. We also don't race with writers after disabling recording.
1417 * This makes it easy to figure out the first and the last page to be
1418 * removed from the list. We unlink all the pages in between including
1419 * the first and last pages. This is done in a busy loop so that we
1420 * lose the least number of traces.
1421 * The pages are freed after we restart recording and unlock readers.
1422 */
1423 tail_page = &cpu_buffer->tail_page->list;
1424
1425 /*
1426 * tail page might be on reader page, we remove the next page
1427 * from the ring buffer
1428 */
1429 if (cpu_buffer->tail_page == cpu_buffer->reader_page)
1430 tail_page = rb_list_head(tail_page->next);
1431 to_remove = tail_page;
1432
1433 /* start of pages to remove */
1434 first_page = list_entry(rb_list_head(to_remove->next),
1435 struct buffer_page, list);
1436
1437 for (nr_removed = 0; nr_removed < nr_pages; nr_removed++) {
1438 to_remove = rb_list_head(to_remove)->next;
1439 head_bit |= (unsigned long)to_remove & RB_PAGE_HEAD;
1440 }
1441
1442 next_page = rb_list_head(to_remove)->next;
1443
1444 /*
1445 * Now we remove all pages between tail_page and next_page.
1446 * Make sure that we have head_bit value preserved for the
1447 * next page
1448 */
1449 tail_page->next = (struct list_head *)((unsigned long)next_page |
1450 head_bit);
1451 next_page = rb_list_head(next_page);
1452 next_page->prev = tail_page;
1453
1454 /* make sure pages points to a valid page in the ring buffer */
1455 cpu_buffer->pages = next_page;
1456
1457 /* update head page */
1458 if (head_bit)
1459 cpu_buffer->head_page = list_entry(next_page,
1460 struct buffer_page, list);
1461
1462 /*
1463 * change read pointer to make sure any read iterators reset
1464 * themselves
1465 */
1466 cpu_buffer->read = 0;
1467
1468 /* pages are removed, resume tracing and then free the pages */
1469 atomic_dec(&cpu_buffer->record_disabled);
1470 raw_spin_unlock_irq(&cpu_buffer->reader_lock);
1471
1472 RB_WARN_ON(cpu_buffer, list_empty(cpu_buffer->pages));
1473
1474 /* last buffer page to remove */
1475 last_page = list_entry(rb_list_head(to_remove), struct buffer_page,
1476 list);
1477 tmp_iter_page = first_page;
1478
1479 do {
1480 to_remove_page = tmp_iter_page;
1481 rb_inc_page(cpu_buffer, &tmp_iter_page);
1482
1483 /* update the counters */
1484 page_entries = rb_page_entries(to_remove_page);
1485 if (page_entries) {
1486 /*
1487 * If something was added to this page, it was full
1488 * since it is not the tail page. So we deduct the
1489 * bytes consumed in ring buffer from here.
1490 * Increment overrun to account for the lost events.
1491 */
1492 local_add(page_entries, &cpu_buffer->overrun);
1493 local_sub(BUF_PAGE_SIZE, &cpu_buffer->entries_bytes);
1494 }
1495
1496 /*
1497 * We have already removed references to this list item, just
1498 * free up the buffer_page and its page
1499 */
1500 free_buffer_page(to_remove_page);
1501 nr_removed--;
1502
1503 } while (to_remove_page != last_page);
1504
1505 RB_WARN_ON(cpu_buffer, nr_removed);
1506
1507 return nr_removed == 0;
1508}
1509
1510static int
1511rb_insert_pages(struct ring_buffer_per_cpu *cpu_buffer)
1512{
1513 struct list_head *pages = &cpu_buffer->new_pages;
1514 int retries, success;
1515
1516 raw_spin_lock_irq(&cpu_buffer->reader_lock);
1517 /*
1518 * We are holding the reader lock, so the reader page won't be swapped
1519 * in the ring buffer. Now we are racing with the writer trying to
1520 * move head page and the tail page.
1521 * We are going to adapt the reader page update process where:
1522 * 1. We first splice the start and end of list of new pages between
1523 * the head page and its previous page.
1524 * 2. We cmpxchg the prev_page->next to point from head page to the
1525 * start of new pages list.
1526 * 3. Finally, we update the head->prev to the end of new list.
1527 *
1528 * We will try this process 10 times, to make sure that we don't keep
1529 * spinning.
1530 */
1531 retries = 10;
1532 success = 0;
1533 while (retries--) {
1534 struct list_head *head_page, *prev_page, *r;
1535 struct list_head *last_page, *first_page;
1536 struct list_head *head_page_with_bit;
1537
1538 head_page = &rb_set_head_page(cpu_buffer)->list;
1539 if (!head_page)
1540 break;
1541 prev_page = head_page->prev;
1542
1543 first_page = pages->next;
1544 last_page = pages->prev;
1545
1546 head_page_with_bit = (struct list_head *)
1547 ((unsigned long)head_page | RB_PAGE_HEAD);
1548
1549 last_page->next = head_page_with_bit;
1550 first_page->prev = prev_page;
1551
1552 r = cmpxchg(&prev_page->next, head_page_with_bit, first_page);
1553
1554 if (r == head_page_with_bit) {
1555 /*
1556 * yay, we replaced the page pointer to our new list,
1557 * now, we just have to update to head page's prev
1558 * pointer to point to end of list
1559 */
1560 head_page->prev = last_page;
1561 success = 1;
1562 break;
1563 }
1564 }
1565
1566 if (success)
1567 INIT_LIST_HEAD(pages);
1568 /*
1569 * If we weren't successful in adding in new pages, warn and stop
1570 * tracing
1571 */
1572 RB_WARN_ON(cpu_buffer, !success);
1573 raw_spin_unlock_irq(&cpu_buffer->reader_lock);
1574
1575 /* free pages if they weren't inserted */
1576 if (!success) {
1577 struct buffer_page *bpage, *tmp;
1578 list_for_each_entry_safe(bpage, tmp, &cpu_buffer->new_pages,
1579 list) {
1580 list_del_init(&bpage->list);
1581 free_buffer_page(bpage);
1582 }
1583 }
1584 return success;
1585}
1586
1587static void rb_update_pages(struct ring_buffer_per_cpu *cpu_buffer)
1588{
1589 int success;
1590
1591 if (cpu_buffer->nr_pages_to_update > 0)
1592 success = rb_insert_pages(cpu_buffer);
1593 else
1594 success = rb_remove_pages(cpu_buffer,
1595 -cpu_buffer->nr_pages_to_update);
1596
1597 if (success)
1598 cpu_buffer->nr_pages += cpu_buffer->nr_pages_to_update;
1599}
1600
1601static void update_pages_handler(struct work_struct *work)
1602{
1603 struct ring_buffer_per_cpu *cpu_buffer = container_of(work,
1604 struct ring_buffer_per_cpu, update_pages_work);
1605 rb_update_pages(cpu_buffer);
1606 complete(&cpu_buffer->update_done);
1607}
1608
1609/**
1610 * ring_buffer_resize - resize the ring buffer
1611 * @buffer: the buffer to resize.
1612 * @size: the new size.
1613 * @cpu_id: the cpu buffer to resize
1614 *
1615 * Minimum size is 2 * BUF_PAGE_SIZE.
1616 *
1617 * Returns 0 on success and < 0 on failure.
1618 */
1619int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size,
1620 int cpu_id)
1621{
1622 struct ring_buffer_per_cpu *cpu_buffer;
1623 unsigned nr_pages;
1624 int cpu, err = 0;
1625
1626 /*
1627 * Always succeed at resizing a non-existent buffer:
1628 */
1629 if (!buffer)
1630 return size;
1631
1632 /* Make sure the requested buffer exists */
1633 if (cpu_id != RING_BUFFER_ALL_CPUS &&
1634 !cpumask_test_cpu(cpu_id, buffer->cpumask))
1635 return size;
1636
1637 size = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
1638 size *= BUF_PAGE_SIZE;
1639
1640 /* we need a minimum of two pages */
1641 if (size < BUF_PAGE_SIZE * 2)
1642 size = BUF_PAGE_SIZE * 2;
1643
1644 nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
1645
1646 /*
1647 * Don't succeed if resizing is disabled, as a reader might be
1648 * manipulating the ring buffer and is expecting a sane state while
1649 * this is true.
1650 */
1651 if (atomic_read(&buffer->resize_disabled))
1652 return -EBUSY;
1653
1654 /* prevent another thread from changing buffer sizes */
1655 mutex_lock(&buffer->mutex);
1656
1657 if (cpu_id == RING_BUFFER_ALL_CPUS) {
1658 /* calculate the pages to update */
1659 for_each_buffer_cpu(buffer, cpu) {
1660 cpu_buffer = buffer->buffers[cpu];
1661
1662 cpu_buffer->nr_pages_to_update = nr_pages -
1663 cpu_buffer->nr_pages;
1664 /*
1665 * nothing more to do for removing pages or no update
1666 */
1667 if (cpu_buffer->nr_pages_to_update <= 0)
1668 continue;
1669 /*
1670 * to add pages, make sure all new pages can be
1671 * allocated without receiving ENOMEM
1672 */
1673 INIT_LIST_HEAD(&cpu_buffer->new_pages);
1674 if (__rb_allocate_pages(cpu_buffer->nr_pages_to_update,
1675 &cpu_buffer->new_pages, cpu)) {
1676 /* not enough memory for new pages */
1677 err = -ENOMEM;
1678 goto out_err;
1679 }
1680 }
1681
1682 get_online_cpus();
1683 /*
1684 * Fire off all the required work handlers
1685 * We can't schedule on offline CPUs, but it's not necessary
1686 * since we can change their buffer sizes without any race.
1687 */
1688 for_each_buffer_cpu(buffer, cpu) {
1689 cpu_buffer = buffer->buffers[cpu];
1690 if (!cpu_buffer->nr_pages_to_update)
1691 continue;
1692
1693 /* The update must run on the CPU that is being updated. */
1694 preempt_disable();
1695 if (cpu == smp_processor_id() || !cpu_online(cpu)) {
1696 rb_update_pages(cpu_buffer);
1697 cpu_buffer->nr_pages_to_update = 0;
1698 } else {
1699 /*
1700 * Can not disable preemption for schedule_work_on()
1701 * on PREEMPT_RT.
1702 */
1703 preempt_enable();
1704 schedule_work_on(cpu,
1705 &cpu_buffer->update_pages_work);
1706 preempt_disable();
1707 }
1708 preempt_enable();
1709 }
1710
1711 /* wait for all the updates to complete */
1712 for_each_buffer_cpu(buffer, cpu) {
1713 cpu_buffer = buffer->buffers[cpu];
1714 if (!cpu_buffer->nr_pages_to_update)
1715 continue;
1716
1717 if (cpu_online(cpu))
1718 wait_for_completion(&cpu_buffer->update_done);
1719 cpu_buffer->nr_pages_to_update = 0;
1720 }
1721
1722 put_online_cpus();
1723 } else {
1724 /* Make sure this CPU has been intitialized */
1725 if (!cpumask_test_cpu(cpu_id, buffer->cpumask))
1726 goto out;
1727
1728 cpu_buffer = buffer->buffers[cpu_id];
1729
1730 if (nr_pages == cpu_buffer->nr_pages)
1731 goto out;
1732
1733 cpu_buffer->nr_pages_to_update = nr_pages -
1734 cpu_buffer->nr_pages;
1735
1736 INIT_LIST_HEAD(&cpu_buffer->new_pages);
1737 if (cpu_buffer->nr_pages_to_update > 0 &&
1738 __rb_allocate_pages(cpu_buffer->nr_pages_to_update,
1739 &cpu_buffer->new_pages, cpu_id)) {
1740 err = -ENOMEM;
1741 goto out_err;
1742 }
1743
1744 get_online_cpus();
1745
1746 preempt_disable();
1747 /* The update must run on the CPU that is being updated. */
1748 if (cpu_id == smp_processor_id() || !cpu_online(cpu_id))
1749 rb_update_pages(cpu_buffer);
1750 else {
1751 /*
1752 * Can not disable preemption for schedule_work_on()
1753 * on PREEMPT_RT.
1754 */
1755 preempt_enable();
1756 schedule_work_on(cpu_id,
1757 &cpu_buffer->update_pages_work);
1758 wait_for_completion(&cpu_buffer->update_done);
1759 preempt_disable();
1760 }
1761 preempt_enable();
1762
1763 cpu_buffer->nr_pages_to_update = 0;
1764 put_online_cpus();
1765 }
1766
1767 out:
1768 /*
1769 * The ring buffer resize can happen with the ring buffer
1770 * enabled, so that the update disturbs the tracing as little
1771 * as possible. But if the buffer is disabled, we do not need
1772 * to worry about that, and we can take the time to verify
1773 * that the buffer is not corrupt.
1774 */
1775 if (atomic_read(&buffer->record_disabled)) {
1776 atomic_inc(&buffer->record_disabled);
1777 /*
1778 * Even though the buffer was disabled, we must make sure
1779 * that it is truly disabled before calling rb_check_pages.
1780 * There could have been a race between checking
1781 * record_disable and incrementing it.
1782 */
1783 synchronize_sched();
1784 for_each_buffer_cpu(buffer, cpu) {
1785 cpu_buffer = buffer->buffers[cpu];
1786 rb_check_pages(cpu_buffer);
1787 }
1788 atomic_dec(&buffer->record_disabled);
1789 }
1790
1791 mutex_unlock(&buffer->mutex);
1792 return size;
1793
1794 out_err:
1795 for_each_buffer_cpu(buffer, cpu) {
1796 struct buffer_page *bpage, *tmp;
1797
1798 cpu_buffer = buffer->buffers[cpu];
1799 cpu_buffer->nr_pages_to_update = 0;
1800
1801 if (list_empty(&cpu_buffer->new_pages))
1802 continue;
1803
1804 list_for_each_entry_safe(bpage, tmp, &cpu_buffer->new_pages,
1805 list) {
1806 list_del_init(&bpage->list);
1807 free_buffer_page(bpage);
1808 }
1809 }
1810 mutex_unlock(&buffer->mutex);
1811 return err;
1812}
1813EXPORT_SYMBOL_GPL(ring_buffer_resize);
1814
1815void ring_buffer_change_overwrite(struct ring_buffer *buffer, int val)
1816{
1817 mutex_lock(&buffer->mutex);
1818 if (val)
1819 buffer->flags |= RB_FL_OVERWRITE;
1820 else
1821 buffer->flags &= ~RB_FL_OVERWRITE;
1822 mutex_unlock(&buffer->mutex);
1823}
1824EXPORT_SYMBOL_GPL(ring_buffer_change_overwrite);
1825
1826static inline void *
1827__rb_data_page_index(struct buffer_data_page *bpage, unsigned index)
1828{
1829 return bpage->data + index;
1830}
1831
1832static inline void *__rb_page_index(struct buffer_page *bpage, unsigned index)
1833{
1834 return bpage->page->data + index;
1835}
1836
1837static inline struct ring_buffer_event *
1838rb_reader_event(struct ring_buffer_per_cpu *cpu_buffer)
1839{
1840 return __rb_page_index(cpu_buffer->reader_page,
1841 cpu_buffer->reader_page->read);
1842}
1843
1844static inline struct ring_buffer_event *
1845rb_iter_head_event(struct ring_buffer_iter *iter)
1846{
1847 return __rb_page_index(iter->head_page, iter->head);
1848}
1849
1850static inline unsigned rb_page_commit(struct buffer_page *bpage)
1851{
1852 return local_read(&bpage->page->commit);
1853}
1854
1855/* Size is determined by what has been committed */
1856static inline unsigned rb_page_size(struct buffer_page *bpage)
1857{
1858 return rb_page_commit(bpage);
1859}
1860
1861static inline unsigned
1862rb_commit_index(struct ring_buffer_per_cpu *cpu_buffer)
1863{
1864 return rb_page_commit(cpu_buffer->commit_page);
1865}
1866
1867static inline unsigned
1868rb_event_index(struct ring_buffer_event *event)
1869{
1870 unsigned long addr = (unsigned long)event;
1871
1872 return (addr & ~PAGE_MASK) - BUF_PAGE_HDR_SIZE;
1873}
1874
1875static inline int
1876rb_event_is_commit(struct ring_buffer_per_cpu *cpu_buffer,
1877 struct ring_buffer_event *event)
1878{
1879 unsigned long addr = (unsigned long)event;
1880 unsigned long index;
1881
1882 index = rb_event_index(event);
1883 addr &= PAGE_MASK;
1884
1885 return cpu_buffer->commit_page->page == (void *)addr &&
1886 rb_commit_index(cpu_buffer) == index;
1887}
1888
1889static void
1890rb_set_commit_to_write(struct ring_buffer_per_cpu *cpu_buffer)
1891{
1892 unsigned long max_count;
1893
1894 /*
1895 * We only race with interrupts and NMIs on this CPU.
1896 * If we own the commit event, then we can commit
1897 * all others that interrupted us, since the interruptions
1898 * are in stack format (they finish before they come
1899 * back to us). This allows us to do a simple loop to
1900 * assign the commit to the tail.
1901 */
1902 again:
1903 max_count = cpu_buffer->nr_pages * 100;
1904
1905 while (cpu_buffer->commit_page != cpu_buffer->tail_page) {
1906 if (RB_WARN_ON(cpu_buffer, !(--max_count)))
1907 return;
1908 if (RB_WARN_ON(cpu_buffer,
1909 rb_is_reader_page(cpu_buffer->tail_page)))
1910 return;
1911 local_set(&cpu_buffer->commit_page->page->commit,
1912 rb_page_write(cpu_buffer->commit_page));
1913 rb_inc_page(cpu_buffer, &cpu_buffer->commit_page);
1914 cpu_buffer->write_stamp =
1915 cpu_buffer->commit_page->page->time_stamp;
1916 /* add barrier to keep gcc from optimizing too much */
1917 barrier();
1918 }
1919 while (rb_commit_index(cpu_buffer) !=
1920 rb_page_write(cpu_buffer->commit_page)) {
1921
1922 local_set(&cpu_buffer->commit_page->page->commit,
1923 rb_page_write(cpu_buffer->commit_page));
1924 RB_WARN_ON(cpu_buffer,
1925 local_read(&cpu_buffer->commit_page->page->commit) &
1926 ~RB_WRITE_MASK);
1927 barrier();
1928 }
1929
1930 /* again, keep gcc from optimizing */
1931 barrier();
1932
1933 /*
1934 * If an interrupt came in just after the first while loop
1935 * and pushed the tail page forward, we will be left with
1936 * a dangling commit that will never go forward.
1937 */
1938 if (unlikely(cpu_buffer->commit_page != cpu_buffer->tail_page))
1939 goto again;
1940}
1941
1942static void rb_reset_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
1943{
1944 cpu_buffer->read_stamp = cpu_buffer->reader_page->page->time_stamp;
1945 cpu_buffer->reader_page->read = 0;
1946}
1947
1948static void rb_inc_iter(struct ring_buffer_iter *iter)
1949{
1950 struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
1951
1952 /*
1953 * The iterator could be on the reader page (it starts there).
1954 * But the head could have moved, since the reader was
1955 * found. Check for this case and assign the iterator
1956 * to the head page instead of next.
1957 */
1958 if (iter->head_page == cpu_buffer->reader_page)
1959 iter->head_page = rb_set_head_page(cpu_buffer);
1960 else
1961 rb_inc_page(cpu_buffer, &iter->head_page);
1962
1963 iter->read_stamp = iter->head_page->page->time_stamp;
1964 iter->head = 0;
1965}
1966
1967/* Slow path, do not inline */
1968static noinline struct ring_buffer_event *
1969rb_add_time_stamp(struct ring_buffer_event *event, u64 delta)
1970{
1971 event->type_len = RINGBUF_TYPE_TIME_EXTEND;
1972
1973 /* Not the first event on the page? */
1974 if (rb_event_index(event)) {
1975 event->time_delta = delta & TS_MASK;
1976 event->array[0] = delta >> TS_SHIFT;
1977 } else {
1978 /* nope, just zero it */
1979 event->time_delta = 0;
1980 event->array[0] = 0;
1981 }
1982
1983 return skip_time_extend(event);
1984}
1985
1986/**
1987 * rb_update_event - update event type and data
1988 * @event: the even to update
1989 * @type: the type of event
1990 * @length: the size of the event field in the ring buffer
1991 *
1992 * Update the type and data fields of the event. The length
1993 * is the actual size that is written to the ring buffer,
1994 * and with this, we can determine what to place into the
1995 * data field.
1996 */
1997static void
1998rb_update_event(struct ring_buffer_per_cpu *cpu_buffer,
1999 struct ring_buffer_event *event, unsigned length,
2000 int add_timestamp, u64 delta)
2001{
2002 /* Only a commit updates the timestamp */
2003 if (unlikely(!rb_event_is_commit(cpu_buffer, event)))
2004 delta = 0;
2005
2006 /*
2007 * If we need to add a timestamp, then we
2008 * add it to the start of the resevered space.
2009 */
2010 if (unlikely(add_timestamp)) {
2011 event = rb_add_time_stamp(event, delta);
2012 length -= RB_LEN_TIME_EXTEND;
2013 delta = 0;
2014 }
2015
2016 event->time_delta = delta;
2017 length -= RB_EVNT_HDR_SIZE;
2018 if (length > RB_MAX_SMALL_DATA || RB_FORCE_8BYTE_ALIGNMENT) {
2019 event->type_len = 0;
2020 event->array[0] = length;
2021 } else
2022 event->type_len = DIV_ROUND_UP(length, RB_ALIGNMENT);
2023}
2024
2025/*
2026 * rb_handle_head_page - writer hit the head page
2027 *
2028 * Returns: +1 to retry page
2029 * 0 to continue
2030 * -1 on error
2031 */
2032static int
2033rb_handle_head_page(struct ring_buffer_per_cpu *cpu_buffer,
2034 struct buffer_page *tail_page,
2035 struct buffer_page *next_page)
2036{
2037 struct buffer_page *new_head;
2038 int entries;
2039 int type;
2040 int ret;
2041
2042 entries = rb_page_entries(next_page);
2043
2044 /*
2045 * The hard part is here. We need to move the head
2046 * forward, and protect against both readers on
2047 * other CPUs and writers coming in via interrupts.
2048 */
2049 type = rb_head_page_set_update(cpu_buffer, next_page, tail_page,
2050 RB_PAGE_HEAD);
2051
2052 /*
2053 * type can be one of four:
2054 * NORMAL - an interrupt already moved it for us
2055 * HEAD - we are the first to get here.
2056 * UPDATE - we are the interrupt interrupting
2057 * a current move.
2058 * MOVED - a reader on another CPU moved the next
2059 * pointer to its reader page. Give up
2060 * and try again.
2061 */
2062
2063 switch (type) {
2064 case RB_PAGE_HEAD:
2065 /*
2066 * We changed the head to UPDATE, thus
2067 * it is our responsibility to update
2068 * the counters.
2069 */
2070 local_add(entries, &cpu_buffer->overrun);
2071 local_sub(BUF_PAGE_SIZE, &cpu_buffer->entries_bytes);
2072
2073 /*
2074 * The entries will be zeroed out when we move the
2075 * tail page.
2076 */
2077
2078 /* still more to do */
2079 break;
2080
2081 case RB_PAGE_UPDATE:
2082 /*
2083 * This is an interrupt that interrupt the
2084 * previous update. Still more to do.
2085 */
2086 break;
2087 case RB_PAGE_NORMAL:
2088 /*
2089 * An interrupt came in before the update
2090 * and processed this for us.
2091 * Nothing left to do.
2092 */
2093 return 1;
2094 case RB_PAGE_MOVED:
2095 /*
2096 * The reader is on another CPU and just did
2097 * a swap with our next_page.
2098 * Try again.
2099 */
2100 return 1;
2101 default:
2102 RB_WARN_ON(cpu_buffer, 1); /* WTF??? */
2103 return -1;
2104 }
2105
2106 /*
2107 * Now that we are here, the old head pointer is
2108 * set to UPDATE. This will keep the reader from
2109 * swapping the head page with the reader page.
2110 * The reader (on another CPU) will spin till
2111 * we are finished.
2112 *
2113 * We just need to protect against interrupts
2114 * doing the job. We will set the next pointer
2115 * to HEAD. After that, we set the old pointer
2116 * to NORMAL, but only if it was HEAD before.
2117 * otherwise we are an interrupt, and only
2118 * want the outer most commit to reset it.
2119 */
2120 new_head = next_page;
2121 rb_inc_page(cpu_buffer, &new_head);
2122
2123 ret = rb_head_page_set_head(cpu_buffer, new_head, next_page,
2124 RB_PAGE_NORMAL);
2125
2126 /*
2127 * Valid returns are:
2128 * HEAD - an interrupt came in and already set it.
2129 * NORMAL - One of two things:
2130 * 1) We really set it.
2131 * 2) A bunch of interrupts came in and moved
2132 * the page forward again.
2133 */
2134 switch (ret) {
2135 case RB_PAGE_HEAD:
2136 case RB_PAGE_NORMAL:
2137 /* OK */
2138 break;
2139 default:
2140 RB_WARN_ON(cpu_buffer, 1);
2141 return -1;
2142 }
2143
2144 /*
2145 * It is possible that an interrupt came in,
2146 * set the head up, then more interrupts came in
2147 * and moved it again. When we get back here,
2148 * the page would have been set to NORMAL but we
2149 * just set it back to HEAD.
2150 *
2151 * How do you detect this? Well, if that happened
2152 * the tail page would have moved.
2153 */
2154 if (ret == RB_PAGE_NORMAL) {
2155 /*
2156 * If the tail had moved passed next, then we need
2157 * to reset the pointer.
2158 */
2159 if (cpu_buffer->tail_page != tail_page &&
2160 cpu_buffer->tail_page != next_page)
2161 rb_head_page_set_normal(cpu_buffer, new_head,
2162 next_page,
2163 RB_PAGE_HEAD);
2164 }
2165
2166 /*
2167 * If this was the outer most commit (the one that
2168 * changed the original pointer from HEAD to UPDATE),
2169 * then it is up to us to reset it to NORMAL.
2170 */
2171 if (type == RB_PAGE_HEAD) {
2172 ret = rb_head_page_set_normal(cpu_buffer, next_page,
2173 tail_page,
2174 RB_PAGE_UPDATE);
2175 if (RB_WARN_ON(cpu_buffer,
2176 ret != RB_PAGE_UPDATE))
2177 return -1;
2178 }
2179
2180 return 0;
2181}
2182
2183static unsigned rb_calculate_event_length(unsigned length)
2184{
2185 struct ring_buffer_event event; /* Used only for sizeof array */
2186
2187 /* zero length can cause confusions */
2188 if (!length)
2189 length = 1;
2190
2191 if (length > RB_MAX_SMALL_DATA || RB_FORCE_8BYTE_ALIGNMENT)
2192 length += sizeof(event.array[0]);
2193
2194 length += RB_EVNT_HDR_SIZE;
2195 length = ALIGN(length, RB_ARCH_ALIGNMENT);
2196
2197 return length;
2198}
2199
2200static inline void
2201rb_reset_tail(struct ring_buffer_per_cpu *cpu_buffer,
2202 struct buffer_page *tail_page,
2203 unsigned long tail, unsigned long length)
2204{
2205 struct ring_buffer_event *event;
2206
2207 /*
2208 * Only the event that crossed the page boundary
2209 * must fill the old tail_page with padding.
2210 */
2211 if (tail >= BUF_PAGE_SIZE) {
2212 /*
2213 * If the page was filled, then we still need
2214 * to update the real_end. Reset it to zero
2215 * and the reader will ignore it.
2216 */
2217 if (tail == BUF_PAGE_SIZE)
2218 tail_page->real_end = 0;
2219
2220 local_sub(length, &tail_page->write);
2221 return;
2222 }
2223
2224 event = __rb_page_index(tail_page, tail);
2225 kmemcheck_annotate_bitfield(event, bitfield);
2226
2227 /* account for padding bytes */
2228 local_add(BUF_PAGE_SIZE - tail, &cpu_buffer->entries_bytes);
2229
2230 /*
2231 * Save the original length to the meta data.
2232 * This will be used by the reader to add lost event
2233 * counter.
2234 */
2235 tail_page->real_end = tail;
2236
2237 /*
2238 * If this event is bigger than the minimum size, then
2239 * we need to be careful that we don't subtract the
2240 * write counter enough to allow another writer to slip
2241 * in on this page.
2242 * We put in a discarded commit instead, to make sure
2243 * that this space is not used again.
2244 *
2245 * If we are less than the minimum size, we don't need to
2246 * worry about it.
2247 */
2248 if (tail > (BUF_PAGE_SIZE - RB_EVNT_MIN_SIZE)) {
2249 /* No room for any events */
2250
2251 /* Mark the rest of the page with padding */
2252 rb_event_set_padding(event);
2253
2254 /* Set the write back to the previous setting */
2255 local_sub(length, &tail_page->write);
2256 return;
2257 }
2258
2259 /* Put in a discarded event */
2260 event->array[0] = (BUF_PAGE_SIZE - tail) - RB_EVNT_HDR_SIZE;
2261 event->type_len = RINGBUF_TYPE_PADDING;
2262 /* time delta must be non zero */
2263 event->time_delta = 1;
2264
2265 /* Set write to end of buffer */
2266 length = (tail + length) - BUF_PAGE_SIZE;
2267 local_sub(length, &tail_page->write);
2268}
2269
2270/*
2271 * This is the slow path, force gcc not to inline it.
2272 */
2273static noinline struct ring_buffer_event *
2274rb_move_tail(struct ring_buffer_per_cpu *cpu_buffer,
2275 unsigned long length, unsigned long tail,
2276 struct buffer_page *tail_page, u64 ts)
2277{
2278 struct buffer_page *commit_page = cpu_buffer->commit_page;
2279 struct ring_buffer *buffer = cpu_buffer->buffer;
2280 struct buffer_page *next_page;
2281 int ret;
2282
2283 next_page = tail_page;
2284
2285 rb_inc_page(cpu_buffer, &next_page);
2286
2287 /*
2288 * If for some reason, we had an interrupt storm that made
2289 * it all the way around the buffer, bail, and warn
2290 * about it.
2291 */
2292 if (unlikely(next_page == commit_page)) {
2293 local_inc(&cpu_buffer->commit_overrun);
2294 goto out_reset;
2295 }
2296
2297 /*
2298 * This is where the fun begins!
2299 *
2300 * We are fighting against races between a reader that
2301 * could be on another CPU trying to swap its reader
2302 * page with the buffer head.
2303 *
2304 * We are also fighting against interrupts coming in and
2305 * moving the head or tail on us as well.
2306 *
2307 * If the next page is the head page then we have filled
2308 * the buffer, unless the commit page is still on the
2309 * reader page.
2310 */
2311 if (rb_is_head_page(cpu_buffer, next_page, &tail_page->list)) {
2312
2313 /*
2314 * If the commit is not on the reader page, then
2315 * move the header page.
2316 */
2317 if (!rb_is_reader_page(cpu_buffer->commit_page)) {
2318 /*
2319 * If we are not in overwrite mode,
2320 * this is easy, just stop here.
2321 */
2322 if (!(buffer->flags & RB_FL_OVERWRITE)) {
2323 local_inc(&cpu_buffer->dropped_events);
2324 goto out_reset;
2325 }
2326
2327 ret = rb_handle_head_page(cpu_buffer,
2328 tail_page,
2329 next_page);
2330 if (ret < 0)
2331 goto out_reset;
2332 if (ret)
2333 goto out_again;
2334 } else {
2335 /*
2336 * We need to be careful here too. The
2337 * commit page could still be on the reader
2338 * page. We could have a small buffer, and
2339 * have filled up the buffer with events
2340 * from interrupts and such, and wrapped.
2341 *
2342 * Note, if the tail page is also the on the
2343 * reader_page, we let it move out.
2344 */
2345 if (unlikely((cpu_buffer->commit_page !=
2346 cpu_buffer->tail_page) &&
2347 (cpu_buffer->commit_page ==
2348 cpu_buffer->reader_page))) {
2349 local_inc(&cpu_buffer->commit_overrun);
2350 goto out_reset;
2351 }
2352 }
2353 }
2354
2355 ret = rb_tail_page_update(cpu_buffer, tail_page, next_page);
2356 if (ret) {
2357 /*
2358 * Nested commits always have zero deltas, so
2359 * just reread the time stamp
2360 */
2361 ts = rb_time_stamp(buffer);
2362 next_page->page->time_stamp = ts;
2363 }
2364
2365 out_again:
2366
2367 rb_reset_tail(cpu_buffer, tail_page, tail, length);
2368
2369 /* fail and let the caller try again */
2370 return ERR_PTR(-EAGAIN);
2371
2372 out_reset:
2373 /* reset write */
2374 rb_reset_tail(cpu_buffer, tail_page, tail, length);
2375
2376 return NULL;
2377}
2378
2379static struct ring_buffer_event *
2380__rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
2381 unsigned long length, u64 ts,
2382 u64 delta, int add_timestamp)
2383{
2384 struct buffer_page *tail_page;
2385 struct ring_buffer_event *event;
2386 unsigned long tail, write;
2387
2388 /*
2389 * If the time delta since the last event is too big to
2390 * hold in the time field of the event, then we append a
2391 * TIME EXTEND event ahead of the data event.
2392 */
2393 if (unlikely(add_timestamp))
2394 length += RB_LEN_TIME_EXTEND;
2395
2396 tail_page = cpu_buffer->tail_page;
2397 write = local_add_return(length, &tail_page->write);
2398
2399 /* set write to only the index of the write */
2400 write &= RB_WRITE_MASK;
2401 tail = write - length;
2402
2403 /*
2404 * If this is the first commit on the page, then it has the same
2405 * timestamp as the page itself.
2406 */
2407 if (!tail)
2408 delta = 0;
2409
2410 /* See if we shot pass the end of this buffer page */
2411 if (unlikely(write > BUF_PAGE_SIZE))
2412 return rb_move_tail(cpu_buffer, length, tail,
2413 tail_page, ts);
2414
2415 /* We reserved something on the buffer */
2416
2417 event = __rb_page_index(tail_page, tail);
2418 kmemcheck_annotate_bitfield(event, bitfield);
2419 rb_update_event(cpu_buffer, event, length, add_timestamp, delta);
2420
2421 local_inc(&tail_page->entries);
2422
2423 /*
2424 * If this is the first commit on the page, then update
2425 * its timestamp.
2426 */
2427 if (!tail)
2428 tail_page->page->time_stamp = ts;
2429
2430 /* account for these added bytes */
2431 local_add(length, &cpu_buffer->entries_bytes);
2432
2433 return event;
2434}
2435
2436static inline int
2437rb_try_to_discard(struct ring_buffer_per_cpu *cpu_buffer,
2438 struct ring_buffer_event *event)
2439{
2440 unsigned long new_index, old_index;
2441 struct buffer_page *bpage;
2442 unsigned long index;
2443 unsigned long addr;
2444
2445 new_index = rb_event_index(event);
2446 old_index = new_index + rb_event_ts_length(event);
2447 addr = (unsigned long)event;
2448 addr &= PAGE_MASK;
2449
2450 bpage = cpu_buffer->tail_page;
2451
2452 if (bpage->page == (void *)addr && rb_page_write(bpage) == old_index) {
2453 unsigned long write_mask =
2454 local_read(&bpage->write) & ~RB_WRITE_MASK;
2455 unsigned long event_length = rb_event_length(event);
2456 /*
2457 * This is on the tail page. It is possible that
2458 * a write could come in and move the tail page
2459 * and write to the next page. That is fine
2460 * because we just shorten what is on this page.
2461 */
2462 old_index += write_mask;
2463 new_index += write_mask;
2464 index = local_cmpxchg(&bpage->write, old_index, new_index);
2465 if (index == old_index) {
2466 /* update counters */
2467 local_sub(event_length, &cpu_buffer->entries_bytes);
2468 return 1;
2469 }
2470 }
2471
2472 /* could not discard */
2473 return 0;
2474}
2475
2476static void rb_start_commit(struct ring_buffer_per_cpu *cpu_buffer)
2477{
2478 local_inc(&cpu_buffer->committing);
2479 local_inc(&cpu_buffer->commits);
2480}
2481
2482static inline void rb_end_commit(struct ring_buffer_per_cpu *cpu_buffer)
2483{
2484 unsigned long commits;
2485
2486 if (RB_WARN_ON(cpu_buffer,
2487 !local_read(&cpu_buffer->committing)))
2488 return;
2489
2490 again:
2491 commits = local_read(&cpu_buffer->commits);
2492 /* synchronize with interrupts */
2493 barrier();
2494 if (local_read(&cpu_buffer->committing) == 1)
2495 rb_set_commit_to_write(cpu_buffer);
2496
2497 local_dec(&cpu_buffer->committing);
2498
2499 /* synchronize with interrupts */
2500 barrier();
2501
2502 /*
2503 * Need to account for interrupts coming in between the
2504 * updating of the commit page and the clearing of the
2505 * committing counter.
2506 */
2507 if (unlikely(local_read(&cpu_buffer->commits) != commits) &&
2508 !local_read(&cpu_buffer->committing)) {
2509 local_inc(&cpu_buffer->committing);
2510 goto again;
2511 }
2512}
2513
2514static struct ring_buffer_event *
2515rb_reserve_next_event(struct ring_buffer *buffer,
2516 struct ring_buffer_per_cpu *cpu_buffer,
2517 unsigned long length)
2518{
2519 struct ring_buffer_event *event;
2520 u64 ts, delta;
2521 int nr_loops = 0;
2522 int add_timestamp;
2523 u64 diff;
2524
2525 rb_start_commit(cpu_buffer);
2526
2527#ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
2528 /*
2529 * Due to the ability to swap a cpu buffer from a buffer
2530 * it is possible it was swapped before we committed.
2531 * (committing stops a swap). We check for it here and
2532 * if it happened, we have to fail the write.
2533 */
2534 barrier();
2535 if (unlikely(ACCESS_ONCE(cpu_buffer->buffer) != buffer)) {
2536 local_dec(&cpu_buffer->committing);
2537 local_dec(&cpu_buffer->commits);
2538 return NULL;
2539 }
2540#endif
2541
2542 length = rb_calculate_event_length(length);
2543 again:
2544 add_timestamp = 0;
2545 delta = 0;
2546
2547 /*
2548 * We allow for interrupts to reenter here and do a trace.
2549 * If one does, it will cause this original code to loop
2550 * back here. Even with heavy interrupts happening, this
2551 * should only happen a few times in a row. If this happens
2552 * 1000 times in a row, there must be either an interrupt
2553 * storm or we have something buggy.
2554 * Bail!
2555 */
2556 if (RB_WARN_ON(cpu_buffer, ++nr_loops > 1000))
2557 goto out_fail;
2558
2559 ts = rb_time_stamp(cpu_buffer->buffer);
2560 diff = ts - cpu_buffer->write_stamp;
2561
2562 /* make sure this diff is calculated here */
2563 barrier();
2564
2565 /* Did the write stamp get updated already? */
2566 if (likely(ts >= cpu_buffer->write_stamp)) {
2567 delta = diff;
2568 if (unlikely(test_time_stamp(delta))) {
2569 int local_clock_stable = 1;
2570#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
2571 local_clock_stable = sched_clock_stable();
2572#endif
2573 WARN_ONCE(delta > (1ULL << 59),
2574 KERN_WARNING "Delta way too big! %llu ts=%llu write stamp = %llu\n%s",
2575 (unsigned long long)delta,
2576 (unsigned long long)ts,
2577 (unsigned long long)cpu_buffer->write_stamp,
2578 local_clock_stable ? "" :
2579 "If you just came from a suspend/resume,\n"
2580 "please switch to the trace global clock:\n"
2581 " echo global > /sys/kernel/debug/tracing/trace_clock\n");
2582 add_timestamp = 1;
2583 }
2584 }
2585
2586 event = __rb_reserve_next(cpu_buffer, length, ts,
2587 delta, add_timestamp);
2588 if (unlikely(PTR_ERR(event) == -EAGAIN))
2589 goto again;
2590
2591 if (!event)
2592 goto out_fail;
2593
2594 return event;
2595
2596 out_fail:
2597 rb_end_commit(cpu_buffer);
2598 return NULL;
2599}
2600
2601#ifdef CONFIG_TRACING
2602
2603/*
2604 * The lock and unlock are done within a preempt disable section.
2605 * The current_context per_cpu variable can only be modified
2606 * by the current task between lock and unlock. But it can
2607 * be modified more than once via an interrupt. To pass this
2608 * information from the lock to the unlock without having to
2609 * access the 'in_interrupt()' functions again (which do show
2610 * a bit of overhead in something as critical as function tracing,
2611 * we use a bitmask trick.
2612 *
2613 * bit 0 = NMI context
2614 * bit 1 = IRQ context
2615 * bit 2 = SoftIRQ context
2616 * bit 3 = normal context.
2617 *
2618 * This works because this is the order of contexts that can
2619 * preempt other contexts. A SoftIRQ never preempts an IRQ
2620 * context.
2621 *
2622 * When the context is determined, the corresponding bit is
2623 * checked and set (if it was set, then a recursion of that context
2624 * happened).
2625 *
2626 * On unlock, we need to clear this bit. To do so, just subtract
2627 * 1 from the current_context and AND it to itself.
2628 *
2629 * (binary)
2630 * 101 - 1 = 100
2631 * 101 & 100 = 100 (clearing bit zero)
2632 *
2633 * 1010 - 1 = 1001
2634 * 1010 & 1001 = 1000 (clearing bit 1)
2635 *
2636 * The least significant bit can be cleared this way, and it
2637 * just so happens that it is the same bit corresponding to
2638 * the current context.
2639 */
2640static DEFINE_PER_CPU(unsigned int, current_context);
2641
2642static __always_inline int trace_recursive_lock(void)
2643{
2644 unsigned int val = this_cpu_read(current_context);
2645 int bit;
2646
2647 if (in_interrupt()) {
2648 if (in_nmi())
2649 bit = 0;
2650 else if (in_irq())
2651 bit = 1;
2652 else
2653 bit = 2;
2654 } else
2655 bit = 3;
2656
2657 if (unlikely(val & (1 << bit)))
2658 return 1;
2659
2660 val |= (1 << bit);
2661 this_cpu_write(current_context, val);
2662
2663 return 0;
2664}
2665
2666static __always_inline void trace_recursive_unlock(void)
2667{
2668 unsigned int val = this_cpu_read(current_context);
2669
2670 val--;
2671 val &= this_cpu_read(current_context);
2672 this_cpu_write(current_context, val);
2673}
2674
2675#else
2676
2677#define trace_recursive_lock() (0)
2678#define trace_recursive_unlock() do { } while (0)
2679
2680#endif
2681
2682/**
2683 * ring_buffer_lock_reserve - reserve a part of the buffer
2684 * @buffer: the ring buffer to reserve from
2685 * @length: the length of the data to reserve (excluding event header)
2686 *
2687 * Returns a reseverd event on the ring buffer to copy directly to.
2688 * The user of this interface will need to get the body to write into
2689 * and can use the ring_buffer_event_data() interface.
2690 *
2691 * The length is the length of the data needed, not the event length
2692 * which also includes the event header.
2693 *
2694 * Must be paired with ring_buffer_unlock_commit, unless NULL is returned.
2695 * If NULL is returned, then nothing has been allocated or locked.
2696 */
2697struct ring_buffer_event *
2698ring_buffer_lock_reserve(struct ring_buffer *buffer, unsigned long length)
2699{
2700 struct ring_buffer_per_cpu *cpu_buffer;
2701 struct ring_buffer_event *event;
2702 int cpu;
2703
2704 if (ring_buffer_flags != RB_BUFFERS_ON)
2705 return NULL;
2706
2707 /* If we are tracing schedule, we don't want to recurse */
2708 preempt_disable_notrace();
2709
2710 if (atomic_read(&buffer->record_disabled))
2711 goto out_nocheck;
2712
2713 if (trace_recursive_lock())
2714 goto out_nocheck;
2715
2716 cpu = raw_smp_processor_id();
2717
2718 if (!cpumask_test_cpu(cpu, buffer->cpumask))
2719 goto out;
2720
2721 cpu_buffer = buffer->buffers[cpu];
2722
2723 if (atomic_read(&cpu_buffer->record_disabled))
2724 goto out;
2725
2726 if (length > BUF_MAX_DATA_SIZE)
2727 goto out;
2728
2729 event = rb_reserve_next_event(buffer, cpu_buffer, length);
2730 if (!event)
2731 goto out;
2732
2733 return event;
2734
2735 out:
2736 trace_recursive_unlock();
2737
2738 out_nocheck:
2739 preempt_enable_notrace();
2740 return NULL;
2741}
2742EXPORT_SYMBOL_GPL(ring_buffer_lock_reserve);
2743
2744static void
2745rb_update_write_stamp(struct ring_buffer_per_cpu *cpu_buffer,
2746 struct ring_buffer_event *event)
2747{
2748 u64 delta;
2749
2750 /*
2751 * The event first in the commit queue updates the
2752 * time stamp.
2753 */
2754 if (rb_event_is_commit(cpu_buffer, event)) {
2755 /*
2756 * A commit event that is first on a page
2757 * updates the write timestamp with the page stamp
2758 */
2759 if (!rb_event_index(event))
2760 cpu_buffer->write_stamp =
2761 cpu_buffer->commit_page->page->time_stamp;
2762 else if (event->type_len == RINGBUF_TYPE_TIME_EXTEND) {
2763 delta = event->array[0];
2764 delta <<= TS_SHIFT;
2765 delta += event->time_delta;
2766 cpu_buffer->write_stamp += delta;
2767 } else
2768 cpu_buffer->write_stamp += event->time_delta;
2769 }
2770}
2771
2772static void rb_commit(struct ring_buffer_per_cpu *cpu_buffer,
2773 struct ring_buffer_event *event)
2774{
2775 local_inc(&cpu_buffer->entries);
2776 rb_update_write_stamp(cpu_buffer, event);
2777 rb_end_commit(cpu_buffer);
2778}
2779
2780static __always_inline void
2781rb_wakeups(struct ring_buffer *buffer, struct ring_buffer_per_cpu *cpu_buffer)
2782{
2783 if (buffer->irq_work.waiters_pending) {
2784 buffer->irq_work.waiters_pending = false;
2785 /* irq_work_queue() supplies it's own memory barriers */
2786 irq_work_queue(&buffer->irq_work.work);
2787 }
2788
2789 if (cpu_buffer->irq_work.waiters_pending) {
2790 cpu_buffer->irq_work.waiters_pending = false;
2791 /* irq_work_queue() supplies it's own memory barriers */
2792 irq_work_queue(&cpu_buffer->irq_work.work);
2793 }
2794}
2795
2796/**
2797 * ring_buffer_unlock_commit - commit a reserved
2798 * @buffer: The buffer to commit to
2799 * @event: The event pointer to commit.
2800 *
2801 * This commits the data to the ring buffer, and releases any locks held.
2802 *
2803 * Must be paired with ring_buffer_lock_reserve.
2804 */
2805int ring_buffer_unlock_commit(struct ring_buffer *buffer,
2806 struct ring_buffer_event *event)
2807{
2808 struct ring_buffer_per_cpu *cpu_buffer;
2809 int cpu = raw_smp_processor_id();
2810
2811 cpu_buffer = buffer->buffers[cpu];
2812
2813 rb_commit(cpu_buffer, event);
2814
2815 rb_wakeups(buffer, cpu_buffer);
2816
2817 trace_recursive_unlock();
2818
2819 preempt_enable_notrace();
2820
2821 return 0;
2822}
2823EXPORT_SYMBOL_GPL(ring_buffer_unlock_commit);
2824
2825static inline void rb_event_discard(struct ring_buffer_event *event)
2826{
2827 if (event->type_len == RINGBUF_TYPE_TIME_EXTEND)
2828 event = skip_time_extend(event);
2829
2830 /* array[0] holds the actual length for the discarded event */
2831 event->array[0] = rb_event_data_length(event) - RB_EVNT_HDR_SIZE;
2832 event->type_len = RINGBUF_TYPE_PADDING;
2833 /* time delta must be non zero */
2834 if (!event->time_delta)
2835 event->time_delta = 1;
2836}
2837
2838/*
2839 * Decrement the entries to the page that an event is on.
2840 * The event does not even need to exist, only the pointer
2841 * to the page it is on. This may only be called before the commit
2842 * takes place.
2843 */
2844static inline void
2845rb_decrement_entry(struct ring_buffer_per_cpu *cpu_buffer,
2846 struct ring_buffer_event *event)
2847{
2848 unsigned long addr = (unsigned long)event;
2849 struct buffer_page *bpage = cpu_buffer->commit_page;
2850 struct buffer_page *start;
2851
2852 addr &= PAGE_MASK;
2853
2854 /* Do the likely case first */
2855 if (likely(bpage->page == (void *)addr)) {
2856 local_dec(&bpage->entries);
2857 return;
2858 }
2859
2860 /*
2861 * Because the commit page may be on the reader page we
2862 * start with the next page and check the end loop there.
2863 */
2864 rb_inc_page(cpu_buffer, &bpage);
2865 start = bpage;
2866 do {
2867 if (bpage->page == (void *)addr) {
2868 local_dec(&bpage->entries);
2869 return;
2870 }
2871 rb_inc_page(cpu_buffer, &bpage);
2872 } while (bpage != start);
2873
2874 /* commit not part of this buffer?? */
2875 RB_WARN_ON(cpu_buffer, 1);
2876}
2877
2878/**
2879 * ring_buffer_commit_discard - discard an event that has not been committed
2880 * @buffer: the ring buffer
2881 * @event: non committed event to discard
2882 *
2883 * Sometimes an event that is in the ring buffer needs to be ignored.
2884 * This function lets the user discard an event in the ring buffer
2885 * and then that event will not be read later.
2886 *
2887 * This function only works if it is called before the the item has been
2888 * committed. It will try to free the event from the ring buffer
2889 * if another event has not been added behind it.
2890 *
2891 * If another event has been added behind it, it will set the event
2892 * up as discarded, and perform the commit.
2893 *
2894 * If this function is called, do not call ring_buffer_unlock_commit on
2895 * the event.
2896 */
2897void ring_buffer_discard_commit(struct ring_buffer *buffer,
2898 struct ring_buffer_event *event)
2899{
2900 struct ring_buffer_per_cpu *cpu_buffer;
2901 int cpu;
2902
2903 /* The event is discarded regardless */
2904 rb_event_discard(event);
2905
2906 cpu = smp_processor_id();
2907 cpu_buffer = buffer->buffers[cpu];
2908
2909 /*
2910 * This must only be called if the event has not been
2911 * committed yet. Thus we can assume that preemption
2912 * is still disabled.
2913 */
2914 RB_WARN_ON(buffer, !local_read(&cpu_buffer->committing));
2915
2916 rb_decrement_entry(cpu_buffer, event);
2917 if (rb_try_to_discard(cpu_buffer, event))
2918 goto out;
2919
2920 /*
2921 * The commit is still visible by the reader, so we
2922 * must still update the timestamp.
2923 */
2924 rb_update_write_stamp(cpu_buffer, event);
2925 out:
2926 rb_end_commit(cpu_buffer);
2927
2928 trace_recursive_unlock();
2929
2930 preempt_enable_notrace();
2931
2932}
2933EXPORT_SYMBOL_GPL(ring_buffer_discard_commit);
2934
2935/**
2936 * ring_buffer_write - write data to the buffer without reserving
2937 * @buffer: The ring buffer to write to.
2938 * @length: The length of the data being written (excluding the event header)
2939 * @data: The data to write to the buffer.
2940 *
2941 * This is like ring_buffer_lock_reserve and ring_buffer_unlock_commit as
2942 * one function. If you already have the data to write to the buffer, it
2943 * may be easier to simply call this function.
2944 *
2945 * Note, like ring_buffer_lock_reserve, the length is the length of the data
2946 * and not the length of the event which would hold the header.
2947 */
2948int ring_buffer_write(struct ring_buffer *buffer,
2949 unsigned long length,
2950 void *data)
2951{
2952 struct ring_buffer_per_cpu *cpu_buffer;
2953 struct ring_buffer_event *event;
2954 void *body;
2955 int ret = -EBUSY;
2956 int cpu;
2957
2958 if (ring_buffer_flags != RB_BUFFERS_ON)
2959 return -EBUSY;
2960
2961 preempt_disable_notrace();
2962
2963 if (atomic_read(&buffer->record_disabled))
2964 goto out;
2965
2966 cpu = raw_smp_processor_id();
2967
2968 if (!cpumask_test_cpu(cpu, buffer->cpumask))
2969 goto out;
2970
2971 cpu_buffer = buffer->buffers[cpu];
2972
2973 if (atomic_read(&cpu_buffer->record_disabled))
2974 goto out;
2975
2976 if (length > BUF_MAX_DATA_SIZE)
2977 goto out;
2978
2979 event = rb_reserve_next_event(buffer, cpu_buffer, length);
2980 if (!event)
2981 goto out;
2982
2983 body = rb_event_data(event);
2984
2985 memcpy(body, data, length);
2986
2987 rb_commit(cpu_buffer, event);
2988
2989 rb_wakeups(buffer, cpu_buffer);
2990
2991 ret = 0;
2992 out:
2993 preempt_enable_notrace();
2994
2995 return ret;
2996}
2997EXPORT_SYMBOL_GPL(ring_buffer_write);
2998
2999static int rb_per_cpu_empty(struct ring_buffer_per_cpu *cpu_buffer)
3000{
3001 struct buffer_page *reader = cpu_buffer->reader_page;
3002 struct buffer_page *head = rb_set_head_page(cpu_buffer);
3003 struct buffer_page *commit = cpu_buffer->commit_page;
3004
3005 /* In case of error, head will be NULL */
3006 if (unlikely(!head))
3007 return 1;
3008
3009 return reader->read == rb_page_commit(reader) &&
3010 (commit == reader ||
3011 (commit == head &&
3012 head->read == rb_page_commit(commit)));
3013}
3014
3015/**
3016 * ring_buffer_record_disable - stop all writes into the buffer
3017 * @buffer: The ring buffer to stop writes to.
3018 *
3019 * This prevents all writes to the buffer. Any attempt to write
3020 * to the buffer after this will fail and return NULL.
3021 *
3022 * The caller should call synchronize_sched() after this.
3023 */
3024void ring_buffer_record_disable(struct ring_buffer *buffer)
3025{
3026 atomic_inc(&buffer->record_disabled);
3027}
3028EXPORT_SYMBOL_GPL(ring_buffer_record_disable);
3029
3030/**
3031 * ring_buffer_record_enable - enable writes to the buffer
3032 * @buffer: The ring buffer to enable writes
3033 *
3034 * Note, multiple disables will need the same number of enables
3035 * to truly enable the writing (much like preempt_disable).
3036 */
3037void ring_buffer_record_enable(struct ring_buffer *buffer)
3038{
3039 atomic_dec(&buffer->record_disabled);
3040}
3041EXPORT_SYMBOL_GPL(ring_buffer_record_enable);
3042
3043/**
3044 * ring_buffer_record_off - stop all writes into the buffer
3045 * @buffer: The ring buffer to stop writes to.
3046 *
3047 * This prevents all writes to the buffer. Any attempt to write
3048 * to the buffer after this will fail and return NULL.
3049 *
3050 * This is different than ring_buffer_record_disable() as
3051 * it works like an on/off switch, where as the disable() version
3052 * must be paired with a enable().
3053 */
3054void ring_buffer_record_off(struct ring_buffer *buffer)
3055{
3056 unsigned int rd;
3057 unsigned int new_rd;
3058
3059 do {
3060 rd = atomic_read(&buffer->record_disabled);
3061 new_rd = rd | RB_BUFFER_OFF;
3062 } while (atomic_cmpxchg(&buffer->record_disabled, rd, new_rd) != rd);
3063}
3064EXPORT_SYMBOL_GPL(ring_buffer_record_off);
3065
3066/**
3067 * ring_buffer_record_on - restart writes into the buffer
3068 * @buffer: The ring buffer to start writes to.
3069 *
3070 * This enables all writes to the buffer that was disabled by
3071 * ring_buffer_record_off().
3072 *
3073 * This is different than ring_buffer_record_enable() as
3074 * it works like an on/off switch, where as the enable() version
3075 * must be paired with a disable().
3076 */
3077void ring_buffer_record_on(struct ring_buffer *buffer)
3078{
3079 unsigned int rd;
3080 unsigned int new_rd;
3081
3082 do {
3083 rd = atomic_read(&buffer->record_disabled);
3084 new_rd = rd & ~RB_BUFFER_OFF;
3085 } while (atomic_cmpxchg(&buffer->record_disabled, rd, new_rd) != rd);
3086}
3087EXPORT_SYMBOL_GPL(ring_buffer_record_on);
3088
3089/**
3090 * ring_buffer_record_is_on - return true if the ring buffer can write
3091 * @buffer: The ring buffer to see if write is enabled
3092 *
3093 * Returns true if the ring buffer is in a state that it accepts writes.
3094 */
3095int ring_buffer_record_is_on(struct ring_buffer *buffer)
3096{
3097 return !atomic_read(&buffer->record_disabled);
3098}
3099
3100/**
3101 * ring_buffer_record_disable_cpu - stop all writes into the cpu_buffer
3102 * @buffer: The ring buffer to stop writes to.
3103 * @cpu: The CPU buffer to stop
3104 *
3105 * This prevents all writes to the buffer. Any attempt to write
3106 * to the buffer after this will fail and return NULL.
3107 *
3108 * The caller should call synchronize_sched() after this.
3109 */
3110void ring_buffer_record_disable_cpu(struct ring_buffer *buffer, int cpu)
3111{
3112 struct ring_buffer_per_cpu *cpu_buffer;
3113
3114 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3115 return;
3116
3117 cpu_buffer = buffer->buffers[cpu];
3118 atomic_inc(&cpu_buffer->record_disabled);
3119}
3120EXPORT_SYMBOL_GPL(ring_buffer_record_disable_cpu);
3121
3122/**
3123 * ring_buffer_record_enable_cpu - enable writes to the buffer
3124 * @buffer: The ring buffer to enable writes
3125 * @cpu: The CPU to enable.
3126 *
3127 * Note, multiple disables will need the same number of enables
3128 * to truly enable the writing (much like preempt_disable).
3129 */
3130void ring_buffer_record_enable_cpu(struct ring_buffer *buffer, int cpu)
3131{
3132 struct ring_buffer_per_cpu *cpu_buffer;
3133
3134 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3135 return;
3136
3137 cpu_buffer = buffer->buffers[cpu];
3138 atomic_dec(&cpu_buffer->record_disabled);
3139}
3140EXPORT_SYMBOL_GPL(ring_buffer_record_enable_cpu);
3141
3142/*
3143 * The total entries in the ring buffer is the running counter
3144 * of entries entered into the ring buffer, minus the sum of
3145 * the entries read from the ring buffer and the number of
3146 * entries that were overwritten.
3147 */
3148static inline unsigned long
3149rb_num_of_entries(struct ring_buffer_per_cpu *cpu_buffer)
3150{
3151 return local_read(&cpu_buffer->entries) -
3152 (local_read(&cpu_buffer->overrun) + cpu_buffer->read);
3153}
3154
3155/**
3156 * ring_buffer_oldest_event_ts - get the oldest event timestamp from the buffer
3157 * @buffer: The ring buffer
3158 * @cpu: The per CPU buffer to read from.
3159 */
3160u64 ring_buffer_oldest_event_ts(struct ring_buffer *buffer, int cpu)
3161{
3162 unsigned long flags;
3163 struct ring_buffer_per_cpu *cpu_buffer;
3164 struct buffer_page *bpage;
3165 u64 ret = 0;
3166
3167 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3168 return 0;
3169
3170 cpu_buffer = buffer->buffers[cpu];
3171 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
3172 /*
3173 * if the tail is on reader_page, oldest time stamp is on the reader
3174 * page
3175 */
3176 if (cpu_buffer->tail_page == cpu_buffer->reader_page)
3177 bpage = cpu_buffer->reader_page;
3178 else
3179 bpage = rb_set_head_page(cpu_buffer);
3180 if (bpage)
3181 ret = bpage->page->time_stamp;
3182 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
3183
3184 return ret;
3185}
3186EXPORT_SYMBOL_GPL(ring_buffer_oldest_event_ts);
3187
3188/**
3189 * ring_buffer_bytes_cpu - get the number of bytes consumed in a cpu buffer
3190 * @buffer: The ring buffer
3191 * @cpu: The per CPU buffer to read from.
3192 */
3193unsigned long ring_buffer_bytes_cpu(struct ring_buffer *buffer, int cpu)
3194{
3195 struct ring_buffer_per_cpu *cpu_buffer;
3196 unsigned long ret;
3197
3198 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3199 return 0;
3200
3201 cpu_buffer = buffer->buffers[cpu];
3202 ret = local_read(&cpu_buffer->entries_bytes) - cpu_buffer->read_bytes;
3203
3204 return ret;
3205}
3206EXPORT_SYMBOL_GPL(ring_buffer_bytes_cpu);
3207
3208/**
3209 * ring_buffer_entries_cpu - get the number of entries in a cpu buffer
3210 * @buffer: The ring buffer
3211 * @cpu: The per CPU buffer to get the entries from.
3212 */
3213unsigned long ring_buffer_entries_cpu(struct ring_buffer *buffer, int cpu)
3214{
3215 struct ring_buffer_per_cpu *cpu_buffer;
3216
3217 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3218 return 0;
3219
3220 cpu_buffer = buffer->buffers[cpu];
3221
3222 return rb_num_of_entries(cpu_buffer);
3223}
3224EXPORT_SYMBOL_GPL(ring_buffer_entries_cpu);
3225
3226/**
3227 * ring_buffer_overrun_cpu - get the number of overruns caused by the ring
3228 * buffer wrapping around (only if RB_FL_OVERWRITE is on).
3229 * @buffer: The ring buffer
3230 * @cpu: The per CPU buffer to get the number of overruns from
3231 */
3232unsigned long ring_buffer_overrun_cpu(struct ring_buffer *buffer, int cpu)
3233{
3234 struct ring_buffer_per_cpu *cpu_buffer;
3235 unsigned long ret;
3236
3237 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3238 return 0;
3239
3240 cpu_buffer = buffer->buffers[cpu];
3241 ret = local_read(&cpu_buffer->overrun);
3242
3243 return ret;
3244}
3245EXPORT_SYMBOL_GPL(ring_buffer_overrun_cpu);
3246
3247/**
3248 * ring_buffer_commit_overrun_cpu - get the number of overruns caused by
3249 * commits failing due to the buffer wrapping around while there are uncommitted
3250 * events, such as during an interrupt storm.
3251 * @buffer: The ring buffer
3252 * @cpu: The per CPU buffer to get the number of overruns from
3253 */
3254unsigned long
3255ring_buffer_commit_overrun_cpu(struct ring_buffer *buffer, int cpu)
3256{
3257 struct ring_buffer_per_cpu *cpu_buffer;
3258 unsigned long ret;
3259
3260 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3261 return 0;
3262
3263 cpu_buffer = buffer->buffers[cpu];
3264 ret = local_read(&cpu_buffer->commit_overrun);
3265
3266 return ret;
3267}
3268EXPORT_SYMBOL_GPL(ring_buffer_commit_overrun_cpu);
3269
3270/**
3271 * ring_buffer_dropped_events_cpu - get the number of dropped events caused by
3272 * the ring buffer filling up (only if RB_FL_OVERWRITE is off).
3273 * @buffer: The ring buffer
3274 * @cpu: The per CPU buffer to get the number of overruns from
3275 */
3276unsigned long
3277ring_buffer_dropped_events_cpu(struct ring_buffer *buffer, int cpu)
3278{
3279 struct ring_buffer_per_cpu *cpu_buffer;
3280 unsigned long ret;
3281
3282 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3283 return 0;
3284
3285 cpu_buffer = buffer->buffers[cpu];
3286 ret = local_read(&cpu_buffer->dropped_events);
3287
3288 return ret;
3289}
3290EXPORT_SYMBOL_GPL(ring_buffer_dropped_events_cpu);
3291
3292/**
3293 * ring_buffer_read_events_cpu - get the number of events successfully read
3294 * @buffer: The ring buffer
3295 * @cpu: The per CPU buffer to get the number of events read
3296 */
3297unsigned long
3298ring_buffer_read_events_cpu(struct ring_buffer *buffer, int cpu)
3299{
3300 struct ring_buffer_per_cpu *cpu_buffer;
3301
3302 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3303 return 0;
3304
3305 cpu_buffer = buffer->buffers[cpu];
3306 return cpu_buffer->read;
3307}
3308EXPORT_SYMBOL_GPL(ring_buffer_read_events_cpu);
3309
3310/**
3311 * ring_buffer_entries - get the number of entries in a buffer
3312 * @buffer: The ring buffer
3313 *
3314 * Returns the total number of entries in the ring buffer
3315 * (all CPU entries)
3316 */
3317unsigned long ring_buffer_entries(struct ring_buffer *buffer)
3318{
3319 struct ring_buffer_per_cpu *cpu_buffer;
3320 unsigned long entries = 0;
3321 int cpu;
3322
3323 /* if you care about this being correct, lock the buffer */
3324 for_each_buffer_cpu(buffer, cpu) {
3325 cpu_buffer = buffer->buffers[cpu];
3326 entries += rb_num_of_entries(cpu_buffer);
3327 }
3328
3329 return entries;
3330}
3331EXPORT_SYMBOL_GPL(ring_buffer_entries);
3332
3333/**
3334 * ring_buffer_overruns - get the number of overruns in buffer
3335 * @buffer: The ring buffer
3336 *
3337 * Returns the total number of overruns in the ring buffer
3338 * (all CPU entries)
3339 */
3340unsigned long ring_buffer_overruns(struct ring_buffer *buffer)
3341{
3342 struct ring_buffer_per_cpu *cpu_buffer;
3343 unsigned long overruns = 0;
3344 int cpu;
3345
3346 /* if you care about this being correct, lock the buffer */
3347 for_each_buffer_cpu(buffer, cpu) {
3348 cpu_buffer = buffer->buffers[cpu];
3349 overruns += local_read(&cpu_buffer->overrun);
3350 }
3351
3352 return overruns;
3353}
3354EXPORT_SYMBOL_GPL(ring_buffer_overruns);
3355
3356static void rb_iter_reset(struct ring_buffer_iter *iter)
3357{
3358 struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
3359
3360 /* Iterator usage is expected to have record disabled */
3361 if (list_empty(&cpu_buffer->reader_page->list)) {
3362 iter->head_page = rb_set_head_page(cpu_buffer);
3363 if (unlikely(!iter->head_page))
3364 return;
3365 iter->head = iter->head_page->read;
3366 } else {
3367 iter->head_page = cpu_buffer->reader_page;
3368 iter->head = cpu_buffer->reader_page->read;
3369 }
3370 if (iter->head)
3371 iter->read_stamp = cpu_buffer->read_stamp;
3372 else
3373 iter->read_stamp = iter->head_page->page->time_stamp;
3374 iter->cache_reader_page = cpu_buffer->reader_page;
3375 iter->cache_read = cpu_buffer->read;
3376}
3377
3378/**
3379 * ring_buffer_iter_reset - reset an iterator
3380 * @iter: The iterator to reset
3381 *
3382 * Resets the iterator, so that it will start from the beginning
3383 * again.
3384 */
3385void ring_buffer_iter_reset(struct ring_buffer_iter *iter)
3386{
3387 struct ring_buffer_per_cpu *cpu_buffer;
3388 unsigned long flags;
3389
3390 if (!iter)
3391 return;
3392
3393 cpu_buffer = iter->cpu_buffer;
3394
3395 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
3396 rb_iter_reset(iter);
3397 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
3398}
3399EXPORT_SYMBOL_GPL(ring_buffer_iter_reset);
3400
3401/**
3402 * ring_buffer_iter_empty - check if an iterator has no more to read
3403 * @iter: The iterator to check
3404 */
3405int ring_buffer_iter_empty(struct ring_buffer_iter *iter)
3406{
3407 struct ring_buffer_per_cpu *cpu_buffer;
3408
3409 cpu_buffer = iter->cpu_buffer;
3410
3411 return iter->head_page == cpu_buffer->commit_page &&
3412 iter->head == rb_commit_index(cpu_buffer);
3413}
3414EXPORT_SYMBOL_GPL(ring_buffer_iter_empty);
3415
3416static void
3417rb_update_read_stamp(struct ring_buffer_per_cpu *cpu_buffer,
3418 struct ring_buffer_event *event)
3419{
3420 u64 delta;
3421
3422 switch (event->type_len) {
3423 case RINGBUF_TYPE_PADDING:
3424 return;
3425
3426 case RINGBUF_TYPE_TIME_EXTEND:
3427 delta = event->array[0];
3428 delta <<= TS_SHIFT;
3429 delta += event->time_delta;
3430 cpu_buffer->read_stamp += delta;
3431 return;
3432
3433 case RINGBUF_TYPE_TIME_STAMP:
3434 /* FIXME: not implemented */
3435 return;
3436
3437 case RINGBUF_TYPE_DATA:
3438 cpu_buffer->read_stamp += event->time_delta;
3439 return;
3440
3441 default:
3442 BUG();
3443 }
3444 return;
3445}
3446
3447static void
3448rb_update_iter_read_stamp(struct ring_buffer_iter *iter,
3449 struct ring_buffer_event *event)
3450{
3451 u64 delta;
3452
3453 switch (event->type_len) {
3454 case RINGBUF_TYPE_PADDING:
3455 return;
3456
3457 case RINGBUF_TYPE_TIME_EXTEND:
3458 delta = event->array[0];
3459 delta <<= TS_SHIFT;
3460 delta += event->time_delta;
3461 iter->read_stamp += delta;
3462 return;
3463
3464 case RINGBUF_TYPE_TIME_STAMP:
3465 /* FIXME: not implemented */
3466 return;
3467
3468 case RINGBUF_TYPE_DATA:
3469 iter->read_stamp += event->time_delta;
3470 return;
3471
3472 default:
3473 BUG();
3474 }
3475 return;
3476}
3477
3478static struct buffer_page *
3479rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
3480{
3481 struct buffer_page *reader = NULL;
3482 unsigned long overwrite;
3483 unsigned long flags;
3484 int nr_loops = 0;
3485 int ret;
3486
3487 local_irq_save(flags);
3488 arch_spin_lock(&cpu_buffer->lock);
3489
3490 again:
3491 /*
3492 * This should normally only loop twice. But because the
3493 * start of the reader inserts an empty page, it causes
3494 * a case where we will loop three times. There should be no
3495 * reason to loop four times (that I know of).
3496 */
3497 if (RB_WARN_ON(cpu_buffer, ++nr_loops > 3)) {
3498 reader = NULL;
3499 goto out;
3500 }
3501
3502 reader = cpu_buffer->reader_page;
3503
3504 /* If there's more to read, return this page */
3505 if (cpu_buffer->reader_page->read < rb_page_size(reader))
3506 goto out;
3507
3508 /* Never should we have an index greater than the size */
3509 if (RB_WARN_ON(cpu_buffer,
3510 cpu_buffer->reader_page->read > rb_page_size(reader)))
3511 goto out;
3512
3513 /* check if we caught up to the tail */
3514 reader = NULL;
3515 if (cpu_buffer->commit_page == cpu_buffer->reader_page)
3516 goto out;
3517
3518 /* Don't bother swapping if the ring buffer is empty */
3519 if (rb_num_of_entries(cpu_buffer) == 0)
3520 goto out;
3521
3522 /*
3523 * Reset the reader page to size zero.
3524 */
3525 local_set(&cpu_buffer->reader_page->write, 0);
3526 local_set(&cpu_buffer->reader_page->entries, 0);
3527 local_set(&cpu_buffer->reader_page->page->commit, 0);
3528 cpu_buffer->reader_page->real_end = 0;
3529
3530 spin:
3531 /*
3532 * Splice the empty reader page into the list around the head.
3533 */
3534 reader = rb_set_head_page(cpu_buffer);
3535 if (!reader)
3536 goto out;
3537 cpu_buffer->reader_page->list.next = rb_list_head(reader->list.next);
3538 cpu_buffer->reader_page->list.prev = reader->list.prev;
3539
3540 /*
3541 * cpu_buffer->pages just needs to point to the buffer, it
3542 * has no specific buffer page to point to. Lets move it out
3543 * of our way so we don't accidentally swap it.
3544 */
3545 cpu_buffer->pages = reader->list.prev;
3546
3547 /* The reader page will be pointing to the new head */
3548 rb_set_list_to_head(cpu_buffer, &cpu_buffer->reader_page->list);
3549
3550 /*
3551 * We want to make sure we read the overruns after we set up our
3552 * pointers to the next object. The writer side does a
3553 * cmpxchg to cross pages which acts as the mb on the writer
3554 * side. Note, the reader will constantly fail the swap
3555 * while the writer is updating the pointers, so this
3556 * guarantees that the overwrite recorded here is the one we
3557 * want to compare with the last_overrun.
3558 */
3559 smp_mb();
3560 overwrite = local_read(&(cpu_buffer->overrun));
3561
3562 /*
3563 * Here's the tricky part.
3564 *
3565 * We need to move the pointer past the header page.
3566 * But we can only do that if a writer is not currently
3567 * moving it. The page before the header page has the
3568 * flag bit '1' set if it is pointing to the page we want.
3569 * but if the writer is in the process of moving it
3570 * than it will be '2' or already moved '0'.
3571 */
3572
3573 ret = rb_head_page_replace(reader, cpu_buffer->reader_page);
3574
3575 /*
3576 * If we did not convert it, then we must try again.
3577 */
3578 if (!ret)
3579 goto spin;
3580
3581 /*
3582 * Yeah! We succeeded in replacing the page.
3583 *
3584 * Now make the new head point back to the reader page.
3585 */
3586 rb_list_head(reader->list.next)->prev = &cpu_buffer->reader_page->list;
3587 rb_inc_page(cpu_buffer, &cpu_buffer->head_page);
3588
3589 /* Finally update the reader page to the new head */
3590 cpu_buffer->reader_page = reader;
3591 rb_reset_reader_page(cpu_buffer);
3592
3593 if (overwrite != cpu_buffer->last_overrun) {
3594 cpu_buffer->lost_events = overwrite - cpu_buffer->last_overrun;
3595 cpu_buffer->last_overrun = overwrite;
3596 }
3597
3598 goto again;
3599
3600 out:
3601 arch_spin_unlock(&cpu_buffer->lock);
3602 local_irq_restore(flags);
3603
3604 return reader;
3605}
3606
3607static void rb_advance_reader(struct ring_buffer_per_cpu *cpu_buffer)
3608{
3609 struct ring_buffer_event *event;
3610 struct buffer_page *reader;
3611 unsigned length;
3612
3613 reader = rb_get_reader_page(cpu_buffer);
3614
3615 /* This function should not be called when buffer is empty */
3616 if (RB_WARN_ON(cpu_buffer, !reader))
3617 return;
3618
3619 event = rb_reader_event(cpu_buffer);
3620
3621 if (event->type_len <= RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
3622 cpu_buffer->read++;
3623
3624 rb_update_read_stamp(cpu_buffer, event);
3625
3626 length = rb_event_length(event);
3627 cpu_buffer->reader_page->read += length;
3628}
3629
3630static void rb_advance_iter(struct ring_buffer_iter *iter)
3631{
3632 struct ring_buffer_per_cpu *cpu_buffer;
3633 struct ring_buffer_event *event;
3634 unsigned length;
3635
3636 cpu_buffer = iter->cpu_buffer;
3637
3638 /*
3639 * Check if we are at the end of the buffer.
3640 */
3641 if (iter->head >= rb_page_size(iter->head_page)) {
3642 /* discarded commits can make the page empty */
3643 if (iter->head_page == cpu_buffer->commit_page)
3644 return;
3645 rb_inc_iter(iter);
3646 return;
3647 }
3648
3649 event = rb_iter_head_event(iter);
3650
3651 length = rb_event_length(event);
3652
3653 /*
3654 * This should not be called to advance the header if we are
3655 * at the tail of the buffer.
3656 */
3657 if (RB_WARN_ON(cpu_buffer,
3658 (iter->head_page == cpu_buffer->commit_page) &&
3659 (iter->head + length > rb_commit_index(cpu_buffer))))
3660 return;
3661
3662 rb_update_iter_read_stamp(iter, event);
3663
3664 iter->head += length;
3665
3666 /* check for end of page padding */
3667 if ((iter->head >= rb_page_size(iter->head_page)) &&
3668 (iter->head_page != cpu_buffer->commit_page))
3669 rb_inc_iter(iter);
3670}
3671
3672static int rb_lost_events(struct ring_buffer_per_cpu *cpu_buffer)
3673{
3674 return cpu_buffer->lost_events;
3675}
3676
3677static struct ring_buffer_event *
3678rb_buffer_peek(struct ring_buffer_per_cpu *cpu_buffer, u64 *ts,
3679 unsigned long *lost_events)
3680{
3681 struct ring_buffer_event *event;
3682 struct buffer_page *reader;
3683 int nr_loops = 0;
3684
3685 again:
3686 /*
3687 * We repeat when a time extend is encountered.
3688 * Since the time extend is always attached to a data event,
3689 * we should never loop more than once.
3690 * (We never hit the following condition more than twice).
3691 */
3692 if (RB_WARN_ON(cpu_buffer, ++nr_loops > 2))
3693 return NULL;
3694
3695 reader = rb_get_reader_page(cpu_buffer);
3696 if (!reader)
3697 return NULL;
3698
3699 event = rb_reader_event(cpu_buffer);
3700
3701 switch (event->type_len) {
3702 case RINGBUF_TYPE_PADDING:
3703 if (rb_null_event(event))
3704 RB_WARN_ON(cpu_buffer, 1);
3705 /*
3706 * Because the writer could be discarding every
3707 * event it creates (which would probably be bad)
3708 * if we were to go back to "again" then we may never
3709 * catch up, and will trigger the warn on, or lock
3710 * the box. Return the padding, and we will release
3711 * the current locks, and try again.
3712 */
3713 return event;
3714
3715 case RINGBUF_TYPE_TIME_EXTEND:
3716 /* Internal data, OK to advance */
3717 rb_advance_reader(cpu_buffer);
3718 goto again;
3719
3720 case RINGBUF_TYPE_TIME_STAMP:
3721 /* FIXME: not implemented */
3722 rb_advance_reader(cpu_buffer);
3723 goto again;
3724
3725 case RINGBUF_TYPE_DATA:
3726 if (ts) {
3727 *ts = cpu_buffer->read_stamp + event->time_delta;
3728 ring_buffer_normalize_time_stamp(cpu_buffer->buffer,
3729 cpu_buffer->cpu, ts);
3730 }
3731 if (lost_events)
3732 *lost_events = rb_lost_events(cpu_buffer);
3733 return event;
3734
3735 default:
3736 BUG();
3737 }
3738
3739 return NULL;
3740}
3741EXPORT_SYMBOL_GPL(ring_buffer_peek);
3742
3743static struct ring_buffer_event *
3744rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
3745{
3746 struct ring_buffer *buffer;
3747 struct ring_buffer_per_cpu *cpu_buffer;
3748 struct ring_buffer_event *event;
3749 int nr_loops = 0;
3750
3751 cpu_buffer = iter->cpu_buffer;
3752 buffer = cpu_buffer->buffer;
3753
3754 /*
3755 * Check if someone performed a consuming read to
3756 * the buffer. A consuming read invalidates the iterator
3757 * and we need to reset the iterator in this case.
3758 */
3759 if (unlikely(iter->cache_read != cpu_buffer->read ||
3760 iter->cache_reader_page != cpu_buffer->reader_page))
3761 rb_iter_reset(iter);
3762
3763 again:
3764 if (ring_buffer_iter_empty(iter))
3765 return NULL;
3766
3767 /*
3768 * We repeat when a time extend is encountered.
3769 * Since the time extend is always attached to a data event,
3770 * we should never loop more than once.
3771 * (We never hit the following condition more than twice).
3772 */
3773 if (RB_WARN_ON(cpu_buffer, ++nr_loops > 2))
3774 return NULL;
3775
3776 if (rb_per_cpu_empty(cpu_buffer))
3777 return NULL;
3778
3779 if (iter->head >= local_read(&iter->head_page->page->commit)) {
3780 rb_inc_iter(iter);
3781 goto again;
3782 }
3783
3784 event = rb_iter_head_event(iter);
3785
3786 switch (event->type_len) {
3787 case RINGBUF_TYPE_PADDING:
3788 if (rb_null_event(event)) {
3789 rb_inc_iter(iter);
3790 goto again;
3791 }
3792 rb_advance_iter(iter);
3793 return event;
3794
3795 case RINGBUF_TYPE_TIME_EXTEND:
3796 /* Internal data, OK to advance */
3797 rb_advance_iter(iter);
3798 goto again;
3799
3800 case RINGBUF_TYPE_TIME_STAMP:
3801 /* FIXME: not implemented */
3802 rb_advance_iter(iter);
3803 goto again;
3804
3805 case RINGBUF_TYPE_DATA:
3806 if (ts) {
3807 *ts = iter->read_stamp + event->time_delta;
3808 ring_buffer_normalize_time_stamp(buffer,
3809 cpu_buffer->cpu, ts);
3810 }
3811 return event;
3812
3813 default:
3814 BUG();
3815 }
3816
3817 return NULL;
3818}
3819EXPORT_SYMBOL_GPL(ring_buffer_iter_peek);
3820
3821static inline int rb_ok_to_lock(void)
3822{
3823 /*
3824 * If an NMI die dumps out the content of the ring buffer
3825 * do not grab locks. We also permanently disable the ring
3826 * buffer too. A one time deal is all you get from reading
3827 * the ring buffer from an NMI.
3828 */
3829 if (likely(!in_nmi()))
3830 return 1;
3831
3832 tracing_off_permanent();
3833 return 0;
3834}
3835
3836/**
3837 * ring_buffer_peek - peek at the next event to be read
3838 * @buffer: The ring buffer to read
3839 * @cpu: The cpu to peak at
3840 * @ts: The timestamp counter of this event.
3841 * @lost_events: a variable to store if events were lost (may be NULL)
3842 *
3843 * This will return the event that will be read next, but does
3844 * not consume the data.
3845 */
3846struct ring_buffer_event *
3847ring_buffer_peek(struct ring_buffer *buffer, int cpu, u64 *ts,
3848 unsigned long *lost_events)
3849{
3850 struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
3851 struct ring_buffer_event *event;
3852 unsigned long flags;
3853 int dolock;
3854
3855 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3856 return NULL;
3857
3858 dolock = rb_ok_to_lock();
3859 again:
3860 local_irq_save(flags);
3861 if (dolock)
3862 raw_spin_lock(&cpu_buffer->reader_lock);
3863 event = rb_buffer_peek(cpu_buffer, ts, lost_events);
3864 if (event && event->type_len == RINGBUF_TYPE_PADDING)
3865 rb_advance_reader(cpu_buffer);
3866 if (dolock)
3867 raw_spin_unlock(&cpu_buffer->reader_lock);
3868 local_irq_restore(flags);
3869
3870 if (event && event->type_len == RINGBUF_TYPE_PADDING)
3871 goto again;
3872
3873 return event;
3874}
3875
3876/**
3877 * ring_buffer_iter_peek - peek at the next event to be read
3878 * @iter: The ring buffer iterator
3879 * @ts: The timestamp counter of this event.
3880 *
3881 * This will return the event that will be read next, but does
3882 * not increment the iterator.
3883 */
3884struct ring_buffer_event *
3885ring_buffer_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
3886{
3887 struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
3888 struct ring_buffer_event *event;
3889 unsigned long flags;
3890
3891 again:
3892 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
3893 event = rb_iter_peek(iter, ts);
3894 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
3895
3896 if (event && event->type_len == RINGBUF_TYPE_PADDING)
3897 goto again;
3898
3899 return event;
3900}
3901
3902/**
3903 * ring_buffer_consume - return an event and consume it
3904 * @buffer: The ring buffer to get the next event from
3905 * @cpu: the cpu to read the buffer from
3906 * @ts: a variable to store the timestamp (may be NULL)
3907 * @lost_events: a variable to store if events were lost (may be NULL)
3908 *
3909 * Returns the next event in the ring buffer, and that event is consumed.
3910 * Meaning, that sequential reads will keep returning a different event,
3911 * and eventually empty the ring buffer if the producer is slower.
3912 */
3913struct ring_buffer_event *
3914ring_buffer_consume(struct ring_buffer *buffer, int cpu, u64 *ts,
3915 unsigned long *lost_events)
3916{
3917 struct ring_buffer_per_cpu *cpu_buffer;
3918 struct ring_buffer_event *event = NULL;
3919 unsigned long flags;
3920 int dolock;
3921
3922 dolock = rb_ok_to_lock();
3923
3924 again:
3925 /* might be called in atomic */
3926 preempt_disable();
3927
3928 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3929 goto out;
3930
3931 cpu_buffer = buffer->buffers[cpu];
3932 local_irq_save(flags);
3933 if (dolock)
3934 raw_spin_lock(&cpu_buffer->reader_lock);
3935
3936 event = rb_buffer_peek(cpu_buffer, ts, lost_events);
3937 if (event) {
3938 cpu_buffer->lost_events = 0;
3939 rb_advance_reader(cpu_buffer);
3940 }
3941
3942 if (dolock)
3943 raw_spin_unlock(&cpu_buffer->reader_lock);
3944 local_irq_restore(flags);
3945
3946 out:
3947 preempt_enable();
3948
3949 if (event && event->type_len == RINGBUF_TYPE_PADDING)
3950 goto again;
3951
3952 return event;
3953}
3954EXPORT_SYMBOL_GPL(ring_buffer_consume);
3955
3956/**
3957 * ring_buffer_read_prepare - Prepare for a non consuming read of the buffer
3958 * @buffer: The ring buffer to read from
3959 * @cpu: The cpu buffer to iterate over
3960 *
3961 * This performs the initial preparations necessary to iterate
3962 * through the buffer. Memory is allocated, buffer recording
3963 * is disabled, and the iterator pointer is returned to the caller.
3964 *
3965 * Disabling buffer recordng prevents the reading from being
3966 * corrupted. This is not a consuming read, so a producer is not
3967 * expected.
3968 *
3969 * After a sequence of ring_buffer_read_prepare calls, the user is
3970 * expected to make at least one call to ring_buffer_read_prepare_sync.
3971 * Afterwards, ring_buffer_read_start is invoked to get things going
3972 * for real.
3973 *
3974 * This overall must be paired with ring_buffer_read_finish.
3975 */
3976struct ring_buffer_iter *
3977ring_buffer_read_prepare(struct ring_buffer *buffer, int cpu)
3978{
3979 struct ring_buffer_per_cpu *cpu_buffer;
3980 struct ring_buffer_iter *iter;
3981
3982 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3983 return NULL;
3984
3985 iter = kmalloc(sizeof(*iter), GFP_KERNEL);
3986 if (!iter)
3987 return NULL;
3988
3989 cpu_buffer = buffer->buffers[cpu];
3990
3991 iter->cpu_buffer = cpu_buffer;
3992
3993 atomic_inc(&buffer->resize_disabled);
3994 atomic_inc(&cpu_buffer->record_disabled);
3995
3996 return iter;
3997}
3998EXPORT_SYMBOL_GPL(ring_buffer_read_prepare);
3999
4000/**
4001 * ring_buffer_read_prepare_sync - Synchronize a set of prepare calls
4002 *
4003 * All previously invoked ring_buffer_read_prepare calls to prepare
4004 * iterators will be synchronized. Afterwards, read_buffer_read_start
4005 * calls on those iterators are allowed.
4006 */
4007void
4008ring_buffer_read_prepare_sync(void)
4009{
4010 synchronize_sched();
4011}
4012EXPORT_SYMBOL_GPL(ring_buffer_read_prepare_sync);
4013
4014/**
4015 * ring_buffer_read_start - start a non consuming read of the buffer
4016 * @iter: The iterator returned by ring_buffer_read_prepare
4017 *
4018 * This finalizes the startup of an iteration through the buffer.
4019 * The iterator comes from a call to ring_buffer_read_prepare and
4020 * an intervening ring_buffer_read_prepare_sync must have been
4021 * performed.
4022 *
4023 * Must be paired with ring_buffer_read_finish.
4024 */
4025void
4026ring_buffer_read_start(struct ring_buffer_iter *iter)
4027{
4028 struct ring_buffer_per_cpu *cpu_buffer;
4029 unsigned long flags;
4030
4031 if (!iter)
4032 return;
4033
4034 cpu_buffer = iter->cpu_buffer;
4035
4036 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
4037 arch_spin_lock(&cpu_buffer->lock);
4038 rb_iter_reset(iter);
4039 arch_spin_unlock(&cpu_buffer->lock);
4040 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
4041}
4042EXPORT_SYMBOL_GPL(ring_buffer_read_start);
4043
4044/**
4045 * ring_buffer_read_finish - finish reading the iterator of the buffer
4046 * @iter: The iterator retrieved by ring_buffer_start
4047 *
4048 * This re-enables the recording to the buffer, and frees the
4049 * iterator.
4050 */
4051void
4052ring_buffer_read_finish(struct ring_buffer_iter *iter)
4053{
4054 struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
4055 unsigned long flags;
4056
4057 /*
4058 * Ring buffer is disabled from recording, here's a good place
4059 * to check the integrity of the ring buffer.
4060 * Must prevent readers from trying to read, as the check
4061 * clears the HEAD page and readers require it.
4062 */
4063 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
4064 rb_check_pages(cpu_buffer);
4065 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
4066
4067 atomic_dec(&cpu_buffer->record_disabled);
4068 atomic_dec(&cpu_buffer->buffer->resize_disabled);
4069 kfree(iter);
4070}
4071EXPORT_SYMBOL_GPL(ring_buffer_read_finish);
4072
4073/**
4074 * ring_buffer_read - read the next item in the ring buffer by the iterator
4075 * @iter: The ring buffer iterator
4076 * @ts: The time stamp of the event read.
4077 *
4078 * This reads the next event in the ring buffer and increments the iterator.
4079 */
4080struct ring_buffer_event *
4081ring_buffer_read(struct ring_buffer_iter *iter, u64 *ts)
4082{
4083 struct ring_buffer_event *event;
4084 struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
4085 unsigned long flags;
4086
4087 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
4088 again:
4089 event = rb_iter_peek(iter, ts);
4090 if (!event)
4091 goto out;
4092
4093 if (event->type_len == RINGBUF_TYPE_PADDING)
4094 goto again;
4095
4096 rb_advance_iter(iter);
4097 out:
4098 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
4099
4100 return event;
4101}
4102EXPORT_SYMBOL_GPL(ring_buffer_read);
4103
4104/**
4105 * ring_buffer_size - return the size of the ring buffer (in bytes)
4106 * @buffer: The ring buffer.
4107 */
4108unsigned long ring_buffer_size(struct ring_buffer *buffer, int cpu)
4109{
4110 /*
4111 * Earlier, this method returned
4112 * BUF_PAGE_SIZE * buffer->nr_pages
4113 * Since the nr_pages field is now removed, we have converted this to
4114 * return the per cpu buffer value.
4115 */
4116 if (!cpumask_test_cpu(cpu, buffer->cpumask))
4117 return 0;
4118
4119 return BUF_PAGE_SIZE * buffer->buffers[cpu]->nr_pages;
4120}
4121EXPORT_SYMBOL_GPL(ring_buffer_size);
4122
4123static void
4124rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
4125{
4126 rb_head_page_deactivate(cpu_buffer);
4127
4128 cpu_buffer->head_page
4129 = list_entry(cpu_buffer->pages, struct buffer_page, list);
4130 local_set(&cpu_buffer->head_page->write, 0);
4131 local_set(&cpu_buffer->head_page->entries, 0);
4132 local_set(&cpu_buffer->head_page->page->commit, 0);
4133
4134 cpu_buffer->head_page->read = 0;
4135
4136 cpu_buffer->tail_page = cpu_buffer->head_page;
4137 cpu_buffer->commit_page = cpu_buffer->head_page;
4138
4139 INIT_LIST_HEAD(&cpu_buffer->reader_page->list);
4140 INIT_LIST_HEAD(&cpu_buffer->new_pages);
4141 local_set(&cpu_buffer->reader_page->write, 0);
4142 local_set(&cpu_buffer->reader_page->entries, 0);
4143 local_set(&cpu_buffer->reader_page->page->commit, 0);
4144 cpu_buffer->reader_page->read = 0;
4145
4146 local_set(&cpu_buffer->entries_bytes, 0);
4147 local_set(&cpu_buffer->overrun, 0);
4148 local_set(&cpu_buffer->commit_overrun, 0);
4149 local_set(&cpu_buffer->dropped_events, 0);
4150 local_set(&cpu_buffer->entries, 0);
4151 local_set(&cpu_buffer->committing, 0);
4152 local_set(&cpu_buffer->commits, 0);
4153 cpu_buffer->read = 0;
4154 cpu_buffer->read_bytes = 0;
4155
4156 cpu_buffer->write_stamp = 0;
4157 cpu_buffer->read_stamp = 0;
4158
4159 cpu_buffer->lost_events = 0;
4160 cpu_buffer->last_overrun = 0;
4161
4162 rb_head_page_activate(cpu_buffer);
4163}
4164
4165/**
4166 * ring_buffer_reset_cpu - reset a ring buffer per CPU buffer
4167 * @buffer: The ring buffer to reset a per cpu buffer of
4168 * @cpu: The CPU buffer to be reset
4169 */
4170void ring_buffer_reset_cpu(struct ring_buffer *buffer, int cpu)
4171{
4172 struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
4173 unsigned long flags;
4174
4175 if (!cpumask_test_cpu(cpu, buffer->cpumask))
4176 return;
4177
4178 atomic_inc(&buffer->resize_disabled);
4179 atomic_inc(&cpu_buffer->record_disabled);
4180
4181 /* Make sure all commits have finished */
4182 synchronize_sched();
4183
4184 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
4185
4186 if (RB_WARN_ON(cpu_buffer, local_read(&cpu_buffer->committing)))
4187 goto out;
4188
4189 arch_spin_lock(&cpu_buffer->lock);
4190
4191 rb_reset_cpu(cpu_buffer);
4192
4193 arch_spin_unlock(&cpu_buffer->lock);
4194
4195 out:
4196 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
4197
4198 atomic_dec(&cpu_buffer->record_disabled);
4199 atomic_dec(&buffer->resize_disabled);
4200}
4201EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu);
4202
4203/**
4204 * ring_buffer_reset - reset a ring buffer
4205 * @buffer: The ring buffer to reset all cpu buffers
4206 */
4207void ring_buffer_reset(struct ring_buffer *buffer)
4208{
4209 int cpu;
4210
4211 for_each_buffer_cpu(buffer, cpu)
4212 ring_buffer_reset_cpu(buffer, cpu);
4213}
4214EXPORT_SYMBOL_GPL(ring_buffer_reset);
4215
4216/**
4217 * rind_buffer_empty - is the ring buffer empty?
4218 * @buffer: The ring buffer to test
4219 */
4220int ring_buffer_empty(struct ring_buffer *buffer)
4221{
4222 struct ring_buffer_per_cpu *cpu_buffer;
4223 unsigned long flags;
4224 int dolock;
4225 int cpu;
4226 int ret;
4227
4228 dolock = rb_ok_to_lock();
4229
4230 /* yes this is racy, but if you don't like the race, lock the buffer */
4231 for_each_buffer_cpu(buffer, cpu) {
4232 cpu_buffer = buffer->buffers[cpu];
4233 local_irq_save(flags);
4234 if (dolock)
4235 raw_spin_lock(&cpu_buffer->reader_lock);
4236 ret = rb_per_cpu_empty(cpu_buffer);
4237 if (dolock)
4238 raw_spin_unlock(&cpu_buffer->reader_lock);
4239 local_irq_restore(flags);
4240
4241 if (!ret)
4242 return 0;
4243 }
4244
4245 return 1;
4246}
4247EXPORT_SYMBOL_GPL(ring_buffer_empty);
4248
4249/**
4250 * ring_buffer_empty_cpu - is a cpu buffer of a ring buffer empty?
4251 * @buffer: The ring buffer
4252 * @cpu: The CPU buffer to test
4253 */
4254int ring_buffer_empty_cpu(struct ring_buffer *buffer, int cpu)
4255{
4256 struct ring_buffer_per_cpu *cpu_buffer;
4257 unsigned long flags;
4258 int dolock;
4259 int ret;
4260
4261 if (!cpumask_test_cpu(cpu, buffer->cpumask))
4262 return 1;
4263
4264 dolock = rb_ok_to_lock();
4265
4266 cpu_buffer = buffer->buffers[cpu];
4267 local_irq_save(flags);
4268 if (dolock)
4269 raw_spin_lock(&cpu_buffer->reader_lock);
4270 ret = rb_per_cpu_empty(cpu_buffer);
4271 if (dolock)
4272 raw_spin_unlock(&cpu_buffer->reader_lock);
4273 local_irq_restore(flags);
4274
4275 return ret;
4276}
4277EXPORT_SYMBOL_GPL(ring_buffer_empty_cpu);
4278
4279#ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
4280/**
4281 * ring_buffer_swap_cpu - swap a CPU buffer between two ring buffers
4282 * @buffer_a: One buffer to swap with
4283 * @buffer_b: The other buffer to swap with
4284 *
4285 * This function is useful for tracers that want to take a "snapshot"
4286 * of a CPU buffer and has another back up buffer lying around.
4287 * it is expected that the tracer handles the cpu buffer not being
4288 * used at the moment.
4289 */
4290int ring_buffer_swap_cpu(struct ring_buffer *buffer_a,
4291 struct ring_buffer *buffer_b, int cpu)
4292{
4293 struct ring_buffer_per_cpu *cpu_buffer_a;
4294 struct ring_buffer_per_cpu *cpu_buffer_b;
4295 int ret = -EINVAL;
4296
4297 if (!cpumask_test_cpu(cpu, buffer_a->cpumask) ||
4298 !cpumask_test_cpu(cpu, buffer_b->cpumask))
4299 goto out;
4300
4301 cpu_buffer_a = buffer_a->buffers[cpu];
4302 cpu_buffer_b = buffer_b->buffers[cpu];
4303
4304 /* At least make sure the two buffers are somewhat the same */
4305 if (cpu_buffer_a->nr_pages != cpu_buffer_b->nr_pages)
4306 goto out;
4307
4308 ret = -EAGAIN;
4309
4310 if (ring_buffer_flags != RB_BUFFERS_ON)
4311 goto out;
4312
4313 if (atomic_read(&buffer_a->record_disabled))
4314 goto out;
4315
4316 if (atomic_read(&buffer_b->record_disabled))
4317 goto out;
4318
4319 if (atomic_read(&cpu_buffer_a->record_disabled))
4320 goto out;
4321
4322 if (atomic_read(&cpu_buffer_b->record_disabled))
4323 goto out;
4324
4325 /*
4326 * We can't do a synchronize_sched here because this
4327 * function can be called in atomic context.
4328 * Normally this will be called from the same CPU as cpu.
4329 * If not it's up to the caller to protect this.
4330 */
4331 atomic_inc(&cpu_buffer_a->record_disabled);
4332 atomic_inc(&cpu_buffer_b->record_disabled);
4333
4334 ret = -EBUSY;
4335 if (local_read(&cpu_buffer_a->committing))
4336 goto out_dec;
4337 if (local_read(&cpu_buffer_b->committing))
4338 goto out_dec;
4339
4340 buffer_a->buffers[cpu] = cpu_buffer_b;
4341 buffer_b->buffers[cpu] = cpu_buffer_a;
4342
4343 cpu_buffer_b->buffer = buffer_a;
4344 cpu_buffer_a->buffer = buffer_b;
4345
4346 ret = 0;
4347
4348out_dec:
4349 atomic_dec(&cpu_buffer_a->record_disabled);
4350 atomic_dec(&cpu_buffer_b->record_disabled);
4351out:
4352 return ret;
4353}
4354EXPORT_SYMBOL_GPL(ring_buffer_swap_cpu);
4355#endif /* CONFIG_RING_BUFFER_ALLOW_SWAP */
4356
4357/**
4358 * ring_buffer_alloc_read_page - allocate a page to read from buffer
4359 * @buffer: the buffer to allocate for.
4360 * @cpu: the cpu buffer to allocate.
4361 *
4362 * This function is used in conjunction with ring_buffer_read_page.
4363 * When reading a full page from the ring buffer, these functions
4364 * can be used to speed up the process. The calling function should
4365 * allocate a few pages first with this function. Then when it
4366 * needs to get pages from the ring buffer, it passes the result
4367 * of this function into ring_buffer_read_page, which will swap
4368 * the page that was allocated, with the read page of the buffer.
4369 *
4370 * Returns:
4371 * The page allocated, or NULL on error.
4372 */
4373void *ring_buffer_alloc_read_page(struct ring_buffer *buffer, int cpu)
4374{
4375 struct buffer_data_page *bpage;
4376 struct page *page;
4377
4378 page = alloc_pages_node(cpu_to_node(cpu),
4379 GFP_KERNEL | __GFP_NORETRY, 0);
4380 if (!page)
4381 return NULL;
4382
4383 bpage = page_address(page);
4384
4385 rb_init_page(bpage);
4386
4387 return bpage;
4388}
4389EXPORT_SYMBOL_GPL(ring_buffer_alloc_read_page);
4390
4391/**
4392 * ring_buffer_free_read_page - free an allocated read page
4393 * @buffer: the buffer the page was allocate for
4394 * @data: the page to free
4395 *
4396 * Free a page allocated from ring_buffer_alloc_read_page.
4397 */
4398void ring_buffer_free_read_page(struct ring_buffer *buffer, void *data)
4399{
4400 free_page((unsigned long)data);
4401}
4402EXPORT_SYMBOL_GPL(ring_buffer_free_read_page);
4403
4404/**
4405 * ring_buffer_read_page - extract a page from the ring buffer
4406 * @buffer: buffer to extract from
4407 * @data_page: the page to use allocated from ring_buffer_alloc_read_page
4408 * @len: amount to extract
4409 * @cpu: the cpu of the buffer to extract
4410 * @full: should the extraction only happen when the page is full.
4411 *
4412 * This function will pull out a page from the ring buffer and consume it.
4413 * @data_page must be the address of the variable that was returned
4414 * from ring_buffer_alloc_read_page. This is because the page might be used
4415 * to swap with a page in the ring buffer.
4416 *
4417 * for example:
4418 * rpage = ring_buffer_alloc_read_page(buffer, cpu);
4419 * if (!rpage)
4420 * return error;
4421 * ret = ring_buffer_read_page(buffer, &rpage, len, cpu, 0);
4422 * if (ret >= 0)
4423 * process_page(rpage, ret);
4424 *
4425 * When @full is set, the function will not return true unless
4426 * the writer is off the reader page.
4427 *
4428 * Note: it is up to the calling functions to handle sleeps and wakeups.
4429 * The ring buffer can be used anywhere in the kernel and can not
4430 * blindly call wake_up. The layer that uses the ring buffer must be
4431 * responsible for that.
4432 *
4433 * Returns:
4434 * >=0 if data has been transferred, returns the offset of consumed data.
4435 * <0 if no data has been transferred.
4436 */
4437int ring_buffer_read_page(struct ring_buffer *buffer,
4438 void **data_page, size_t len, int cpu, int full)
4439{
4440 struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
4441 struct ring_buffer_event *event;
4442 struct buffer_data_page *bpage;
4443 struct buffer_page *reader;
4444 unsigned long missed_events;
4445 unsigned long flags;
4446 unsigned int commit;
4447 unsigned int read;
4448 u64 save_timestamp;
4449 int ret = -1;
4450
4451 if (!cpumask_test_cpu(cpu, buffer->cpumask))
4452 goto out;
4453
4454 /*
4455 * If len is not big enough to hold the page header, then
4456 * we can not copy anything.
4457 */
4458 if (len <= BUF_PAGE_HDR_SIZE)
4459 goto out;
4460
4461 len -= BUF_PAGE_HDR_SIZE;
4462
4463 if (!data_page)
4464 goto out;
4465
4466 bpage = *data_page;
4467 if (!bpage)
4468 goto out;
4469
4470 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
4471
4472 reader = rb_get_reader_page(cpu_buffer);
4473 if (!reader)
4474 goto out_unlock;
4475
4476 event = rb_reader_event(cpu_buffer);
4477
4478 read = reader->read;
4479 commit = rb_page_commit(reader);
4480
4481 /* Check if any events were dropped */
4482 missed_events = cpu_buffer->lost_events;
4483
4484 /*
4485 * If this page has been partially read or
4486 * if len is not big enough to read the rest of the page or
4487 * a writer is still on the page, then
4488 * we must copy the data from the page to the buffer.
4489 * Otherwise, we can simply swap the page with the one passed in.
4490 */
4491 if (read || (len < (commit - read)) ||
4492 cpu_buffer->reader_page == cpu_buffer->commit_page) {
4493 struct buffer_data_page *rpage = cpu_buffer->reader_page->page;
4494 unsigned int rpos = read;
4495 unsigned int pos = 0;
4496 unsigned int size;
4497
4498 if (full)
4499 goto out_unlock;
4500
4501 if (len > (commit - read))
4502 len = (commit - read);
4503
4504 /* Always keep the time extend and data together */
4505 size = rb_event_ts_length(event);
4506
4507 if (len < size)
4508 goto out_unlock;
4509
4510 /* save the current timestamp, since the user will need it */
4511 save_timestamp = cpu_buffer->read_stamp;
4512
4513 /* Need to copy one event at a time */
4514 do {
4515 /* We need the size of one event, because
4516 * rb_advance_reader only advances by one event,
4517 * whereas rb_event_ts_length may include the size of
4518 * one or two events.
4519 * We have already ensured there's enough space if this
4520 * is a time extend. */
4521 size = rb_event_length(event);
4522 memcpy(bpage->data + pos, rpage->data + rpos, size);
4523
4524 len -= size;
4525
4526 rb_advance_reader(cpu_buffer);
4527 rpos = reader->read;
4528 pos += size;
4529
4530 if (rpos >= commit)
4531 break;
4532
4533 event = rb_reader_event(cpu_buffer);
4534 /* Always keep the time extend and data together */
4535 size = rb_event_ts_length(event);
4536 } while (len >= size);
4537
4538 /* update bpage */
4539 local_set(&bpage->commit, pos);
4540 bpage->time_stamp = save_timestamp;
4541
4542 /* we copied everything to the beginning */
4543 read = 0;
4544 } else {
4545 /* update the entry counter */
4546 cpu_buffer->read += rb_page_entries(reader);
4547 cpu_buffer->read_bytes += BUF_PAGE_SIZE;
4548
4549 /* swap the pages */
4550 rb_init_page(bpage);
4551 bpage = reader->page;
4552 reader->page = *data_page;
4553 local_set(&reader->write, 0);
4554 local_set(&reader->entries, 0);
4555 reader->read = 0;
4556 *data_page = bpage;
4557
4558 /*
4559 * Use the real_end for the data size,
4560 * This gives us a chance to store the lost events
4561 * on the page.
4562 */
4563 if (reader->real_end)
4564 local_set(&bpage->commit, reader->real_end);
4565 }
4566 ret = read;
4567
4568 cpu_buffer->lost_events = 0;
4569
4570 commit = local_read(&bpage->commit);
4571 /*
4572 * Set a flag in the commit field if we lost events
4573 */
4574 if (missed_events) {
4575 /* If there is room at the end of the page to save the
4576 * missed events, then record it there.
4577 */
4578 if (BUF_PAGE_SIZE - commit >= sizeof(missed_events)) {
4579 memcpy(&bpage->data[commit], &missed_events,
4580 sizeof(missed_events));
4581 local_add(RB_MISSED_STORED, &bpage->commit);
4582 commit += sizeof(missed_events);
4583 }
4584 local_add(RB_MISSED_EVENTS, &bpage->commit);
4585 }
4586
4587 /*
4588 * This page may be off to user land. Zero it out here.
4589 */
4590 if (commit < BUF_PAGE_SIZE)
4591 memset(&bpage->data[commit], 0, BUF_PAGE_SIZE - commit);
4592
4593 out_unlock:
4594 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
4595
4596 out:
4597 return ret;
4598}
4599EXPORT_SYMBOL_GPL(ring_buffer_read_page);
4600
4601#ifdef CONFIG_HOTPLUG_CPU
4602static int rb_cpu_notify(struct notifier_block *self,
4603 unsigned long action, void *hcpu)
4604{
4605 struct ring_buffer *buffer =
4606 container_of(self, struct ring_buffer, cpu_notify);
4607 long cpu = (long)hcpu;
4608 int cpu_i, nr_pages_same;
4609 unsigned int nr_pages;
4610
4611 switch (action) {
4612 case CPU_UP_PREPARE:
4613 case CPU_UP_PREPARE_FROZEN:
4614 if (cpumask_test_cpu(cpu, buffer->cpumask))
4615 return NOTIFY_OK;
4616
4617 nr_pages = 0;
4618 nr_pages_same = 1;
4619 /* check if all cpu sizes are same */
4620 for_each_buffer_cpu(buffer, cpu_i) {
4621 /* fill in the size from first enabled cpu */
4622 if (nr_pages == 0)
4623 nr_pages = buffer->buffers[cpu_i]->nr_pages;
4624 if (nr_pages != buffer->buffers[cpu_i]->nr_pages) {
4625 nr_pages_same = 0;
4626 break;
4627 }
4628 }
4629 /* allocate minimum pages, user can later expand it */
4630 if (!nr_pages_same)
4631 nr_pages = 2;
4632 buffer->buffers[cpu] =
4633 rb_allocate_cpu_buffer(buffer, nr_pages, cpu);
4634 if (!buffer->buffers[cpu]) {
4635 WARN(1, "failed to allocate ring buffer on CPU %ld\n",
4636 cpu);
4637 return NOTIFY_OK;
4638 }
4639 smp_wmb();
4640 cpumask_set_cpu(cpu, buffer->cpumask);
4641 break;
4642 case CPU_DOWN_PREPARE:
4643 case CPU_DOWN_PREPARE_FROZEN:
4644 /*
4645 * Do nothing.
4646 * If we were to free the buffer, then the user would
4647 * lose any trace that was in the buffer.
4648 */
4649 break;
4650 default:
4651 break;
4652 }
4653 return NOTIFY_OK;
4654}
4655#endif
4656
4657#ifdef CONFIG_RING_BUFFER_STARTUP_TEST
4658/*
4659 * This is a basic integrity check of the ring buffer.
4660 * Late in the boot cycle this test will run when configured in.
4661 * It will kick off a thread per CPU that will go into a loop
4662 * writing to the per cpu ring buffer various sizes of data.
4663 * Some of the data will be large items, some small.
4664 *
4665 * Another thread is created that goes into a spin, sending out
4666 * IPIs to the other CPUs to also write into the ring buffer.
4667 * this is to test the nesting ability of the buffer.
4668 *
4669 * Basic stats are recorded and reported. If something in the
4670 * ring buffer should happen that's not expected, a big warning
4671 * is displayed and all ring buffers are disabled.
4672 */
4673static struct task_struct *rb_threads[NR_CPUS] __initdata;
4674
4675struct rb_test_data {
4676 struct ring_buffer *buffer;
4677 unsigned long events;
4678 unsigned long bytes_written;
4679 unsigned long bytes_alloc;
4680 unsigned long bytes_dropped;
4681 unsigned long events_nested;
4682 unsigned long bytes_written_nested;
4683 unsigned long bytes_alloc_nested;
4684 unsigned long bytes_dropped_nested;
4685 int min_size_nested;
4686 int max_size_nested;
4687 int max_size;
4688 int min_size;
4689 int cpu;
4690 int cnt;
4691};
4692
4693static struct rb_test_data rb_data[NR_CPUS] __initdata;
4694
4695/* 1 meg per cpu */
4696#define RB_TEST_BUFFER_SIZE 1048576
4697
4698static char rb_string[] __initdata =
4699 "abcdefghijklmnopqrstuvwxyz1234567890!@#$%^&*()?+\\"
4700 "?+|:';\",.<>/?abcdefghijklmnopqrstuvwxyz1234567890"
4701 "!@#$%^&*()?+\\?+|:';\",.<>/?abcdefghijklmnopqrstuv";
4702
4703static bool rb_test_started __initdata;
4704
4705struct rb_item {
4706 int size;
4707 char str[];
4708};
4709
4710static __init int rb_write_something(struct rb_test_data *data, bool nested)
4711{
4712 struct ring_buffer_event *event;
4713 struct rb_item *item;
4714 bool started;
4715 int event_len;
4716 int size;
4717 int len;
4718 int cnt;
4719
4720 /* Have nested writes different that what is written */
4721 cnt = data->cnt + (nested ? 27 : 0);
4722
4723 /* Multiply cnt by ~e, to make some unique increment */
4724 size = (data->cnt * 68 / 25) % (sizeof(rb_string) - 1);
4725
4726 len = size + sizeof(struct rb_item);
4727
4728 started = rb_test_started;
4729 /* read rb_test_started before checking buffer enabled */
4730 smp_rmb();
4731
4732 event = ring_buffer_lock_reserve(data->buffer, len);
4733 if (!event) {
4734 /* Ignore dropped events before test starts. */
4735 if (started) {
4736 if (nested)
4737 data->bytes_dropped += len;
4738 else
4739 data->bytes_dropped_nested += len;
4740 }
4741 return len;
4742 }
4743
4744 event_len = ring_buffer_event_length(event);
4745
4746 if (RB_WARN_ON(data->buffer, event_len < len))
4747 goto out;
4748
4749 item = ring_buffer_event_data(event);
4750 item->size = size;
4751 memcpy(item->str, rb_string, size);
4752
4753 if (nested) {
4754 data->bytes_alloc_nested += event_len;
4755 data->bytes_written_nested += len;
4756 data->events_nested++;
4757 if (!data->min_size_nested || len < data->min_size_nested)
4758 data->min_size_nested = len;
4759 if (len > data->max_size_nested)
4760 data->max_size_nested = len;
4761 } else {
4762 data->bytes_alloc += event_len;
4763 data->bytes_written += len;
4764 data->events++;
4765 if (!data->min_size || len < data->min_size)
4766 data->max_size = len;
4767 if (len > data->max_size)
4768 data->max_size = len;
4769 }
4770
4771 out:
4772 ring_buffer_unlock_commit(data->buffer, event);
4773
4774 return 0;
4775}
4776
4777static __init int rb_test(void *arg)
4778{
4779 struct rb_test_data *data = arg;
4780
4781 while (!kthread_should_stop()) {
4782 rb_write_something(data, false);
4783 data->cnt++;
4784
4785 set_current_state(TASK_INTERRUPTIBLE);
4786 /* Now sleep between a min of 100-300us and a max of 1ms */
4787 usleep_range(((data->cnt % 3) + 1) * 100, 1000);
4788 }
4789
4790 return 0;
4791}
4792
4793static __init void rb_ipi(void *ignore)
4794{
4795 struct rb_test_data *data;
4796 int cpu = smp_processor_id();
4797
4798 data = &rb_data[cpu];
4799 rb_write_something(data, true);
4800}
4801
4802static __init int rb_hammer_test(void *arg)
4803{
4804 while (!kthread_should_stop()) {
4805
4806 /* Send an IPI to all cpus to write data! */
4807 smp_call_function(rb_ipi, NULL, 1);
4808 /* No sleep, but for non preempt, let others run */
4809 schedule();
4810 }
4811
4812 return 0;
4813}
4814
4815static __init int test_ringbuffer(void)
4816{
4817 struct task_struct *rb_hammer;
4818 struct ring_buffer *buffer;
4819 int cpu;
4820 int ret = 0;
4821
4822 pr_info("Running ring buffer tests...\n");
4823
4824 buffer = ring_buffer_alloc(RB_TEST_BUFFER_SIZE, RB_FL_OVERWRITE);
4825 if (WARN_ON(!buffer))
4826 return 0;
4827
4828 /* Disable buffer so that threads can't write to it yet */
4829 ring_buffer_record_off(buffer);
4830
4831 for_each_online_cpu(cpu) {
4832 rb_data[cpu].buffer = buffer;
4833 rb_data[cpu].cpu = cpu;
4834 rb_data[cpu].cnt = cpu;
4835 rb_threads[cpu] = kthread_create(rb_test, &rb_data[cpu],
4836 "rbtester/%d", cpu);
4837 if (WARN_ON(!rb_threads[cpu])) {
4838 pr_cont("FAILED\n");
4839 ret = -1;
4840 goto out_free;
4841 }
4842
4843 kthread_bind(rb_threads[cpu], cpu);
4844 wake_up_process(rb_threads[cpu]);
4845 }
4846
4847 /* Now create the rb hammer! */
4848 rb_hammer = kthread_run(rb_hammer_test, NULL, "rbhammer");
4849 if (WARN_ON(!rb_hammer)) {
4850 pr_cont("FAILED\n");
4851 ret = -1;
4852 goto out_free;
4853 }
4854
4855 ring_buffer_record_on(buffer);
4856 /*
4857 * Show buffer is enabled before setting rb_test_started.
4858 * Yes there's a small race window where events could be
4859 * dropped and the thread wont catch it. But when a ring
4860 * buffer gets enabled, there will always be some kind of
4861 * delay before other CPUs see it. Thus, we don't care about
4862 * those dropped events. We care about events dropped after
4863 * the threads see that the buffer is active.
4864 */
4865 smp_wmb();
4866 rb_test_started = true;
4867
4868 set_current_state(TASK_INTERRUPTIBLE);
4869 /* Just run for 10 seconds */;
4870 schedule_timeout(10 * HZ);
4871
4872 kthread_stop(rb_hammer);
4873
4874 out_free:
4875 for_each_online_cpu(cpu) {
4876 if (!rb_threads[cpu])
4877 break;
4878 kthread_stop(rb_threads[cpu]);
4879 }
4880 if (ret) {
4881 ring_buffer_free(buffer);
4882 return ret;
4883 }
4884
4885 /* Report! */
4886 pr_info("finished\n");
4887 for_each_online_cpu(cpu) {
4888 struct ring_buffer_event *event;
4889 struct rb_test_data *data = &rb_data[cpu];
4890 struct rb_item *item;
4891 unsigned long total_events;
4892 unsigned long total_dropped;
4893 unsigned long total_written;
4894 unsigned long total_alloc;
4895 unsigned long total_read = 0;
4896 unsigned long total_size = 0;
4897 unsigned long total_len = 0;
4898 unsigned long total_lost = 0;
4899 unsigned long lost;
4900 int big_event_size;
4901 int small_event_size;
4902
4903 ret = -1;
4904
4905 total_events = data->events + data->events_nested;
4906 total_written = data->bytes_written + data->bytes_written_nested;
4907 total_alloc = data->bytes_alloc + data->bytes_alloc_nested;
4908 total_dropped = data->bytes_dropped + data->bytes_dropped_nested;
4909
4910 big_event_size = data->max_size + data->max_size_nested;
4911 small_event_size = data->min_size + data->min_size_nested;
4912
4913 pr_info("CPU %d:\n", cpu);
4914 pr_info(" events: %ld\n", total_events);
4915 pr_info(" dropped bytes: %ld\n", total_dropped);
4916 pr_info(" alloced bytes: %ld\n", total_alloc);
4917 pr_info(" written bytes: %ld\n", total_written);
4918 pr_info(" biggest event: %d\n", big_event_size);
4919 pr_info(" smallest event: %d\n", small_event_size);
4920
4921 if (RB_WARN_ON(buffer, total_dropped))
4922 break;
4923
4924 ret = 0;
4925
4926 while ((event = ring_buffer_consume(buffer, cpu, NULL, &lost))) {
4927 total_lost += lost;
4928 item = ring_buffer_event_data(event);
4929 total_len += ring_buffer_event_length(event);
4930 total_size += item->size + sizeof(struct rb_item);
4931 if (memcmp(&item->str[0], rb_string, item->size) != 0) {
4932 pr_info("FAILED!\n");
4933 pr_info("buffer had: %.*s\n", item->size, item->str);
4934 pr_info("expected: %.*s\n", item->size, rb_string);
4935 RB_WARN_ON(buffer, 1);
4936 ret = -1;
4937 break;
4938 }
4939 total_read++;
4940 }
4941 if (ret)
4942 break;
4943
4944 ret = -1;
4945
4946 pr_info(" read events: %ld\n", total_read);
4947 pr_info(" lost events: %ld\n", total_lost);
4948 pr_info(" total events: %ld\n", total_lost + total_read);
4949 pr_info(" recorded len bytes: %ld\n", total_len);
4950 pr_info(" recorded size bytes: %ld\n", total_size);
4951 if (total_lost)
4952 pr_info(" With dropped events, record len and size may not match\n"
4953 " alloced and written from above\n");
4954 if (!total_lost) {
4955 if (RB_WARN_ON(buffer, total_len != total_alloc ||
4956 total_size != total_written))
4957 break;
4958 }
4959 if (RB_WARN_ON(buffer, total_lost + total_read != total_events))
4960 break;
4961
4962 ret = 0;
4963 }
4964 if (!ret)
4965 pr_info("Ring buffer PASSED!\n");
4966
4967 ring_buffer_free(buffer);
4968 return 0;
4969}
4970
4971late_initcall(test_ringbuffer);
4972#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
26/*
27 * The ring buffer header is special. We must manually up keep it.
28 */
29int ring_buffer_print_entry_header(struct trace_seq *s)
30{
31 int ret;
32
33 ret = trace_seq_printf(s, "# compressed entry header\n");
34 ret = trace_seq_printf(s, "\ttype_len : 5 bits\n");
35 ret = trace_seq_printf(s, "\ttime_delta : 27 bits\n");
36 ret = trace_seq_printf(s, "\tarray : 32 bits\n");
37 ret = trace_seq_printf(s, "\n");
38 ret = trace_seq_printf(s, "\tpadding : type == %d\n",
39 RINGBUF_TYPE_PADDING);
40 ret = trace_seq_printf(s, "\ttime_extend : type == %d\n",
41 RINGBUF_TYPE_TIME_EXTEND);
42 ret = trace_seq_printf(s, "\tdata max type_len == %d\n",
43 RINGBUF_TYPE_DATA_TYPE_LEN_MAX);
44
45 return ret;
46}
47
48/*
49 * The ring buffer is made up of a list of pages. A separate list of pages is
50 * allocated for each CPU. A writer may only write to a buffer that is
51 * associated with the CPU it is currently executing on. A reader may read
52 * from any per cpu buffer.
53 *
54 * The reader is special. For each per cpu buffer, the reader has its own
55 * reader page. When a reader has read the entire reader page, this reader
56 * page is swapped with another page in the ring buffer.
57 *
58 * Now, as long as the writer is off the reader page, the reader can do what
59 * ever it wants with that page. The writer will never write to that page
60 * again (as long as it is out of the ring buffer).
61 *
62 * Here's some silly ASCII art.
63 *
64 * +------+
65 * |reader| RING BUFFER
66 * |page |
67 * +------+ +---+ +---+ +---+
68 * | |-->| |-->| |
69 * +---+ +---+ +---+
70 * ^ |
71 * | |
72 * +---------------+
73 *
74 *
75 * +------+
76 * |reader| RING BUFFER
77 * |page |------------------v
78 * +------+ +---+ +---+ +---+
79 * | |-->| |-->| |
80 * +---+ +---+ +---+
81 * ^ |
82 * | |
83 * +---------------+
84 *
85 *
86 * +------+
87 * |reader| RING BUFFER
88 * |page |------------------v
89 * +------+ +---+ +---+ +---+
90 * ^ | |-->| |-->| |
91 * | +---+ +---+ +---+
92 * | |
93 * | |
94 * +------------------------------+
95 *
96 *
97 * +------+
98 * |buffer| RING BUFFER
99 * |page |------------------v
100 * +------+ +---+ +---+ +---+
101 * ^ | | | |-->| |
102 * | New +---+ +---+ +---+
103 * | Reader------^ |
104 * | page |
105 * +------------------------------+
106 *
107 *
108 * After we make this swap, the reader can hand this page off to the splice
109 * code and be done with it. It can even allocate a new page if it needs to
110 * and swap that into the ring buffer.
111 *
112 * We will be using cmpxchg soon to make all this lockless.
113 *
114 */
115
116/*
117 * A fast way to enable or disable all ring buffers is to
118 * call tracing_on or tracing_off. Turning off the ring buffers
119 * prevents all ring buffers from being recorded to.
120 * Turning this switch on, makes it OK to write to the
121 * ring buffer, if the ring buffer is enabled itself.
122 *
123 * There's three layers that must be on in order to write
124 * to the ring buffer.
125 *
126 * 1) This global flag must be set.
127 * 2) The ring buffer must be enabled for recording.
128 * 3) The per cpu buffer must be enabled for recording.
129 *
130 * In case of an anomaly, this global flag has a bit set that
131 * will permantly disable all ring buffers.
132 */
133
134/*
135 * Global flag to disable all recording to ring buffers
136 * This has two bits: ON, DISABLED
137 *
138 * ON DISABLED
139 * ---- ----------
140 * 0 0 : ring buffers are off
141 * 1 0 : ring buffers are on
142 * X 1 : ring buffers are permanently disabled
143 */
144
145enum {
146 RB_BUFFERS_ON_BIT = 0,
147 RB_BUFFERS_DISABLED_BIT = 1,
148};
149
150enum {
151 RB_BUFFERS_ON = 1 << RB_BUFFERS_ON_BIT,
152 RB_BUFFERS_DISABLED = 1 << RB_BUFFERS_DISABLED_BIT,
153};
154
155static unsigned long ring_buffer_flags __read_mostly = RB_BUFFERS_ON;
156
157#define BUF_PAGE_HDR_SIZE offsetof(struct buffer_data_page, data)
158
159/**
160 * tracing_on - enable all tracing buffers
161 *
162 * This function enables all tracing buffers that may have been
163 * disabled with tracing_off.
164 */
165void tracing_on(void)
166{
167 set_bit(RB_BUFFERS_ON_BIT, &ring_buffer_flags);
168}
169EXPORT_SYMBOL_GPL(tracing_on);
170
171/**
172 * tracing_off - turn off all tracing buffers
173 *
174 * This function stops all tracing buffers from recording data.
175 * It does not disable any overhead the tracers themselves may
176 * be causing. This function simply causes all recording to
177 * the ring buffers to fail.
178 */
179void tracing_off(void)
180{
181 clear_bit(RB_BUFFERS_ON_BIT, &ring_buffer_flags);
182}
183EXPORT_SYMBOL_GPL(tracing_off);
184
185/**
186 * tracing_off_permanent - permanently disable ring buffers
187 *
188 * This function, once called, will disable all ring buffers
189 * permanently.
190 */
191void tracing_off_permanent(void)
192{
193 set_bit(RB_BUFFERS_DISABLED_BIT, &ring_buffer_flags);
194}
195
196/**
197 * tracing_is_on - show state of ring buffers enabled
198 */
199int tracing_is_on(void)
200{
201 return ring_buffer_flags == RB_BUFFERS_ON;
202}
203EXPORT_SYMBOL_GPL(tracing_is_on);
204
205#define RB_EVNT_HDR_SIZE (offsetof(struct ring_buffer_event, array))
206#define RB_ALIGNMENT 4U
207#define RB_MAX_SMALL_DATA (RB_ALIGNMENT * RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
208#define RB_EVNT_MIN_SIZE 8U /* two 32bit words */
209
210#if !defined(CONFIG_64BIT) || defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
211# define RB_FORCE_8BYTE_ALIGNMENT 0
212# define RB_ARCH_ALIGNMENT RB_ALIGNMENT
213#else
214# define RB_FORCE_8BYTE_ALIGNMENT 1
215# define RB_ARCH_ALIGNMENT 8U
216#endif
217
218/* define RINGBUF_TYPE_DATA for 'case RINGBUF_TYPE_DATA:' */
219#define RINGBUF_TYPE_DATA 0 ... RINGBUF_TYPE_DATA_TYPE_LEN_MAX
220
221enum {
222 RB_LEN_TIME_EXTEND = 8,
223 RB_LEN_TIME_STAMP = 16,
224};
225
226#define skip_time_extend(event) \
227 ((struct ring_buffer_event *)((char *)event + RB_LEN_TIME_EXTEND))
228
229static inline int rb_null_event(struct ring_buffer_event *event)
230{
231 return event->type_len == RINGBUF_TYPE_PADDING && !event->time_delta;
232}
233
234static void rb_event_set_padding(struct ring_buffer_event *event)
235{
236 /* padding has a NULL time_delta */
237 event->type_len = RINGBUF_TYPE_PADDING;
238 event->time_delta = 0;
239}
240
241static unsigned
242rb_event_data_length(struct ring_buffer_event *event)
243{
244 unsigned length;
245
246 if (event->type_len)
247 length = event->type_len * RB_ALIGNMENT;
248 else
249 length = event->array[0];
250 return length + RB_EVNT_HDR_SIZE;
251}
252
253/*
254 * Return the length of the given event. Will return
255 * the length of the time extend if the event is a
256 * time extend.
257 */
258static inline unsigned
259rb_event_length(struct ring_buffer_event *event)
260{
261 switch (event->type_len) {
262 case RINGBUF_TYPE_PADDING:
263 if (rb_null_event(event))
264 /* undefined */
265 return -1;
266 return event->array[0] + RB_EVNT_HDR_SIZE;
267
268 case RINGBUF_TYPE_TIME_EXTEND:
269 return RB_LEN_TIME_EXTEND;
270
271 case RINGBUF_TYPE_TIME_STAMP:
272 return RB_LEN_TIME_STAMP;
273
274 case RINGBUF_TYPE_DATA:
275 return rb_event_data_length(event);
276 default:
277 BUG();
278 }
279 /* not hit */
280 return 0;
281}
282
283/*
284 * Return total length of time extend and data,
285 * or just the event length for all other events.
286 */
287static inline unsigned
288rb_event_ts_length(struct ring_buffer_event *event)
289{
290 unsigned len = 0;
291
292 if (event->type_len == RINGBUF_TYPE_TIME_EXTEND) {
293 /* time extends include the data event after it */
294 len = RB_LEN_TIME_EXTEND;
295 event = skip_time_extend(event);
296 }
297 return len + rb_event_length(event);
298}
299
300/**
301 * ring_buffer_event_length - return the length of the event
302 * @event: the event to get the length of
303 *
304 * Returns the size of the data load of a data event.
305 * If the event is something other than a data event, it
306 * returns the size of the event itself. With the exception
307 * of a TIME EXTEND, where it still returns the size of the
308 * data load of the data event after it.
309 */
310unsigned ring_buffer_event_length(struct ring_buffer_event *event)
311{
312 unsigned length;
313
314 if (event->type_len == RINGBUF_TYPE_TIME_EXTEND)
315 event = skip_time_extend(event);
316
317 length = rb_event_length(event);
318 if (event->type_len > RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
319 return length;
320 length -= RB_EVNT_HDR_SIZE;
321 if (length > RB_MAX_SMALL_DATA + sizeof(event->array[0]))
322 length -= sizeof(event->array[0]);
323 return length;
324}
325EXPORT_SYMBOL_GPL(ring_buffer_event_length);
326
327/* inline for ring buffer fast paths */
328static void *
329rb_event_data(struct ring_buffer_event *event)
330{
331 if (event->type_len == RINGBUF_TYPE_TIME_EXTEND)
332 event = skip_time_extend(event);
333 BUG_ON(event->type_len > RINGBUF_TYPE_DATA_TYPE_LEN_MAX);
334 /* If length is in len field, then array[0] has the data */
335 if (event->type_len)
336 return (void *)&event->array[0];
337 /* Otherwise length is in array[0] and array[1] has the data */
338 return (void *)&event->array[1];
339}
340
341/**
342 * ring_buffer_event_data - return the data of the event
343 * @event: the event to get the data from
344 */
345void *ring_buffer_event_data(struct ring_buffer_event *event)
346{
347 return rb_event_data(event);
348}
349EXPORT_SYMBOL_GPL(ring_buffer_event_data);
350
351#define for_each_buffer_cpu(buffer, cpu) \
352 for_each_cpu(cpu, buffer->cpumask)
353
354#define TS_SHIFT 27
355#define TS_MASK ((1ULL << TS_SHIFT) - 1)
356#define TS_DELTA_TEST (~TS_MASK)
357
358/* Flag when events were overwritten */
359#define RB_MISSED_EVENTS (1 << 31)
360/* Missed count stored at end */
361#define RB_MISSED_STORED (1 << 30)
362
363struct buffer_data_page {
364 u64 time_stamp; /* page time stamp */
365 local_t commit; /* write committed index */
366 unsigned char data[]; /* data of buffer page */
367};
368
369/*
370 * Note, the buffer_page list must be first. The buffer pages
371 * are allocated in cache lines, which means that each buffer
372 * page will be at the beginning of a cache line, and thus
373 * the least significant bits will be zero. We use this to
374 * add flags in the list struct pointers, to make the ring buffer
375 * lockless.
376 */
377struct buffer_page {
378 struct list_head list; /* list of buffer pages */
379 local_t write; /* index for next write */
380 unsigned read; /* index for next read */
381 local_t entries; /* entries on this page */
382 unsigned long real_end; /* real end of data */
383 struct buffer_data_page *page; /* Actual data page */
384};
385
386/*
387 * The buffer page counters, write and entries, must be reset
388 * atomically when crossing page boundaries. To synchronize this
389 * update, two counters are inserted into the number. One is
390 * the actual counter for the write position or count on the page.
391 *
392 * The other is a counter of updaters. Before an update happens
393 * the update partition of the counter is incremented. This will
394 * allow the updater to update the counter atomically.
395 *
396 * The counter is 20 bits, and the state data is 12.
397 */
398#define RB_WRITE_MASK 0xfffff
399#define RB_WRITE_INTCNT (1 << 20)
400
401static void rb_init_page(struct buffer_data_page *bpage)
402{
403 local_set(&bpage->commit, 0);
404}
405
406/**
407 * ring_buffer_page_len - the size of data on the page.
408 * @page: The page to read
409 *
410 * Returns the amount of data on the page, including buffer page header.
411 */
412size_t ring_buffer_page_len(void *page)
413{
414 return local_read(&((struct buffer_data_page *)page)->commit)
415 + BUF_PAGE_HDR_SIZE;
416}
417
418/*
419 * Also stolen from mm/slob.c. Thanks to Mathieu Desnoyers for pointing
420 * this issue out.
421 */
422static void free_buffer_page(struct buffer_page *bpage)
423{
424 free_page((unsigned long)bpage->page);
425 kfree(bpage);
426}
427
428/*
429 * We need to fit the time_stamp delta into 27 bits.
430 */
431static inline int test_time_stamp(u64 delta)
432{
433 if (delta & TS_DELTA_TEST)
434 return 1;
435 return 0;
436}
437
438#define BUF_PAGE_SIZE (PAGE_SIZE - BUF_PAGE_HDR_SIZE)
439
440/* Max payload is BUF_PAGE_SIZE - header (8bytes) */
441#define BUF_MAX_DATA_SIZE (BUF_PAGE_SIZE - (sizeof(u32) * 2))
442
443int ring_buffer_print_page_header(struct trace_seq *s)
444{
445 struct buffer_data_page field;
446 int ret;
447
448 ret = trace_seq_printf(s, "\tfield: u64 timestamp;\t"
449 "offset:0;\tsize:%u;\tsigned:%u;\n",
450 (unsigned int)sizeof(field.time_stamp),
451 (unsigned int)is_signed_type(u64));
452
453 ret = trace_seq_printf(s, "\tfield: local_t commit;\t"
454 "offset:%u;\tsize:%u;\tsigned:%u;\n",
455 (unsigned int)offsetof(typeof(field), commit),
456 (unsigned int)sizeof(field.commit),
457 (unsigned int)is_signed_type(long));
458
459 ret = trace_seq_printf(s, "\tfield: int overwrite;\t"
460 "offset:%u;\tsize:%u;\tsigned:%u;\n",
461 (unsigned int)offsetof(typeof(field), commit),
462 1,
463 (unsigned int)is_signed_type(long));
464
465 ret = trace_seq_printf(s, "\tfield: char data;\t"
466 "offset:%u;\tsize:%u;\tsigned:%u;\n",
467 (unsigned int)offsetof(typeof(field), data),
468 (unsigned int)BUF_PAGE_SIZE,
469 (unsigned int)is_signed_type(char));
470
471 return ret;
472}
473
474/*
475 * head_page == tail_page && head == tail then buffer is empty.
476 */
477struct ring_buffer_per_cpu {
478 int cpu;
479 atomic_t record_disabled;
480 struct ring_buffer *buffer;
481 spinlock_t reader_lock; /* serialize readers */
482 arch_spinlock_t lock;
483 struct lock_class_key lock_key;
484 struct list_head *pages;
485 struct buffer_page *head_page; /* read from head */
486 struct buffer_page *tail_page; /* write to tail */
487 struct buffer_page *commit_page; /* committed pages */
488 struct buffer_page *reader_page;
489 unsigned long lost_events;
490 unsigned long last_overrun;
491 local_t commit_overrun;
492 local_t overrun;
493 local_t entries;
494 local_t committing;
495 local_t commits;
496 unsigned long read;
497 u64 write_stamp;
498 u64 read_stamp;
499};
500
501struct ring_buffer {
502 unsigned pages;
503 unsigned flags;
504 int cpus;
505 atomic_t record_disabled;
506 cpumask_var_t cpumask;
507
508 struct lock_class_key *reader_lock_key;
509
510 struct mutex mutex;
511
512 struct ring_buffer_per_cpu **buffers;
513
514#ifdef CONFIG_HOTPLUG_CPU
515 struct notifier_block cpu_notify;
516#endif
517 u64 (*clock)(void);
518};
519
520struct ring_buffer_iter {
521 struct ring_buffer_per_cpu *cpu_buffer;
522 unsigned long head;
523 struct buffer_page *head_page;
524 struct buffer_page *cache_reader_page;
525 unsigned long cache_read;
526 u64 read_stamp;
527};
528
529/* buffer may be either ring_buffer or ring_buffer_per_cpu */
530#define RB_WARN_ON(b, cond) \
531 ({ \
532 int _____ret = unlikely(cond); \
533 if (_____ret) { \
534 if (__same_type(*(b), struct ring_buffer_per_cpu)) { \
535 struct ring_buffer_per_cpu *__b = \
536 (void *)b; \
537 atomic_inc(&__b->buffer->record_disabled); \
538 } else \
539 atomic_inc(&b->record_disabled); \
540 WARN_ON(1); \
541 } \
542 _____ret; \
543 })
544
545/* Up this if you want to test the TIME_EXTENTS and normalization */
546#define DEBUG_SHIFT 0
547
548static inline u64 rb_time_stamp(struct ring_buffer *buffer)
549{
550 /* shift to debug/test normalization and TIME_EXTENTS */
551 return buffer->clock() << DEBUG_SHIFT;
552}
553
554u64 ring_buffer_time_stamp(struct ring_buffer *buffer, int cpu)
555{
556 u64 time;
557
558 preempt_disable_notrace();
559 time = rb_time_stamp(buffer);
560 preempt_enable_no_resched_notrace();
561
562 return time;
563}
564EXPORT_SYMBOL_GPL(ring_buffer_time_stamp);
565
566void ring_buffer_normalize_time_stamp(struct ring_buffer *buffer,
567 int cpu, u64 *ts)
568{
569 /* Just stupid testing the normalize function and deltas */
570 *ts >>= DEBUG_SHIFT;
571}
572EXPORT_SYMBOL_GPL(ring_buffer_normalize_time_stamp);
573
574/*
575 * Making the ring buffer lockless makes things tricky.
576 * Although writes only happen on the CPU that they are on,
577 * and they only need to worry about interrupts. Reads can
578 * happen on any CPU.
579 *
580 * The reader page is always off the ring buffer, but when the
581 * reader finishes with a page, it needs to swap its page with
582 * a new one from the buffer. The reader needs to take from
583 * the head (writes go to the tail). But if a writer is in overwrite
584 * mode and wraps, it must push the head page forward.
585 *
586 * Here lies the problem.
587 *
588 * The reader must be careful to replace only the head page, and
589 * not another one. As described at the top of the file in the
590 * ASCII art, the reader sets its old page to point to the next
591 * page after head. It then sets the page after head to point to
592 * the old reader page. But if the writer moves the head page
593 * during this operation, the reader could end up with the tail.
594 *
595 * We use cmpxchg to help prevent this race. We also do something
596 * special with the page before head. We set the LSB to 1.
597 *
598 * When the writer must push the page forward, it will clear the
599 * bit that points to the head page, move the head, and then set
600 * the bit that points to the new head page.
601 *
602 * We also don't want an interrupt coming in and moving the head
603 * page on another writer. Thus we use the second LSB to catch
604 * that too. Thus:
605 *
606 * head->list->prev->next bit 1 bit 0
607 * ------- -------
608 * Normal page 0 0
609 * Points to head page 0 1
610 * New head page 1 0
611 *
612 * Note we can not trust the prev pointer of the head page, because:
613 *
614 * +----+ +-----+ +-----+
615 * | |------>| T |---X--->| N |
616 * | |<------| | | |
617 * +----+ +-----+ +-----+
618 * ^ ^ |
619 * | +-----+ | |
620 * +----------| R |----------+ |
621 * | |<-----------+
622 * +-----+
623 *
624 * Key: ---X--> HEAD flag set in pointer
625 * T Tail page
626 * R Reader page
627 * N Next page
628 *
629 * (see __rb_reserve_next() to see where this happens)
630 *
631 * What the above shows is that the reader just swapped out
632 * the reader page with a page in the buffer, but before it
633 * could make the new header point back to the new page added
634 * it was preempted by a writer. The writer moved forward onto
635 * the new page added by the reader and is about to move forward
636 * again.
637 *
638 * You can see, it is legitimate for the previous pointer of
639 * the head (or any page) not to point back to itself. But only
640 * temporarially.
641 */
642
643#define RB_PAGE_NORMAL 0UL
644#define RB_PAGE_HEAD 1UL
645#define RB_PAGE_UPDATE 2UL
646
647
648#define RB_FLAG_MASK 3UL
649
650/* PAGE_MOVED is not part of the mask */
651#define RB_PAGE_MOVED 4UL
652
653/*
654 * rb_list_head - remove any bit
655 */
656static struct list_head *rb_list_head(struct list_head *list)
657{
658 unsigned long val = (unsigned long)list;
659
660 return (struct list_head *)(val & ~RB_FLAG_MASK);
661}
662
663/*
664 * rb_is_head_page - test if the given page is the head page
665 *
666 * Because the reader may move the head_page pointer, we can
667 * not trust what the head page is (it may be pointing to
668 * the reader page). But if the next page is a header page,
669 * its flags will be non zero.
670 */
671static inline int
672rb_is_head_page(struct ring_buffer_per_cpu *cpu_buffer,
673 struct buffer_page *page, struct list_head *list)
674{
675 unsigned long val;
676
677 val = (unsigned long)list->next;
678
679 if ((val & ~RB_FLAG_MASK) != (unsigned long)&page->list)
680 return RB_PAGE_MOVED;
681
682 return val & RB_FLAG_MASK;
683}
684
685/*
686 * rb_is_reader_page
687 *
688 * The unique thing about the reader page, is that, if the
689 * writer is ever on it, the previous pointer never points
690 * back to the reader page.
691 */
692static int rb_is_reader_page(struct buffer_page *page)
693{
694 struct list_head *list = page->list.prev;
695
696 return rb_list_head(list->next) != &page->list;
697}
698
699/*
700 * rb_set_list_to_head - set a list_head to be pointing to head.
701 */
702static void rb_set_list_to_head(struct ring_buffer_per_cpu *cpu_buffer,
703 struct list_head *list)
704{
705 unsigned long *ptr;
706
707 ptr = (unsigned long *)&list->next;
708 *ptr |= RB_PAGE_HEAD;
709 *ptr &= ~RB_PAGE_UPDATE;
710}
711
712/*
713 * rb_head_page_activate - sets up head page
714 */
715static void rb_head_page_activate(struct ring_buffer_per_cpu *cpu_buffer)
716{
717 struct buffer_page *head;
718
719 head = cpu_buffer->head_page;
720 if (!head)
721 return;
722
723 /*
724 * Set the previous list pointer to have the HEAD flag.
725 */
726 rb_set_list_to_head(cpu_buffer, head->list.prev);
727}
728
729static void rb_list_head_clear(struct list_head *list)
730{
731 unsigned long *ptr = (unsigned long *)&list->next;
732
733 *ptr &= ~RB_FLAG_MASK;
734}
735
736/*
737 * rb_head_page_dactivate - clears head page ptr (for free list)
738 */
739static void
740rb_head_page_deactivate(struct ring_buffer_per_cpu *cpu_buffer)
741{
742 struct list_head *hd;
743
744 /* Go through the whole list and clear any pointers found. */
745 rb_list_head_clear(cpu_buffer->pages);
746
747 list_for_each(hd, cpu_buffer->pages)
748 rb_list_head_clear(hd);
749}
750
751static int rb_head_page_set(struct ring_buffer_per_cpu *cpu_buffer,
752 struct buffer_page *head,
753 struct buffer_page *prev,
754 int old_flag, int new_flag)
755{
756 struct list_head *list;
757 unsigned long val = (unsigned long)&head->list;
758 unsigned long ret;
759
760 list = &prev->list;
761
762 val &= ~RB_FLAG_MASK;
763
764 ret = cmpxchg((unsigned long *)&list->next,
765 val | old_flag, val | new_flag);
766
767 /* check if the reader took the page */
768 if ((ret & ~RB_FLAG_MASK) != val)
769 return RB_PAGE_MOVED;
770
771 return ret & RB_FLAG_MASK;
772}
773
774static int rb_head_page_set_update(struct ring_buffer_per_cpu *cpu_buffer,
775 struct buffer_page *head,
776 struct buffer_page *prev,
777 int old_flag)
778{
779 return rb_head_page_set(cpu_buffer, head, prev,
780 old_flag, RB_PAGE_UPDATE);
781}
782
783static int rb_head_page_set_head(struct ring_buffer_per_cpu *cpu_buffer,
784 struct buffer_page *head,
785 struct buffer_page *prev,
786 int old_flag)
787{
788 return rb_head_page_set(cpu_buffer, head, prev,
789 old_flag, RB_PAGE_HEAD);
790}
791
792static int rb_head_page_set_normal(struct ring_buffer_per_cpu *cpu_buffer,
793 struct buffer_page *head,
794 struct buffer_page *prev,
795 int old_flag)
796{
797 return rb_head_page_set(cpu_buffer, head, prev,
798 old_flag, RB_PAGE_NORMAL);
799}
800
801static inline void rb_inc_page(struct ring_buffer_per_cpu *cpu_buffer,
802 struct buffer_page **bpage)
803{
804 struct list_head *p = rb_list_head((*bpage)->list.next);
805
806 *bpage = list_entry(p, struct buffer_page, list);
807}
808
809static struct buffer_page *
810rb_set_head_page(struct ring_buffer_per_cpu *cpu_buffer)
811{
812 struct buffer_page *head;
813 struct buffer_page *page;
814 struct list_head *list;
815 int i;
816
817 if (RB_WARN_ON(cpu_buffer, !cpu_buffer->head_page))
818 return NULL;
819
820 /* sanity check */
821 list = cpu_buffer->pages;
822 if (RB_WARN_ON(cpu_buffer, rb_list_head(list->prev->next) != list))
823 return NULL;
824
825 page = head = cpu_buffer->head_page;
826 /*
827 * It is possible that the writer moves the header behind
828 * where we started, and we miss in one loop.
829 * A second loop should grab the header, but we'll do
830 * three loops just because I'm paranoid.
831 */
832 for (i = 0; i < 3; i++) {
833 do {
834 if (rb_is_head_page(cpu_buffer, page, page->list.prev)) {
835 cpu_buffer->head_page = page;
836 return page;
837 }
838 rb_inc_page(cpu_buffer, &page);
839 } while (page != head);
840 }
841
842 RB_WARN_ON(cpu_buffer, 1);
843
844 return NULL;
845}
846
847static int rb_head_page_replace(struct buffer_page *old,
848 struct buffer_page *new)
849{
850 unsigned long *ptr = (unsigned long *)&old->list.prev->next;
851 unsigned long val;
852 unsigned long ret;
853
854 val = *ptr & ~RB_FLAG_MASK;
855 val |= RB_PAGE_HEAD;
856
857 ret = cmpxchg(ptr, val, (unsigned long)&new->list);
858
859 return ret == val;
860}
861
862/*
863 * rb_tail_page_update - move the tail page forward
864 *
865 * Returns 1 if moved tail page, 0 if someone else did.
866 */
867static int rb_tail_page_update(struct ring_buffer_per_cpu *cpu_buffer,
868 struct buffer_page *tail_page,
869 struct buffer_page *next_page)
870{
871 struct buffer_page *old_tail;
872 unsigned long old_entries;
873 unsigned long old_write;
874 int ret = 0;
875
876 /*
877 * The tail page now needs to be moved forward.
878 *
879 * We need to reset the tail page, but without messing
880 * with possible erasing of data brought in by interrupts
881 * that have moved the tail page and are currently on it.
882 *
883 * We add a counter to the write field to denote this.
884 */
885 old_write = local_add_return(RB_WRITE_INTCNT, &next_page->write);
886 old_entries = local_add_return(RB_WRITE_INTCNT, &next_page->entries);
887
888 /*
889 * Just make sure we have seen our old_write and synchronize
890 * with any interrupts that come in.
891 */
892 barrier();
893
894 /*
895 * If the tail page is still the same as what we think
896 * it is, then it is up to us to update the tail
897 * pointer.
898 */
899 if (tail_page == cpu_buffer->tail_page) {
900 /* Zero the write counter */
901 unsigned long val = old_write & ~RB_WRITE_MASK;
902 unsigned long eval = old_entries & ~RB_WRITE_MASK;
903
904 /*
905 * This will only succeed if an interrupt did
906 * not come in and change it. In which case, we
907 * do not want to modify it.
908 *
909 * We add (void) to let the compiler know that we do not care
910 * about the return value of these functions. We use the
911 * cmpxchg to only update if an interrupt did not already
912 * do it for us. If the cmpxchg fails, we don't care.
913 */
914 (void)local_cmpxchg(&next_page->write, old_write, val);
915 (void)local_cmpxchg(&next_page->entries, old_entries, eval);
916
917 /*
918 * No need to worry about races with clearing out the commit.
919 * it only can increment when a commit takes place. But that
920 * only happens in the outer most nested commit.
921 */
922 local_set(&next_page->page->commit, 0);
923
924 old_tail = cmpxchg(&cpu_buffer->tail_page,
925 tail_page, next_page);
926
927 if (old_tail == tail_page)
928 ret = 1;
929 }
930
931 return ret;
932}
933
934static int rb_check_bpage(struct ring_buffer_per_cpu *cpu_buffer,
935 struct buffer_page *bpage)
936{
937 unsigned long val = (unsigned long)bpage;
938
939 if (RB_WARN_ON(cpu_buffer, val & RB_FLAG_MASK))
940 return 1;
941
942 return 0;
943}
944
945/**
946 * rb_check_list - make sure a pointer to a list has the last bits zero
947 */
948static int rb_check_list(struct ring_buffer_per_cpu *cpu_buffer,
949 struct list_head *list)
950{
951 if (RB_WARN_ON(cpu_buffer, rb_list_head(list->prev) != list->prev))
952 return 1;
953 if (RB_WARN_ON(cpu_buffer, rb_list_head(list->next) != list->next))
954 return 1;
955 return 0;
956}
957
958/**
959 * check_pages - integrity check of buffer pages
960 * @cpu_buffer: CPU buffer with pages to test
961 *
962 * As a safety measure we check to make sure the data pages have not
963 * been corrupted.
964 */
965static int rb_check_pages(struct ring_buffer_per_cpu *cpu_buffer)
966{
967 struct list_head *head = cpu_buffer->pages;
968 struct buffer_page *bpage, *tmp;
969
970 rb_head_page_deactivate(cpu_buffer);
971
972 if (RB_WARN_ON(cpu_buffer, head->next->prev != head))
973 return -1;
974 if (RB_WARN_ON(cpu_buffer, head->prev->next != head))
975 return -1;
976
977 if (rb_check_list(cpu_buffer, head))
978 return -1;
979
980 list_for_each_entry_safe(bpage, tmp, head, list) {
981 if (RB_WARN_ON(cpu_buffer,
982 bpage->list.next->prev != &bpage->list))
983 return -1;
984 if (RB_WARN_ON(cpu_buffer,
985 bpage->list.prev->next != &bpage->list))
986 return -1;
987 if (rb_check_list(cpu_buffer, &bpage->list))
988 return -1;
989 }
990
991 rb_head_page_activate(cpu_buffer);
992
993 return 0;
994}
995
996static int rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
997 unsigned nr_pages)
998{
999 struct buffer_page *bpage, *tmp;
1000 LIST_HEAD(pages);
1001 unsigned i;
1002
1003 WARN_ON(!nr_pages);
1004
1005 for (i = 0; i < nr_pages; i++) {
1006 struct page *page;
1007 /*
1008 * __GFP_NORETRY flag makes sure that the allocation fails
1009 * gracefully without invoking oom-killer and the system is
1010 * not destabilized.
1011 */
1012 bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
1013 GFP_KERNEL | __GFP_NORETRY,
1014 cpu_to_node(cpu_buffer->cpu));
1015 if (!bpage)
1016 goto free_pages;
1017
1018 rb_check_bpage(cpu_buffer, bpage);
1019
1020 list_add(&bpage->list, &pages);
1021
1022 page = alloc_pages_node(cpu_to_node(cpu_buffer->cpu),
1023 GFP_KERNEL | __GFP_NORETRY, 0);
1024 if (!page)
1025 goto free_pages;
1026 bpage->page = page_address(page);
1027 rb_init_page(bpage->page);
1028 }
1029
1030 /*
1031 * The ring buffer page list is a circular list that does not
1032 * start and end with a list head. All page list items point to
1033 * other pages.
1034 */
1035 cpu_buffer->pages = pages.next;
1036 list_del(&pages);
1037
1038 rb_check_pages(cpu_buffer);
1039
1040 return 0;
1041
1042 free_pages:
1043 list_for_each_entry_safe(bpage, tmp, &pages, list) {
1044 list_del_init(&bpage->list);
1045 free_buffer_page(bpage);
1046 }
1047 return -ENOMEM;
1048}
1049
1050static struct ring_buffer_per_cpu *
1051rb_allocate_cpu_buffer(struct ring_buffer *buffer, int cpu)
1052{
1053 struct ring_buffer_per_cpu *cpu_buffer;
1054 struct buffer_page *bpage;
1055 struct page *page;
1056 int ret;
1057
1058 cpu_buffer = kzalloc_node(ALIGN(sizeof(*cpu_buffer), cache_line_size()),
1059 GFP_KERNEL, cpu_to_node(cpu));
1060 if (!cpu_buffer)
1061 return NULL;
1062
1063 cpu_buffer->cpu = cpu;
1064 cpu_buffer->buffer = buffer;
1065 spin_lock_init(&cpu_buffer->reader_lock);
1066 lockdep_set_class(&cpu_buffer->reader_lock, buffer->reader_lock_key);
1067 cpu_buffer->lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
1068
1069 bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
1070 GFP_KERNEL, cpu_to_node(cpu));
1071 if (!bpage)
1072 goto fail_free_buffer;
1073
1074 rb_check_bpage(cpu_buffer, bpage);
1075
1076 cpu_buffer->reader_page = bpage;
1077 page = alloc_pages_node(cpu_to_node(cpu), GFP_KERNEL, 0);
1078 if (!page)
1079 goto fail_free_reader;
1080 bpage->page = page_address(page);
1081 rb_init_page(bpage->page);
1082
1083 INIT_LIST_HEAD(&cpu_buffer->reader_page->list);
1084
1085 ret = rb_allocate_pages(cpu_buffer, buffer->pages);
1086 if (ret < 0)
1087 goto fail_free_reader;
1088
1089 cpu_buffer->head_page
1090 = list_entry(cpu_buffer->pages, struct buffer_page, list);
1091 cpu_buffer->tail_page = cpu_buffer->commit_page = cpu_buffer->head_page;
1092
1093 rb_head_page_activate(cpu_buffer);
1094
1095 return cpu_buffer;
1096
1097 fail_free_reader:
1098 free_buffer_page(cpu_buffer->reader_page);
1099
1100 fail_free_buffer:
1101 kfree(cpu_buffer);
1102 return NULL;
1103}
1104
1105static void rb_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
1106{
1107 struct list_head *head = cpu_buffer->pages;
1108 struct buffer_page *bpage, *tmp;
1109
1110 free_buffer_page(cpu_buffer->reader_page);
1111
1112 rb_head_page_deactivate(cpu_buffer);
1113
1114 if (head) {
1115 list_for_each_entry_safe(bpage, tmp, head, list) {
1116 list_del_init(&bpage->list);
1117 free_buffer_page(bpage);
1118 }
1119 bpage = list_entry(head, struct buffer_page, list);
1120 free_buffer_page(bpage);
1121 }
1122
1123 kfree(cpu_buffer);
1124}
1125
1126#ifdef CONFIG_HOTPLUG_CPU
1127static int rb_cpu_notify(struct notifier_block *self,
1128 unsigned long action, void *hcpu);
1129#endif
1130
1131/**
1132 * ring_buffer_alloc - allocate a new ring_buffer
1133 * @size: the size in bytes per cpu that is needed.
1134 * @flags: attributes to set for the ring buffer.
1135 *
1136 * Currently the only flag that is available is the RB_FL_OVERWRITE
1137 * flag. This flag means that the buffer will overwrite old data
1138 * when the buffer wraps. If this flag is not set, the buffer will
1139 * drop data when the tail hits the head.
1140 */
1141struct ring_buffer *__ring_buffer_alloc(unsigned long size, unsigned flags,
1142 struct lock_class_key *key)
1143{
1144 struct ring_buffer *buffer;
1145 int bsize;
1146 int cpu;
1147
1148 /* keep it in its own cache line */
1149 buffer = kzalloc(ALIGN(sizeof(*buffer), cache_line_size()),
1150 GFP_KERNEL);
1151 if (!buffer)
1152 return NULL;
1153
1154 if (!alloc_cpumask_var(&buffer->cpumask, GFP_KERNEL))
1155 goto fail_free_buffer;
1156
1157 buffer->pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
1158 buffer->flags = flags;
1159 buffer->clock = trace_clock_local;
1160 buffer->reader_lock_key = key;
1161
1162 /* need at least two pages */
1163 if (buffer->pages < 2)
1164 buffer->pages = 2;
1165
1166 /*
1167 * In case of non-hotplug cpu, if the ring-buffer is allocated
1168 * in early initcall, it will not be notified of secondary cpus.
1169 * In that off case, we need to allocate for all possible cpus.
1170 */
1171#ifdef CONFIG_HOTPLUG_CPU
1172 get_online_cpus();
1173 cpumask_copy(buffer->cpumask, cpu_online_mask);
1174#else
1175 cpumask_copy(buffer->cpumask, cpu_possible_mask);
1176#endif
1177 buffer->cpus = nr_cpu_ids;
1178
1179 bsize = sizeof(void *) * nr_cpu_ids;
1180 buffer->buffers = kzalloc(ALIGN(bsize, cache_line_size()),
1181 GFP_KERNEL);
1182 if (!buffer->buffers)
1183 goto fail_free_cpumask;
1184
1185 for_each_buffer_cpu(buffer, cpu) {
1186 buffer->buffers[cpu] =
1187 rb_allocate_cpu_buffer(buffer, cpu);
1188 if (!buffer->buffers[cpu])
1189 goto fail_free_buffers;
1190 }
1191
1192#ifdef CONFIG_HOTPLUG_CPU
1193 buffer->cpu_notify.notifier_call = rb_cpu_notify;
1194 buffer->cpu_notify.priority = 0;
1195 register_cpu_notifier(&buffer->cpu_notify);
1196#endif
1197
1198 put_online_cpus();
1199 mutex_init(&buffer->mutex);
1200
1201 return buffer;
1202
1203 fail_free_buffers:
1204 for_each_buffer_cpu(buffer, cpu) {
1205 if (buffer->buffers[cpu])
1206 rb_free_cpu_buffer(buffer->buffers[cpu]);
1207 }
1208 kfree(buffer->buffers);
1209
1210 fail_free_cpumask:
1211 free_cpumask_var(buffer->cpumask);
1212 put_online_cpus();
1213
1214 fail_free_buffer:
1215 kfree(buffer);
1216 return NULL;
1217}
1218EXPORT_SYMBOL_GPL(__ring_buffer_alloc);
1219
1220/**
1221 * ring_buffer_free - free a ring buffer.
1222 * @buffer: the buffer to free.
1223 */
1224void
1225ring_buffer_free(struct ring_buffer *buffer)
1226{
1227 int cpu;
1228
1229 get_online_cpus();
1230
1231#ifdef CONFIG_HOTPLUG_CPU
1232 unregister_cpu_notifier(&buffer->cpu_notify);
1233#endif
1234
1235 for_each_buffer_cpu(buffer, cpu)
1236 rb_free_cpu_buffer(buffer->buffers[cpu]);
1237
1238 put_online_cpus();
1239
1240 kfree(buffer->buffers);
1241 free_cpumask_var(buffer->cpumask);
1242
1243 kfree(buffer);
1244}
1245EXPORT_SYMBOL_GPL(ring_buffer_free);
1246
1247void ring_buffer_set_clock(struct ring_buffer *buffer,
1248 u64 (*clock)(void))
1249{
1250 buffer->clock = clock;
1251}
1252
1253static void rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer);
1254
1255static void
1256rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned nr_pages)
1257{
1258 struct buffer_page *bpage;
1259 struct list_head *p;
1260 unsigned i;
1261
1262 spin_lock_irq(&cpu_buffer->reader_lock);
1263 rb_head_page_deactivate(cpu_buffer);
1264
1265 for (i = 0; i < nr_pages; i++) {
1266 if (RB_WARN_ON(cpu_buffer, list_empty(cpu_buffer->pages)))
1267 goto out;
1268 p = cpu_buffer->pages->next;
1269 bpage = list_entry(p, struct buffer_page, list);
1270 list_del_init(&bpage->list);
1271 free_buffer_page(bpage);
1272 }
1273 if (RB_WARN_ON(cpu_buffer, list_empty(cpu_buffer->pages)))
1274 goto out;
1275
1276 rb_reset_cpu(cpu_buffer);
1277 rb_check_pages(cpu_buffer);
1278
1279out:
1280 spin_unlock_irq(&cpu_buffer->reader_lock);
1281}
1282
1283static void
1284rb_insert_pages(struct ring_buffer_per_cpu *cpu_buffer,
1285 struct list_head *pages, unsigned nr_pages)
1286{
1287 struct buffer_page *bpage;
1288 struct list_head *p;
1289 unsigned i;
1290
1291 spin_lock_irq(&cpu_buffer->reader_lock);
1292 rb_head_page_deactivate(cpu_buffer);
1293
1294 for (i = 0; i < nr_pages; i++) {
1295 if (RB_WARN_ON(cpu_buffer, list_empty(pages)))
1296 goto out;
1297 p = pages->next;
1298 bpage = list_entry(p, struct buffer_page, list);
1299 list_del_init(&bpage->list);
1300 list_add_tail(&bpage->list, cpu_buffer->pages);
1301 }
1302 rb_reset_cpu(cpu_buffer);
1303 rb_check_pages(cpu_buffer);
1304
1305out:
1306 spin_unlock_irq(&cpu_buffer->reader_lock);
1307}
1308
1309/**
1310 * ring_buffer_resize - resize the ring buffer
1311 * @buffer: the buffer to resize.
1312 * @size: the new size.
1313 *
1314 * Minimum size is 2 * BUF_PAGE_SIZE.
1315 *
1316 * Returns -1 on failure.
1317 */
1318int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size)
1319{
1320 struct ring_buffer_per_cpu *cpu_buffer;
1321 unsigned nr_pages, rm_pages, new_pages;
1322 struct buffer_page *bpage, *tmp;
1323 unsigned long buffer_size;
1324 LIST_HEAD(pages);
1325 int i, cpu;
1326
1327 /*
1328 * Always succeed at resizing a non-existent buffer:
1329 */
1330 if (!buffer)
1331 return size;
1332
1333 size = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
1334 size *= BUF_PAGE_SIZE;
1335 buffer_size = buffer->pages * BUF_PAGE_SIZE;
1336
1337 /* we need a minimum of two pages */
1338 if (size < BUF_PAGE_SIZE * 2)
1339 size = BUF_PAGE_SIZE * 2;
1340
1341 if (size == buffer_size)
1342 return size;
1343
1344 atomic_inc(&buffer->record_disabled);
1345
1346 /* Make sure all writers are done with this buffer. */
1347 synchronize_sched();
1348
1349 mutex_lock(&buffer->mutex);
1350 get_online_cpus();
1351
1352 nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
1353
1354 if (size < buffer_size) {
1355
1356 /* easy case, just free pages */
1357 if (RB_WARN_ON(buffer, nr_pages >= buffer->pages))
1358 goto out_fail;
1359
1360 rm_pages = buffer->pages - nr_pages;
1361
1362 for_each_buffer_cpu(buffer, cpu) {
1363 cpu_buffer = buffer->buffers[cpu];
1364 rb_remove_pages(cpu_buffer, rm_pages);
1365 }
1366 goto out;
1367 }
1368
1369 /*
1370 * This is a bit more difficult. We only want to add pages
1371 * when we can allocate enough for all CPUs. We do this
1372 * by allocating all the pages and storing them on a local
1373 * link list. If we succeed in our allocation, then we
1374 * add these pages to the cpu_buffers. Otherwise we just free
1375 * them all and return -ENOMEM;
1376 */
1377 if (RB_WARN_ON(buffer, nr_pages <= buffer->pages))
1378 goto out_fail;
1379
1380 new_pages = nr_pages - buffer->pages;
1381
1382 for_each_buffer_cpu(buffer, cpu) {
1383 for (i = 0; i < new_pages; i++) {
1384 struct page *page;
1385 /*
1386 * __GFP_NORETRY flag makes sure that the allocation
1387 * fails gracefully without invoking oom-killer and
1388 * the system is not destabilized.
1389 */
1390 bpage = kzalloc_node(ALIGN(sizeof(*bpage),
1391 cache_line_size()),
1392 GFP_KERNEL | __GFP_NORETRY,
1393 cpu_to_node(cpu));
1394 if (!bpage)
1395 goto free_pages;
1396 list_add(&bpage->list, &pages);
1397 page = alloc_pages_node(cpu_to_node(cpu),
1398 GFP_KERNEL | __GFP_NORETRY, 0);
1399 if (!page)
1400 goto free_pages;
1401 bpage->page = page_address(page);
1402 rb_init_page(bpage->page);
1403 }
1404 }
1405
1406 for_each_buffer_cpu(buffer, cpu) {
1407 cpu_buffer = buffer->buffers[cpu];
1408 rb_insert_pages(cpu_buffer, &pages, new_pages);
1409 }
1410
1411 if (RB_WARN_ON(buffer, !list_empty(&pages)))
1412 goto out_fail;
1413
1414 out:
1415 buffer->pages = nr_pages;
1416 put_online_cpus();
1417 mutex_unlock(&buffer->mutex);
1418
1419 atomic_dec(&buffer->record_disabled);
1420
1421 return size;
1422
1423 free_pages:
1424 list_for_each_entry_safe(bpage, tmp, &pages, list) {
1425 list_del_init(&bpage->list);
1426 free_buffer_page(bpage);
1427 }
1428 put_online_cpus();
1429 mutex_unlock(&buffer->mutex);
1430 atomic_dec(&buffer->record_disabled);
1431 return -ENOMEM;
1432
1433 /*
1434 * Something went totally wrong, and we are too paranoid
1435 * to even clean up the mess.
1436 */
1437 out_fail:
1438 put_online_cpus();
1439 mutex_unlock(&buffer->mutex);
1440 atomic_dec(&buffer->record_disabled);
1441 return -1;
1442}
1443EXPORT_SYMBOL_GPL(ring_buffer_resize);
1444
1445void ring_buffer_change_overwrite(struct ring_buffer *buffer, int val)
1446{
1447 mutex_lock(&buffer->mutex);
1448 if (val)
1449 buffer->flags |= RB_FL_OVERWRITE;
1450 else
1451 buffer->flags &= ~RB_FL_OVERWRITE;
1452 mutex_unlock(&buffer->mutex);
1453}
1454EXPORT_SYMBOL_GPL(ring_buffer_change_overwrite);
1455
1456static inline void *
1457__rb_data_page_index(struct buffer_data_page *bpage, unsigned index)
1458{
1459 return bpage->data + index;
1460}
1461
1462static inline void *__rb_page_index(struct buffer_page *bpage, unsigned index)
1463{
1464 return bpage->page->data + index;
1465}
1466
1467static inline struct ring_buffer_event *
1468rb_reader_event(struct ring_buffer_per_cpu *cpu_buffer)
1469{
1470 return __rb_page_index(cpu_buffer->reader_page,
1471 cpu_buffer->reader_page->read);
1472}
1473
1474static inline struct ring_buffer_event *
1475rb_iter_head_event(struct ring_buffer_iter *iter)
1476{
1477 return __rb_page_index(iter->head_page, iter->head);
1478}
1479
1480static inline unsigned long rb_page_write(struct buffer_page *bpage)
1481{
1482 return local_read(&bpage->write) & RB_WRITE_MASK;
1483}
1484
1485static inline unsigned rb_page_commit(struct buffer_page *bpage)
1486{
1487 return local_read(&bpage->page->commit);
1488}
1489
1490static inline unsigned long rb_page_entries(struct buffer_page *bpage)
1491{
1492 return local_read(&bpage->entries) & RB_WRITE_MASK;
1493}
1494
1495/* Size is determined by what has been committed */
1496static inline unsigned rb_page_size(struct buffer_page *bpage)
1497{
1498 return rb_page_commit(bpage);
1499}
1500
1501static inline unsigned
1502rb_commit_index(struct ring_buffer_per_cpu *cpu_buffer)
1503{
1504 return rb_page_commit(cpu_buffer->commit_page);
1505}
1506
1507static inline unsigned
1508rb_event_index(struct ring_buffer_event *event)
1509{
1510 unsigned long addr = (unsigned long)event;
1511
1512 return (addr & ~PAGE_MASK) - BUF_PAGE_HDR_SIZE;
1513}
1514
1515static inline int
1516rb_event_is_commit(struct ring_buffer_per_cpu *cpu_buffer,
1517 struct ring_buffer_event *event)
1518{
1519 unsigned long addr = (unsigned long)event;
1520 unsigned long index;
1521
1522 index = rb_event_index(event);
1523 addr &= PAGE_MASK;
1524
1525 return cpu_buffer->commit_page->page == (void *)addr &&
1526 rb_commit_index(cpu_buffer) == index;
1527}
1528
1529static void
1530rb_set_commit_to_write(struct ring_buffer_per_cpu *cpu_buffer)
1531{
1532 unsigned long max_count;
1533
1534 /*
1535 * We only race with interrupts and NMIs on this CPU.
1536 * If we own the commit event, then we can commit
1537 * all others that interrupted us, since the interruptions
1538 * are in stack format (they finish before they come
1539 * back to us). This allows us to do a simple loop to
1540 * assign the commit to the tail.
1541 */
1542 again:
1543 max_count = cpu_buffer->buffer->pages * 100;
1544
1545 while (cpu_buffer->commit_page != cpu_buffer->tail_page) {
1546 if (RB_WARN_ON(cpu_buffer, !(--max_count)))
1547 return;
1548 if (RB_WARN_ON(cpu_buffer,
1549 rb_is_reader_page(cpu_buffer->tail_page)))
1550 return;
1551 local_set(&cpu_buffer->commit_page->page->commit,
1552 rb_page_write(cpu_buffer->commit_page));
1553 rb_inc_page(cpu_buffer, &cpu_buffer->commit_page);
1554 cpu_buffer->write_stamp =
1555 cpu_buffer->commit_page->page->time_stamp;
1556 /* add barrier to keep gcc from optimizing too much */
1557 barrier();
1558 }
1559 while (rb_commit_index(cpu_buffer) !=
1560 rb_page_write(cpu_buffer->commit_page)) {
1561
1562 local_set(&cpu_buffer->commit_page->page->commit,
1563 rb_page_write(cpu_buffer->commit_page));
1564 RB_WARN_ON(cpu_buffer,
1565 local_read(&cpu_buffer->commit_page->page->commit) &
1566 ~RB_WRITE_MASK);
1567 barrier();
1568 }
1569
1570 /* again, keep gcc from optimizing */
1571 barrier();
1572
1573 /*
1574 * If an interrupt came in just after the first while loop
1575 * and pushed the tail page forward, we will be left with
1576 * a dangling commit that will never go forward.
1577 */
1578 if (unlikely(cpu_buffer->commit_page != cpu_buffer->tail_page))
1579 goto again;
1580}
1581
1582static void rb_reset_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
1583{
1584 cpu_buffer->read_stamp = cpu_buffer->reader_page->page->time_stamp;
1585 cpu_buffer->reader_page->read = 0;
1586}
1587
1588static void rb_inc_iter(struct ring_buffer_iter *iter)
1589{
1590 struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
1591
1592 /*
1593 * The iterator could be on the reader page (it starts there).
1594 * But the head could have moved, since the reader was
1595 * found. Check for this case and assign the iterator
1596 * to the head page instead of next.
1597 */
1598 if (iter->head_page == cpu_buffer->reader_page)
1599 iter->head_page = rb_set_head_page(cpu_buffer);
1600 else
1601 rb_inc_page(cpu_buffer, &iter->head_page);
1602
1603 iter->read_stamp = iter->head_page->page->time_stamp;
1604 iter->head = 0;
1605}
1606
1607/* Slow path, do not inline */
1608static noinline struct ring_buffer_event *
1609rb_add_time_stamp(struct ring_buffer_event *event, u64 delta)
1610{
1611 event->type_len = RINGBUF_TYPE_TIME_EXTEND;
1612
1613 /* Not the first event on the page? */
1614 if (rb_event_index(event)) {
1615 event->time_delta = delta & TS_MASK;
1616 event->array[0] = delta >> TS_SHIFT;
1617 } else {
1618 /* nope, just zero it */
1619 event->time_delta = 0;
1620 event->array[0] = 0;
1621 }
1622
1623 return skip_time_extend(event);
1624}
1625
1626/**
1627 * ring_buffer_update_event - update event type and data
1628 * @event: the even to update
1629 * @type: the type of event
1630 * @length: the size of the event field in the ring buffer
1631 *
1632 * Update the type and data fields of the event. The length
1633 * is the actual size that is written to the ring buffer,
1634 * and with this, we can determine what to place into the
1635 * data field.
1636 */
1637static void
1638rb_update_event(struct ring_buffer_per_cpu *cpu_buffer,
1639 struct ring_buffer_event *event, unsigned length,
1640 int add_timestamp, u64 delta)
1641{
1642 /* Only a commit updates the timestamp */
1643 if (unlikely(!rb_event_is_commit(cpu_buffer, event)))
1644 delta = 0;
1645
1646 /*
1647 * If we need to add a timestamp, then we
1648 * add it to the start of the resevered space.
1649 */
1650 if (unlikely(add_timestamp)) {
1651 event = rb_add_time_stamp(event, delta);
1652 length -= RB_LEN_TIME_EXTEND;
1653 delta = 0;
1654 }
1655
1656 event->time_delta = delta;
1657 length -= RB_EVNT_HDR_SIZE;
1658 if (length > RB_MAX_SMALL_DATA || RB_FORCE_8BYTE_ALIGNMENT) {
1659 event->type_len = 0;
1660 event->array[0] = length;
1661 } else
1662 event->type_len = DIV_ROUND_UP(length, RB_ALIGNMENT);
1663}
1664
1665/*
1666 * rb_handle_head_page - writer hit the head page
1667 *
1668 * Returns: +1 to retry page
1669 * 0 to continue
1670 * -1 on error
1671 */
1672static int
1673rb_handle_head_page(struct ring_buffer_per_cpu *cpu_buffer,
1674 struct buffer_page *tail_page,
1675 struct buffer_page *next_page)
1676{
1677 struct buffer_page *new_head;
1678 int entries;
1679 int type;
1680 int ret;
1681
1682 entries = rb_page_entries(next_page);
1683
1684 /*
1685 * The hard part is here. We need to move the head
1686 * forward, and protect against both readers on
1687 * other CPUs and writers coming in via interrupts.
1688 */
1689 type = rb_head_page_set_update(cpu_buffer, next_page, tail_page,
1690 RB_PAGE_HEAD);
1691
1692 /*
1693 * type can be one of four:
1694 * NORMAL - an interrupt already moved it for us
1695 * HEAD - we are the first to get here.
1696 * UPDATE - we are the interrupt interrupting
1697 * a current move.
1698 * MOVED - a reader on another CPU moved the next
1699 * pointer to its reader page. Give up
1700 * and try again.
1701 */
1702
1703 switch (type) {
1704 case RB_PAGE_HEAD:
1705 /*
1706 * We changed the head to UPDATE, thus
1707 * it is our responsibility to update
1708 * the counters.
1709 */
1710 local_add(entries, &cpu_buffer->overrun);
1711
1712 /*
1713 * The entries will be zeroed out when we move the
1714 * tail page.
1715 */
1716
1717 /* still more to do */
1718 break;
1719
1720 case RB_PAGE_UPDATE:
1721 /*
1722 * This is an interrupt that interrupt the
1723 * previous update. Still more to do.
1724 */
1725 break;
1726 case RB_PAGE_NORMAL:
1727 /*
1728 * An interrupt came in before the update
1729 * and processed this for us.
1730 * Nothing left to do.
1731 */
1732 return 1;
1733 case RB_PAGE_MOVED:
1734 /*
1735 * The reader is on another CPU and just did
1736 * a swap with our next_page.
1737 * Try again.
1738 */
1739 return 1;
1740 default:
1741 RB_WARN_ON(cpu_buffer, 1); /* WTF??? */
1742 return -1;
1743 }
1744
1745 /*
1746 * Now that we are here, the old head pointer is
1747 * set to UPDATE. This will keep the reader from
1748 * swapping the head page with the reader page.
1749 * The reader (on another CPU) will spin till
1750 * we are finished.
1751 *
1752 * We just need to protect against interrupts
1753 * doing the job. We will set the next pointer
1754 * to HEAD. After that, we set the old pointer
1755 * to NORMAL, but only if it was HEAD before.
1756 * otherwise we are an interrupt, and only
1757 * want the outer most commit to reset it.
1758 */
1759 new_head = next_page;
1760 rb_inc_page(cpu_buffer, &new_head);
1761
1762 ret = rb_head_page_set_head(cpu_buffer, new_head, next_page,
1763 RB_PAGE_NORMAL);
1764
1765 /*
1766 * Valid returns are:
1767 * HEAD - an interrupt came in and already set it.
1768 * NORMAL - One of two things:
1769 * 1) We really set it.
1770 * 2) A bunch of interrupts came in and moved
1771 * the page forward again.
1772 */
1773 switch (ret) {
1774 case RB_PAGE_HEAD:
1775 case RB_PAGE_NORMAL:
1776 /* OK */
1777 break;
1778 default:
1779 RB_WARN_ON(cpu_buffer, 1);
1780 return -1;
1781 }
1782
1783 /*
1784 * It is possible that an interrupt came in,
1785 * set the head up, then more interrupts came in
1786 * and moved it again. When we get back here,
1787 * the page would have been set to NORMAL but we
1788 * just set it back to HEAD.
1789 *
1790 * How do you detect this? Well, if that happened
1791 * the tail page would have moved.
1792 */
1793 if (ret == RB_PAGE_NORMAL) {
1794 /*
1795 * If the tail had moved passed next, then we need
1796 * to reset the pointer.
1797 */
1798 if (cpu_buffer->tail_page != tail_page &&
1799 cpu_buffer->tail_page != next_page)
1800 rb_head_page_set_normal(cpu_buffer, new_head,
1801 next_page,
1802 RB_PAGE_HEAD);
1803 }
1804
1805 /*
1806 * If this was the outer most commit (the one that
1807 * changed the original pointer from HEAD to UPDATE),
1808 * then it is up to us to reset it to NORMAL.
1809 */
1810 if (type == RB_PAGE_HEAD) {
1811 ret = rb_head_page_set_normal(cpu_buffer, next_page,
1812 tail_page,
1813 RB_PAGE_UPDATE);
1814 if (RB_WARN_ON(cpu_buffer,
1815 ret != RB_PAGE_UPDATE))
1816 return -1;
1817 }
1818
1819 return 0;
1820}
1821
1822static unsigned rb_calculate_event_length(unsigned length)
1823{
1824 struct ring_buffer_event event; /* Used only for sizeof array */
1825
1826 /* zero length can cause confusions */
1827 if (!length)
1828 length = 1;
1829
1830 if (length > RB_MAX_SMALL_DATA || RB_FORCE_8BYTE_ALIGNMENT)
1831 length += sizeof(event.array[0]);
1832
1833 length += RB_EVNT_HDR_SIZE;
1834 length = ALIGN(length, RB_ARCH_ALIGNMENT);
1835
1836 return length;
1837}
1838
1839static inline void
1840rb_reset_tail(struct ring_buffer_per_cpu *cpu_buffer,
1841 struct buffer_page *tail_page,
1842 unsigned long tail, unsigned long length)
1843{
1844 struct ring_buffer_event *event;
1845
1846 /*
1847 * Only the event that crossed the page boundary
1848 * must fill the old tail_page with padding.
1849 */
1850 if (tail >= BUF_PAGE_SIZE) {
1851 /*
1852 * If the page was filled, then we still need
1853 * to update the real_end. Reset it to zero
1854 * and the reader will ignore it.
1855 */
1856 if (tail == BUF_PAGE_SIZE)
1857 tail_page->real_end = 0;
1858
1859 local_sub(length, &tail_page->write);
1860 return;
1861 }
1862
1863 event = __rb_page_index(tail_page, tail);
1864 kmemcheck_annotate_bitfield(event, bitfield);
1865
1866 /*
1867 * Save the original length to the meta data.
1868 * This will be used by the reader to add lost event
1869 * counter.
1870 */
1871 tail_page->real_end = tail;
1872
1873 /*
1874 * If this event is bigger than the minimum size, then
1875 * we need to be careful that we don't subtract the
1876 * write counter enough to allow another writer to slip
1877 * in on this page.
1878 * We put in a discarded commit instead, to make sure
1879 * that this space is not used again.
1880 *
1881 * If we are less than the minimum size, we don't need to
1882 * worry about it.
1883 */
1884 if (tail > (BUF_PAGE_SIZE - RB_EVNT_MIN_SIZE)) {
1885 /* No room for any events */
1886
1887 /* Mark the rest of the page with padding */
1888 rb_event_set_padding(event);
1889
1890 /* Set the write back to the previous setting */
1891 local_sub(length, &tail_page->write);
1892 return;
1893 }
1894
1895 /* Put in a discarded event */
1896 event->array[0] = (BUF_PAGE_SIZE - tail) - RB_EVNT_HDR_SIZE;
1897 event->type_len = RINGBUF_TYPE_PADDING;
1898 /* time delta must be non zero */
1899 event->time_delta = 1;
1900
1901 /* Set write to end of buffer */
1902 length = (tail + length) - BUF_PAGE_SIZE;
1903 local_sub(length, &tail_page->write);
1904}
1905
1906/*
1907 * This is the slow path, force gcc not to inline it.
1908 */
1909static noinline struct ring_buffer_event *
1910rb_move_tail(struct ring_buffer_per_cpu *cpu_buffer,
1911 unsigned long length, unsigned long tail,
1912 struct buffer_page *tail_page, u64 ts)
1913{
1914 struct buffer_page *commit_page = cpu_buffer->commit_page;
1915 struct ring_buffer *buffer = cpu_buffer->buffer;
1916 struct buffer_page *next_page;
1917 int ret;
1918
1919 next_page = tail_page;
1920
1921 rb_inc_page(cpu_buffer, &next_page);
1922
1923 /*
1924 * If for some reason, we had an interrupt storm that made
1925 * it all the way around the buffer, bail, and warn
1926 * about it.
1927 */
1928 if (unlikely(next_page == commit_page)) {
1929 local_inc(&cpu_buffer->commit_overrun);
1930 goto out_reset;
1931 }
1932
1933 /*
1934 * This is where the fun begins!
1935 *
1936 * We are fighting against races between a reader that
1937 * could be on another CPU trying to swap its reader
1938 * page with the buffer head.
1939 *
1940 * We are also fighting against interrupts coming in and
1941 * moving the head or tail on us as well.
1942 *
1943 * If the next page is the head page then we have filled
1944 * the buffer, unless the commit page is still on the
1945 * reader page.
1946 */
1947 if (rb_is_head_page(cpu_buffer, next_page, &tail_page->list)) {
1948
1949 /*
1950 * If the commit is not on the reader page, then
1951 * move the header page.
1952 */
1953 if (!rb_is_reader_page(cpu_buffer->commit_page)) {
1954 /*
1955 * If we are not in overwrite mode,
1956 * this is easy, just stop here.
1957 */
1958 if (!(buffer->flags & RB_FL_OVERWRITE))
1959 goto out_reset;
1960
1961 ret = rb_handle_head_page(cpu_buffer,
1962 tail_page,
1963 next_page);
1964 if (ret < 0)
1965 goto out_reset;
1966 if (ret)
1967 goto out_again;
1968 } else {
1969 /*
1970 * We need to be careful here too. The
1971 * commit page could still be on the reader
1972 * page. We could have a small buffer, and
1973 * have filled up the buffer with events
1974 * from interrupts and such, and wrapped.
1975 *
1976 * Note, if the tail page is also the on the
1977 * reader_page, we let it move out.
1978 */
1979 if (unlikely((cpu_buffer->commit_page !=
1980 cpu_buffer->tail_page) &&
1981 (cpu_buffer->commit_page ==
1982 cpu_buffer->reader_page))) {
1983 local_inc(&cpu_buffer->commit_overrun);
1984 goto out_reset;
1985 }
1986 }
1987 }
1988
1989 ret = rb_tail_page_update(cpu_buffer, tail_page, next_page);
1990 if (ret) {
1991 /*
1992 * Nested commits always have zero deltas, so
1993 * just reread the time stamp
1994 */
1995 ts = rb_time_stamp(buffer);
1996 next_page->page->time_stamp = ts;
1997 }
1998
1999 out_again:
2000
2001 rb_reset_tail(cpu_buffer, tail_page, tail, length);
2002
2003 /* fail and let the caller try again */
2004 return ERR_PTR(-EAGAIN);
2005
2006 out_reset:
2007 /* reset write */
2008 rb_reset_tail(cpu_buffer, tail_page, tail, length);
2009
2010 return NULL;
2011}
2012
2013static struct ring_buffer_event *
2014__rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
2015 unsigned long length, u64 ts,
2016 u64 delta, int add_timestamp)
2017{
2018 struct buffer_page *tail_page;
2019 struct ring_buffer_event *event;
2020 unsigned long tail, write;
2021
2022 /*
2023 * If the time delta since the last event is too big to
2024 * hold in the time field of the event, then we append a
2025 * TIME EXTEND event ahead of the data event.
2026 */
2027 if (unlikely(add_timestamp))
2028 length += RB_LEN_TIME_EXTEND;
2029
2030 tail_page = cpu_buffer->tail_page;
2031 write = local_add_return(length, &tail_page->write);
2032
2033 /* set write to only the index of the write */
2034 write &= RB_WRITE_MASK;
2035 tail = write - length;
2036
2037 /* See if we shot pass the end of this buffer page */
2038 if (unlikely(write > BUF_PAGE_SIZE))
2039 return rb_move_tail(cpu_buffer, length, tail,
2040 tail_page, ts);
2041
2042 /* We reserved something on the buffer */
2043
2044 event = __rb_page_index(tail_page, tail);
2045 kmemcheck_annotate_bitfield(event, bitfield);
2046 rb_update_event(cpu_buffer, event, length, add_timestamp, delta);
2047
2048 local_inc(&tail_page->entries);
2049
2050 /*
2051 * If this is the first commit on the page, then update
2052 * its timestamp.
2053 */
2054 if (!tail)
2055 tail_page->page->time_stamp = ts;
2056
2057 return event;
2058}
2059
2060static inline int
2061rb_try_to_discard(struct ring_buffer_per_cpu *cpu_buffer,
2062 struct ring_buffer_event *event)
2063{
2064 unsigned long new_index, old_index;
2065 struct buffer_page *bpage;
2066 unsigned long index;
2067 unsigned long addr;
2068
2069 new_index = rb_event_index(event);
2070 old_index = new_index + rb_event_ts_length(event);
2071 addr = (unsigned long)event;
2072 addr &= PAGE_MASK;
2073
2074 bpage = cpu_buffer->tail_page;
2075
2076 if (bpage->page == (void *)addr && rb_page_write(bpage) == old_index) {
2077 unsigned long write_mask =
2078 local_read(&bpage->write) & ~RB_WRITE_MASK;
2079 /*
2080 * This is on the tail page. It is possible that
2081 * a write could come in and move the tail page
2082 * and write to the next page. That is fine
2083 * because we just shorten what is on this page.
2084 */
2085 old_index += write_mask;
2086 new_index += write_mask;
2087 index = local_cmpxchg(&bpage->write, old_index, new_index);
2088 if (index == old_index)
2089 return 1;
2090 }
2091
2092 /* could not discard */
2093 return 0;
2094}
2095
2096static void rb_start_commit(struct ring_buffer_per_cpu *cpu_buffer)
2097{
2098 local_inc(&cpu_buffer->committing);
2099 local_inc(&cpu_buffer->commits);
2100}
2101
2102static inline void rb_end_commit(struct ring_buffer_per_cpu *cpu_buffer)
2103{
2104 unsigned long commits;
2105
2106 if (RB_WARN_ON(cpu_buffer,
2107 !local_read(&cpu_buffer->committing)))
2108 return;
2109
2110 again:
2111 commits = local_read(&cpu_buffer->commits);
2112 /* synchronize with interrupts */
2113 barrier();
2114 if (local_read(&cpu_buffer->committing) == 1)
2115 rb_set_commit_to_write(cpu_buffer);
2116
2117 local_dec(&cpu_buffer->committing);
2118
2119 /* synchronize with interrupts */
2120 barrier();
2121
2122 /*
2123 * Need to account for interrupts coming in between the
2124 * updating of the commit page and the clearing of the
2125 * committing counter.
2126 */
2127 if (unlikely(local_read(&cpu_buffer->commits) != commits) &&
2128 !local_read(&cpu_buffer->committing)) {
2129 local_inc(&cpu_buffer->committing);
2130 goto again;
2131 }
2132}
2133
2134static struct ring_buffer_event *
2135rb_reserve_next_event(struct ring_buffer *buffer,
2136 struct ring_buffer_per_cpu *cpu_buffer,
2137 unsigned long length)
2138{
2139 struct ring_buffer_event *event;
2140 u64 ts, delta;
2141 int nr_loops = 0;
2142 int add_timestamp;
2143 u64 diff;
2144
2145 rb_start_commit(cpu_buffer);
2146
2147#ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
2148 /*
2149 * Due to the ability to swap a cpu buffer from a buffer
2150 * it is possible it was swapped before we committed.
2151 * (committing stops a swap). We check for it here and
2152 * if it happened, we have to fail the write.
2153 */
2154 barrier();
2155 if (unlikely(ACCESS_ONCE(cpu_buffer->buffer) != buffer)) {
2156 local_dec(&cpu_buffer->committing);
2157 local_dec(&cpu_buffer->commits);
2158 return NULL;
2159 }
2160#endif
2161
2162 length = rb_calculate_event_length(length);
2163 again:
2164 add_timestamp = 0;
2165 delta = 0;
2166
2167 /*
2168 * We allow for interrupts to reenter here and do a trace.
2169 * If one does, it will cause this original code to loop
2170 * back here. Even with heavy interrupts happening, this
2171 * should only happen a few times in a row. If this happens
2172 * 1000 times in a row, there must be either an interrupt
2173 * storm or we have something buggy.
2174 * Bail!
2175 */
2176 if (RB_WARN_ON(cpu_buffer, ++nr_loops > 1000))
2177 goto out_fail;
2178
2179 ts = rb_time_stamp(cpu_buffer->buffer);
2180 diff = ts - cpu_buffer->write_stamp;
2181
2182 /* make sure this diff is calculated here */
2183 barrier();
2184
2185 /* Did the write stamp get updated already? */
2186 if (likely(ts >= cpu_buffer->write_stamp)) {
2187 delta = diff;
2188 if (unlikely(test_time_stamp(delta))) {
2189 int local_clock_stable = 1;
2190#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
2191 local_clock_stable = sched_clock_stable;
2192#endif
2193 WARN_ONCE(delta > (1ULL << 59),
2194 KERN_WARNING "Delta way too big! %llu ts=%llu write stamp = %llu\n%s",
2195 (unsigned long long)delta,
2196 (unsigned long long)ts,
2197 (unsigned long long)cpu_buffer->write_stamp,
2198 local_clock_stable ? "" :
2199 "If you just came from a suspend/resume,\n"
2200 "please switch to the trace global clock:\n"
2201 " echo global > /sys/kernel/debug/tracing/trace_clock\n");
2202 add_timestamp = 1;
2203 }
2204 }
2205
2206 event = __rb_reserve_next(cpu_buffer, length, ts,
2207 delta, add_timestamp);
2208 if (unlikely(PTR_ERR(event) == -EAGAIN))
2209 goto again;
2210
2211 if (!event)
2212 goto out_fail;
2213
2214 return event;
2215
2216 out_fail:
2217 rb_end_commit(cpu_buffer);
2218 return NULL;
2219}
2220
2221#ifdef CONFIG_TRACING
2222
2223#define TRACE_RECURSIVE_DEPTH 16
2224
2225/* Keep this code out of the fast path cache */
2226static noinline void trace_recursive_fail(void)
2227{
2228 /* Disable all tracing before we do anything else */
2229 tracing_off_permanent();
2230
2231 printk_once(KERN_WARNING "Tracing recursion: depth[%ld]:"
2232 "HC[%lu]:SC[%lu]:NMI[%lu]\n",
2233 trace_recursion_buffer(),
2234 hardirq_count() >> HARDIRQ_SHIFT,
2235 softirq_count() >> SOFTIRQ_SHIFT,
2236 in_nmi());
2237
2238 WARN_ON_ONCE(1);
2239}
2240
2241static inline int trace_recursive_lock(void)
2242{
2243 trace_recursion_inc();
2244
2245 if (likely(trace_recursion_buffer() < TRACE_RECURSIVE_DEPTH))
2246 return 0;
2247
2248 trace_recursive_fail();
2249
2250 return -1;
2251}
2252
2253static inline void trace_recursive_unlock(void)
2254{
2255 WARN_ON_ONCE(!trace_recursion_buffer());
2256
2257 trace_recursion_dec();
2258}
2259
2260#else
2261
2262#define trace_recursive_lock() (0)
2263#define trace_recursive_unlock() do { } while (0)
2264
2265#endif
2266
2267/**
2268 * ring_buffer_lock_reserve - reserve a part of the buffer
2269 * @buffer: the ring buffer to reserve from
2270 * @length: the length of the data to reserve (excluding event header)
2271 *
2272 * Returns a reseverd event on the ring buffer to copy directly to.
2273 * The user of this interface will need to get the body to write into
2274 * and can use the ring_buffer_event_data() interface.
2275 *
2276 * The length is the length of the data needed, not the event length
2277 * which also includes the event header.
2278 *
2279 * Must be paired with ring_buffer_unlock_commit, unless NULL is returned.
2280 * If NULL is returned, then nothing has been allocated or locked.
2281 */
2282struct ring_buffer_event *
2283ring_buffer_lock_reserve(struct ring_buffer *buffer, unsigned long length)
2284{
2285 struct ring_buffer_per_cpu *cpu_buffer;
2286 struct ring_buffer_event *event;
2287 int cpu;
2288
2289 if (ring_buffer_flags != RB_BUFFERS_ON)
2290 return NULL;
2291
2292 /* If we are tracing schedule, we don't want to recurse */
2293 preempt_disable_notrace();
2294
2295 if (atomic_read(&buffer->record_disabled))
2296 goto out_nocheck;
2297
2298 if (trace_recursive_lock())
2299 goto out_nocheck;
2300
2301 cpu = raw_smp_processor_id();
2302
2303 if (!cpumask_test_cpu(cpu, buffer->cpumask))
2304 goto out;
2305
2306 cpu_buffer = buffer->buffers[cpu];
2307
2308 if (atomic_read(&cpu_buffer->record_disabled))
2309 goto out;
2310
2311 if (length > BUF_MAX_DATA_SIZE)
2312 goto out;
2313
2314 event = rb_reserve_next_event(buffer, cpu_buffer, length);
2315 if (!event)
2316 goto out;
2317
2318 return event;
2319
2320 out:
2321 trace_recursive_unlock();
2322
2323 out_nocheck:
2324 preempt_enable_notrace();
2325 return NULL;
2326}
2327EXPORT_SYMBOL_GPL(ring_buffer_lock_reserve);
2328
2329static void
2330rb_update_write_stamp(struct ring_buffer_per_cpu *cpu_buffer,
2331 struct ring_buffer_event *event)
2332{
2333 u64 delta;
2334
2335 /*
2336 * The event first in the commit queue updates the
2337 * time stamp.
2338 */
2339 if (rb_event_is_commit(cpu_buffer, event)) {
2340 /*
2341 * A commit event that is first on a page
2342 * updates the write timestamp with the page stamp
2343 */
2344 if (!rb_event_index(event))
2345 cpu_buffer->write_stamp =
2346 cpu_buffer->commit_page->page->time_stamp;
2347 else if (event->type_len == RINGBUF_TYPE_TIME_EXTEND) {
2348 delta = event->array[0];
2349 delta <<= TS_SHIFT;
2350 delta += event->time_delta;
2351 cpu_buffer->write_stamp += delta;
2352 } else
2353 cpu_buffer->write_stamp += event->time_delta;
2354 }
2355}
2356
2357static void rb_commit(struct ring_buffer_per_cpu *cpu_buffer,
2358 struct ring_buffer_event *event)
2359{
2360 local_inc(&cpu_buffer->entries);
2361 rb_update_write_stamp(cpu_buffer, event);
2362 rb_end_commit(cpu_buffer);
2363}
2364
2365/**
2366 * ring_buffer_unlock_commit - commit a reserved
2367 * @buffer: The buffer to commit to
2368 * @event: The event pointer to commit.
2369 *
2370 * This commits the data to the ring buffer, and releases any locks held.
2371 *
2372 * Must be paired with ring_buffer_lock_reserve.
2373 */
2374int ring_buffer_unlock_commit(struct ring_buffer *buffer,
2375 struct ring_buffer_event *event)
2376{
2377 struct ring_buffer_per_cpu *cpu_buffer;
2378 int cpu = raw_smp_processor_id();
2379
2380 cpu_buffer = buffer->buffers[cpu];
2381
2382 rb_commit(cpu_buffer, event);
2383
2384 trace_recursive_unlock();
2385
2386 preempt_enable_notrace();
2387
2388 return 0;
2389}
2390EXPORT_SYMBOL_GPL(ring_buffer_unlock_commit);
2391
2392static inline void rb_event_discard(struct ring_buffer_event *event)
2393{
2394 if (event->type_len == RINGBUF_TYPE_TIME_EXTEND)
2395 event = skip_time_extend(event);
2396
2397 /* array[0] holds the actual length for the discarded event */
2398 event->array[0] = rb_event_data_length(event) - RB_EVNT_HDR_SIZE;
2399 event->type_len = RINGBUF_TYPE_PADDING;
2400 /* time delta must be non zero */
2401 if (!event->time_delta)
2402 event->time_delta = 1;
2403}
2404
2405/*
2406 * Decrement the entries to the page that an event is on.
2407 * The event does not even need to exist, only the pointer
2408 * to the page it is on. This may only be called before the commit
2409 * takes place.
2410 */
2411static inline void
2412rb_decrement_entry(struct ring_buffer_per_cpu *cpu_buffer,
2413 struct ring_buffer_event *event)
2414{
2415 unsigned long addr = (unsigned long)event;
2416 struct buffer_page *bpage = cpu_buffer->commit_page;
2417 struct buffer_page *start;
2418
2419 addr &= PAGE_MASK;
2420
2421 /* Do the likely case first */
2422 if (likely(bpage->page == (void *)addr)) {
2423 local_dec(&bpage->entries);
2424 return;
2425 }
2426
2427 /*
2428 * Because the commit page may be on the reader page we
2429 * start with the next page and check the end loop there.
2430 */
2431 rb_inc_page(cpu_buffer, &bpage);
2432 start = bpage;
2433 do {
2434 if (bpage->page == (void *)addr) {
2435 local_dec(&bpage->entries);
2436 return;
2437 }
2438 rb_inc_page(cpu_buffer, &bpage);
2439 } while (bpage != start);
2440
2441 /* commit not part of this buffer?? */
2442 RB_WARN_ON(cpu_buffer, 1);
2443}
2444
2445/**
2446 * ring_buffer_commit_discard - discard an event that has not been committed
2447 * @buffer: the ring buffer
2448 * @event: non committed event to discard
2449 *
2450 * Sometimes an event that is in the ring buffer needs to be ignored.
2451 * This function lets the user discard an event in the ring buffer
2452 * and then that event will not be read later.
2453 *
2454 * This function only works if it is called before the the item has been
2455 * committed. It will try to free the event from the ring buffer
2456 * if another event has not been added behind it.
2457 *
2458 * If another event has been added behind it, it will set the event
2459 * up as discarded, and perform the commit.
2460 *
2461 * If this function is called, do not call ring_buffer_unlock_commit on
2462 * the event.
2463 */
2464void ring_buffer_discard_commit(struct ring_buffer *buffer,
2465 struct ring_buffer_event *event)
2466{
2467 struct ring_buffer_per_cpu *cpu_buffer;
2468 int cpu;
2469
2470 /* The event is discarded regardless */
2471 rb_event_discard(event);
2472
2473 cpu = smp_processor_id();
2474 cpu_buffer = buffer->buffers[cpu];
2475
2476 /*
2477 * This must only be called if the event has not been
2478 * committed yet. Thus we can assume that preemption
2479 * is still disabled.
2480 */
2481 RB_WARN_ON(buffer, !local_read(&cpu_buffer->committing));
2482
2483 rb_decrement_entry(cpu_buffer, event);
2484 if (rb_try_to_discard(cpu_buffer, event))
2485 goto out;
2486
2487 /*
2488 * The commit is still visible by the reader, so we
2489 * must still update the timestamp.
2490 */
2491 rb_update_write_stamp(cpu_buffer, event);
2492 out:
2493 rb_end_commit(cpu_buffer);
2494
2495 trace_recursive_unlock();
2496
2497 preempt_enable_notrace();
2498
2499}
2500EXPORT_SYMBOL_GPL(ring_buffer_discard_commit);
2501
2502/**
2503 * ring_buffer_write - write data to the buffer without reserving
2504 * @buffer: The ring buffer to write to.
2505 * @length: The length of the data being written (excluding the event header)
2506 * @data: The data to write to the buffer.
2507 *
2508 * This is like ring_buffer_lock_reserve and ring_buffer_unlock_commit as
2509 * one function. If you already have the data to write to the buffer, it
2510 * may be easier to simply call this function.
2511 *
2512 * Note, like ring_buffer_lock_reserve, the length is the length of the data
2513 * and not the length of the event which would hold the header.
2514 */
2515int ring_buffer_write(struct ring_buffer *buffer,
2516 unsigned long length,
2517 void *data)
2518{
2519 struct ring_buffer_per_cpu *cpu_buffer;
2520 struct ring_buffer_event *event;
2521 void *body;
2522 int ret = -EBUSY;
2523 int cpu;
2524
2525 if (ring_buffer_flags != RB_BUFFERS_ON)
2526 return -EBUSY;
2527
2528 preempt_disable_notrace();
2529
2530 if (atomic_read(&buffer->record_disabled))
2531 goto out;
2532
2533 cpu = raw_smp_processor_id();
2534
2535 if (!cpumask_test_cpu(cpu, buffer->cpumask))
2536 goto out;
2537
2538 cpu_buffer = buffer->buffers[cpu];
2539
2540 if (atomic_read(&cpu_buffer->record_disabled))
2541 goto out;
2542
2543 if (length > BUF_MAX_DATA_SIZE)
2544 goto out;
2545
2546 event = rb_reserve_next_event(buffer, cpu_buffer, length);
2547 if (!event)
2548 goto out;
2549
2550 body = rb_event_data(event);
2551
2552 memcpy(body, data, length);
2553
2554 rb_commit(cpu_buffer, event);
2555
2556 ret = 0;
2557 out:
2558 preempt_enable_notrace();
2559
2560 return ret;
2561}
2562EXPORT_SYMBOL_GPL(ring_buffer_write);
2563
2564static int rb_per_cpu_empty(struct ring_buffer_per_cpu *cpu_buffer)
2565{
2566 struct buffer_page *reader = cpu_buffer->reader_page;
2567 struct buffer_page *head = rb_set_head_page(cpu_buffer);
2568 struct buffer_page *commit = cpu_buffer->commit_page;
2569
2570 /* In case of error, head will be NULL */
2571 if (unlikely(!head))
2572 return 1;
2573
2574 return reader->read == rb_page_commit(reader) &&
2575 (commit == reader ||
2576 (commit == head &&
2577 head->read == rb_page_commit(commit)));
2578}
2579
2580/**
2581 * ring_buffer_record_disable - stop all writes into the buffer
2582 * @buffer: The ring buffer to stop writes to.
2583 *
2584 * This prevents all writes to the buffer. Any attempt to write
2585 * to the buffer after this will fail and return NULL.
2586 *
2587 * The caller should call synchronize_sched() after this.
2588 */
2589void ring_buffer_record_disable(struct ring_buffer *buffer)
2590{
2591 atomic_inc(&buffer->record_disabled);
2592}
2593EXPORT_SYMBOL_GPL(ring_buffer_record_disable);
2594
2595/**
2596 * ring_buffer_record_enable - enable writes to the buffer
2597 * @buffer: The ring buffer to enable writes
2598 *
2599 * Note, multiple disables will need the same number of enables
2600 * to truly enable the writing (much like preempt_disable).
2601 */
2602void ring_buffer_record_enable(struct ring_buffer *buffer)
2603{
2604 atomic_dec(&buffer->record_disabled);
2605}
2606EXPORT_SYMBOL_GPL(ring_buffer_record_enable);
2607
2608/**
2609 * ring_buffer_record_disable_cpu - stop all writes into the cpu_buffer
2610 * @buffer: The ring buffer to stop writes to.
2611 * @cpu: The CPU buffer to stop
2612 *
2613 * This prevents all writes to the buffer. Any attempt to write
2614 * to the buffer after this will fail and return NULL.
2615 *
2616 * The caller should call synchronize_sched() after this.
2617 */
2618void ring_buffer_record_disable_cpu(struct ring_buffer *buffer, int cpu)
2619{
2620 struct ring_buffer_per_cpu *cpu_buffer;
2621
2622 if (!cpumask_test_cpu(cpu, buffer->cpumask))
2623 return;
2624
2625 cpu_buffer = buffer->buffers[cpu];
2626 atomic_inc(&cpu_buffer->record_disabled);
2627}
2628EXPORT_SYMBOL_GPL(ring_buffer_record_disable_cpu);
2629
2630/**
2631 * ring_buffer_record_enable_cpu - enable writes to the buffer
2632 * @buffer: The ring buffer to enable writes
2633 * @cpu: The CPU to enable.
2634 *
2635 * Note, multiple disables will need the same number of enables
2636 * to truly enable the writing (much like preempt_disable).
2637 */
2638void ring_buffer_record_enable_cpu(struct ring_buffer *buffer, int cpu)
2639{
2640 struct ring_buffer_per_cpu *cpu_buffer;
2641
2642 if (!cpumask_test_cpu(cpu, buffer->cpumask))
2643 return;
2644
2645 cpu_buffer = buffer->buffers[cpu];
2646 atomic_dec(&cpu_buffer->record_disabled);
2647}
2648EXPORT_SYMBOL_GPL(ring_buffer_record_enable_cpu);
2649
2650/*
2651 * The total entries in the ring buffer is the running counter
2652 * of entries entered into the ring buffer, minus the sum of
2653 * the entries read from the ring buffer and the number of
2654 * entries that were overwritten.
2655 */
2656static inline unsigned long
2657rb_num_of_entries(struct ring_buffer_per_cpu *cpu_buffer)
2658{
2659 return local_read(&cpu_buffer->entries) -
2660 (local_read(&cpu_buffer->overrun) + cpu_buffer->read);
2661}
2662
2663/**
2664 * ring_buffer_entries_cpu - get the number of entries in a cpu buffer
2665 * @buffer: The ring buffer
2666 * @cpu: The per CPU buffer to get the entries from.
2667 */
2668unsigned long ring_buffer_entries_cpu(struct ring_buffer *buffer, int cpu)
2669{
2670 struct ring_buffer_per_cpu *cpu_buffer;
2671
2672 if (!cpumask_test_cpu(cpu, buffer->cpumask))
2673 return 0;
2674
2675 cpu_buffer = buffer->buffers[cpu];
2676
2677 return rb_num_of_entries(cpu_buffer);
2678}
2679EXPORT_SYMBOL_GPL(ring_buffer_entries_cpu);
2680
2681/**
2682 * ring_buffer_overrun_cpu - get the number of overruns in a cpu_buffer
2683 * @buffer: The ring buffer
2684 * @cpu: The per CPU buffer to get the number of overruns from
2685 */
2686unsigned long ring_buffer_overrun_cpu(struct ring_buffer *buffer, int cpu)
2687{
2688 struct ring_buffer_per_cpu *cpu_buffer;
2689 unsigned long ret;
2690
2691 if (!cpumask_test_cpu(cpu, buffer->cpumask))
2692 return 0;
2693
2694 cpu_buffer = buffer->buffers[cpu];
2695 ret = local_read(&cpu_buffer->overrun);
2696
2697 return ret;
2698}
2699EXPORT_SYMBOL_GPL(ring_buffer_overrun_cpu);
2700
2701/**
2702 * ring_buffer_commit_overrun_cpu - get the number of overruns caused by commits
2703 * @buffer: The ring buffer
2704 * @cpu: The per CPU buffer to get the number of overruns from
2705 */
2706unsigned long
2707ring_buffer_commit_overrun_cpu(struct ring_buffer *buffer, int cpu)
2708{
2709 struct ring_buffer_per_cpu *cpu_buffer;
2710 unsigned long ret;
2711
2712 if (!cpumask_test_cpu(cpu, buffer->cpumask))
2713 return 0;
2714
2715 cpu_buffer = buffer->buffers[cpu];
2716 ret = local_read(&cpu_buffer->commit_overrun);
2717
2718 return ret;
2719}
2720EXPORT_SYMBOL_GPL(ring_buffer_commit_overrun_cpu);
2721
2722/**
2723 * ring_buffer_entries - get the number of entries in a buffer
2724 * @buffer: The ring buffer
2725 *
2726 * Returns the total number of entries in the ring buffer
2727 * (all CPU entries)
2728 */
2729unsigned long ring_buffer_entries(struct ring_buffer *buffer)
2730{
2731 struct ring_buffer_per_cpu *cpu_buffer;
2732 unsigned long entries = 0;
2733 int cpu;
2734
2735 /* if you care about this being correct, lock the buffer */
2736 for_each_buffer_cpu(buffer, cpu) {
2737 cpu_buffer = buffer->buffers[cpu];
2738 entries += rb_num_of_entries(cpu_buffer);
2739 }
2740
2741 return entries;
2742}
2743EXPORT_SYMBOL_GPL(ring_buffer_entries);
2744
2745/**
2746 * ring_buffer_overruns - get the number of overruns in buffer
2747 * @buffer: The ring buffer
2748 *
2749 * Returns the total number of overruns in the ring buffer
2750 * (all CPU entries)
2751 */
2752unsigned long ring_buffer_overruns(struct ring_buffer *buffer)
2753{
2754 struct ring_buffer_per_cpu *cpu_buffer;
2755 unsigned long overruns = 0;
2756 int cpu;
2757
2758 /* if you care about this being correct, lock the buffer */
2759 for_each_buffer_cpu(buffer, cpu) {
2760 cpu_buffer = buffer->buffers[cpu];
2761 overruns += local_read(&cpu_buffer->overrun);
2762 }
2763
2764 return overruns;
2765}
2766EXPORT_SYMBOL_GPL(ring_buffer_overruns);
2767
2768static void rb_iter_reset(struct ring_buffer_iter *iter)
2769{
2770 struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
2771
2772 /* Iterator usage is expected to have record disabled */
2773 if (list_empty(&cpu_buffer->reader_page->list)) {
2774 iter->head_page = rb_set_head_page(cpu_buffer);
2775 if (unlikely(!iter->head_page))
2776 return;
2777 iter->head = iter->head_page->read;
2778 } else {
2779 iter->head_page = cpu_buffer->reader_page;
2780 iter->head = cpu_buffer->reader_page->read;
2781 }
2782 if (iter->head)
2783 iter->read_stamp = cpu_buffer->read_stamp;
2784 else
2785 iter->read_stamp = iter->head_page->page->time_stamp;
2786 iter->cache_reader_page = cpu_buffer->reader_page;
2787 iter->cache_read = cpu_buffer->read;
2788}
2789
2790/**
2791 * ring_buffer_iter_reset - reset an iterator
2792 * @iter: The iterator to reset
2793 *
2794 * Resets the iterator, so that it will start from the beginning
2795 * again.
2796 */
2797void ring_buffer_iter_reset(struct ring_buffer_iter *iter)
2798{
2799 struct ring_buffer_per_cpu *cpu_buffer;
2800 unsigned long flags;
2801
2802 if (!iter)
2803 return;
2804
2805 cpu_buffer = iter->cpu_buffer;
2806
2807 spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
2808 rb_iter_reset(iter);
2809 spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
2810}
2811EXPORT_SYMBOL_GPL(ring_buffer_iter_reset);
2812
2813/**
2814 * ring_buffer_iter_empty - check if an iterator has no more to read
2815 * @iter: The iterator to check
2816 */
2817int ring_buffer_iter_empty(struct ring_buffer_iter *iter)
2818{
2819 struct ring_buffer_per_cpu *cpu_buffer;
2820
2821 cpu_buffer = iter->cpu_buffer;
2822
2823 return iter->head_page == cpu_buffer->commit_page &&
2824 iter->head == rb_commit_index(cpu_buffer);
2825}
2826EXPORT_SYMBOL_GPL(ring_buffer_iter_empty);
2827
2828static void
2829rb_update_read_stamp(struct ring_buffer_per_cpu *cpu_buffer,
2830 struct ring_buffer_event *event)
2831{
2832 u64 delta;
2833
2834 switch (event->type_len) {
2835 case RINGBUF_TYPE_PADDING:
2836 return;
2837
2838 case RINGBUF_TYPE_TIME_EXTEND:
2839 delta = event->array[0];
2840 delta <<= TS_SHIFT;
2841 delta += event->time_delta;
2842 cpu_buffer->read_stamp += delta;
2843 return;
2844
2845 case RINGBUF_TYPE_TIME_STAMP:
2846 /* FIXME: not implemented */
2847 return;
2848
2849 case RINGBUF_TYPE_DATA:
2850 cpu_buffer->read_stamp += event->time_delta;
2851 return;
2852
2853 default:
2854 BUG();
2855 }
2856 return;
2857}
2858
2859static void
2860rb_update_iter_read_stamp(struct ring_buffer_iter *iter,
2861 struct ring_buffer_event *event)
2862{
2863 u64 delta;
2864
2865 switch (event->type_len) {
2866 case RINGBUF_TYPE_PADDING:
2867 return;
2868
2869 case RINGBUF_TYPE_TIME_EXTEND:
2870 delta = event->array[0];
2871 delta <<= TS_SHIFT;
2872 delta += event->time_delta;
2873 iter->read_stamp += delta;
2874 return;
2875
2876 case RINGBUF_TYPE_TIME_STAMP:
2877 /* FIXME: not implemented */
2878 return;
2879
2880 case RINGBUF_TYPE_DATA:
2881 iter->read_stamp += event->time_delta;
2882 return;
2883
2884 default:
2885 BUG();
2886 }
2887 return;
2888}
2889
2890static struct buffer_page *
2891rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
2892{
2893 struct buffer_page *reader = NULL;
2894 unsigned long overwrite;
2895 unsigned long flags;
2896 int nr_loops = 0;
2897 int ret;
2898
2899 local_irq_save(flags);
2900 arch_spin_lock(&cpu_buffer->lock);
2901
2902 again:
2903 /*
2904 * This should normally only loop twice. But because the
2905 * start of the reader inserts an empty page, it causes
2906 * a case where we will loop three times. There should be no
2907 * reason to loop four times (that I know of).
2908 */
2909 if (RB_WARN_ON(cpu_buffer, ++nr_loops > 3)) {
2910 reader = NULL;
2911 goto out;
2912 }
2913
2914 reader = cpu_buffer->reader_page;
2915
2916 /* If there's more to read, return this page */
2917 if (cpu_buffer->reader_page->read < rb_page_size(reader))
2918 goto out;
2919
2920 /* Never should we have an index greater than the size */
2921 if (RB_WARN_ON(cpu_buffer,
2922 cpu_buffer->reader_page->read > rb_page_size(reader)))
2923 goto out;
2924
2925 /* check if we caught up to the tail */
2926 reader = NULL;
2927 if (cpu_buffer->commit_page == cpu_buffer->reader_page)
2928 goto out;
2929
2930 /*
2931 * Reset the reader page to size zero.
2932 */
2933 local_set(&cpu_buffer->reader_page->write, 0);
2934 local_set(&cpu_buffer->reader_page->entries, 0);
2935 local_set(&cpu_buffer->reader_page->page->commit, 0);
2936 cpu_buffer->reader_page->real_end = 0;
2937
2938 spin:
2939 /*
2940 * Splice the empty reader page into the list around the head.
2941 */
2942 reader = rb_set_head_page(cpu_buffer);
2943 cpu_buffer->reader_page->list.next = rb_list_head(reader->list.next);
2944 cpu_buffer->reader_page->list.prev = reader->list.prev;
2945
2946 /*
2947 * cpu_buffer->pages just needs to point to the buffer, it
2948 * has no specific buffer page to point to. Lets move it out
2949 * of our way so we don't accidentally swap it.
2950 */
2951 cpu_buffer->pages = reader->list.prev;
2952
2953 /* The reader page will be pointing to the new head */
2954 rb_set_list_to_head(cpu_buffer, &cpu_buffer->reader_page->list);
2955
2956 /*
2957 * We want to make sure we read the overruns after we set up our
2958 * pointers to the next object. The writer side does a
2959 * cmpxchg to cross pages which acts as the mb on the writer
2960 * side. Note, the reader will constantly fail the swap
2961 * while the writer is updating the pointers, so this
2962 * guarantees that the overwrite recorded here is the one we
2963 * want to compare with the last_overrun.
2964 */
2965 smp_mb();
2966 overwrite = local_read(&(cpu_buffer->overrun));
2967
2968 /*
2969 * Here's the tricky part.
2970 *
2971 * We need to move the pointer past the header page.
2972 * But we can only do that if a writer is not currently
2973 * moving it. The page before the header page has the
2974 * flag bit '1' set if it is pointing to the page we want.
2975 * but if the writer is in the process of moving it
2976 * than it will be '2' or already moved '0'.
2977 */
2978
2979 ret = rb_head_page_replace(reader, cpu_buffer->reader_page);
2980
2981 /*
2982 * If we did not convert it, then we must try again.
2983 */
2984 if (!ret)
2985 goto spin;
2986
2987 /*
2988 * Yeah! We succeeded in replacing the page.
2989 *
2990 * Now make the new head point back to the reader page.
2991 */
2992 rb_list_head(reader->list.next)->prev = &cpu_buffer->reader_page->list;
2993 rb_inc_page(cpu_buffer, &cpu_buffer->head_page);
2994
2995 /* Finally update the reader page to the new head */
2996 cpu_buffer->reader_page = reader;
2997 rb_reset_reader_page(cpu_buffer);
2998
2999 if (overwrite != cpu_buffer->last_overrun) {
3000 cpu_buffer->lost_events = overwrite - cpu_buffer->last_overrun;
3001 cpu_buffer->last_overrun = overwrite;
3002 }
3003
3004 goto again;
3005
3006 out:
3007 arch_spin_unlock(&cpu_buffer->lock);
3008 local_irq_restore(flags);
3009
3010 return reader;
3011}
3012
3013static void rb_advance_reader(struct ring_buffer_per_cpu *cpu_buffer)
3014{
3015 struct ring_buffer_event *event;
3016 struct buffer_page *reader;
3017 unsigned length;
3018
3019 reader = rb_get_reader_page(cpu_buffer);
3020
3021 /* This function should not be called when buffer is empty */
3022 if (RB_WARN_ON(cpu_buffer, !reader))
3023 return;
3024
3025 event = rb_reader_event(cpu_buffer);
3026
3027 if (event->type_len <= RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
3028 cpu_buffer->read++;
3029
3030 rb_update_read_stamp(cpu_buffer, event);
3031
3032 length = rb_event_length(event);
3033 cpu_buffer->reader_page->read += length;
3034}
3035
3036static void rb_advance_iter(struct ring_buffer_iter *iter)
3037{
3038 struct ring_buffer_per_cpu *cpu_buffer;
3039 struct ring_buffer_event *event;
3040 unsigned length;
3041
3042 cpu_buffer = iter->cpu_buffer;
3043
3044 /*
3045 * Check if we are at the end of the buffer.
3046 */
3047 if (iter->head >= rb_page_size(iter->head_page)) {
3048 /* discarded commits can make the page empty */
3049 if (iter->head_page == cpu_buffer->commit_page)
3050 return;
3051 rb_inc_iter(iter);
3052 return;
3053 }
3054
3055 event = rb_iter_head_event(iter);
3056
3057 length = rb_event_length(event);
3058
3059 /*
3060 * This should not be called to advance the header if we are
3061 * at the tail of the buffer.
3062 */
3063 if (RB_WARN_ON(cpu_buffer,
3064 (iter->head_page == cpu_buffer->commit_page) &&
3065 (iter->head + length > rb_commit_index(cpu_buffer))))
3066 return;
3067
3068 rb_update_iter_read_stamp(iter, event);
3069
3070 iter->head += length;
3071
3072 /* check for end of page padding */
3073 if ((iter->head >= rb_page_size(iter->head_page)) &&
3074 (iter->head_page != cpu_buffer->commit_page))
3075 rb_advance_iter(iter);
3076}
3077
3078static int rb_lost_events(struct ring_buffer_per_cpu *cpu_buffer)
3079{
3080 return cpu_buffer->lost_events;
3081}
3082
3083static struct ring_buffer_event *
3084rb_buffer_peek(struct ring_buffer_per_cpu *cpu_buffer, u64 *ts,
3085 unsigned long *lost_events)
3086{
3087 struct ring_buffer_event *event;
3088 struct buffer_page *reader;
3089 int nr_loops = 0;
3090
3091 again:
3092 /*
3093 * We repeat when a time extend is encountered.
3094 * Since the time extend is always attached to a data event,
3095 * we should never loop more than once.
3096 * (We never hit the following condition more than twice).
3097 */
3098 if (RB_WARN_ON(cpu_buffer, ++nr_loops > 2))
3099 return NULL;
3100
3101 reader = rb_get_reader_page(cpu_buffer);
3102 if (!reader)
3103 return NULL;
3104
3105 event = rb_reader_event(cpu_buffer);
3106
3107 switch (event->type_len) {
3108 case RINGBUF_TYPE_PADDING:
3109 if (rb_null_event(event))
3110 RB_WARN_ON(cpu_buffer, 1);
3111 /*
3112 * Because the writer could be discarding every
3113 * event it creates (which would probably be bad)
3114 * if we were to go back to "again" then we may never
3115 * catch up, and will trigger the warn on, or lock
3116 * the box. Return the padding, and we will release
3117 * the current locks, and try again.
3118 */
3119 return event;
3120
3121 case RINGBUF_TYPE_TIME_EXTEND:
3122 /* Internal data, OK to advance */
3123 rb_advance_reader(cpu_buffer);
3124 goto again;
3125
3126 case RINGBUF_TYPE_TIME_STAMP:
3127 /* FIXME: not implemented */
3128 rb_advance_reader(cpu_buffer);
3129 goto again;
3130
3131 case RINGBUF_TYPE_DATA:
3132 if (ts) {
3133 *ts = cpu_buffer->read_stamp + event->time_delta;
3134 ring_buffer_normalize_time_stamp(cpu_buffer->buffer,
3135 cpu_buffer->cpu, ts);
3136 }
3137 if (lost_events)
3138 *lost_events = rb_lost_events(cpu_buffer);
3139 return event;
3140
3141 default:
3142 BUG();
3143 }
3144
3145 return NULL;
3146}
3147EXPORT_SYMBOL_GPL(ring_buffer_peek);
3148
3149static struct ring_buffer_event *
3150rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
3151{
3152 struct ring_buffer *buffer;
3153 struct ring_buffer_per_cpu *cpu_buffer;
3154 struct ring_buffer_event *event;
3155 int nr_loops = 0;
3156
3157 cpu_buffer = iter->cpu_buffer;
3158 buffer = cpu_buffer->buffer;
3159
3160 /*
3161 * Check if someone performed a consuming read to
3162 * the buffer. A consuming read invalidates the iterator
3163 * and we need to reset the iterator in this case.
3164 */
3165 if (unlikely(iter->cache_read != cpu_buffer->read ||
3166 iter->cache_reader_page != cpu_buffer->reader_page))
3167 rb_iter_reset(iter);
3168
3169 again:
3170 if (ring_buffer_iter_empty(iter))
3171 return NULL;
3172
3173 /*
3174 * We repeat when a time extend is encountered.
3175 * Since the time extend is always attached to a data event,
3176 * we should never loop more than once.
3177 * (We never hit the following condition more than twice).
3178 */
3179 if (RB_WARN_ON(cpu_buffer, ++nr_loops > 2))
3180 return NULL;
3181
3182 if (rb_per_cpu_empty(cpu_buffer))
3183 return NULL;
3184
3185 if (iter->head >= local_read(&iter->head_page->page->commit)) {
3186 rb_inc_iter(iter);
3187 goto again;
3188 }
3189
3190 event = rb_iter_head_event(iter);
3191
3192 switch (event->type_len) {
3193 case RINGBUF_TYPE_PADDING:
3194 if (rb_null_event(event)) {
3195 rb_inc_iter(iter);
3196 goto again;
3197 }
3198 rb_advance_iter(iter);
3199 return event;
3200
3201 case RINGBUF_TYPE_TIME_EXTEND:
3202 /* Internal data, OK to advance */
3203 rb_advance_iter(iter);
3204 goto again;
3205
3206 case RINGBUF_TYPE_TIME_STAMP:
3207 /* FIXME: not implemented */
3208 rb_advance_iter(iter);
3209 goto again;
3210
3211 case RINGBUF_TYPE_DATA:
3212 if (ts) {
3213 *ts = iter->read_stamp + event->time_delta;
3214 ring_buffer_normalize_time_stamp(buffer,
3215 cpu_buffer->cpu, ts);
3216 }
3217 return event;
3218
3219 default:
3220 BUG();
3221 }
3222
3223 return NULL;
3224}
3225EXPORT_SYMBOL_GPL(ring_buffer_iter_peek);
3226
3227static inline int rb_ok_to_lock(void)
3228{
3229 /*
3230 * If an NMI die dumps out the content of the ring buffer
3231 * do not grab locks. We also permanently disable the ring
3232 * buffer too. A one time deal is all you get from reading
3233 * the ring buffer from an NMI.
3234 */
3235 if (likely(!in_nmi()))
3236 return 1;
3237
3238 tracing_off_permanent();
3239 return 0;
3240}
3241
3242/**
3243 * ring_buffer_peek - peek at the next event to be read
3244 * @buffer: The ring buffer to read
3245 * @cpu: The cpu to peak at
3246 * @ts: The timestamp counter of this event.
3247 * @lost_events: a variable to store if events were lost (may be NULL)
3248 *
3249 * This will return the event that will be read next, but does
3250 * not consume the data.
3251 */
3252struct ring_buffer_event *
3253ring_buffer_peek(struct ring_buffer *buffer, int cpu, u64 *ts,
3254 unsigned long *lost_events)
3255{
3256 struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
3257 struct ring_buffer_event *event;
3258 unsigned long flags;
3259 int dolock;
3260
3261 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3262 return NULL;
3263
3264 dolock = rb_ok_to_lock();
3265 again:
3266 local_irq_save(flags);
3267 if (dolock)
3268 spin_lock(&cpu_buffer->reader_lock);
3269 event = rb_buffer_peek(cpu_buffer, ts, lost_events);
3270 if (event && event->type_len == RINGBUF_TYPE_PADDING)
3271 rb_advance_reader(cpu_buffer);
3272 if (dolock)
3273 spin_unlock(&cpu_buffer->reader_lock);
3274 local_irq_restore(flags);
3275
3276 if (event && event->type_len == RINGBUF_TYPE_PADDING)
3277 goto again;
3278
3279 return event;
3280}
3281
3282/**
3283 * ring_buffer_iter_peek - peek at the next event to be read
3284 * @iter: The ring buffer iterator
3285 * @ts: The timestamp counter of this event.
3286 *
3287 * This will return the event that will be read next, but does
3288 * not increment the iterator.
3289 */
3290struct ring_buffer_event *
3291ring_buffer_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
3292{
3293 struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
3294 struct ring_buffer_event *event;
3295 unsigned long flags;
3296
3297 again:
3298 spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
3299 event = rb_iter_peek(iter, ts);
3300 spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
3301
3302 if (event && event->type_len == RINGBUF_TYPE_PADDING)
3303 goto again;
3304
3305 return event;
3306}
3307
3308/**
3309 * ring_buffer_consume - return an event and consume it
3310 * @buffer: The ring buffer to get the next event from
3311 * @cpu: the cpu to read the buffer from
3312 * @ts: a variable to store the timestamp (may be NULL)
3313 * @lost_events: a variable to store if events were lost (may be NULL)
3314 *
3315 * Returns the next event in the ring buffer, and that event is consumed.
3316 * Meaning, that sequential reads will keep returning a different event,
3317 * and eventually empty the ring buffer if the producer is slower.
3318 */
3319struct ring_buffer_event *
3320ring_buffer_consume(struct ring_buffer *buffer, int cpu, u64 *ts,
3321 unsigned long *lost_events)
3322{
3323 struct ring_buffer_per_cpu *cpu_buffer;
3324 struct ring_buffer_event *event = NULL;
3325 unsigned long flags;
3326 int dolock;
3327
3328 dolock = rb_ok_to_lock();
3329
3330 again:
3331 /* might be called in atomic */
3332 preempt_disable();
3333
3334 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3335 goto out;
3336
3337 cpu_buffer = buffer->buffers[cpu];
3338 local_irq_save(flags);
3339 if (dolock)
3340 spin_lock(&cpu_buffer->reader_lock);
3341
3342 event = rb_buffer_peek(cpu_buffer, ts, lost_events);
3343 if (event) {
3344 cpu_buffer->lost_events = 0;
3345 rb_advance_reader(cpu_buffer);
3346 }
3347
3348 if (dolock)
3349 spin_unlock(&cpu_buffer->reader_lock);
3350 local_irq_restore(flags);
3351
3352 out:
3353 preempt_enable();
3354
3355 if (event && event->type_len == RINGBUF_TYPE_PADDING)
3356 goto again;
3357
3358 return event;
3359}
3360EXPORT_SYMBOL_GPL(ring_buffer_consume);
3361
3362/**
3363 * ring_buffer_read_prepare - Prepare for a non consuming read of the buffer
3364 * @buffer: The ring buffer to read from
3365 * @cpu: The cpu buffer to iterate over
3366 *
3367 * This performs the initial preparations necessary to iterate
3368 * through the buffer. Memory is allocated, buffer recording
3369 * is disabled, and the iterator pointer is returned to the caller.
3370 *
3371 * Disabling buffer recordng prevents the reading from being
3372 * corrupted. This is not a consuming read, so a producer is not
3373 * expected.
3374 *
3375 * After a sequence of ring_buffer_read_prepare calls, the user is
3376 * expected to make at least one call to ring_buffer_prepare_sync.
3377 * Afterwards, ring_buffer_read_start is invoked to get things going
3378 * for real.
3379 *
3380 * This overall must be paired with ring_buffer_finish.
3381 */
3382struct ring_buffer_iter *
3383ring_buffer_read_prepare(struct ring_buffer *buffer, int cpu)
3384{
3385 struct ring_buffer_per_cpu *cpu_buffer;
3386 struct ring_buffer_iter *iter;
3387
3388 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3389 return NULL;
3390
3391 iter = kmalloc(sizeof(*iter), GFP_KERNEL);
3392 if (!iter)
3393 return NULL;
3394
3395 cpu_buffer = buffer->buffers[cpu];
3396
3397 iter->cpu_buffer = cpu_buffer;
3398
3399 atomic_inc(&cpu_buffer->record_disabled);
3400
3401 return iter;
3402}
3403EXPORT_SYMBOL_GPL(ring_buffer_read_prepare);
3404
3405/**
3406 * ring_buffer_read_prepare_sync - Synchronize a set of prepare calls
3407 *
3408 * All previously invoked ring_buffer_read_prepare calls to prepare
3409 * iterators will be synchronized. Afterwards, read_buffer_read_start
3410 * calls on those iterators are allowed.
3411 */
3412void
3413ring_buffer_read_prepare_sync(void)
3414{
3415 synchronize_sched();
3416}
3417EXPORT_SYMBOL_GPL(ring_buffer_read_prepare_sync);
3418
3419/**
3420 * ring_buffer_read_start - start a non consuming read of the buffer
3421 * @iter: The iterator returned by ring_buffer_read_prepare
3422 *
3423 * This finalizes the startup of an iteration through the buffer.
3424 * The iterator comes from a call to ring_buffer_read_prepare and
3425 * an intervening ring_buffer_read_prepare_sync must have been
3426 * performed.
3427 *
3428 * Must be paired with ring_buffer_finish.
3429 */
3430void
3431ring_buffer_read_start(struct ring_buffer_iter *iter)
3432{
3433 struct ring_buffer_per_cpu *cpu_buffer;
3434 unsigned long flags;
3435
3436 if (!iter)
3437 return;
3438
3439 cpu_buffer = iter->cpu_buffer;
3440
3441 spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
3442 arch_spin_lock(&cpu_buffer->lock);
3443 rb_iter_reset(iter);
3444 arch_spin_unlock(&cpu_buffer->lock);
3445 spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
3446}
3447EXPORT_SYMBOL_GPL(ring_buffer_read_start);
3448
3449/**
3450 * ring_buffer_finish - finish reading the iterator of the buffer
3451 * @iter: The iterator retrieved by ring_buffer_start
3452 *
3453 * This re-enables the recording to the buffer, and frees the
3454 * iterator.
3455 */
3456void
3457ring_buffer_read_finish(struct ring_buffer_iter *iter)
3458{
3459 struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
3460
3461 atomic_dec(&cpu_buffer->record_disabled);
3462 kfree(iter);
3463}
3464EXPORT_SYMBOL_GPL(ring_buffer_read_finish);
3465
3466/**
3467 * ring_buffer_read - read the next item in the ring buffer by the iterator
3468 * @iter: The ring buffer iterator
3469 * @ts: The time stamp of the event read.
3470 *
3471 * This reads the next event in the ring buffer and increments the iterator.
3472 */
3473struct ring_buffer_event *
3474ring_buffer_read(struct ring_buffer_iter *iter, u64 *ts)
3475{
3476 struct ring_buffer_event *event;
3477 struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
3478 unsigned long flags;
3479
3480 spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
3481 again:
3482 event = rb_iter_peek(iter, ts);
3483 if (!event)
3484 goto out;
3485
3486 if (event->type_len == RINGBUF_TYPE_PADDING)
3487 goto again;
3488
3489 rb_advance_iter(iter);
3490 out:
3491 spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
3492
3493 return event;
3494}
3495EXPORT_SYMBOL_GPL(ring_buffer_read);
3496
3497/**
3498 * ring_buffer_size - return the size of the ring buffer (in bytes)
3499 * @buffer: The ring buffer.
3500 */
3501unsigned long ring_buffer_size(struct ring_buffer *buffer)
3502{
3503 return BUF_PAGE_SIZE * buffer->pages;
3504}
3505EXPORT_SYMBOL_GPL(ring_buffer_size);
3506
3507static void
3508rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
3509{
3510 rb_head_page_deactivate(cpu_buffer);
3511
3512 cpu_buffer->head_page
3513 = list_entry(cpu_buffer->pages, struct buffer_page, list);
3514 local_set(&cpu_buffer->head_page->write, 0);
3515 local_set(&cpu_buffer->head_page->entries, 0);
3516 local_set(&cpu_buffer->head_page->page->commit, 0);
3517
3518 cpu_buffer->head_page->read = 0;
3519
3520 cpu_buffer->tail_page = cpu_buffer->head_page;
3521 cpu_buffer->commit_page = cpu_buffer->head_page;
3522
3523 INIT_LIST_HEAD(&cpu_buffer->reader_page->list);
3524 local_set(&cpu_buffer->reader_page->write, 0);
3525 local_set(&cpu_buffer->reader_page->entries, 0);
3526 local_set(&cpu_buffer->reader_page->page->commit, 0);
3527 cpu_buffer->reader_page->read = 0;
3528
3529 local_set(&cpu_buffer->commit_overrun, 0);
3530 local_set(&cpu_buffer->overrun, 0);
3531 local_set(&cpu_buffer->entries, 0);
3532 local_set(&cpu_buffer->committing, 0);
3533 local_set(&cpu_buffer->commits, 0);
3534 cpu_buffer->read = 0;
3535
3536 cpu_buffer->write_stamp = 0;
3537 cpu_buffer->read_stamp = 0;
3538
3539 cpu_buffer->lost_events = 0;
3540 cpu_buffer->last_overrun = 0;
3541
3542 rb_head_page_activate(cpu_buffer);
3543}
3544
3545/**
3546 * ring_buffer_reset_cpu - reset a ring buffer per CPU buffer
3547 * @buffer: The ring buffer to reset a per cpu buffer of
3548 * @cpu: The CPU buffer to be reset
3549 */
3550void ring_buffer_reset_cpu(struct ring_buffer *buffer, int cpu)
3551{
3552 struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
3553 unsigned long flags;
3554
3555 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3556 return;
3557
3558 atomic_inc(&cpu_buffer->record_disabled);
3559
3560 spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
3561
3562 if (RB_WARN_ON(cpu_buffer, local_read(&cpu_buffer->committing)))
3563 goto out;
3564
3565 arch_spin_lock(&cpu_buffer->lock);
3566
3567 rb_reset_cpu(cpu_buffer);
3568
3569 arch_spin_unlock(&cpu_buffer->lock);
3570
3571 out:
3572 spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
3573
3574 atomic_dec(&cpu_buffer->record_disabled);
3575}
3576EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu);
3577
3578/**
3579 * ring_buffer_reset - reset a ring buffer
3580 * @buffer: The ring buffer to reset all cpu buffers
3581 */
3582void ring_buffer_reset(struct ring_buffer *buffer)
3583{
3584 int cpu;
3585
3586 for_each_buffer_cpu(buffer, cpu)
3587 ring_buffer_reset_cpu(buffer, cpu);
3588}
3589EXPORT_SYMBOL_GPL(ring_buffer_reset);
3590
3591/**
3592 * rind_buffer_empty - is the ring buffer empty?
3593 * @buffer: The ring buffer to test
3594 */
3595int ring_buffer_empty(struct ring_buffer *buffer)
3596{
3597 struct ring_buffer_per_cpu *cpu_buffer;
3598 unsigned long flags;
3599 int dolock;
3600 int cpu;
3601 int ret;
3602
3603 dolock = rb_ok_to_lock();
3604
3605 /* yes this is racy, but if you don't like the race, lock the buffer */
3606 for_each_buffer_cpu(buffer, cpu) {
3607 cpu_buffer = buffer->buffers[cpu];
3608 local_irq_save(flags);
3609 if (dolock)
3610 spin_lock(&cpu_buffer->reader_lock);
3611 ret = rb_per_cpu_empty(cpu_buffer);
3612 if (dolock)
3613 spin_unlock(&cpu_buffer->reader_lock);
3614 local_irq_restore(flags);
3615
3616 if (!ret)
3617 return 0;
3618 }
3619
3620 return 1;
3621}
3622EXPORT_SYMBOL_GPL(ring_buffer_empty);
3623
3624/**
3625 * ring_buffer_empty_cpu - is a cpu buffer of a ring buffer empty?
3626 * @buffer: The ring buffer
3627 * @cpu: The CPU buffer to test
3628 */
3629int ring_buffer_empty_cpu(struct ring_buffer *buffer, int cpu)
3630{
3631 struct ring_buffer_per_cpu *cpu_buffer;
3632 unsigned long flags;
3633 int dolock;
3634 int ret;
3635
3636 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3637 return 1;
3638
3639 dolock = rb_ok_to_lock();
3640
3641 cpu_buffer = buffer->buffers[cpu];
3642 local_irq_save(flags);
3643 if (dolock)
3644 spin_lock(&cpu_buffer->reader_lock);
3645 ret = rb_per_cpu_empty(cpu_buffer);
3646 if (dolock)
3647 spin_unlock(&cpu_buffer->reader_lock);
3648 local_irq_restore(flags);
3649
3650 return ret;
3651}
3652EXPORT_SYMBOL_GPL(ring_buffer_empty_cpu);
3653
3654#ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
3655/**
3656 * ring_buffer_swap_cpu - swap a CPU buffer between two ring buffers
3657 * @buffer_a: One buffer to swap with
3658 * @buffer_b: The other buffer to swap with
3659 *
3660 * This function is useful for tracers that want to take a "snapshot"
3661 * of a CPU buffer and has another back up buffer lying around.
3662 * it is expected that the tracer handles the cpu buffer not being
3663 * used at the moment.
3664 */
3665int ring_buffer_swap_cpu(struct ring_buffer *buffer_a,
3666 struct ring_buffer *buffer_b, int cpu)
3667{
3668 struct ring_buffer_per_cpu *cpu_buffer_a;
3669 struct ring_buffer_per_cpu *cpu_buffer_b;
3670 int ret = -EINVAL;
3671
3672 if (!cpumask_test_cpu(cpu, buffer_a->cpumask) ||
3673 !cpumask_test_cpu(cpu, buffer_b->cpumask))
3674 goto out;
3675
3676 /* At least make sure the two buffers are somewhat the same */
3677 if (buffer_a->pages != buffer_b->pages)
3678 goto out;
3679
3680 ret = -EAGAIN;
3681
3682 if (ring_buffer_flags != RB_BUFFERS_ON)
3683 goto out;
3684
3685 if (atomic_read(&buffer_a->record_disabled))
3686 goto out;
3687
3688 if (atomic_read(&buffer_b->record_disabled))
3689 goto out;
3690
3691 cpu_buffer_a = buffer_a->buffers[cpu];
3692 cpu_buffer_b = buffer_b->buffers[cpu];
3693
3694 if (atomic_read(&cpu_buffer_a->record_disabled))
3695 goto out;
3696
3697 if (atomic_read(&cpu_buffer_b->record_disabled))
3698 goto out;
3699
3700 /*
3701 * We can't do a synchronize_sched here because this
3702 * function can be called in atomic context.
3703 * Normally this will be called from the same CPU as cpu.
3704 * If not it's up to the caller to protect this.
3705 */
3706 atomic_inc(&cpu_buffer_a->record_disabled);
3707 atomic_inc(&cpu_buffer_b->record_disabled);
3708
3709 ret = -EBUSY;
3710 if (local_read(&cpu_buffer_a->committing))
3711 goto out_dec;
3712 if (local_read(&cpu_buffer_b->committing))
3713 goto out_dec;
3714
3715 buffer_a->buffers[cpu] = cpu_buffer_b;
3716 buffer_b->buffers[cpu] = cpu_buffer_a;
3717
3718 cpu_buffer_b->buffer = buffer_a;
3719 cpu_buffer_a->buffer = buffer_b;
3720
3721 ret = 0;
3722
3723out_dec:
3724 atomic_dec(&cpu_buffer_a->record_disabled);
3725 atomic_dec(&cpu_buffer_b->record_disabled);
3726out:
3727 return ret;
3728}
3729EXPORT_SYMBOL_GPL(ring_buffer_swap_cpu);
3730#endif /* CONFIG_RING_BUFFER_ALLOW_SWAP */
3731
3732/**
3733 * ring_buffer_alloc_read_page - allocate a page to read from buffer
3734 * @buffer: the buffer to allocate for.
3735 *
3736 * This function is used in conjunction with ring_buffer_read_page.
3737 * When reading a full page from the ring buffer, these functions
3738 * can be used to speed up the process. The calling function should
3739 * allocate a few pages first with this function. Then when it
3740 * needs to get pages from the ring buffer, it passes the result
3741 * of this function into ring_buffer_read_page, which will swap
3742 * the page that was allocated, with the read page of the buffer.
3743 *
3744 * Returns:
3745 * The page allocated, or NULL on error.
3746 */
3747void *ring_buffer_alloc_read_page(struct ring_buffer *buffer, int cpu)
3748{
3749 struct buffer_data_page *bpage;
3750 struct page *page;
3751
3752 page = alloc_pages_node(cpu_to_node(cpu),
3753 GFP_KERNEL | __GFP_NORETRY, 0);
3754 if (!page)
3755 return NULL;
3756
3757 bpage = page_address(page);
3758
3759 rb_init_page(bpage);
3760
3761 return bpage;
3762}
3763EXPORT_SYMBOL_GPL(ring_buffer_alloc_read_page);
3764
3765/**
3766 * ring_buffer_free_read_page - free an allocated read page
3767 * @buffer: the buffer the page was allocate for
3768 * @data: the page to free
3769 *
3770 * Free a page allocated from ring_buffer_alloc_read_page.
3771 */
3772void ring_buffer_free_read_page(struct ring_buffer *buffer, void *data)
3773{
3774 free_page((unsigned long)data);
3775}
3776EXPORT_SYMBOL_GPL(ring_buffer_free_read_page);
3777
3778/**
3779 * ring_buffer_read_page - extract a page from the ring buffer
3780 * @buffer: buffer to extract from
3781 * @data_page: the page to use allocated from ring_buffer_alloc_read_page
3782 * @len: amount to extract
3783 * @cpu: the cpu of the buffer to extract
3784 * @full: should the extraction only happen when the page is full.
3785 *
3786 * This function will pull out a page from the ring buffer and consume it.
3787 * @data_page must be the address of the variable that was returned
3788 * from ring_buffer_alloc_read_page. This is because the page might be used
3789 * to swap with a page in the ring buffer.
3790 *
3791 * for example:
3792 * rpage = ring_buffer_alloc_read_page(buffer);
3793 * if (!rpage)
3794 * return error;
3795 * ret = ring_buffer_read_page(buffer, &rpage, len, cpu, 0);
3796 * if (ret >= 0)
3797 * process_page(rpage, ret);
3798 *
3799 * When @full is set, the function will not return true unless
3800 * the writer is off the reader page.
3801 *
3802 * Note: it is up to the calling functions to handle sleeps and wakeups.
3803 * The ring buffer can be used anywhere in the kernel and can not
3804 * blindly call wake_up. The layer that uses the ring buffer must be
3805 * responsible for that.
3806 *
3807 * Returns:
3808 * >=0 if data has been transferred, returns the offset of consumed data.
3809 * <0 if no data has been transferred.
3810 */
3811int ring_buffer_read_page(struct ring_buffer *buffer,
3812 void **data_page, size_t len, int cpu, int full)
3813{
3814 struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
3815 struct ring_buffer_event *event;
3816 struct buffer_data_page *bpage;
3817 struct buffer_page *reader;
3818 unsigned long missed_events;
3819 unsigned long flags;
3820 unsigned int commit;
3821 unsigned int read;
3822 u64 save_timestamp;
3823 int ret = -1;
3824
3825 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3826 goto out;
3827
3828 /*
3829 * If len is not big enough to hold the page header, then
3830 * we can not copy anything.
3831 */
3832 if (len <= BUF_PAGE_HDR_SIZE)
3833 goto out;
3834
3835 len -= BUF_PAGE_HDR_SIZE;
3836
3837 if (!data_page)
3838 goto out;
3839
3840 bpage = *data_page;
3841 if (!bpage)
3842 goto out;
3843
3844 spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
3845
3846 reader = rb_get_reader_page(cpu_buffer);
3847 if (!reader)
3848 goto out_unlock;
3849
3850 event = rb_reader_event(cpu_buffer);
3851
3852 read = reader->read;
3853 commit = rb_page_commit(reader);
3854
3855 /* Check if any events were dropped */
3856 missed_events = cpu_buffer->lost_events;
3857
3858 /*
3859 * If this page has been partially read or
3860 * if len is not big enough to read the rest of the page or
3861 * a writer is still on the page, then
3862 * we must copy the data from the page to the buffer.
3863 * Otherwise, we can simply swap the page with the one passed in.
3864 */
3865 if (read || (len < (commit - read)) ||
3866 cpu_buffer->reader_page == cpu_buffer->commit_page) {
3867 struct buffer_data_page *rpage = cpu_buffer->reader_page->page;
3868 unsigned int rpos = read;
3869 unsigned int pos = 0;
3870 unsigned int size;
3871
3872 if (full)
3873 goto out_unlock;
3874
3875 if (len > (commit - read))
3876 len = (commit - read);
3877
3878 /* Always keep the time extend and data together */
3879 size = rb_event_ts_length(event);
3880
3881 if (len < size)
3882 goto out_unlock;
3883
3884 /* save the current timestamp, since the user will need it */
3885 save_timestamp = cpu_buffer->read_stamp;
3886
3887 /* Need to copy one event at a time */
3888 do {
3889 /* We need the size of one event, because
3890 * rb_advance_reader only advances by one event,
3891 * whereas rb_event_ts_length may include the size of
3892 * one or two events.
3893 * We have already ensured there's enough space if this
3894 * is a time extend. */
3895 size = rb_event_length(event);
3896 memcpy(bpage->data + pos, rpage->data + rpos, size);
3897
3898 len -= size;
3899
3900 rb_advance_reader(cpu_buffer);
3901 rpos = reader->read;
3902 pos += size;
3903
3904 if (rpos >= commit)
3905 break;
3906
3907 event = rb_reader_event(cpu_buffer);
3908 /* Always keep the time extend and data together */
3909 size = rb_event_ts_length(event);
3910 } while (len >= size);
3911
3912 /* update bpage */
3913 local_set(&bpage->commit, pos);
3914 bpage->time_stamp = save_timestamp;
3915
3916 /* we copied everything to the beginning */
3917 read = 0;
3918 } else {
3919 /* update the entry counter */
3920 cpu_buffer->read += rb_page_entries(reader);
3921
3922 /* swap the pages */
3923 rb_init_page(bpage);
3924 bpage = reader->page;
3925 reader->page = *data_page;
3926 local_set(&reader->write, 0);
3927 local_set(&reader->entries, 0);
3928 reader->read = 0;
3929 *data_page = bpage;
3930
3931 /*
3932 * Use the real_end for the data size,
3933 * This gives us a chance to store the lost events
3934 * on the page.
3935 */
3936 if (reader->real_end)
3937 local_set(&bpage->commit, reader->real_end);
3938 }
3939 ret = read;
3940
3941 cpu_buffer->lost_events = 0;
3942
3943 commit = local_read(&bpage->commit);
3944 /*
3945 * Set a flag in the commit field if we lost events
3946 */
3947 if (missed_events) {
3948 /* If there is room at the end of the page to save the
3949 * missed events, then record it there.
3950 */
3951 if (BUF_PAGE_SIZE - commit >= sizeof(missed_events)) {
3952 memcpy(&bpage->data[commit], &missed_events,
3953 sizeof(missed_events));
3954 local_add(RB_MISSED_STORED, &bpage->commit);
3955 commit += sizeof(missed_events);
3956 }
3957 local_add(RB_MISSED_EVENTS, &bpage->commit);
3958 }
3959
3960 /*
3961 * This page may be off to user land. Zero it out here.
3962 */
3963 if (commit < BUF_PAGE_SIZE)
3964 memset(&bpage->data[commit], 0, BUF_PAGE_SIZE - commit);
3965
3966 out_unlock:
3967 spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
3968
3969 out:
3970 return ret;
3971}
3972EXPORT_SYMBOL_GPL(ring_buffer_read_page);
3973
3974#ifdef CONFIG_TRACING
3975static ssize_t
3976rb_simple_read(struct file *filp, char __user *ubuf,
3977 size_t cnt, loff_t *ppos)
3978{
3979 unsigned long *p = filp->private_data;
3980 char buf[64];
3981 int r;
3982
3983 if (test_bit(RB_BUFFERS_DISABLED_BIT, p))
3984 r = sprintf(buf, "permanently disabled\n");
3985 else
3986 r = sprintf(buf, "%d\n", test_bit(RB_BUFFERS_ON_BIT, p));
3987
3988 return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
3989}
3990
3991static ssize_t
3992rb_simple_write(struct file *filp, const char __user *ubuf,
3993 size_t cnt, loff_t *ppos)
3994{
3995 unsigned long *p = filp->private_data;
3996 unsigned long val;
3997 int ret;
3998
3999 ret = kstrtoul_from_user(ubuf, cnt, 10, &val);
4000 if (ret)
4001 return ret;
4002
4003 if (val)
4004 set_bit(RB_BUFFERS_ON_BIT, p);
4005 else
4006 clear_bit(RB_BUFFERS_ON_BIT, p);
4007
4008 (*ppos)++;
4009
4010 return cnt;
4011}
4012
4013static const struct file_operations rb_simple_fops = {
4014 .open = tracing_open_generic,
4015 .read = rb_simple_read,
4016 .write = rb_simple_write,
4017 .llseek = default_llseek,
4018};
4019
4020
4021static __init int rb_init_debugfs(void)
4022{
4023 struct dentry *d_tracer;
4024
4025 d_tracer = tracing_init_dentry();
4026
4027 trace_create_file("tracing_on", 0644, d_tracer,
4028 &ring_buffer_flags, &rb_simple_fops);
4029
4030 return 0;
4031}
4032
4033fs_initcall(rb_init_debugfs);
4034#endif
4035
4036#ifdef CONFIG_HOTPLUG_CPU
4037static int rb_cpu_notify(struct notifier_block *self,
4038 unsigned long action, void *hcpu)
4039{
4040 struct ring_buffer *buffer =
4041 container_of(self, struct ring_buffer, cpu_notify);
4042 long cpu = (long)hcpu;
4043
4044 switch (action) {
4045 case CPU_UP_PREPARE:
4046 case CPU_UP_PREPARE_FROZEN:
4047 if (cpumask_test_cpu(cpu, buffer->cpumask))
4048 return NOTIFY_OK;
4049
4050 buffer->buffers[cpu] =
4051 rb_allocate_cpu_buffer(buffer, cpu);
4052 if (!buffer->buffers[cpu]) {
4053 WARN(1, "failed to allocate ring buffer on CPU %ld\n",
4054 cpu);
4055 return NOTIFY_OK;
4056 }
4057 smp_wmb();
4058 cpumask_set_cpu(cpu, buffer->cpumask);
4059 break;
4060 case CPU_DOWN_PREPARE:
4061 case CPU_DOWN_PREPARE_FROZEN:
4062 /*
4063 * Do nothing.
4064 * If we were to free the buffer, then the user would
4065 * lose any trace that was in the buffer.
4066 */
4067 break;
4068 default:
4069 break;
4070 }
4071 return NOTIFY_OK;
4072}
4073#endif