1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Generic ring buffer
4 *
5 * Copyright (C) 2008 Steven Rostedt <srostedt@redhat.com>
6 */
7#include <linux/trace_events.h>
8#include <linux/ring_buffer.h>
9#include <linux/trace_clock.h>
10#include <linux/sched/clock.h>
11#include <linux/trace_seq.h>
12#include <linux/spinlock.h>
13#include <linux/irq_work.h>
14#include <linux/uaccess.h>
15#include <linux/hardirq.h>
16#include <linux/kthread.h> /* for self test */
17#include <linux/module.h>
18#include <linux/percpu.h>
19#include <linux/mutex.h>
20#include <linux/delay.h>
21#include <linux/slab.h>
22#include <linux/init.h>
23#include <linux/hash.h>
24#include <linux/list.h>
25#include <linux/cpu.h>
26#include <linux/oom.h>
27
28#include <asm/local.h>
29
30static void update_pages_handler(struct work_struct *work);
31
32/*
33 * The ring buffer header is special. We must manually up keep it.
34 */
35int ring_buffer_print_entry_header(struct trace_seq *s)
36{
37 trace_seq_puts(s, "# compressed entry header\n");
38 trace_seq_puts(s, "\ttype_len : 5 bits\n");
39 trace_seq_puts(s, "\ttime_delta : 27 bits\n");
40 trace_seq_puts(s, "\tarray : 32 bits\n");
41 trace_seq_putc(s, '\n');
42 trace_seq_printf(s, "\tpadding : type == %d\n",
43 RINGBUF_TYPE_PADDING);
44 trace_seq_printf(s, "\ttime_extend : type == %d\n",
45 RINGBUF_TYPE_TIME_EXTEND);
46 trace_seq_printf(s, "\ttime_stamp : type == %d\n",
47 RINGBUF_TYPE_TIME_STAMP);
48 trace_seq_printf(s, "\tdata max type_len == %d\n",
49 RINGBUF_TYPE_DATA_TYPE_LEN_MAX);
50
51 return !trace_seq_has_overflowed(s);
52}
53
54/*
55 * The ring buffer is made up of a list of pages. A separate list of pages is
56 * allocated for each CPU. A writer may only write to a buffer that is
57 * associated with the CPU it is currently executing on. A reader may read
58 * from any per cpu buffer.
59 *
60 * The reader is special. For each per cpu buffer, the reader has its own
61 * reader page. When a reader has read the entire reader page, this reader
62 * page is swapped with another page in the ring buffer.
63 *
64 * Now, as long as the writer is off the reader page, the reader can do what
65 * ever it wants with that page. The writer will never write to that page
66 * again (as long as it is out of the ring buffer).
67 *
68 * Here's some silly ASCII art.
69 *
70 * +------+
71 * |reader| RING BUFFER
72 * |page |
73 * +------+ +---+ +---+ +---+
74 * | |-->| |-->| |
75 * +---+ +---+ +---+
76 * ^ |
77 * | |
78 * +---------------+
79 *
80 *
81 * +------+
82 * |reader| RING BUFFER
83 * |page |------------------v
84 * +------+ +---+ +---+ +---+
85 * | |-->| |-->| |
86 * +---+ +---+ +---+
87 * ^ |
88 * | |
89 * +---------------+
90 *
91 *
92 * +------+
93 * |reader| RING BUFFER
94 * |page |------------------v
95 * +------+ +---+ +---+ +---+
96 * ^ | |-->| |-->| |
97 * | +---+ +---+ +---+
98 * | |
99 * | |
100 * +------------------------------+
101 *
102 *
103 * +------+
104 * |buffer| RING BUFFER
105 * |page |------------------v
106 * +------+ +---+ +---+ +---+
107 * ^ | | | |-->| |
108 * | New +---+ +---+ +---+
109 * | Reader------^ |
110 * | page |
111 * +------------------------------+
112 *
113 *
114 * After we make this swap, the reader can hand this page off to the splice
115 * code and be done with it. It can even allocate a new page if it needs to
116 * and swap that into the ring buffer.
117 *
118 * We will be using cmpxchg soon to make all this lockless.
119 *
120 */
121
122/* Used for individual buffers (after the counter) */
123#define RB_BUFFER_OFF (1 << 20)
124
125#define BUF_PAGE_HDR_SIZE offsetof(struct buffer_data_page, data)
126
127#define RB_EVNT_HDR_SIZE (offsetof(struct ring_buffer_event, array))
128#define RB_ALIGNMENT 4U
129#define RB_MAX_SMALL_DATA (RB_ALIGNMENT * RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
130#define RB_EVNT_MIN_SIZE 8U /* two 32bit words */
131
132#ifndef CONFIG_HAVE_64BIT_ALIGNED_ACCESS
133# define RB_FORCE_8BYTE_ALIGNMENT 0
134# define RB_ARCH_ALIGNMENT RB_ALIGNMENT
135#else
136# define RB_FORCE_8BYTE_ALIGNMENT 1
137# define RB_ARCH_ALIGNMENT 8U
138#endif
139
140#define RB_ALIGN_DATA __aligned(RB_ARCH_ALIGNMENT)
141
142/* define RINGBUF_TYPE_DATA for 'case RINGBUF_TYPE_DATA:' */
143#define RINGBUF_TYPE_DATA 0 ... RINGBUF_TYPE_DATA_TYPE_LEN_MAX
144
145enum {
146 RB_LEN_TIME_EXTEND = 8,
147 RB_LEN_TIME_STAMP = 8,
148};
149
150#define skip_time_extend(event) \
151 ((struct ring_buffer_event *)((char *)event + RB_LEN_TIME_EXTEND))
152
153#define extended_time(event) \
154 (event->type_len >= RINGBUF_TYPE_TIME_EXTEND)
155
156static inline int rb_null_event(struct ring_buffer_event *event)
157{
158 return event->type_len == RINGBUF_TYPE_PADDING && !event->time_delta;
159}
160
161static void rb_event_set_padding(struct ring_buffer_event *event)
162{
163 /* padding has a NULL time_delta */
164 event->type_len = RINGBUF_TYPE_PADDING;
165 event->time_delta = 0;
166}
167
168static unsigned
169rb_event_data_length(struct ring_buffer_event *event)
170{
171 unsigned length;
172
173 if (event->type_len)
174 length = event->type_len * RB_ALIGNMENT;
175 else
176 length = event->array[0];
177 return length + RB_EVNT_HDR_SIZE;
178}
179
180/*
181 * Return the length of the given event. Will return
182 * the length of the time extend if the event is a
183 * time extend.
184 */
185static inline unsigned
186rb_event_length(struct ring_buffer_event *event)
187{
188 switch (event->type_len) {
189 case RINGBUF_TYPE_PADDING:
190 if (rb_null_event(event))
191 /* undefined */
192 return -1;
193 return event->array[0] + RB_EVNT_HDR_SIZE;
194
195 case RINGBUF_TYPE_TIME_EXTEND:
196 return RB_LEN_TIME_EXTEND;
197
198 case RINGBUF_TYPE_TIME_STAMP:
199 return RB_LEN_TIME_STAMP;
200
201 case RINGBUF_TYPE_DATA:
202 return rb_event_data_length(event);
203 default:
204 BUG();
205 }
206 /* not hit */
207 return 0;
208}
209
210/*
211 * Return total length of time extend and data,
212 * or just the event length for all other events.
213 */
214static inline unsigned
215rb_event_ts_length(struct ring_buffer_event *event)
216{
217 unsigned len = 0;
218
219 if (extended_time(event)) {
220 /* time extends include the data event after it */
221 len = RB_LEN_TIME_EXTEND;
222 event = skip_time_extend(event);
223 }
224 return len + rb_event_length(event);
225}
226
227/**
228 * ring_buffer_event_length - return the length of the event
229 * @event: the event to get the length of
230 *
231 * Returns the size of the data load of a data event.
232 * If the event is something other than a data event, it
233 * returns the size of the event itself. With the exception
234 * of a TIME EXTEND, where it still returns the size of the
235 * data load of the data event after it.
236 */
237unsigned ring_buffer_event_length(struct ring_buffer_event *event)
238{
239 unsigned length;
240
241 if (extended_time(event))
242 event = skip_time_extend(event);
243
244 length = rb_event_length(event);
245 if (event->type_len > RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
246 return length;
247 length -= RB_EVNT_HDR_SIZE;
248 if (length > RB_MAX_SMALL_DATA + sizeof(event->array[0]))
249 length -= sizeof(event->array[0]);
250 return length;
251}
252EXPORT_SYMBOL_GPL(ring_buffer_event_length);
253
254/* inline for ring buffer fast paths */
255static __always_inline void *
256rb_event_data(struct ring_buffer_event *event)
257{
258 if (extended_time(event))
259 event = skip_time_extend(event);
260 BUG_ON(event->type_len > RINGBUF_TYPE_DATA_TYPE_LEN_MAX);
261 /* If length is in len field, then array[0] has the data */
262 if (event->type_len)
263 return (void *)&event->array[0];
264 /* Otherwise length is in array[0] and array[1] has the data */
265 return (void *)&event->array[1];
266}
267
268/**
269 * ring_buffer_event_data - return the data of the event
270 * @event: the event to get the data from
271 */
272void *ring_buffer_event_data(struct ring_buffer_event *event)
273{
274 return rb_event_data(event);
275}
276EXPORT_SYMBOL_GPL(ring_buffer_event_data);
277
278#define for_each_buffer_cpu(buffer, cpu) \
279 for_each_cpu(cpu, buffer->cpumask)
280
281#define TS_SHIFT 27
282#define TS_MASK ((1ULL << TS_SHIFT) - 1)
283#define TS_DELTA_TEST (~TS_MASK)
284
285/**
286 * ring_buffer_event_time_stamp - return the event's extended timestamp
287 * @event: the event to get the timestamp of
288 *
289 * Returns the extended timestamp associated with a data event.
290 * An extended time_stamp is a 64-bit timestamp represented
291 * internally in a special way that makes the best use of space
292 * contained within a ring buffer event. This function decodes
293 * it and maps it to a straight u64 value.
294 */
295u64 ring_buffer_event_time_stamp(struct ring_buffer_event *event)
296{
297 u64 ts;
298
299 ts = event->array[0];
300 ts <<= TS_SHIFT;
301 ts += event->time_delta;
302
303 return ts;
304}
305
306/* Flag when events were overwritten */
307#define RB_MISSED_EVENTS (1 << 31)
308/* Missed count stored at end */
309#define RB_MISSED_STORED (1 << 30)
310
311#define RB_MISSED_FLAGS (RB_MISSED_EVENTS|RB_MISSED_STORED)
312
313struct buffer_data_page {
314 u64 time_stamp; /* page time stamp */
315 local_t commit; /* write committed index */
316 unsigned char data[] RB_ALIGN_DATA; /* data of buffer page */
317};
318
319/*
320 * Note, the buffer_page list must be first. The buffer pages
321 * are allocated in cache lines, which means that each buffer
322 * page will be at the beginning of a cache line, and thus
323 * the least significant bits will be zero. We use this to
324 * add flags in the list struct pointers, to make the ring buffer
325 * lockless.
326 */
327struct buffer_page {
328 struct list_head list; /* list of buffer pages */
329 local_t write; /* index for next write */
330 unsigned read; /* index for next read */
331 local_t entries; /* entries on this page */
332 unsigned long real_end; /* real end of data */
333 struct buffer_data_page *page; /* Actual data page */
334};
335
336/*
337 * The buffer page counters, write and entries, must be reset
338 * atomically when crossing page boundaries. To synchronize this
339 * update, two counters are inserted into the number. One is
340 * the actual counter for the write position or count on the page.
341 *
342 * The other is a counter of updaters. Before an update happens
343 * the update partition of the counter is incremented. This will
344 * allow the updater to update the counter atomically.
345 *
346 * The counter is 20 bits, and the state data is 12.
347 */
348#define RB_WRITE_MASK 0xfffff
349#define RB_WRITE_INTCNT (1 << 20)
350
351static void rb_init_page(struct buffer_data_page *bpage)
352{
353 local_set(&bpage->commit, 0);
354}
355
356/*
357 * Also stolen from mm/slob.c. Thanks to Mathieu Desnoyers for pointing
358 * this issue out.
359 */
360static void free_buffer_page(struct buffer_page *bpage)
361{
362 free_page((unsigned long)bpage->page);
363 kfree(bpage);
364}
365
366/*
367 * We need to fit the time_stamp delta into 27 bits.
368 */
369static inline int test_time_stamp(u64 delta)
370{
371 if (delta & TS_DELTA_TEST)
372 return 1;
373 return 0;
374}
375
376#define BUF_PAGE_SIZE (PAGE_SIZE - BUF_PAGE_HDR_SIZE)
377
378/* Max payload is BUF_PAGE_SIZE - header (8bytes) */
379#define BUF_MAX_DATA_SIZE (BUF_PAGE_SIZE - (sizeof(u32) * 2))
380
381int ring_buffer_print_page_header(struct trace_seq *s)
382{
383 struct buffer_data_page field;
384
385 trace_seq_printf(s, "\tfield: u64 timestamp;\t"
386 "offset:0;\tsize:%u;\tsigned:%u;\n",
387 (unsigned int)sizeof(field.time_stamp),
388 (unsigned int)is_signed_type(u64));
389
390 trace_seq_printf(s, "\tfield: local_t commit;\t"
391 "offset:%u;\tsize:%u;\tsigned:%u;\n",
392 (unsigned int)offsetof(typeof(field), commit),
393 (unsigned int)sizeof(field.commit),
394 (unsigned int)is_signed_type(long));
395
396 trace_seq_printf(s, "\tfield: int overwrite;\t"
397 "offset:%u;\tsize:%u;\tsigned:%u;\n",
398 (unsigned int)offsetof(typeof(field), commit),
399 1,
400 (unsigned int)is_signed_type(long));
401
402 trace_seq_printf(s, "\tfield: char data;\t"
403 "offset:%u;\tsize:%u;\tsigned:%u;\n",
404 (unsigned int)offsetof(typeof(field), data),
405 (unsigned int)BUF_PAGE_SIZE,
406 (unsigned int)is_signed_type(char));
407
408 return !trace_seq_has_overflowed(s);
409}
410
411struct rb_irq_work {
412 struct irq_work work;
413 wait_queue_head_t waiters;
414 wait_queue_head_t full_waiters;
415 bool waiters_pending;
416 bool full_waiters_pending;
417 bool wakeup_full;
418};
419
420/*
421 * Structure to hold event state and handle nested events.
422 */
423struct rb_event_info {
424 u64 ts;
425 u64 delta;
426 unsigned long length;
427 struct buffer_page *tail_page;
428 int add_timestamp;
429};
430
431/*
432 * Used for which event context the event is in.
433 * NMI = 0
434 * IRQ = 1
435 * SOFTIRQ = 2
436 * NORMAL = 3
437 *
438 * See trace_recursive_lock() comment below for more details.
439 */
440enum {
441 RB_CTX_NMI,
442 RB_CTX_IRQ,
443 RB_CTX_SOFTIRQ,
444 RB_CTX_NORMAL,
445 RB_CTX_MAX
446};
447
448/*
449 * head_page == tail_page && head == tail then buffer is empty.
450 */
451struct ring_buffer_per_cpu {
452 int cpu;
453 atomic_t record_disabled;
454 struct ring_buffer *buffer;
455 raw_spinlock_t reader_lock; /* serialize readers */
456 arch_spinlock_t lock;
457 struct lock_class_key lock_key;
458 struct buffer_data_page *free_page;
459 unsigned long nr_pages;
460 unsigned int current_context;
461 struct list_head *pages;
462 struct buffer_page *head_page; /* read from head */
463 struct buffer_page *tail_page; /* write to tail */
464 struct buffer_page *commit_page; /* committed pages */
465 struct buffer_page *reader_page;
466 unsigned long lost_events;
467 unsigned long last_overrun;
468 unsigned long nest;
469 local_t entries_bytes;
470 local_t entries;
471 local_t overrun;
472 local_t commit_overrun;
473 local_t dropped_events;
474 local_t committing;
475 local_t commits;
476 local_t pages_touched;
477 local_t pages_read;
478 long last_pages_touch;
479 size_t shortest_full;
480 unsigned long read;
481 unsigned long read_bytes;
482 u64 write_stamp;
483 u64 read_stamp;
484 /* ring buffer pages to update, > 0 to add, < 0 to remove */
485 long nr_pages_to_update;
486 struct list_head new_pages; /* new pages to add */
487 struct work_struct update_pages_work;
488 struct completion update_done;
489
490 struct rb_irq_work irq_work;
491};
492
493struct ring_buffer {
494 unsigned flags;
495 int cpus;
496 atomic_t record_disabled;
497 atomic_t resize_disabled;
498 cpumask_var_t cpumask;
499
500 struct lock_class_key *reader_lock_key;
501
502 struct mutex mutex;
503
504 struct ring_buffer_per_cpu **buffers;
505
506 struct hlist_node node;
507 u64 (*clock)(void);
508
509 struct rb_irq_work irq_work;
510 bool time_stamp_abs;
511};
512
513struct ring_buffer_iter {
514 struct ring_buffer_per_cpu *cpu_buffer;
515 unsigned long head;
516 struct buffer_page *head_page;
517 struct buffer_page *cache_reader_page;
518 unsigned long cache_read;
519 u64 read_stamp;
520};
521
522/**
523 * ring_buffer_nr_pages - get the number of buffer pages in the ring buffer
524 * @buffer: The ring_buffer to get the number of pages from
525 * @cpu: The cpu of the ring_buffer to get the number of pages from
526 *
527 * Returns the number of pages used by a per_cpu buffer of the ring buffer.
528 */
529size_t ring_buffer_nr_pages(struct ring_buffer *buffer, int cpu)
530{
531 return buffer->buffers[cpu]->nr_pages;
532}
533
534/**
535 * ring_buffer_nr_pages_dirty - get the number of used pages in the ring buffer
536 * @buffer: The ring_buffer to get the number of pages from
537 * @cpu: The cpu of the ring_buffer to get the number of pages from
538 *
539 * Returns the number of pages that have content in the ring buffer.
540 */
541size_t ring_buffer_nr_dirty_pages(struct ring_buffer *buffer, int cpu)
542{
543 size_t read;
544 size_t cnt;
545
546 read = local_read(&buffer->buffers[cpu]->pages_read);
547 cnt = local_read(&buffer->buffers[cpu]->pages_touched);
548 /* The reader can read an empty page, but not more than that */
549 if (cnt < read) {
550 WARN_ON_ONCE(read > cnt + 1);
551 return 0;
552 }
553
554 return cnt - read;
555}
556
557/*
558 * rb_wake_up_waiters - wake up tasks waiting for ring buffer input
559 *
560 * Schedules a delayed work to wake up any task that is blocked on the
561 * ring buffer waiters queue.
562 */
563static void rb_wake_up_waiters(struct irq_work *work)
564{
565 struct rb_irq_work *rbwork = container_of(work, struct rb_irq_work, work);
566
567 wake_up_all(&rbwork->waiters);
568 if (rbwork->wakeup_full) {
569 rbwork->wakeup_full = false;
570 wake_up_all(&rbwork->full_waiters);
571 }
572}
573
574/**
575 * ring_buffer_wait - wait for input to the ring buffer
576 * @buffer: buffer to wait on
577 * @cpu: the cpu buffer to wait on
578 * @full: wait until a full page is available, if @cpu != RING_BUFFER_ALL_CPUS
579 *
580 * If @cpu == RING_BUFFER_ALL_CPUS then the task will wake up as soon
581 * as data is added to any of the @buffer's cpu buffers. Otherwise
582 * it will wait for data to be added to a specific cpu buffer.
583 */
584int ring_buffer_wait(struct ring_buffer *buffer, int cpu, int full)
585{
586 struct ring_buffer_per_cpu *uninitialized_var(cpu_buffer);
587 DEFINE_WAIT(wait);
588 struct rb_irq_work *work;
589 int ret = 0;
590
591 /*
592 * Depending on what the caller is waiting for, either any
593 * data in any cpu buffer, or a specific buffer, put the
594 * caller on the appropriate wait queue.
595 */
596 if (cpu == RING_BUFFER_ALL_CPUS) {
597 work = &buffer->irq_work;
598 /* Full only makes sense on per cpu reads */
599 full = 0;
600 } else {
601 if (!cpumask_test_cpu(cpu, buffer->cpumask))
602 return -ENODEV;
603 cpu_buffer = buffer->buffers[cpu];
604 work = &cpu_buffer->irq_work;
605 }
606
607
608 while (true) {
609 if (full)
610 prepare_to_wait(&work->full_waiters, &wait, TASK_INTERRUPTIBLE);
611 else
612 prepare_to_wait(&work->waiters, &wait, TASK_INTERRUPTIBLE);
613
614 /*
615 * The events can happen in critical sections where
616 * checking a work queue can cause deadlocks.
617 * After adding a task to the queue, this flag is set
618 * only to notify events to try to wake up the queue
619 * using irq_work.
620 *
621 * We don't clear it even if the buffer is no longer
622 * empty. The flag only causes the next event to run
623 * irq_work to do the work queue wake up. The worse
624 * that can happen if we race with !trace_empty() is that
625 * an event will cause an irq_work to try to wake up
626 * an empty queue.
627 *
628 * There's no reason to protect this flag either, as
629 * the work queue and irq_work logic will do the necessary
630 * synchronization for the wake ups. The only thing
631 * that is necessary is that the wake up happens after
632 * a task has been queued. It's OK for spurious wake ups.
633 */
634 if (full)
635 work->full_waiters_pending = true;
636 else
637 work->waiters_pending = true;
638
639 if (signal_pending(current)) {
640 ret = -EINTR;
641 break;
642 }
643
644 if (cpu == RING_BUFFER_ALL_CPUS && !ring_buffer_empty(buffer))
645 break;
646
647 if (cpu != RING_BUFFER_ALL_CPUS &&
648 !ring_buffer_empty_cpu(buffer, cpu)) {
649 unsigned long flags;
650 bool pagebusy;
651 size_t nr_pages;
652 size_t dirty;
653
654 if (!full)
655 break;
656
657 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
658 pagebusy = cpu_buffer->reader_page == cpu_buffer->commit_page;
659 nr_pages = cpu_buffer->nr_pages;
660 dirty = ring_buffer_nr_dirty_pages(buffer, cpu);
661 if (!cpu_buffer->shortest_full ||
662 cpu_buffer->shortest_full < full)
663 cpu_buffer->shortest_full = full;
664 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
665 if (!pagebusy &&
666 (!nr_pages || (dirty * 100) > full * nr_pages))
667 break;
668 }
669
670 schedule();
671 }
672
673 if (full)
674 finish_wait(&work->full_waiters, &wait);
675 else
676 finish_wait(&work->waiters, &wait);
677
678 return ret;
679}
680
681/**
682 * ring_buffer_poll_wait - poll on buffer input
683 * @buffer: buffer to wait on
684 * @cpu: the cpu buffer to wait on
685 * @filp: the file descriptor
686 * @poll_table: The poll descriptor
687 *
688 * If @cpu == RING_BUFFER_ALL_CPUS then the task will wake up as soon
689 * as data is added to any of the @buffer's cpu buffers. Otherwise
690 * it will wait for data to be added to a specific cpu buffer.
691 *
692 * Returns EPOLLIN | EPOLLRDNORM if data exists in the buffers,
693 * zero otherwise.
694 */
695__poll_t ring_buffer_poll_wait(struct ring_buffer *buffer, int cpu,
696 struct file *filp, poll_table *poll_table)
697{
698 struct ring_buffer_per_cpu *cpu_buffer;
699 struct rb_irq_work *work;
700
701 if (cpu == RING_BUFFER_ALL_CPUS)
702 work = &buffer->irq_work;
703 else {
704 if (!cpumask_test_cpu(cpu, buffer->cpumask))
705 return -EINVAL;
706
707 cpu_buffer = buffer->buffers[cpu];
708 work = &cpu_buffer->irq_work;
709 }
710
711 poll_wait(filp, &work->waiters, poll_table);
712 work->waiters_pending = true;
713 /*
714 * There's a tight race between setting the waiters_pending and
715 * checking if the ring buffer is empty. Once the waiters_pending bit
716 * is set, the next event will wake the task up, but we can get stuck
717 * if there's only a single event in.
718 *
719 * FIXME: Ideally, we need a memory barrier on the writer side as well,
720 * but adding a memory barrier to all events will cause too much of a
721 * performance hit in the fast path. We only need a memory barrier when
722 * the buffer goes from empty to having content. But as this race is
723 * extremely small, and it's not a problem if another event comes in, we
724 * will fix it later.
725 */
726 smp_mb();
727
728 if ((cpu == RING_BUFFER_ALL_CPUS && !ring_buffer_empty(buffer)) ||
729 (cpu != RING_BUFFER_ALL_CPUS && !ring_buffer_empty_cpu(buffer, cpu)))
730 return EPOLLIN | EPOLLRDNORM;
731 return 0;
732}
733
734/* buffer may be either ring_buffer or ring_buffer_per_cpu */
735#define RB_WARN_ON(b, cond) \
736 ({ \
737 int _____ret = unlikely(cond); \
738 if (_____ret) { \
739 if (__same_type(*(b), struct ring_buffer_per_cpu)) { \
740 struct ring_buffer_per_cpu *__b = \
741 (void *)b; \
742 atomic_inc(&__b->buffer->record_disabled); \
743 } else \
744 atomic_inc(&b->record_disabled); \
745 WARN_ON(1); \
746 } \
747 _____ret; \
748 })
749
750/* Up this if you want to test the TIME_EXTENTS and normalization */
751#define DEBUG_SHIFT 0
752
753static inline u64 rb_time_stamp(struct ring_buffer *buffer)
754{
755 /* shift to debug/test normalization and TIME_EXTENTS */
756 return buffer->clock() << DEBUG_SHIFT;
757}
758
759u64 ring_buffer_time_stamp(struct ring_buffer *buffer, int cpu)
760{
761 u64 time;
762
763 preempt_disable_notrace();
764 time = rb_time_stamp(buffer);
765 preempt_enable_no_resched_notrace();
766
767 return time;
768}
769EXPORT_SYMBOL_GPL(ring_buffer_time_stamp);
770
771void ring_buffer_normalize_time_stamp(struct ring_buffer *buffer,
772 int cpu, u64 *ts)
773{
774 /* Just stupid testing the normalize function and deltas */
775 *ts >>= DEBUG_SHIFT;
776}
777EXPORT_SYMBOL_GPL(ring_buffer_normalize_time_stamp);
778
779/*
780 * Making the ring buffer lockless makes things tricky.
781 * Although writes only happen on the CPU that they are on,
782 * and they only need to worry about interrupts. Reads can
783 * happen on any CPU.
784 *
785 * The reader page is always off the ring buffer, but when the
786 * reader finishes with a page, it needs to swap its page with
787 * a new one from the buffer. The reader needs to take from
788 * the head (writes go to the tail). But if a writer is in overwrite
789 * mode and wraps, it must push the head page forward.
790 *
791 * Here lies the problem.
792 *
793 * The reader must be careful to replace only the head page, and
794 * not another one. As described at the top of the file in the
795 * ASCII art, the reader sets its old page to point to the next
796 * page after head. It then sets the page after head to point to
797 * the old reader page. But if the writer moves the head page
798 * during this operation, the reader could end up with the tail.
799 *
800 * We use cmpxchg to help prevent this race. We also do something
801 * special with the page before head. We set the LSB to 1.
802 *
803 * When the writer must push the page forward, it will clear the
804 * bit that points to the head page, move the head, and then set
805 * the bit that points to the new head page.
806 *
807 * We also don't want an interrupt coming in and moving the head
808 * page on another writer. Thus we use the second LSB to catch
809 * that too. Thus:
810 *
811 * head->list->prev->next bit 1 bit 0
812 * ------- -------
813 * Normal page 0 0
814 * Points to head page 0 1
815 * New head page 1 0
816 *
817 * Note we can not trust the prev pointer of the head page, because:
818 *
819 * +----+ +-----+ +-----+
820 * | |------>| T |---X--->| N |
821 * | |<------| | | |
822 * +----+ +-----+ +-----+
823 * ^ ^ |
824 * | +-----+ | |
825 * +----------| R |----------+ |
826 * | |<-----------+
827 * +-----+
828 *
829 * Key: ---X--> HEAD flag set in pointer
830 * T Tail page
831 * R Reader page
832 * N Next page
833 *
834 * (see __rb_reserve_next() to see where this happens)
835 *
836 * What the above shows is that the reader just swapped out
837 * the reader page with a page in the buffer, but before it
838 * could make the new header point back to the new page added
839 * it was preempted by a writer. The writer moved forward onto
840 * the new page added by the reader and is about to move forward
841 * again.
842 *
843 * You can see, it is legitimate for the previous pointer of
844 * the head (or any page) not to point back to itself. But only
845 * temporarily.
846 */
847
848#define RB_PAGE_NORMAL 0UL
849#define RB_PAGE_HEAD 1UL
850#define RB_PAGE_UPDATE 2UL
851
852
853#define RB_FLAG_MASK 3UL
854
855/* PAGE_MOVED is not part of the mask */
856#define RB_PAGE_MOVED 4UL
857
858/*
859 * rb_list_head - remove any bit
860 */
861static struct list_head *rb_list_head(struct list_head *list)
862{
863 unsigned long val = (unsigned long)list;
864
865 return (struct list_head *)(val & ~RB_FLAG_MASK);
866}
867
868/*
869 * rb_is_head_page - test if the given page is the head page
870 *
871 * Because the reader may move the head_page pointer, we can
872 * not trust what the head page is (it may be pointing to
873 * the reader page). But if the next page is a header page,
874 * its flags will be non zero.
875 */
876static inline int
877rb_is_head_page(struct ring_buffer_per_cpu *cpu_buffer,
878 struct buffer_page *page, struct list_head *list)
879{
880 unsigned long val;
881
882 val = (unsigned long)list->next;
883
884 if ((val & ~RB_FLAG_MASK) != (unsigned long)&page->list)
885 return RB_PAGE_MOVED;
886
887 return val & RB_FLAG_MASK;
888}
889
890/*
891 * rb_is_reader_page
892 *
893 * The unique thing about the reader page, is that, if the
894 * writer is ever on it, the previous pointer never points
895 * back to the reader page.
896 */
897static bool rb_is_reader_page(struct buffer_page *page)
898{
899 struct list_head *list = page->list.prev;
900
901 return rb_list_head(list->next) != &page->list;
902}
903
904/*
905 * rb_set_list_to_head - set a list_head to be pointing to head.
906 */
907static void rb_set_list_to_head(struct ring_buffer_per_cpu *cpu_buffer,
908 struct list_head *list)
909{
910 unsigned long *ptr;
911
912 ptr = (unsigned long *)&list->next;
913 *ptr |= RB_PAGE_HEAD;
914 *ptr &= ~RB_PAGE_UPDATE;
915}
916
917/*
918 * rb_head_page_activate - sets up head page
919 */
920static void rb_head_page_activate(struct ring_buffer_per_cpu *cpu_buffer)
921{
922 struct buffer_page *head;
923
924 head = cpu_buffer->head_page;
925 if (!head)
926 return;
927
928 /*
929 * Set the previous list pointer to have the HEAD flag.
930 */
931 rb_set_list_to_head(cpu_buffer, head->list.prev);
932}
933
934static void rb_list_head_clear(struct list_head *list)
935{
936 unsigned long *ptr = (unsigned long *)&list->next;
937
938 *ptr &= ~RB_FLAG_MASK;
939}
940
941/*
942 * rb_head_page_deactivate - clears head page ptr (for free list)
943 */
944static void
945rb_head_page_deactivate(struct ring_buffer_per_cpu *cpu_buffer)
946{
947 struct list_head *hd;
948
949 /* Go through the whole list and clear any pointers found. */
950 rb_list_head_clear(cpu_buffer->pages);
951
952 list_for_each(hd, cpu_buffer->pages)
953 rb_list_head_clear(hd);
954}
955
956static int rb_head_page_set(struct ring_buffer_per_cpu *cpu_buffer,
957 struct buffer_page *head,
958 struct buffer_page *prev,
959 int old_flag, int new_flag)
960{
961 struct list_head *list;
962 unsigned long val = (unsigned long)&head->list;
963 unsigned long ret;
964
965 list = &prev->list;
966
967 val &= ~RB_FLAG_MASK;
968
969 ret = cmpxchg((unsigned long *)&list->next,
970 val | old_flag, val | new_flag);
971
972 /* check if the reader took the page */
973 if ((ret & ~RB_FLAG_MASK) != val)
974 return RB_PAGE_MOVED;
975
976 return ret & RB_FLAG_MASK;
977}
978
979static int rb_head_page_set_update(struct ring_buffer_per_cpu *cpu_buffer,
980 struct buffer_page *head,
981 struct buffer_page *prev,
982 int old_flag)
983{
984 return rb_head_page_set(cpu_buffer, head, prev,
985 old_flag, RB_PAGE_UPDATE);
986}
987
988static int rb_head_page_set_head(struct ring_buffer_per_cpu *cpu_buffer,
989 struct buffer_page *head,
990 struct buffer_page *prev,
991 int old_flag)
992{
993 return rb_head_page_set(cpu_buffer, head, prev,
994 old_flag, RB_PAGE_HEAD);
995}
996
997static int rb_head_page_set_normal(struct ring_buffer_per_cpu *cpu_buffer,
998 struct buffer_page *head,
999 struct buffer_page *prev,
1000 int old_flag)
1001{
1002 return rb_head_page_set(cpu_buffer, head, prev,
1003 old_flag, RB_PAGE_NORMAL);
1004}
1005
1006static inline void rb_inc_page(struct ring_buffer_per_cpu *cpu_buffer,
1007 struct buffer_page **bpage)
1008{
1009 struct list_head *p = rb_list_head((*bpage)->list.next);
1010
1011 *bpage = list_entry(p, struct buffer_page, list);
1012}
1013
1014static struct buffer_page *
1015rb_set_head_page(struct ring_buffer_per_cpu *cpu_buffer)
1016{
1017 struct buffer_page *head;
1018 struct buffer_page *page;
1019 struct list_head *list;
1020 int i;
1021
1022 if (RB_WARN_ON(cpu_buffer, !cpu_buffer->head_page))
1023 return NULL;
1024
1025 /* sanity check */
1026 list = cpu_buffer->pages;
1027 if (RB_WARN_ON(cpu_buffer, rb_list_head(list->prev->next) != list))
1028 return NULL;
1029
1030 page = head = cpu_buffer->head_page;
1031 /*
1032 * It is possible that the writer moves the header behind
1033 * where we started, and we miss in one loop.
1034 * A second loop should grab the header, but we'll do
1035 * three loops just because I'm paranoid.
1036 */
1037 for (i = 0; i < 3; i++) {
1038 do {
1039 if (rb_is_head_page(cpu_buffer, page, page->list.prev)) {
1040 cpu_buffer->head_page = page;
1041 return page;
1042 }
1043 rb_inc_page(cpu_buffer, &page);
1044 } while (page != head);
1045 }
1046
1047 RB_WARN_ON(cpu_buffer, 1);
1048
1049 return NULL;
1050}
1051
1052static int rb_head_page_replace(struct buffer_page *old,
1053 struct buffer_page *new)
1054{
1055 unsigned long *ptr = (unsigned long *)&old->list.prev->next;
1056 unsigned long val;
1057 unsigned long ret;
1058
1059 val = *ptr & ~RB_FLAG_MASK;
1060 val |= RB_PAGE_HEAD;
1061
1062 ret = cmpxchg(ptr, val, (unsigned long)&new->list);
1063
1064 return ret == val;
1065}
1066
1067/*
1068 * rb_tail_page_update - move the tail page forward
1069 */
1070static void rb_tail_page_update(struct ring_buffer_per_cpu *cpu_buffer,
1071 struct buffer_page *tail_page,
1072 struct buffer_page *next_page)
1073{
1074 unsigned long old_entries;
1075 unsigned long old_write;
1076
1077 /*
1078 * The tail page now needs to be moved forward.
1079 *
1080 * We need to reset the tail page, but without messing
1081 * with possible erasing of data brought in by interrupts
1082 * that have moved the tail page and are currently on it.
1083 *
1084 * We add a counter to the write field to denote this.
1085 */
1086 old_write = local_add_return(RB_WRITE_INTCNT, &next_page->write);
1087 old_entries = local_add_return(RB_WRITE_INTCNT, &next_page->entries);
1088
1089 local_inc(&cpu_buffer->pages_touched);
1090 /*
1091 * Just make sure we have seen our old_write and synchronize
1092 * with any interrupts that come in.
1093 */
1094 barrier();
1095
1096 /*
1097 * If the tail page is still the same as what we think
1098 * it is, then it is up to us to update the tail
1099 * pointer.
1100 */
1101 if (tail_page == READ_ONCE(cpu_buffer->tail_page)) {
1102 /* Zero the write counter */
1103 unsigned long val = old_write & ~RB_WRITE_MASK;
1104 unsigned long eval = old_entries & ~RB_WRITE_MASK;
1105
1106 /*
1107 * This will only succeed if an interrupt did
1108 * not come in and change it. In which case, we
1109 * do not want to modify it.
1110 *
1111 * We add (void) to let the compiler know that we do not care
1112 * about the return value of these functions. We use the
1113 * cmpxchg to only update if an interrupt did not already
1114 * do it for us. If the cmpxchg fails, we don't care.
1115 */
1116 (void)local_cmpxchg(&next_page->write, old_write, val);
1117 (void)local_cmpxchg(&next_page->entries, old_entries, eval);
1118
1119 /*
1120 * No need to worry about races with clearing out the commit.
1121 * it only can increment when a commit takes place. But that
1122 * only happens in the outer most nested commit.
1123 */
1124 local_set(&next_page->page->commit, 0);
1125
1126 /* Again, either we update tail_page or an interrupt does */
1127 (void)cmpxchg(&cpu_buffer->tail_page, tail_page, next_page);
1128 }
1129}
1130
1131static int rb_check_bpage(struct ring_buffer_per_cpu *cpu_buffer,
1132 struct buffer_page *bpage)
1133{
1134 unsigned long val = (unsigned long)bpage;
1135
1136 if (RB_WARN_ON(cpu_buffer, val & RB_FLAG_MASK))
1137 return 1;
1138
1139 return 0;
1140}
1141
1142/**
1143 * rb_check_list - make sure a pointer to a list has the last bits zero
1144 */
1145static int rb_check_list(struct ring_buffer_per_cpu *cpu_buffer,
1146 struct list_head *list)
1147{
1148 if (RB_WARN_ON(cpu_buffer, rb_list_head(list->prev) != list->prev))
1149 return 1;
1150 if (RB_WARN_ON(cpu_buffer, rb_list_head(list->next) != list->next))
1151 return 1;
1152 return 0;
1153}
1154
1155/**
1156 * rb_check_pages - integrity check of buffer pages
1157 * @cpu_buffer: CPU buffer with pages to test
1158 *
1159 * As a safety measure we check to make sure the data pages have not
1160 * been corrupted.
1161 */
1162static int rb_check_pages(struct ring_buffer_per_cpu *cpu_buffer)
1163{
1164 struct list_head *head = cpu_buffer->pages;
1165 struct buffer_page *bpage, *tmp;
1166
1167 /* Reset the head page if it exists */
1168 if (cpu_buffer->head_page)
1169 rb_set_head_page(cpu_buffer);
1170
1171 rb_head_page_deactivate(cpu_buffer);
1172
1173 if (RB_WARN_ON(cpu_buffer, head->next->prev != head))
1174 return -1;
1175 if (RB_WARN_ON(cpu_buffer, head->prev->next != head))
1176 return -1;
1177
1178 if (rb_check_list(cpu_buffer, head))
1179 return -1;
1180
1181 list_for_each_entry_safe(bpage, tmp, head, list) {
1182 if (RB_WARN_ON(cpu_buffer,
1183 bpage->list.next->prev != &bpage->list))
1184 return -1;
1185 if (RB_WARN_ON(cpu_buffer,
1186 bpage->list.prev->next != &bpage->list))
1187 return -1;
1188 if (rb_check_list(cpu_buffer, &bpage->list))
1189 return -1;
1190 }
1191
1192 rb_head_page_activate(cpu_buffer);
1193
1194 return 0;
1195}
1196
1197static int __rb_allocate_pages(long nr_pages, struct list_head *pages, int cpu)
1198{
1199 struct buffer_page *bpage, *tmp;
1200 bool user_thread = current->mm != NULL;
1201 gfp_t mflags;
1202 long i;
1203
1204 /*
1205 * Check if the available memory is there first.
1206 * Note, si_mem_available() only gives us a rough estimate of available
1207 * memory. It may not be accurate. But we don't care, we just want
1208 * to prevent doing any allocation when it is obvious that it is
1209 * not going to succeed.
1210 */
1211 i = si_mem_available();
1212 if (i < nr_pages)
1213 return -ENOMEM;
1214
1215 /*
1216 * __GFP_RETRY_MAYFAIL flag makes sure that the allocation fails
1217 * gracefully without invoking oom-killer and the system is not
1218 * destabilized.
1219 */
1220 mflags = GFP_KERNEL | __GFP_RETRY_MAYFAIL;
1221
1222 /*
1223 * If a user thread allocates too much, and si_mem_available()
1224 * reports there's enough memory, even though there is not.
1225 * Make sure the OOM killer kills this thread. This can happen
1226 * even with RETRY_MAYFAIL because another task may be doing
1227 * an allocation after this task has taken all memory.
1228 * This is the task the OOM killer needs to take out during this
1229 * loop, even if it was triggered by an allocation somewhere else.
1230 */
1231 if (user_thread)
1232 set_current_oom_origin();
1233 for (i = 0; i < nr_pages; i++) {
1234 struct page *page;
1235
1236 bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
1237 mflags, cpu_to_node(cpu));
1238 if (!bpage)
1239 goto free_pages;
1240
1241 list_add(&bpage->list, pages);
1242
1243 page = alloc_pages_node(cpu_to_node(cpu), mflags, 0);
1244 if (!page)
1245 goto free_pages;
1246 bpage->page = page_address(page);
1247 rb_init_page(bpage->page);
1248
1249 if (user_thread && fatal_signal_pending(current))
1250 goto free_pages;
1251 }
1252 if (user_thread)
1253 clear_current_oom_origin();
1254
1255 return 0;
1256
1257free_pages:
1258 list_for_each_entry_safe(bpage, tmp, pages, list) {
1259 list_del_init(&bpage->list);
1260 free_buffer_page(bpage);
1261 }
1262 if (user_thread)
1263 clear_current_oom_origin();
1264
1265 return -ENOMEM;
1266}
1267
1268static int rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
1269 unsigned long nr_pages)
1270{
1271 LIST_HEAD(pages);
1272
1273 WARN_ON(!nr_pages);
1274
1275 if (__rb_allocate_pages(nr_pages, &pages, cpu_buffer->cpu))
1276 return -ENOMEM;
1277
1278 /*
1279 * The ring buffer page list is a circular list that does not
1280 * start and end with a list head. All page list items point to
1281 * other pages.
1282 */
1283 cpu_buffer->pages = pages.next;
1284 list_del(&pages);
1285
1286 cpu_buffer->nr_pages = nr_pages;
1287
1288 rb_check_pages(cpu_buffer);
1289
1290 return 0;
1291}
1292
1293static struct ring_buffer_per_cpu *
1294rb_allocate_cpu_buffer(struct ring_buffer *buffer, long nr_pages, int cpu)
1295{
1296 struct ring_buffer_per_cpu *cpu_buffer;
1297 struct buffer_page *bpage;
1298 struct page *page;
1299 int ret;
1300
1301 cpu_buffer = kzalloc_node(ALIGN(sizeof(*cpu_buffer), cache_line_size()),
1302 GFP_KERNEL, cpu_to_node(cpu));
1303 if (!cpu_buffer)
1304 return NULL;
1305
1306 cpu_buffer->cpu = cpu;
1307 cpu_buffer->buffer = buffer;
1308 raw_spin_lock_init(&cpu_buffer->reader_lock);
1309 lockdep_set_class(&cpu_buffer->reader_lock, buffer->reader_lock_key);
1310 cpu_buffer->lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
1311 INIT_WORK(&cpu_buffer->update_pages_work, update_pages_handler);
1312 init_completion(&cpu_buffer->update_done);
1313 init_irq_work(&cpu_buffer->irq_work.work, rb_wake_up_waiters);
1314 init_waitqueue_head(&cpu_buffer->irq_work.waiters);
1315 init_waitqueue_head(&cpu_buffer->irq_work.full_waiters);
1316
1317 bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
1318 GFP_KERNEL, cpu_to_node(cpu));
1319 if (!bpage)
1320 goto fail_free_buffer;
1321
1322 rb_check_bpage(cpu_buffer, bpage);
1323
1324 cpu_buffer->reader_page = bpage;
1325 page = alloc_pages_node(cpu_to_node(cpu), GFP_KERNEL, 0);
1326 if (!page)
1327 goto fail_free_reader;
1328 bpage->page = page_address(page);
1329 rb_init_page(bpage->page);
1330
1331 INIT_LIST_HEAD(&cpu_buffer->reader_page->list);
1332 INIT_LIST_HEAD(&cpu_buffer->new_pages);
1333
1334 ret = rb_allocate_pages(cpu_buffer, nr_pages);
1335 if (ret < 0)
1336 goto fail_free_reader;
1337
1338 cpu_buffer->head_page
1339 = list_entry(cpu_buffer->pages, struct buffer_page, list);
1340 cpu_buffer->tail_page = cpu_buffer->commit_page = cpu_buffer->head_page;
1341
1342 rb_head_page_activate(cpu_buffer);
1343
1344 return cpu_buffer;
1345
1346 fail_free_reader:
1347 free_buffer_page(cpu_buffer->reader_page);
1348
1349 fail_free_buffer:
1350 kfree(cpu_buffer);
1351 return NULL;
1352}
1353
1354static void rb_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
1355{
1356 struct list_head *head = cpu_buffer->pages;
1357 struct buffer_page *bpage, *tmp;
1358
1359 free_buffer_page(cpu_buffer->reader_page);
1360
1361 rb_head_page_deactivate(cpu_buffer);
1362
1363 if (head) {
1364 list_for_each_entry_safe(bpage, tmp, head, list) {
1365 list_del_init(&bpage->list);
1366 free_buffer_page(bpage);
1367 }
1368 bpage = list_entry(head, struct buffer_page, list);
1369 free_buffer_page(bpage);
1370 }
1371
1372 kfree(cpu_buffer);
1373}
1374
1375/**
1376 * __ring_buffer_alloc - allocate a new ring_buffer
1377 * @size: the size in bytes per cpu that is needed.
1378 * @flags: attributes to set for the ring buffer.
1379 *
1380 * Currently the only flag that is available is the RB_FL_OVERWRITE
1381 * flag. This flag means that the buffer will overwrite old data
1382 * when the buffer wraps. If this flag is not set, the buffer will
1383 * drop data when the tail hits the head.
1384 */
1385struct ring_buffer *__ring_buffer_alloc(unsigned long size, unsigned flags,
1386 struct lock_class_key *key)
1387{
1388 struct ring_buffer *buffer;
1389 long nr_pages;
1390 int bsize;
1391 int cpu;
1392 int ret;
1393
1394 /* keep it in its own cache line */
1395 buffer = kzalloc(ALIGN(sizeof(*buffer), cache_line_size()),
1396 GFP_KERNEL);
1397 if (!buffer)
1398 return NULL;
1399
1400 if (!zalloc_cpumask_var(&buffer->cpumask, GFP_KERNEL))
1401 goto fail_free_buffer;
1402
1403 nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
1404 buffer->flags = flags;
1405 buffer->clock = trace_clock_local;
1406 buffer->reader_lock_key = key;
1407
1408 init_irq_work(&buffer->irq_work.work, rb_wake_up_waiters);
1409 init_waitqueue_head(&buffer->irq_work.waiters);
1410
1411 /* need at least two pages */
1412 if (nr_pages < 2)
1413 nr_pages = 2;
1414
1415 buffer->cpus = nr_cpu_ids;
1416
1417 bsize = sizeof(void *) * nr_cpu_ids;
1418 buffer->buffers = kzalloc(ALIGN(bsize, cache_line_size()),
1419 GFP_KERNEL);
1420 if (!buffer->buffers)
1421 goto fail_free_cpumask;
1422
1423 cpu = raw_smp_processor_id();
1424 cpumask_set_cpu(cpu, buffer->cpumask);
1425 buffer->buffers[cpu] = rb_allocate_cpu_buffer(buffer, nr_pages, cpu);
1426 if (!buffer->buffers[cpu])
1427 goto fail_free_buffers;
1428
1429 ret = cpuhp_state_add_instance(CPUHP_TRACE_RB_PREPARE, &buffer->node);
1430 if (ret < 0)
1431 goto fail_free_buffers;
1432
1433 mutex_init(&buffer->mutex);
1434
1435 return buffer;
1436
1437 fail_free_buffers:
1438 for_each_buffer_cpu(buffer, cpu) {
1439 if (buffer->buffers[cpu])
1440 rb_free_cpu_buffer(buffer->buffers[cpu]);
1441 }
1442 kfree(buffer->buffers);
1443
1444 fail_free_cpumask:
1445 free_cpumask_var(buffer->cpumask);
1446
1447 fail_free_buffer:
1448 kfree(buffer);
1449 return NULL;
1450}
1451EXPORT_SYMBOL_GPL(__ring_buffer_alloc);
1452
1453/**
1454 * ring_buffer_free - free a ring buffer.
1455 * @buffer: the buffer to free.
1456 */
1457void
1458ring_buffer_free(struct ring_buffer *buffer)
1459{
1460 int cpu;
1461
1462 cpuhp_state_remove_instance(CPUHP_TRACE_RB_PREPARE, &buffer->node);
1463
1464 for_each_buffer_cpu(buffer, cpu)
1465 rb_free_cpu_buffer(buffer->buffers[cpu]);
1466
1467 kfree(buffer->buffers);
1468 free_cpumask_var(buffer->cpumask);
1469
1470 kfree(buffer);
1471}
1472EXPORT_SYMBOL_GPL(ring_buffer_free);
1473
1474void ring_buffer_set_clock(struct ring_buffer *buffer,
1475 u64 (*clock)(void))
1476{
1477 buffer->clock = clock;
1478}
1479
1480void ring_buffer_set_time_stamp_abs(struct ring_buffer *buffer, bool abs)
1481{
1482 buffer->time_stamp_abs = abs;
1483}
1484
1485bool ring_buffer_time_stamp_abs(struct ring_buffer *buffer)
1486{
1487 return buffer->time_stamp_abs;
1488}
1489
1490static void rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer);
1491
1492static inline unsigned long rb_page_entries(struct buffer_page *bpage)
1493{
1494 return local_read(&bpage->entries) & RB_WRITE_MASK;
1495}
1496
1497static inline unsigned long rb_page_write(struct buffer_page *bpage)
1498{
1499 return local_read(&bpage->write) & RB_WRITE_MASK;
1500}
1501
1502static int
1503rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned long nr_pages)
1504{
1505 struct list_head *tail_page, *to_remove, *next_page;
1506 struct buffer_page *to_remove_page, *tmp_iter_page;
1507 struct buffer_page *last_page, *first_page;
1508 unsigned long nr_removed;
1509 unsigned long head_bit;
1510 int page_entries;
1511
1512 head_bit = 0;
1513
1514 raw_spin_lock_irq(&cpu_buffer->reader_lock);
1515 atomic_inc(&cpu_buffer->record_disabled);
1516 /*
1517 * We don't race with the readers since we have acquired the reader
1518 * lock. We also don't race with writers after disabling recording.
1519 * This makes it easy to figure out the first and the last page to be
1520 * removed from the list. We unlink all the pages in between including
1521 * the first and last pages. This is done in a busy loop so that we
1522 * lose the least number of traces.
1523 * The pages are freed after we restart recording and unlock readers.
1524 */
1525 tail_page = &cpu_buffer->tail_page->list;
1526
1527 /*
1528 * tail page might be on reader page, we remove the next page
1529 * from the ring buffer
1530 */
1531 if (cpu_buffer->tail_page == cpu_buffer->reader_page)
1532 tail_page = rb_list_head(tail_page->next);
1533 to_remove = tail_page;
1534
1535 /* start of pages to remove */
1536 first_page = list_entry(rb_list_head(to_remove->next),
1537 struct buffer_page, list);
1538
1539 for (nr_removed = 0; nr_removed < nr_pages; nr_removed++) {
1540 to_remove = rb_list_head(to_remove)->next;
1541 head_bit |= (unsigned long)to_remove & RB_PAGE_HEAD;
1542 }
1543
1544 next_page = rb_list_head(to_remove)->next;
1545
1546 /*
1547 * Now we remove all pages between tail_page and next_page.
1548 * Make sure that we have head_bit value preserved for the
1549 * next page
1550 */
1551 tail_page->next = (struct list_head *)((unsigned long)next_page |
1552 head_bit);
1553 next_page = rb_list_head(next_page);
1554 next_page->prev = tail_page;
1555
1556 /* make sure pages points to a valid page in the ring buffer */
1557 cpu_buffer->pages = next_page;
1558
1559 /* update head page */
1560 if (head_bit)
1561 cpu_buffer->head_page = list_entry(next_page,
1562 struct buffer_page, list);
1563
1564 /*
1565 * change read pointer to make sure any read iterators reset
1566 * themselves
1567 */
1568 cpu_buffer->read = 0;
1569
1570 /* pages are removed, resume tracing and then free the pages */
1571 atomic_dec(&cpu_buffer->record_disabled);
1572 raw_spin_unlock_irq(&cpu_buffer->reader_lock);
1573
1574 RB_WARN_ON(cpu_buffer, list_empty(cpu_buffer->pages));
1575
1576 /* last buffer page to remove */
1577 last_page = list_entry(rb_list_head(to_remove), struct buffer_page,
1578 list);
1579 tmp_iter_page = first_page;
1580
1581 do {
1582 cond_resched();
1583
1584 to_remove_page = tmp_iter_page;
1585 rb_inc_page(cpu_buffer, &tmp_iter_page);
1586
1587 /* update the counters */
1588 page_entries = rb_page_entries(to_remove_page);
1589 if (page_entries) {
1590 /*
1591 * If something was added to this page, it was full
1592 * since it is not the tail page. So we deduct the
1593 * bytes consumed in ring buffer from here.
1594 * Increment overrun to account for the lost events.
1595 */
1596 local_add(page_entries, &cpu_buffer->overrun);
1597 local_sub(BUF_PAGE_SIZE, &cpu_buffer->entries_bytes);
1598 }
1599
1600 /*
1601 * We have already removed references to this list item, just
1602 * free up the buffer_page and its page
1603 */
1604 free_buffer_page(to_remove_page);
1605 nr_removed--;
1606
1607 } while (to_remove_page != last_page);
1608
1609 RB_WARN_ON(cpu_buffer, nr_removed);
1610
1611 return nr_removed == 0;
1612}
1613
1614static int
1615rb_insert_pages(struct ring_buffer_per_cpu *cpu_buffer)
1616{
1617 struct list_head *pages = &cpu_buffer->new_pages;
1618 int retries, success;
1619
1620 raw_spin_lock_irq(&cpu_buffer->reader_lock);
1621 /*
1622 * We are holding the reader lock, so the reader page won't be swapped
1623 * in the ring buffer. Now we are racing with the writer trying to
1624 * move head page and the tail page.
1625 * We are going to adapt the reader page update process where:
1626 * 1. We first splice the start and end of list of new pages between
1627 * the head page and its previous page.
1628 * 2. We cmpxchg the prev_page->next to point from head page to the
1629 * start of new pages list.
1630 * 3. Finally, we update the head->prev to the end of new list.
1631 *
1632 * We will try this process 10 times, to make sure that we don't keep
1633 * spinning.
1634 */
1635 retries = 10;
1636 success = 0;
1637 while (retries--) {
1638 struct list_head *head_page, *prev_page, *r;
1639 struct list_head *last_page, *first_page;
1640 struct list_head *head_page_with_bit;
1641
1642 head_page = &rb_set_head_page(cpu_buffer)->list;
1643 if (!head_page)
1644 break;
1645 prev_page = head_page->prev;
1646
1647 first_page = pages->next;
1648 last_page = pages->prev;
1649
1650 head_page_with_bit = (struct list_head *)
1651 ((unsigned long)head_page | RB_PAGE_HEAD);
1652
1653 last_page->next = head_page_with_bit;
1654 first_page->prev = prev_page;
1655
1656 r = cmpxchg(&prev_page->next, head_page_with_bit, first_page);
1657
1658 if (r == head_page_with_bit) {
1659 /*
1660 * yay, we replaced the page pointer to our new list,
1661 * now, we just have to update to head page's prev
1662 * pointer to point to end of list
1663 */
1664 head_page->prev = last_page;
1665 success = 1;
1666 break;
1667 }
1668 }
1669
1670 if (success)
1671 INIT_LIST_HEAD(pages);
1672 /*
1673 * If we weren't successful in adding in new pages, warn and stop
1674 * tracing
1675 */
1676 RB_WARN_ON(cpu_buffer, !success);
1677 raw_spin_unlock_irq(&cpu_buffer->reader_lock);
1678
1679 /* free pages if they weren't inserted */
1680 if (!success) {
1681 struct buffer_page *bpage, *tmp;
1682 list_for_each_entry_safe(bpage, tmp, &cpu_buffer->new_pages,
1683 list) {
1684 list_del_init(&bpage->list);
1685 free_buffer_page(bpage);
1686 }
1687 }
1688 return success;
1689}
1690
1691static void rb_update_pages(struct ring_buffer_per_cpu *cpu_buffer)
1692{
1693 int success;
1694
1695 if (cpu_buffer->nr_pages_to_update > 0)
1696 success = rb_insert_pages(cpu_buffer);
1697 else
1698 success = rb_remove_pages(cpu_buffer,
1699 -cpu_buffer->nr_pages_to_update);
1700
1701 if (success)
1702 cpu_buffer->nr_pages += cpu_buffer->nr_pages_to_update;
1703}
1704
1705static void update_pages_handler(struct work_struct *work)
1706{
1707 struct ring_buffer_per_cpu *cpu_buffer = container_of(work,
1708 struct ring_buffer_per_cpu, update_pages_work);
1709 rb_update_pages(cpu_buffer);
1710 complete(&cpu_buffer->update_done);
1711}
1712
1713/**
1714 * ring_buffer_resize - resize the ring buffer
1715 * @buffer: the buffer to resize.
1716 * @size: the new size.
1717 * @cpu_id: the cpu buffer to resize
1718 *
1719 * Minimum size is 2 * BUF_PAGE_SIZE.
1720 *
1721 * Returns 0 on success and < 0 on failure.
1722 */
1723int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size,
1724 int cpu_id)
1725{
1726 struct ring_buffer_per_cpu *cpu_buffer;
1727 unsigned long nr_pages;
1728 int cpu, err = 0;
1729
1730 /*
1731 * Always succeed at resizing a non-existent buffer:
1732 */
1733 if (!buffer)
1734 return size;
1735
1736 /* Make sure the requested buffer exists */
1737 if (cpu_id != RING_BUFFER_ALL_CPUS &&
1738 !cpumask_test_cpu(cpu_id, buffer->cpumask))
1739 return size;
1740
1741 nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
1742
1743 /* we need a minimum of two pages */
1744 if (nr_pages < 2)
1745 nr_pages = 2;
1746
1747 size = nr_pages * BUF_PAGE_SIZE;
1748
1749 /*
1750 * Don't succeed if resizing is disabled, as a reader might be
1751 * manipulating the ring buffer and is expecting a sane state while
1752 * this is true.
1753 */
1754 if (atomic_read(&buffer->resize_disabled))
1755 return -EBUSY;
1756
1757 /* prevent another thread from changing buffer sizes */
1758 mutex_lock(&buffer->mutex);
1759
1760 if (cpu_id == RING_BUFFER_ALL_CPUS) {
1761 /* calculate the pages to update */
1762 for_each_buffer_cpu(buffer, cpu) {
1763 cpu_buffer = buffer->buffers[cpu];
1764
1765 cpu_buffer->nr_pages_to_update = nr_pages -
1766 cpu_buffer->nr_pages;
1767 /*
1768 * nothing more to do for removing pages or no update
1769 */
1770 if (cpu_buffer->nr_pages_to_update <= 0)
1771 continue;
1772 /*
1773 * to add pages, make sure all new pages can be
1774 * allocated without receiving ENOMEM
1775 */
1776 INIT_LIST_HEAD(&cpu_buffer->new_pages);
1777 if (__rb_allocate_pages(cpu_buffer->nr_pages_to_update,
1778 &cpu_buffer->new_pages, cpu)) {
1779 /* not enough memory for new pages */
1780 err = -ENOMEM;
1781 goto out_err;
1782 }
1783 }
1784
1785 get_online_cpus();
1786 /*
1787 * Fire off all the required work handlers
1788 * We can't schedule on offline CPUs, but it's not necessary
1789 * since we can change their buffer sizes without any race.
1790 */
1791 for_each_buffer_cpu(buffer, cpu) {
1792 cpu_buffer = buffer->buffers[cpu];
1793 if (!cpu_buffer->nr_pages_to_update)
1794 continue;
1795
1796 /* Can't run something on an offline CPU. */
1797 if (!cpu_online(cpu)) {
1798 rb_update_pages(cpu_buffer);
1799 cpu_buffer->nr_pages_to_update = 0;
1800 } else {
1801 schedule_work_on(cpu,
1802 &cpu_buffer->update_pages_work);
1803 }
1804 }
1805
1806 /* wait for all the updates to complete */
1807 for_each_buffer_cpu(buffer, cpu) {
1808 cpu_buffer = buffer->buffers[cpu];
1809 if (!cpu_buffer->nr_pages_to_update)
1810 continue;
1811
1812 if (cpu_online(cpu))
1813 wait_for_completion(&cpu_buffer->update_done);
1814 cpu_buffer->nr_pages_to_update = 0;
1815 }
1816
1817 put_online_cpus();
1818 } else {
1819 /* Make sure this CPU has been initialized */
1820 if (!cpumask_test_cpu(cpu_id, buffer->cpumask))
1821 goto out;
1822
1823 cpu_buffer = buffer->buffers[cpu_id];
1824
1825 if (nr_pages == cpu_buffer->nr_pages)
1826 goto out;
1827
1828 cpu_buffer->nr_pages_to_update = nr_pages -
1829 cpu_buffer->nr_pages;
1830
1831 INIT_LIST_HEAD(&cpu_buffer->new_pages);
1832 if (cpu_buffer->nr_pages_to_update > 0 &&
1833 __rb_allocate_pages(cpu_buffer->nr_pages_to_update,
1834 &cpu_buffer->new_pages, cpu_id)) {
1835 err = -ENOMEM;
1836 goto out_err;
1837 }
1838
1839 get_online_cpus();
1840
1841 /* Can't run something on an offline CPU. */
1842 if (!cpu_online(cpu_id))
1843 rb_update_pages(cpu_buffer);
1844 else {
1845 schedule_work_on(cpu_id,
1846 &cpu_buffer->update_pages_work);
1847 wait_for_completion(&cpu_buffer->update_done);
1848 }
1849
1850 cpu_buffer->nr_pages_to_update = 0;
1851 put_online_cpus();
1852 }
1853
1854 out:
1855 /*
1856 * The ring buffer resize can happen with the ring buffer
1857 * enabled, so that the update disturbs the tracing as little
1858 * as possible. But if the buffer is disabled, we do not need
1859 * to worry about that, and we can take the time to verify
1860 * that the buffer is not corrupt.
1861 */
1862 if (atomic_read(&buffer->record_disabled)) {
1863 atomic_inc(&buffer->record_disabled);
1864 /*
1865 * Even though the buffer was disabled, we must make sure
1866 * that it is truly disabled before calling rb_check_pages.
1867 * There could have been a race between checking
1868 * record_disable and incrementing it.
1869 */
1870 synchronize_rcu();
1871 for_each_buffer_cpu(buffer, cpu) {
1872 cpu_buffer = buffer->buffers[cpu];
1873 rb_check_pages(cpu_buffer);
1874 }
1875 atomic_dec(&buffer->record_disabled);
1876 }
1877
1878 mutex_unlock(&buffer->mutex);
1879 return size;
1880
1881 out_err:
1882 for_each_buffer_cpu(buffer, cpu) {
1883 struct buffer_page *bpage, *tmp;
1884
1885 cpu_buffer = buffer->buffers[cpu];
1886 cpu_buffer->nr_pages_to_update = 0;
1887
1888 if (list_empty(&cpu_buffer->new_pages))
1889 continue;
1890
1891 list_for_each_entry_safe(bpage, tmp, &cpu_buffer->new_pages,
1892 list) {
1893 list_del_init(&bpage->list);
1894 free_buffer_page(bpage);
1895 }
1896 }
1897 mutex_unlock(&buffer->mutex);
1898 return err;
1899}
1900EXPORT_SYMBOL_GPL(ring_buffer_resize);
1901
1902void ring_buffer_change_overwrite(struct ring_buffer *buffer, int val)
1903{
1904 mutex_lock(&buffer->mutex);
1905 if (val)
1906 buffer->flags |= RB_FL_OVERWRITE;
1907 else
1908 buffer->flags &= ~RB_FL_OVERWRITE;
1909 mutex_unlock(&buffer->mutex);
1910}
1911EXPORT_SYMBOL_GPL(ring_buffer_change_overwrite);
1912
1913static __always_inline void *__rb_page_index(struct buffer_page *bpage, unsigned index)
1914{
1915 return bpage->page->data + index;
1916}
1917
1918static __always_inline struct ring_buffer_event *
1919rb_reader_event(struct ring_buffer_per_cpu *cpu_buffer)
1920{
1921 return __rb_page_index(cpu_buffer->reader_page,
1922 cpu_buffer->reader_page->read);
1923}
1924
1925static __always_inline struct ring_buffer_event *
1926rb_iter_head_event(struct ring_buffer_iter *iter)
1927{
1928 return __rb_page_index(iter->head_page, iter->head);
1929}
1930
1931static __always_inline unsigned rb_page_commit(struct buffer_page *bpage)
1932{
1933 return local_read(&bpage->page->commit);
1934}
1935
1936/* Size is determined by what has been committed */
1937static __always_inline unsigned rb_page_size(struct buffer_page *bpage)
1938{
1939 return rb_page_commit(bpage);
1940}
1941
1942static __always_inline unsigned
1943rb_commit_index(struct ring_buffer_per_cpu *cpu_buffer)
1944{
1945 return rb_page_commit(cpu_buffer->commit_page);
1946}
1947
1948static __always_inline unsigned
1949rb_event_index(struct ring_buffer_event *event)
1950{
1951 unsigned long addr = (unsigned long)event;
1952
1953 return (addr & ~PAGE_MASK) - BUF_PAGE_HDR_SIZE;
1954}
1955
1956static void rb_inc_iter(struct ring_buffer_iter *iter)
1957{
1958 struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
1959
1960 /*
1961 * The iterator could be on the reader page (it starts there).
1962 * But the head could have moved, since the reader was
1963 * found. Check for this case and assign the iterator
1964 * to the head page instead of next.
1965 */
1966 if (iter->head_page == cpu_buffer->reader_page)
1967 iter->head_page = rb_set_head_page(cpu_buffer);
1968 else
1969 rb_inc_page(cpu_buffer, &iter->head_page);
1970
1971 iter->read_stamp = iter->head_page->page->time_stamp;
1972 iter->head = 0;
1973}
1974
1975/*
1976 * rb_handle_head_page - writer hit the head page
1977 *
1978 * Returns: +1 to retry page
1979 * 0 to continue
1980 * -1 on error
1981 */
1982static int
1983rb_handle_head_page(struct ring_buffer_per_cpu *cpu_buffer,
1984 struct buffer_page *tail_page,
1985 struct buffer_page *next_page)
1986{
1987 struct buffer_page *new_head;
1988 int entries;
1989 int type;
1990 int ret;
1991
1992 entries = rb_page_entries(next_page);
1993
1994 /*
1995 * The hard part is here. We need to move the head
1996 * forward, and protect against both readers on
1997 * other CPUs and writers coming in via interrupts.
1998 */
1999 type = rb_head_page_set_update(cpu_buffer, next_page, tail_page,
2000 RB_PAGE_HEAD);
2001
2002 /*
2003 * type can be one of four:
2004 * NORMAL - an interrupt already moved it for us
2005 * HEAD - we are the first to get here.
2006 * UPDATE - we are the interrupt interrupting
2007 * a current move.
2008 * MOVED - a reader on another CPU moved the next
2009 * pointer to its reader page. Give up
2010 * and try again.
2011 */
2012
2013 switch (type) {
2014 case RB_PAGE_HEAD:
2015 /*
2016 * We changed the head to UPDATE, thus
2017 * it is our responsibility to update
2018 * the counters.
2019 */
2020 local_add(entries, &cpu_buffer->overrun);
2021 local_sub(BUF_PAGE_SIZE, &cpu_buffer->entries_bytes);
2022
2023 /*
2024 * The entries will be zeroed out when we move the
2025 * tail page.
2026 */
2027
2028 /* still more to do */
2029 break;
2030
2031 case RB_PAGE_UPDATE:
2032 /*
2033 * This is an interrupt that interrupt the
2034 * previous update. Still more to do.
2035 */
2036 break;
2037 case RB_PAGE_NORMAL:
2038 /*
2039 * An interrupt came in before the update
2040 * and processed this for us.
2041 * Nothing left to do.
2042 */
2043 return 1;
2044 case RB_PAGE_MOVED:
2045 /*
2046 * The reader is on another CPU and just did
2047 * a swap with our next_page.
2048 * Try again.
2049 */
2050 return 1;
2051 default:
2052 RB_WARN_ON(cpu_buffer, 1); /* WTF??? */
2053 return -1;
2054 }
2055
2056 /*
2057 * Now that we are here, the old head pointer is
2058 * set to UPDATE. This will keep the reader from
2059 * swapping the head page with the reader page.
2060 * The reader (on another CPU) will spin till
2061 * we are finished.
2062 *
2063 * We just need to protect against interrupts
2064 * doing the job. We will set the next pointer
2065 * to HEAD. After that, we set the old pointer
2066 * to NORMAL, but only if it was HEAD before.
2067 * otherwise we are an interrupt, and only
2068 * want the outer most commit to reset it.
2069 */
2070 new_head = next_page;
2071 rb_inc_page(cpu_buffer, &new_head);
2072
2073 ret = rb_head_page_set_head(cpu_buffer, new_head, next_page,
2074 RB_PAGE_NORMAL);
2075
2076 /*
2077 * Valid returns are:
2078 * HEAD - an interrupt came in and already set it.
2079 * NORMAL - One of two things:
2080 * 1) We really set it.
2081 * 2) A bunch of interrupts came in and moved
2082 * the page forward again.
2083 */
2084 switch (ret) {
2085 case RB_PAGE_HEAD:
2086 case RB_PAGE_NORMAL:
2087 /* OK */
2088 break;
2089 default:
2090 RB_WARN_ON(cpu_buffer, 1);
2091 return -1;
2092 }
2093
2094 /*
2095 * It is possible that an interrupt came in,
2096 * set the head up, then more interrupts came in
2097 * and moved it again. When we get back here,
2098 * the page would have been set to NORMAL but we
2099 * just set it back to HEAD.
2100 *
2101 * How do you detect this? Well, if that happened
2102 * the tail page would have moved.
2103 */
2104 if (ret == RB_PAGE_NORMAL) {
2105 struct buffer_page *buffer_tail_page;
2106
2107 buffer_tail_page = READ_ONCE(cpu_buffer->tail_page);
2108 /*
2109 * If the tail had moved passed next, then we need
2110 * to reset the pointer.
2111 */
2112 if (buffer_tail_page != tail_page &&
2113 buffer_tail_page != next_page)
2114 rb_head_page_set_normal(cpu_buffer, new_head,
2115 next_page,
2116 RB_PAGE_HEAD);
2117 }
2118
2119 /*
2120 * If this was the outer most commit (the one that
2121 * changed the original pointer from HEAD to UPDATE),
2122 * then it is up to us to reset it to NORMAL.
2123 */
2124 if (type == RB_PAGE_HEAD) {
2125 ret = rb_head_page_set_normal(cpu_buffer, next_page,
2126 tail_page,
2127 RB_PAGE_UPDATE);
2128 if (RB_WARN_ON(cpu_buffer,
2129 ret != RB_PAGE_UPDATE))
2130 return -1;
2131 }
2132
2133 return 0;
2134}
2135
2136static inline void
2137rb_reset_tail(struct ring_buffer_per_cpu *cpu_buffer,
2138 unsigned long tail, struct rb_event_info *info)
2139{
2140 struct buffer_page *tail_page = info->tail_page;
2141 struct ring_buffer_event *event;
2142 unsigned long length = info->length;
2143
2144 /*
2145 * Only the event that crossed the page boundary
2146 * must fill the old tail_page with padding.
2147 */
2148 if (tail >= BUF_PAGE_SIZE) {
2149 /*
2150 * If the page was filled, then we still need
2151 * to update the real_end. Reset it to zero
2152 * and the reader will ignore it.
2153 */
2154 if (tail == BUF_PAGE_SIZE)
2155 tail_page->real_end = 0;
2156
2157 local_sub(length, &tail_page->write);
2158 return;
2159 }
2160
2161 event = __rb_page_index(tail_page, tail);
2162
2163 /* account for padding bytes */
2164 local_add(BUF_PAGE_SIZE - tail, &cpu_buffer->entries_bytes);
2165
2166 /*
2167 * Save the original length to the meta data.
2168 * This will be used by the reader to add lost event
2169 * counter.
2170 */
2171 tail_page->real_end = tail;
2172
2173 /*
2174 * If this event is bigger than the minimum size, then
2175 * we need to be careful that we don't subtract the
2176 * write counter enough to allow another writer to slip
2177 * in on this page.
2178 * We put in a discarded commit instead, to make sure
2179 * that this space is not used again.
2180 *
2181 * If we are less than the minimum size, we don't need to
2182 * worry about it.
2183 */
2184 if (tail > (BUF_PAGE_SIZE - RB_EVNT_MIN_SIZE)) {
2185 /* No room for any events */
2186
2187 /* Mark the rest of the page with padding */
2188 rb_event_set_padding(event);
2189
2190 /* Set the write back to the previous setting */
2191 local_sub(length, &tail_page->write);
2192 return;
2193 }
2194
2195 /* Put in a discarded event */
2196 event->array[0] = (BUF_PAGE_SIZE - tail) - RB_EVNT_HDR_SIZE;
2197 event->type_len = RINGBUF_TYPE_PADDING;
2198 /* time delta must be non zero */
2199 event->time_delta = 1;
2200
2201 /* Set write to end of buffer */
2202 length = (tail + length) - BUF_PAGE_SIZE;
2203 local_sub(length, &tail_page->write);
2204}
2205
2206static inline void rb_end_commit(struct ring_buffer_per_cpu *cpu_buffer);
2207
2208/*
2209 * This is the slow path, force gcc not to inline it.
2210 */
2211static noinline struct ring_buffer_event *
2212rb_move_tail(struct ring_buffer_per_cpu *cpu_buffer,
2213 unsigned long tail, struct rb_event_info *info)
2214{
2215 struct buffer_page *tail_page = info->tail_page;
2216 struct buffer_page *commit_page = cpu_buffer->commit_page;
2217 struct ring_buffer *buffer = cpu_buffer->buffer;
2218 struct buffer_page *next_page;
2219 int ret;
2220
2221 next_page = tail_page;
2222
2223 rb_inc_page(cpu_buffer, &next_page);
2224
2225 /*
2226 * If for some reason, we had an interrupt storm that made
2227 * it all the way around the buffer, bail, and warn
2228 * about it.
2229 */
2230 if (unlikely(next_page == commit_page)) {
2231 local_inc(&cpu_buffer->commit_overrun);
2232 goto out_reset;
2233 }
2234
2235 /*
2236 * This is where the fun begins!
2237 *
2238 * We are fighting against races between a reader that
2239 * could be on another CPU trying to swap its reader
2240 * page with the buffer head.
2241 *
2242 * We are also fighting against interrupts coming in and
2243 * moving the head or tail on us as well.
2244 *
2245 * If the next page is the head page then we have filled
2246 * the buffer, unless the commit page is still on the
2247 * reader page.
2248 */
2249 if (rb_is_head_page(cpu_buffer, next_page, &tail_page->list)) {
2250
2251 /*
2252 * If the commit is not on the reader page, then
2253 * move the header page.
2254 */
2255 if (!rb_is_reader_page(cpu_buffer->commit_page)) {
2256 /*
2257 * If we are not in overwrite mode,
2258 * this is easy, just stop here.
2259 */
2260 if (!(buffer->flags & RB_FL_OVERWRITE)) {
2261 local_inc(&cpu_buffer->dropped_events);
2262 goto out_reset;
2263 }
2264
2265 ret = rb_handle_head_page(cpu_buffer,
2266 tail_page,
2267 next_page);
2268 if (ret < 0)
2269 goto out_reset;
2270 if (ret)
2271 goto out_again;
2272 } else {
2273 /*
2274 * We need to be careful here too. The
2275 * commit page could still be on the reader
2276 * page. We could have a small buffer, and
2277 * have filled up the buffer with events
2278 * from interrupts and such, and wrapped.
2279 *
2280 * Note, if the tail page is also the on the
2281 * reader_page, we let it move out.
2282 */
2283 if (unlikely((cpu_buffer->commit_page !=
2284 cpu_buffer->tail_page) &&
2285 (cpu_buffer->commit_page ==
2286 cpu_buffer->reader_page))) {
2287 local_inc(&cpu_buffer->commit_overrun);
2288 goto out_reset;
2289 }
2290 }
2291 }
2292
2293 rb_tail_page_update(cpu_buffer, tail_page, next_page);
2294
2295 out_again:
2296
2297 rb_reset_tail(cpu_buffer, tail, info);
2298
2299 /* Commit what we have for now. */
2300 rb_end_commit(cpu_buffer);
2301 /* rb_end_commit() decs committing */
2302 local_inc(&cpu_buffer->committing);
2303
2304 /* fail and let the caller try again */
2305 return ERR_PTR(-EAGAIN);
2306
2307 out_reset:
2308 /* reset write */
2309 rb_reset_tail(cpu_buffer, tail, info);
2310
2311 return NULL;
2312}
2313
2314/* Slow path, do not inline */
2315static noinline struct ring_buffer_event *
2316rb_add_time_stamp(struct ring_buffer_event *event, u64 delta, bool abs)
2317{
2318 if (abs)
2319 event->type_len = RINGBUF_TYPE_TIME_STAMP;
2320 else
2321 event->type_len = RINGBUF_TYPE_TIME_EXTEND;
2322
2323 /* Not the first event on the page, or not delta? */
2324 if (abs || rb_event_index(event)) {
2325 event->time_delta = delta & TS_MASK;
2326 event->array[0] = delta >> TS_SHIFT;
2327 } else {
2328 /* nope, just zero it */
2329 event->time_delta = 0;
2330 event->array[0] = 0;
2331 }
2332
2333 return skip_time_extend(event);
2334}
2335
2336static inline bool rb_event_is_commit(struct ring_buffer_per_cpu *cpu_buffer,
2337 struct ring_buffer_event *event);
2338
2339/**
2340 * rb_update_event - update event type and data
2341 * @event: the event to update
2342 * @type: the type of event
2343 * @length: the size of the event field in the ring buffer
2344 *
2345 * Update the type and data fields of the event. The length
2346 * is the actual size that is written to the ring buffer,
2347 * and with this, we can determine what to place into the
2348 * data field.
2349 */
2350static void
2351rb_update_event(struct ring_buffer_per_cpu *cpu_buffer,
2352 struct ring_buffer_event *event,
2353 struct rb_event_info *info)
2354{
2355 unsigned length = info->length;
2356 u64 delta = info->delta;
2357
2358 /* Only a commit updates the timestamp */
2359 if (unlikely(!rb_event_is_commit(cpu_buffer, event)))
2360 delta = 0;
2361
2362 /*
2363 * If we need to add a timestamp, then we
2364 * add it to the start of the reserved space.
2365 */
2366 if (unlikely(info->add_timestamp)) {
2367 bool abs = ring_buffer_time_stamp_abs(cpu_buffer->buffer);
2368
2369 event = rb_add_time_stamp(event, info->delta, abs);
2370 length -= RB_LEN_TIME_EXTEND;
2371 delta = 0;
2372 }
2373
2374 event->time_delta = delta;
2375 length -= RB_EVNT_HDR_SIZE;
2376 if (length > RB_MAX_SMALL_DATA || RB_FORCE_8BYTE_ALIGNMENT) {
2377 event->type_len = 0;
2378 event->array[0] = length;
2379 } else
2380 event->type_len = DIV_ROUND_UP(length, RB_ALIGNMENT);
2381}
2382
2383static unsigned rb_calculate_event_length(unsigned length)
2384{
2385 struct ring_buffer_event event; /* Used only for sizeof array */
2386
2387 /* zero length can cause confusions */
2388 if (!length)
2389 length++;
2390
2391 if (length > RB_MAX_SMALL_DATA || RB_FORCE_8BYTE_ALIGNMENT)
2392 length += sizeof(event.array[0]);
2393
2394 length += RB_EVNT_HDR_SIZE;
2395 length = ALIGN(length, RB_ARCH_ALIGNMENT);
2396
2397 /*
2398 * In case the time delta is larger than the 27 bits for it
2399 * in the header, we need to add a timestamp. If another
2400 * event comes in when trying to discard this one to increase
2401 * the length, then the timestamp will be added in the allocated
2402 * space of this event. If length is bigger than the size needed
2403 * for the TIME_EXTEND, then padding has to be used. The events
2404 * length must be either RB_LEN_TIME_EXTEND, or greater than or equal
2405 * to RB_LEN_TIME_EXTEND + 8, as 8 is the minimum size for padding.
2406 * As length is a multiple of 4, we only need to worry if it
2407 * is 12 (RB_LEN_TIME_EXTEND + 4).
2408 */
2409 if (length == RB_LEN_TIME_EXTEND + RB_ALIGNMENT)
2410 length += RB_ALIGNMENT;
2411
2412 return length;
2413}
2414
2415#ifndef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
2416static inline bool sched_clock_stable(void)
2417{
2418 return true;
2419}
2420#endif
2421
2422static inline int
2423rb_try_to_discard(struct ring_buffer_per_cpu *cpu_buffer,
2424 struct ring_buffer_event *event)
2425{
2426 unsigned long new_index, old_index;
2427 struct buffer_page *bpage;
2428 unsigned long index;
2429 unsigned long addr;
2430
2431 new_index = rb_event_index(event);
2432 old_index = new_index + rb_event_ts_length(event);
2433 addr = (unsigned long)event;
2434 addr &= PAGE_MASK;
2435
2436 bpage = READ_ONCE(cpu_buffer->tail_page);
2437
2438 if (bpage->page == (void *)addr && rb_page_write(bpage) == old_index) {
2439 unsigned long write_mask =
2440 local_read(&bpage->write) & ~RB_WRITE_MASK;
2441 unsigned long event_length = rb_event_length(event);
2442 /*
2443 * This is on the tail page. It is possible that
2444 * a write could come in and move the tail page
2445 * and write to the next page. That is fine
2446 * because we just shorten what is on this page.
2447 */
2448 old_index += write_mask;
2449 new_index += write_mask;
2450 index = local_cmpxchg(&bpage->write, old_index, new_index);
2451 if (index == old_index) {
2452 /* update counters */
2453 local_sub(event_length, &cpu_buffer->entries_bytes);
2454 return 1;
2455 }
2456 }
2457
2458 /* could not discard */
2459 return 0;
2460}
2461
2462static void rb_start_commit(struct ring_buffer_per_cpu *cpu_buffer)
2463{
2464 local_inc(&cpu_buffer->committing);
2465 local_inc(&cpu_buffer->commits);
2466}
2467
2468static __always_inline void
2469rb_set_commit_to_write(struct ring_buffer_per_cpu *cpu_buffer)
2470{
2471 unsigned long max_count;
2472
2473 /*
2474 * We only race with interrupts and NMIs on this CPU.
2475 * If we own the commit event, then we can commit
2476 * all others that interrupted us, since the interruptions
2477 * are in stack format (they finish before they come
2478 * back to us). This allows us to do a simple loop to
2479 * assign the commit to the tail.
2480 */
2481 again:
2482 max_count = cpu_buffer->nr_pages * 100;
2483
2484 while (cpu_buffer->commit_page != READ_ONCE(cpu_buffer->tail_page)) {
2485 if (RB_WARN_ON(cpu_buffer, !(--max_count)))
2486 return;
2487 if (RB_WARN_ON(cpu_buffer,
2488 rb_is_reader_page(cpu_buffer->tail_page)))
2489 return;
2490 local_set(&cpu_buffer->commit_page->page->commit,
2491 rb_page_write(cpu_buffer->commit_page));
2492 rb_inc_page(cpu_buffer, &cpu_buffer->commit_page);
2493 /* Only update the write stamp if the page has an event */
2494 if (rb_page_write(cpu_buffer->commit_page))
2495 cpu_buffer->write_stamp =
2496 cpu_buffer->commit_page->page->time_stamp;
2497 /* add barrier to keep gcc from optimizing too much */
2498 barrier();
2499 }
2500 while (rb_commit_index(cpu_buffer) !=
2501 rb_page_write(cpu_buffer->commit_page)) {
2502
2503 local_set(&cpu_buffer->commit_page->page->commit,
2504 rb_page_write(cpu_buffer->commit_page));
2505 RB_WARN_ON(cpu_buffer,
2506 local_read(&cpu_buffer->commit_page->page->commit) &
2507 ~RB_WRITE_MASK);
2508 barrier();
2509 }
2510
2511 /* again, keep gcc from optimizing */
2512 barrier();
2513
2514 /*
2515 * If an interrupt came in just after the first while loop
2516 * and pushed the tail page forward, we will be left with
2517 * a dangling commit that will never go forward.
2518 */
2519 if (unlikely(cpu_buffer->commit_page != READ_ONCE(cpu_buffer->tail_page)))
2520 goto again;
2521}
2522
2523static __always_inline void rb_end_commit(struct ring_buffer_per_cpu *cpu_buffer)
2524{
2525 unsigned long commits;
2526
2527 if (RB_WARN_ON(cpu_buffer,
2528 !local_read(&cpu_buffer->committing)))
2529 return;
2530
2531 again:
2532 commits = local_read(&cpu_buffer->commits);
2533 /* synchronize with interrupts */
2534 barrier();
2535 if (local_read(&cpu_buffer->committing) == 1)
2536 rb_set_commit_to_write(cpu_buffer);
2537
2538 local_dec(&cpu_buffer->committing);
2539
2540 /* synchronize with interrupts */
2541 barrier();
2542
2543 /*
2544 * Need to account for interrupts coming in between the
2545 * updating of the commit page and the clearing of the
2546 * committing counter.
2547 */
2548 if (unlikely(local_read(&cpu_buffer->commits) != commits) &&
2549 !local_read(&cpu_buffer->committing)) {
2550 local_inc(&cpu_buffer->committing);
2551 goto again;
2552 }
2553}
2554
2555static inline void rb_event_discard(struct ring_buffer_event *event)
2556{
2557 if (extended_time(event))
2558 event = skip_time_extend(event);
2559
2560 /* array[0] holds the actual length for the discarded event */
2561 event->array[0] = rb_event_data_length(event) - RB_EVNT_HDR_SIZE;
2562 event->type_len = RINGBUF_TYPE_PADDING;
2563 /* time delta must be non zero */
2564 if (!event->time_delta)
2565 event->time_delta = 1;
2566}
2567
2568static __always_inline bool
2569rb_event_is_commit(struct ring_buffer_per_cpu *cpu_buffer,
2570 struct ring_buffer_event *event)
2571{
2572 unsigned long addr = (unsigned long)event;
2573 unsigned long index;
2574
2575 index = rb_event_index(event);
2576 addr &= PAGE_MASK;
2577
2578 return cpu_buffer->commit_page->page == (void *)addr &&
2579 rb_commit_index(cpu_buffer) == index;
2580}
2581
2582static __always_inline void
2583rb_update_write_stamp(struct ring_buffer_per_cpu *cpu_buffer,
2584 struct ring_buffer_event *event)
2585{
2586 u64 delta;
2587
2588 /*
2589 * The event first in the commit queue updates the
2590 * time stamp.
2591 */
2592 if (rb_event_is_commit(cpu_buffer, event)) {
2593 /*
2594 * A commit event that is first on a page
2595 * updates the write timestamp with the page stamp
2596 */
2597 if (!rb_event_index(event))
2598 cpu_buffer->write_stamp =
2599 cpu_buffer->commit_page->page->time_stamp;
2600 else if (event->type_len == RINGBUF_TYPE_TIME_EXTEND) {
2601 delta = ring_buffer_event_time_stamp(event);
2602 cpu_buffer->write_stamp += delta;
2603 } else if (event->type_len == RINGBUF_TYPE_TIME_STAMP) {
2604 delta = ring_buffer_event_time_stamp(event);
2605 cpu_buffer->write_stamp = delta;
2606 } else
2607 cpu_buffer->write_stamp += event->time_delta;
2608 }
2609}
2610
2611static void rb_commit(struct ring_buffer_per_cpu *cpu_buffer,
2612 struct ring_buffer_event *event)
2613{
2614 local_inc(&cpu_buffer->entries);
2615 rb_update_write_stamp(cpu_buffer, event);
2616 rb_end_commit(cpu_buffer);
2617}
2618
2619static __always_inline void
2620rb_wakeups(struct ring_buffer *buffer, struct ring_buffer_per_cpu *cpu_buffer)
2621{
2622 size_t nr_pages;
2623 size_t dirty;
2624 size_t full;
2625
2626 if (buffer->irq_work.waiters_pending) {
2627 buffer->irq_work.waiters_pending = false;
2628 /* irq_work_queue() supplies it's own memory barriers */
2629 irq_work_queue(&buffer->irq_work.work);
2630 }
2631
2632 if (cpu_buffer->irq_work.waiters_pending) {
2633 cpu_buffer->irq_work.waiters_pending = false;
2634 /* irq_work_queue() supplies it's own memory barriers */
2635 irq_work_queue(&cpu_buffer->irq_work.work);
2636 }
2637
2638 if (cpu_buffer->last_pages_touch == local_read(&cpu_buffer->pages_touched))
2639 return;
2640
2641 if (cpu_buffer->reader_page == cpu_buffer->commit_page)
2642 return;
2643
2644 if (!cpu_buffer->irq_work.full_waiters_pending)
2645 return;
2646
2647 cpu_buffer->last_pages_touch = local_read(&cpu_buffer->pages_touched);
2648
2649 full = cpu_buffer->shortest_full;
2650 nr_pages = cpu_buffer->nr_pages;
2651 dirty = ring_buffer_nr_dirty_pages(buffer, cpu_buffer->cpu);
2652 if (full && nr_pages && (dirty * 100) <= full * nr_pages)
2653 return;
2654
2655 cpu_buffer->irq_work.wakeup_full = true;
2656 cpu_buffer->irq_work.full_waiters_pending = false;
2657 /* irq_work_queue() supplies it's own memory barriers */
2658 irq_work_queue(&cpu_buffer->irq_work.work);
2659}
2660
2661/*
2662 * The lock and unlock are done within a preempt disable section.
2663 * The current_context per_cpu variable can only be modified
2664 * by the current task between lock and unlock. But it can
2665 * be modified more than once via an interrupt. To pass this
2666 * information from the lock to the unlock without having to
2667 * access the 'in_interrupt()' functions again (which do show
2668 * a bit of overhead in something as critical as function tracing,
2669 * we use a bitmask trick.
2670 *
2671 * bit 0 = NMI context
2672 * bit 1 = IRQ context
2673 * bit 2 = SoftIRQ context
2674 * bit 3 = normal context.
2675 *
2676 * This works because this is the order of contexts that can
2677 * preempt other contexts. A SoftIRQ never preempts an IRQ
2678 * context.
2679 *
2680 * When the context is determined, the corresponding bit is
2681 * checked and set (if it was set, then a recursion of that context
2682 * happened).
2683 *
2684 * On unlock, we need to clear this bit. To do so, just subtract
2685 * 1 from the current_context and AND it to itself.
2686 *
2687 * (binary)
2688 * 101 - 1 = 100
2689 * 101 & 100 = 100 (clearing bit zero)
2690 *
2691 * 1010 - 1 = 1001
2692 * 1010 & 1001 = 1000 (clearing bit 1)
2693 *
2694 * The least significant bit can be cleared this way, and it
2695 * just so happens that it is the same bit corresponding to
2696 * the current context.
2697 */
2698
2699static __always_inline int
2700trace_recursive_lock(struct ring_buffer_per_cpu *cpu_buffer)
2701{
2702 unsigned int val = cpu_buffer->current_context;
2703 unsigned long pc = preempt_count();
2704 int bit;
2705
2706 if (!(pc & (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET)))
2707 bit = RB_CTX_NORMAL;
2708 else
2709 bit = pc & NMI_MASK ? RB_CTX_NMI :
2710 pc & HARDIRQ_MASK ? RB_CTX_IRQ : RB_CTX_SOFTIRQ;
2711
2712 if (unlikely(val & (1 << (bit + cpu_buffer->nest))))
2713 return 1;
2714
2715 val |= (1 << (bit + cpu_buffer->nest));
2716 cpu_buffer->current_context = val;
2717
2718 return 0;
2719}
2720
2721static __always_inline void
2722trace_recursive_unlock(struct ring_buffer_per_cpu *cpu_buffer)
2723{
2724 cpu_buffer->current_context &=
2725 cpu_buffer->current_context - (1 << cpu_buffer->nest);
2726}
2727
2728/* The recursive locking above uses 4 bits */
2729#define NESTED_BITS 4
2730
2731/**
2732 * ring_buffer_nest_start - Allow to trace while nested
2733 * @buffer: The ring buffer to modify
2734 *
2735 * The ring buffer has a safety mechanism to prevent recursion.
2736 * But there may be a case where a trace needs to be done while
2737 * tracing something else. In this case, calling this function
2738 * will allow this function to nest within a currently active
2739 * ring_buffer_lock_reserve().
2740 *
2741 * Call this function before calling another ring_buffer_lock_reserve() and
2742 * call ring_buffer_nest_end() after the nested ring_buffer_unlock_commit().
2743 */
2744void ring_buffer_nest_start(struct ring_buffer *buffer)
2745{
2746 struct ring_buffer_per_cpu *cpu_buffer;
2747 int cpu;
2748
2749 /* Enabled by ring_buffer_nest_end() */
2750 preempt_disable_notrace();
2751 cpu = raw_smp_processor_id();
2752 cpu_buffer = buffer->buffers[cpu];
2753 /* This is the shift value for the above recursive locking */
2754 cpu_buffer->nest += NESTED_BITS;
2755}
2756
2757/**
2758 * ring_buffer_nest_end - Allow to trace while nested
2759 * @buffer: The ring buffer to modify
2760 *
2761 * Must be called after ring_buffer_nest_start() and after the
2762 * ring_buffer_unlock_commit().
2763 */
2764void ring_buffer_nest_end(struct ring_buffer *buffer)
2765{
2766 struct ring_buffer_per_cpu *cpu_buffer;
2767 int cpu;
2768
2769 /* disabled by ring_buffer_nest_start() */
2770 cpu = raw_smp_processor_id();
2771 cpu_buffer = buffer->buffers[cpu];
2772 /* This is the shift value for the above recursive locking */
2773 cpu_buffer->nest -= NESTED_BITS;
2774 preempt_enable_notrace();
2775}
2776
2777/**
2778 * ring_buffer_unlock_commit - commit a reserved
2779 * @buffer: The buffer to commit to
2780 * @event: The event pointer to commit.
2781 *
2782 * This commits the data to the ring buffer, and releases any locks held.
2783 *
2784 * Must be paired with ring_buffer_lock_reserve.
2785 */
2786int ring_buffer_unlock_commit(struct ring_buffer *buffer,
2787 struct ring_buffer_event *event)
2788{
2789 struct ring_buffer_per_cpu *cpu_buffer;
2790 int cpu = raw_smp_processor_id();
2791
2792 cpu_buffer = buffer->buffers[cpu];
2793
2794 rb_commit(cpu_buffer, event);
2795
2796 rb_wakeups(buffer, cpu_buffer);
2797
2798 trace_recursive_unlock(cpu_buffer);
2799
2800 preempt_enable_notrace();
2801
2802 return 0;
2803}
2804EXPORT_SYMBOL_GPL(ring_buffer_unlock_commit);
2805
2806static noinline void
2807rb_handle_timestamp(struct ring_buffer_per_cpu *cpu_buffer,
2808 struct rb_event_info *info)
2809{
2810 WARN_ONCE(info->delta > (1ULL << 59),
2811 KERN_WARNING "Delta way too big! %llu ts=%llu write stamp = %llu\n%s",
2812 (unsigned long long)info->delta,
2813 (unsigned long long)info->ts,
2814 (unsigned long long)cpu_buffer->write_stamp,
2815 sched_clock_stable() ? "" :
2816 "If you just came from a suspend/resume,\n"
2817 "please switch to the trace global clock:\n"
2818 " echo global > /sys/kernel/debug/tracing/trace_clock\n"
2819 "or add trace_clock=global to the kernel command line\n");
2820 info->add_timestamp = 1;
2821}
2822
2823static struct ring_buffer_event *
2824__rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
2825 struct rb_event_info *info)
2826{
2827 struct ring_buffer_event *event;
2828 struct buffer_page *tail_page;
2829 unsigned long tail, write;
2830
2831 /*
2832 * If the time delta since the last event is too big to
2833 * hold in the time field of the event, then we append a
2834 * TIME EXTEND event ahead of the data event.
2835 */
2836 if (unlikely(info->add_timestamp))
2837 info->length += RB_LEN_TIME_EXTEND;
2838
2839 /* Don't let the compiler play games with cpu_buffer->tail_page */
2840 tail_page = info->tail_page = READ_ONCE(cpu_buffer->tail_page);
2841 write = local_add_return(info->length, &tail_page->write);
2842
2843 /* set write to only the index of the write */
2844 write &= RB_WRITE_MASK;
2845 tail = write - info->length;
2846
2847 /*
2848 * If this is the first commit on the page, then it has the same
2849 * timestamp as the page itself.
2850 */
2851 if (!tail && !ring_buffer_time_stamp_abs(cpu_buffer->buffer))
2852 info->delta = 0;
2853
2854 /* See if we shot pass the end of this buffer page */
2855 if (unlikely(write > BUF_PAGE_SIZE))
2856 return rb_move_tail(cpu_buffer, tail, info);
2857
2858 /* We reserved something on the buffer */
2859
2860 event = __rb_page_index(tail_page, tail);
2861 rb_update_event(cpu_buffer, event, info);
2862
2863 local_inc(&tail_page->entries);
2864
2865 /*
2866 * If this is the first commit on the page, then update
2867 * its timestamp.
2868 */
2869 if (!tail)
2870 tail_page->page->time_stamp = info->ts;
2871
2872 /* account for these added bytes */
2873 local_add(info->length, &cpu_buffer->entries_bytes);
2874
2875 return event;
2876}
2877
2878static __always_inline struct ring_buffer_event *
2879rb_reserve_next_event(struct ring_buffer *buffer,
2880 struct ring_buffer_per_cpu *cpu_buffer,
2881 unsigned long length)
2882{
2883 struct ring_buffer_event *event;
2884 struct rb_event_info info;
2885 int nr_loops = 0;
2886 u64 diff;
2887
2888 rb_start_commit(cpu_buffer);
2889
2890#ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
2891 /*
2892 * Due to the ability to swap a cpu buffer from a buffer
2893 * it is possible it was swapped before we committed.
2894 * (committing stops a swap). We check for it here and
2895 * if it happened, we have to fail the write.
2896 */
2897 barrier();
2898 if (unlikely(READ_ONCE(cpu_buffer->buffer) != buffer)) {
2899 local_dec(&cpu_buffer->committing);
2900 local_dec(&cpu_buffer->commits);
2901 return NULL;
2902 }
2903#endif
2904
2905 info.length = rb_calculate_event_length(length);
2906 again:
2907 info.add_timestamp = 0;
2908 info.delta = 0;
2909
2910 /*
2911 * We allow for interrupts to reenter here and do a trace.
2912 * If one does, it will cause this original code to loop
2913 * back here. Even with heavy interrupts happening, this
2914 * should only happen a few times in a row. If this happens
2915 * 1000 times in a row, there must be either an interrupt
2916 * storm or we have something buggy.
2917 * Bail!
2918 */
2919 if (RB_WARN_ON(cpu_buffer, ++nr_loops > 1000))
2920 goto out_fail;
2921
2922 info.ts = rb_time_stamp(cpu_buffer->buffer);
2923 diff = info.ts - cpu_buffer->write_stamp;
2924
2925 /* make sure this diff is calculated here */
2926 barrier();
2927
2928 if (ring_buffer_time_stamp_abs(buffer)) {
2929 info.delta = info.ts;
2930 rb_handle_timestamp(cpu_buffer, &info);
2931 } else /* Did the write stamp get updated already? */
2932 if (likely(info.ts >= cpu_buffer->write_stamp)) {
2933 info.delta = diff;
2934 if (unlikely(test_time_stamp(info.delta)))
2935 rb_handle_timestamp(cpu_buffer, &info);
2936 }
2937
2938 event = __rb_reserve_next(cpu_buffer, &info);
2939
2940 if (unlikely(PTR_ERR(event) == -EAGAIN)) {
2941 if (info.add_timestamp)
2942 info.length -= RB_LEN_TIME_EXTEND;
2943 goto again;
2944 }
2945
2946 if (!event)
2947 goto out_fail;
2948
2949 return event;
2950
2951 out_fail:
2952 rb_end_commit(cpu_buffer);
2953 return NULL;
2954}
2955
2956/**
2957 * ring_buffer_lock_reserve - reserve a part of the buffer
2958 * @buffer: the ring buffer to reserve from
2959 * @length: the length of the data to reserve (excluding event header)
2960 *
2961 * Returns a reserved event on the ring buffer to copy directly to.
2962 * The user of this interface will need to get the body to write into
2963 * and can use the ring_buffer_event_data() interface.
2964 *
2965 * The length is the length of the data needed, not the event length
2966 * which also includes the event header.
2967 *
2968 * Must be paired with ring_buffer_unlock_commit, unless NULL is returned.
2969 * If NULL is returned, then nothing has been allocated or locked.
2970 */
2971struct ring_buffer_event *
2972ring_buffer_lock_reserve(struct ring_buffer *buffer, unsigned long length)
2973{
2974 struct ring_buffer_per_cpu *cpu_buffer;
2975 struct ring_buffer_event *event;
2976 int cpu;
2977
2978 /* If we are tracing schedule, we don't want to recurse */
2979 preempt_disable_notrace();
2980
2981 if (unlikely(atomic_read(&buffer->record_disabled)))
2982 goto out;
2983
2984 cpu = raw_smp_processor_id();
2985
2986 if (unlikely(!cpumask_test_cpu(cpu, buffer->cpumask)))
2987 goto out;
2988
2989 cpu_buffer = buffer->buffers[cpu];
2990
2991 if (unlikely(atomic_read(&cpu_buffer->record_disabled)))
2992 goto out;
2993
2994 if (unlikely(length > BUF_MAX_DATA_SIZE))
2995 goto out;
2996
2997 if (unlikely(trace_recursive_lock(cpu_buffer)))
2998 goto out;
2999
3000 event = rb_reserve_next_event(buffer, cpu_buffer, length);
3001 if (!event)
3002 goto out_unlock;
3003
3004 return event;
3005
3006 out_unlock:
3007 trace_recursive_unlock(cpu_buffer);
3008 out:
3009 preempt_enable_notrace();
3010 return NULL;
3011}
3012EXPORT_SYMBOL_GPL(ring_buffer_lock_reserve);
3013
3014/*
3015 * Decrement the entries to the page that an event is on.
3016 * The event does not even need to exist, only the pointer
3017 * to the page it is on. This may only be called before the commit
3018 * takes place.
3019 */
3020static inline void
3021rb_decrement_entry(struct ring_buffer_per_cpu *cpu_buffer,
3022 struct ring_buffer_event *event)
3023{
3024 unsigned long addr = (unsigned long)event;
3025 struct buffer_page *bpage = cpu_buffer->commit_page;
3026 struct buffer_page *start;
3027
3028 addr &= PAGE_MASK;
3029
3030 /* Do the likely case first */
3031 if (likely(bpage->page == (void *)addr)) {
3032 local_dec(&bpage->entries);
3033 return;
3034 }
3035
3036 /*
3037 * Because the commit page may be on the reader page we
3038 * start with the next page and check the end loop there.
3039 */
3040 rb_inc_page(cpu_buffer, &bpage);
3041 start = bpage;
3042 do {
3043 if (bpage->page == (void *)addr) {
3044 local_dec(&bpage->entries);
3045 return;
3046 }
3047 rb_inc_page(cpu_buffer, &bpage);
3048 } while (bpage != start);
3049
3050 /* commit not part of this buffer?? */
3051 RB_WARN_ON(cpu_buffer, 1);
3052}
3053
3054/**
3055 * ring_buffer_commit_discard - discard an event that has not been committed
3056 * @buffer: the ring buffer
3057 * @event: non committed event to discard
3058 *
3059 * Sometimes an event that is in the ring buffer needs to be ignored.
3060 * This function lets the user discard an event in the ring buffer
3061 * and then that event will not be read later.
3062 *
3063 * This function only works if it is called before the item has been
3064 * committed. It will try to free the event from the ring buffer
3065 * if another event has not been added behind it.
3066 *
3067 * If another event has been added behind it, it will set the event
3068 * up as discarded, and perform the commit.
3069 *
3070 * If this function is called, do not call ring_buffer_unlock_commit on
3071 * the event.
3072 */
3073void ring_buffer_discard_commit(struct ring_buffer *buffer,
3074 struct ring_buffer_event *event)
3075{
3076 struct ring_buffer_per_cpu *cpu_buffer;
3077 int cpu;
3078
3079 /* The event is discarded regardless */
3080 rb_event_discard(event);
3081
3082 cpu = smp_processor_id();
3083 cpu_buffer = buffer->buffers[cpu];
3084
3085 /*
3086 * This must only be called if the event has not been
3087 * committed yet. Thus we can assume that preemption
3088 * is still disabled.
3089 */
3090 RB_WARN_ON(buffer, !local_read(&cpu_buffer->committing));
3091
3092 rb_decrement_entry(cpu_buffer, event);
3093 if (rb_try_to_discard(cpu_buffer, event))
3094 goto out;
3095
3096 /*
3097 * The commit is still visible by the reader, so we
3098 * must still update the timestamp.
3099 */
3100 rb_update_write_stamp(cpu_buffer, event);
3101 out:
3102 rb_end_commit(cpu_buffer);
3103
3104 trace_recursive_unlock(cpu_buffer);
3105
3106 preempt_enable_notrace();
3107
3108}
3109EXPORT_SYMBOL_GPL(ring_buffer_discard_commit);
3110
3111/**
3112 * ring_buffer_write - write data to the buffer without reserving
3113 * @buffer: The ring buffer to write to.
3114 * @length: The length of the data being written (excluding the event header)
3115 * @data: The data to write to the buffer.
3116 *
3117 * This is like ring_buffer_lock_reserve and ring_buffer_unlock_commit as
3118 * one function. If you already have the data to write to the buffer, it
3119 * may be easier to simply call this function.
3120 *
3121 * Note, like ring_buffer_lock_reserve, the length is the length of the data
3122 * and not the length of the event which would hold the header.
3123 */
3124int ring_buffer_write(struct ring_buffer *buffer,
3125 unsigned long length,
3126 void *data)
3127{
3128 struct ring_buffer_per_cpu *cpu_buffer;
3129 struct ring_buffer_event *event;
3130 void *body;
3131 int ret = -EBUSY;
3132 int cpu;
3133
3134 preempt_disable_notrace();
3135
3136 if (atomic_read(&buffer->record_disabled))
3137 goto out;
3138
3139 cpu = raw_smp_processor_id();
3140
3141 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3142 goto out;
3143
3144 cpu_buffer = buffer->buffers[cpu];
3145
3146 if (atomic_read(&cpu_buffer->record_disabled))
3147 goto out;
3148
3149 if (length > BUF_MAX_DATA_SIZE)
3150 goto out;
3151
3152 if (unlikely(trace_recursive_lock(cpu_buffer)))
3153 goto out;
3154
3155 event = rb_reserve_next_event(buffer, cpu_buffer, length);
3156 if (!event)
3157 goto out_unlock;
3158
3159 body = rb_event_data(event);
3160
3161 memcpy(body, data, length);
3162
3163 rb_commit(cpu_buffer, event);
3164
3165 rb_wakeups(buffer, cpu_buffer);
3166
3167 ret = 0;
3168
3169 out_unlock:
3170 trace_recursive_unlock(cpu_buffer);
3171
3172 out:
3173 preempt_enable_notrace();
3174
3175 return ret;
3176}
3177EXPORT_SYMBOL_GPL(ring_buffer_write);
3178
3179static bool rb_per_cpu_empty(struct ring_buffer_per_cpu *cpu_buffer)
3180{
3181 struct buffer_page *reader = cpu_buffer->reader_page;
3182 struct buffer_page *head = rb_set_head_page(cpu_buffer);
3183 struct buffer_page *commit = cpu_buffer->commit_page;
3184
3185 /* In case of error, head will be NULL */
3186 if (unlikely(!head))
3187 return true;
3188
3189 return reader->read == rb_page_commit(reader) &&
3190 (commit == reader ||
3191 (commit == head &&
3192 head->read == rb_page_commit(commit)));
3193}
3194
3195/**
3196 * ring_buffer_record_disable - stop all writes into the buffer
3197 * @buffer: The ring buffer to stop writes to.
3198 *
3199 * This prevents all writes to the buffer. Any attempt to write
3200 * to the buffer after this will fail and return NULL.
3201 *
3202 * The caller should call synchronize_rcu() after this.
3203 */
3204void ring_buffer_record_disable(struct ring_buffer *buffer)
3205{
3206 atomic_inc(&buffer->record_disabled);
3207}
3208EXPORT_SYMBOL_GPL(ring_buffer_record_disable);
3209
3210/**
3211 * ring_buffer_record_enable - enable writes to the buffer
3212 * @buffer: The ring buffer to enable writes
3213 *
3214 * Note, multiple disables will need the same number of enables
3215 * to truly enable the writing (much like preempt_disable).
3216 */
3217void ring_buffer_record_enable(struct ring_buffer *buffer)
3218{
3219 atomic_dec(&buffer->record_disabled);
3220}
3221EXPORT_SYMBOL_GPL(ring_buffer_record_enable);
3222
3223/**
3224 * ring_buffer_record_off - stop all writes into the buffer
3225 * @buffer: The ring buffer to stop writes to.
3226 *
3227 * This prevents all writes to the buffer. Any attempt to write
3228 * to the buffer after this will fail and return NULL.
3229 *
3230 * This is different than ring_buffer_record_disable() as
3231 * it works like an on/off switch, where as the disable() version
3232 * must be paired with a enable().
3233 */
3234void ring_buffer_record_off(struct ring_buffer *buffer)
3235{
3236 unsigned int rd;
3237 unsigned int new_rd;
3238
3239 do {
3240 rd = atomic_read(&buffer->record_disabled);
3241 new_rd = rd | RB_BUFFER_OFF;
3242 } while (atomic_cmpxchg(&buffer->record_disabled, rd, new_rd) != rd);
3243}
3244EXPORT_SYMBOL_GPL(ring_buffer_record_off);
3245
3246/**
3247 * ring_buffer_record_on - restart writes into the buffer
3248 * @buffer: The ring buffer to start writes to.
3249 *
3250 * This enables all writes to the buffer that was disabled by
3251 * ring_buffer_record_off().
3252 *
3253 * This is different than ring_buffer_record_enable() as
3254 * it works like an on/off switch, where as the enable() version
3255 * must be paired with a disable().
3256 */
3257void ring_buffer_record_on(struct ring_buffer *buffer)
3258{
3259 unsigned int rd;
3260 unsigned int new_rd;
3261
3262 do {
3263 rd = atomic_read(&buffer->record_disabled);
3264 new_rd = rd & ~RB_BUFFER_OFF;
3265 } while (atomic_cmpxchg(&buffer->record_disabled, rd, new_rd) != rd);
3266}
3267EXPORT_SYMBOL_GPL(ring_buffer_record_on);
3268
3269/**
3270 * ring_buffer_record_is_on - return true if the ring buffer can write
3271 * @buffer: The ring buffer to see if write is enabled
3272 *
3273 * Returns true if the ring buffer is in a state that it accepts writes.
3274 */
3275bool ring_buffer_record_is_on(struct ring_buffer *buffer)
3276{
3277 return !atomic_read(&buffer->record_disabled);
3278}
3279
3280/**
3281 * ring_buffer_record_is_set_on - return true if the ring buffer is set writable
3282 * @buffer: The ring buffer to see if write is set enabled
3283 *
3284 * Returns true if the ring buffer is set writable by ring_buffer_record_on().
3285 * Note that this does NOT mean it is in a writable state.
3286 *
3287 * It may return true when the ring buffer has been disabled by
3288 * ring_buffer_record_disable(), as that is a temporary disabling of
3289 * the ring buffer.
3290 */
3291bool ring_buffer_record_is_set_on(struct ring_buffer *buffer)
3292{
3293 return !(atomic_read(&buffer->record_disabled) & RB_BUFFER_OFF);
3294}
3295
3296/**
3297 * ring_buffer_record_disable_cpu - stop all writes into the cpu_buffer
3298 * @buffer: The ring buffer to stop writes to.
3299 * @cpu: The CPU buffer to stop
3300 *
3301 * This prevents all writes to the buffer. Any attempt to write
3302 * to the buffer after this will fail and return NULL.
3303 *
3304 * The caller should call synchronize_rcu() after this.
3305 */
3306void ring_buffer_record_disable_cpu(struct ring_buffer *buffer, int cpu)
3307{
3308 struct ring_buffer_per_cpu *cpu_buffer;
3309
3310 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3311 return;
3312
3313 cpu_buffer = buffer->buffers[cpu];
3314 atomic_inc(&cpu_buffer->record_disabled);
3315}
3316EXPORT_SYMBOL_GPL(ring_buffer_record_disable_cpu);
3317
3318/**
3319 * ring_buffer_record_enable_cpu - enable writes to the buffer
3320 * @buffer: The ring buffer to enable writes
3321 * @cpu: The CPU to enable.
3322 *
3323 * Note, multiple disables will need the same number of enables
3324 * to truly enable the writing (much like preempt_disable).
3325 */
3326void ring_buffer_record_enable_cpu(struct ring_buffer *buffer, int cpu)
3327{
3328 struct ring_buffer_per_cpu *cpu_buffer;
3329
3330 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3331 return;
3332
3333 cpu_buffer = buffer->buffers[cpu];
3334 atomic_dec(&cpu_buffer->record_disabled);
3335}
3336EXPORT_SYMBOL_GPL(ring_buffer_record_enable_cpu);
3337
3338/*
3339 * The total entries in the ring buffer is the running counter
3340 * of entries entered into the ring buffer, minus the sum of
3341 * the entries read from the ring buffer and the number of
3342 * entries that were overwritten.
3343 */
3344static inline unsigned long
3345rb_num_of_entries(struct ring_buffer_per_cpu *cpu_buffer)
3346{
3347 return local_read(&cpu_buffer->entries) -
3348 (local_read(&cpu_buffer->overrun) + cpu_buffer->read);
3349}
3350
3351/**
3352 * ring_buffer_oldest_event_ts - get the oldest event timestamp from the buffer
3353 * @buffer: The ring buffer
3354 * @cpu: The per CPU buffer to read from.
3355 */
3356u64 ring_buffer_oldest_event_ts(struct ring_buffer *buffer, int cpu)
3357{
3358 unsigned long flags;
3359 struct ring_buffer_per_cpu *cpu_buffer;
3360 struct buffer_page *bpage;
3361 u64 ret = 0;
3362
3363 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3364 return 0;
3365
3366 cpu_buffer = buffer->buffers[cpu];
3367 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
3368 /*
3369 * if the tail is on reader_page, oldest time stamp is on the reader
3370 * page
3371 */
3372 if (cpu_buffer->tail_page == cpu_buffer->reader_page)
3373 bpage = cpu_buffer->reader_page;
3374 else
3375 bpage = rb_set_head_page(cpu_buffer);
3376 if (bpage)
3377 ret = bpage->page->time_stamp;
3378 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
3379
3380 return ret;
3381}
3382EXPORT_SYMBOL_GPL(ring_buffer_oldest_event_ts);
3383
3384/**
3385 * ring_buffer_bytes_cpu - get the number of bytes consumed in a cpu buffer
3386 * @buffer: The ring buffer
3387 * @cpu: The per CPU buffer to read from.
3388 */
3389unsigned long ring_buffer_bytes_cpu(struct ring_buffer *buffer, int cpu)
3390{
3391 struct ring_buffer_per_cpu *cpu_buffer;
3392 unsigned long ret;
3393
3394 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3395 return 0;
3396
3397 cpu_buffer = buffer->buffers[cpu];
3398 ret = local_read(&cpu_buffer->entries_bytes) - cpu_buffer->read_bytes;
3399
3400 return ret;
3401}
3402EXPORT_SYMBOL_GPL(ring_buffer_bytes_cpu);
3403
3404/**
3405 * ring_buffer_entries_cpu - get the number of entries in a cpu buffer
3406 * @buffer: The ring buffer
3407 * @cpu: The per CPU buffer to get the entries from.
3408 */
3409unsigned long ring_buffer_entries_cpu(struct ring_buffer *buffer, int cpu)
3410{
3411 struct ring_buffer_per_cpu *cpu_buffer;
3412
3413 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3414 return 0;
3415
3416 cpu_buffer = buffer->buffers[cpu];
3417
3418 return rb_num_of_entries(cpu_buffer);
3419}
3420EXPORT_SYMBOL_GPL(ring_buffer_entries_cpu);
3421
3422/**
3423 * ring_buffer_overrun_cpu - get the number of overruns caused by the ring
3424 * buffer wrapping around (only if RB_FL_OVERWRITE is on).
3425 * @buffer: The ring buffer
3426 * @cpu: The per CPU buffer to get the number of overruns from
3427 */
3428unsigned long ring_buffer_overrun_cpu(struct ring_buffer *buffer, int cpu)
3429{
3430 struct ring_buffer_per_cpu *cpu_buffer;
3431 unsigned long ret;
3432
3433 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3434 return 0;
3435
3436 cpu_buffer = buffer->buffers[cpu];
3437 ret = local_read(&cpu_buffer->overrun);
3438
3439 return ret;
3440}
3441EXPORT_SYMBOL_GPL(ring_buffer_overrun_cpu);
3442
3443/**
3444 * ring_buffer_commit_overrun_cpu - get the number of overruns caused by
3445 * commits failing due to the buffer wrapping around while there are uncommitted
3446 * events, such as during an interrupt storm.
3447 * @buffer: The ring buffer
3448 * @cpu: The per CPU buffer to get the number of overruns from
3449 */
3450unsigned long
3451ring_buffer_commit_overrun_cpu(struct ring_buffer *buffer, int cpu)
3452{
3453 struct ring_buffer_per_cpu *cpu_buffer;
3454 unsigned long ret;
3455
3456 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3457 return 0;
3458
3459 cpu_buffer = buffer->buffers[cpu];
3460 ret = local_read(&cpu_buffer->commit_overrun);
3461
3462 return ret;
3463}
3464EXPORT_SYMBOL_GPL(ring_buffer_commit_overrun_cpu);
3465
3466/**
3467 * ring_buffer_dropped_events_cpu - get the number of dropped events caused by
3468 * the ring buffer filling up (only if RB_FL_OVERWRITE is off).
3469 * @buffer: The ring buffer
3470 * @cpu: The per CPU buffer to get the number of overruns from
3471 */
3472unsigned long
3473ring_buffer_dropped_events_cpu(struct ring_buffer *buffer, int cpu)
3474{
3475 struct ring_buffer_per_cpu *cpu_buffer;
3476 unsigned long ret;
3477
3478 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3479 return 0;
3480
3481 cpu_buffer = buffer->buffers[cpu];
3482 ret = local_read(&cpu_buffer->dropped_events);
3483
3484 return ret;
3485}
3486EXPORT_SYMBOL_GPL(ring_buffer_dropped_events_cpu);
3487
3488/**
3489 * ring_buffer_read_events_cpu - get the number of events successfully read
3490 * @buffer: The ring buffer
3491 * @cpu: The per CPU buffer to get the number of events read
3492 */
3493unsigned long
3494ring_buffer_read_events_cpu(struct ring_buffer *buffer, int cpu)
3495{
3496 struct ring_buffer_per_cpu *cpu_buffer;
3497
3498 if (!cpumask_test_cpu(cpu, buffer->cpumask))
3499 return 0;
3500
3501 cpu_buffer = buffer->buffers[cpu];
3502 return cpu_buffer->read;
3503}
3504EXPORT_SYMBOL_GPL(ring_buffer_read_events_cpu);
3505
3506/**
3507 * ring_buffer_entries - get the number of entries in a buffer
3508 * @buffer: The ring buffer
3509 *
3510 * Returns the total number of entries in the ring buffer
3511 * (all CPU entries)
3512 */
3513unsigned long ring_buffer_entries(struct ring_buffer *buffer)
3514{
3515 struct ring_buffer_per_cpu *cpu_buffer;
3516 unsigned long entries = 0;
3517 int cpu;
3518
3519 /* if you care about this being correct, lock the buffer */
3520 for_each_buffer_cpu(buffer, cpu) {
3521 cpu_buffer = buffer->buffers[cpu];
3522 entries += rb_num_of_entries(cpu_buffer);
3523 }
3524
3525 return entries;
3526}
3527EXPORT_SYMBOL_GPL(ring_buffer_entries);
3528
3529/**
3530 * ring_buffer_overruns - get the number of overruns in buffer
3531 * @buffer: The ring buffer
3532 *
3533 * Returns the total number of overruns in the ring buffer
3534 * (all CPU entries)
3535 */
3536unsigned long ring_buffer_overruns(struct ring_buffer *buffer)
3537{
3538 struct ring_buffer_per_cpu *cpu_buffer;
3539 unsigned long overruns = 0;
3540 int cpu;
3541
3542 /* if you care about this being correct, lock the buffer */
3543 for_each_buffer_cpu(buffer, cpu) {
3544 cpu_buffer = buffer->buffers[cpu];
3545 overruns += local_read(&cpu_buffer->overrun);
3546 }
3547
3548 return overruns;
3549}
3550EXPORT_SYMBOL_GPL(ring_buffer_overruns);
3551
3552static void rb_iter_reset(struct ring_buffer_iter *iter)
3553{
3554 struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
3555
3556 /* Iterator usage is expected to have record disabled */
3557 iter->head_page = cpu_buffer->reader_page;
3558 iter->head = cpu_buffer->reader_page->read;
3559
3560 iter->cache_reader_page = iter->head_page;
3561 iter->cache_read = cpu_buffer->read;
3562
3563 if (iter->head)
3564 iter->read_stamp = cpu_buffer->read_stamp;
3565 else
3566 iter->read_stamp = iter->head_page->page->time_stamp;
3567}
3568
3569/**
3570 * ring_buffer_iter_reset - reset an iterator
3571 * @iter: The iterator to reset
3572 *
3573 * Resets the iterator, so that it will start from the beginning
3574 * again.
3575 */
3576void ring_buffer_iter_reset(struct ring_buffer_iter *iter)
3577{
3578 struct ring_buffer_per_cpu *cpu_buffer;
3579 unsigned long flags;
3580
3581 if (!iter)
3582 return;
3583
3584 cpu_buffer = iter->cpu_buffer;
3585
3586 raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
3587 rb_iter_reset(iter);
3588 raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
3589}
3590EXPORT_SYMBOL_GPL(ring_buffer_iter_reset);
3591
3592/**
3593 * ring_buffer_iter_empty - check if an iterator has no more to read
3594 * @iter: The iterator to check
3595 */
3596int ring_buffer_iter_empty(struct ring_buffer_iter *iter)
3597{
3598 struct ring_buffer_per_cpu *cpu_buffer;
3599 struct buffer_page *reader;
3600 struct buffer_page *head_page;
3601 struct buffer_page *commit_page;
3602 unsigned commit;
3603
3604 cpu_buffer = iter->cpu_buffer;
3605
3606 /* Remember, trace recording is off when iterator is in use */
3607 reader = cpu_buffer->reader_page;
3608 head_page = cpu_buffer->head_page;
3609 commit_page = cpu_buffer->commit_page;
3610 commit = rb_page_commit(commit_page);
3611
3612 return ((iter->head_page == commit_page && iter->head == commit) ||
3613 (iter->head_page == reader && commit_page == head_page &&
3614 head_page->read == commit &&
3615 iter->head == rb_page_commit(cpu_buffer->reader_page)));
3616}
3617EXPORT_SYMBOL_GPL(ring_buffer_iter_empty);
3618
3619static void
3620rb_update_read_stamp(struct ring_buffer_per_cpu *cpu_buffer,
3621 struct ring_buffer_event *event)
3622{
3623 u64 delta;
3624
3625 switch (event->type_len) {
3626 case RINGBUF_TYPE_PADDING:
3627 return;
3628
3629 case RINGBUF_TYPE_TIME_EXTEND:
3630 delta = ring_buffer_event_time_stamp(event);
3631 cpu_buffer->read_stamp += delta;
3632 return;
3633
3634 case RINGBUF_TYPE_TIME_STAMP:
3635 delta = ring_buffer_event_time_stamp(event);
3636 cpu_buffer->read_stamp = delta;
3637 return;
3638
3639 case RINGBUF_TYPE_DATA:
3640 cpu_buffer->read_stamp += event->time_delta;
3641 return;
3642
3643 default:
3644 BUG();
3645 }
3646 return;
3647}
3648
3649static void
3650rb_update_iter_read_stamp(struct ring_buffer_iter *iter,
3651 struct ring_buffer_event *event)
3652{
3653 u64 delta;
3654
3655 switch (event->type_len) {
3656 case RINGBUF_TYPE_PADDING:
3657 return;
3658
3659 case RINGBUF_TYPE_TIME_EXTEND:
3660 delta = ring_buffer_event_time_stamp(event);
3661 iter->read_stamp += delta;
3662 return;
3663
3664 case RINGBUF_TYPE_TIME_STAMP:
3665 delta = ring_buffer_event_time_stamp(event);
3666 iter->read_stamp = delta;
3667 return;
3668
3669 case RINGBUF_TYPE_DATA:
3670 iter->read_stamp += event->time_delta;
3671 return;
3672
3673 default:
3674 BUG();
3675 }
3676 return;
3677}
3678
3679static struct buffer_page *
3680rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
3681{
3682 struct buffer_page *reader = NULL;
3683 unsigned long overwrite;
3684 unsigned long flags;
3685 int nr_loops = 0;
3686 int ret;
3687
3688 local_irq_save(flags);
3689 arch_spin_lock(&cpu_buffer->lock);
3690
3691 again:
3692 /*
3693 * This should normally only loop twice. But because the
3694 * start of the reader inserts an empty page, it causes
3695 * a case where we will loop three times. There should be no
3696 * reason to loop four times (that I know of).
3697 */
3698 if (RB_WARN_ON(cpu_buffer, ++nr_loops > 3)) {
3699 reader = NULL;
3700 goto out;
3701 }
3702
3703 reader = cpu_buffer->reader_page;
3704
3705 /* If there's more to read, return this page */
3706 if (cpu_buffer->reader_page->read < rb_page_size(reader))
3707 goto out;
3708
3709 /* Never should we have an index greater than the size */
3710 if (RB_WARN_ON(cpu_buffer,
3711 cpu_buffer->reader_page->read > rb_page_size(reader)))
3712 goto out;
3713
3714 /* check if we caught up to the tail */
3715 reader = NULL;
3716 if (cpu_buffer->commit_page == cpu_buffer->reader_page)
3717 goto out;
3718
3719 /* Don't bother swapping if the ring buffer is empty */
3720 if (rb_num_of_entries(cpu_buffer) == 0)
3721 goto out;
3722
3723 /*
3724 * Reset the reader page to size zero.
3725 */
3726 local_set(&cpu_buffer->reader_page->write, 0);
3727 local_set(&cpu_buffer->reader_page->entries, 0);
3728 local_set(&cpu_buffer->reader_page->page->commit, 0);
3729 cpu_buffer->reader_page->real_end = 0;
3730
3731 spin:
3732 /*
3733 * Splice the empty reader page into the list around the head.
3734 */
3735 reader = rb_set_head_page(cpu_buffer);
3736 if (!reader)
3737 goto out;
3738 cpu_buffer->reader_page->list.next = rb_list_head(reader->list.next);
3739 cpu_buffer->reader_page->list.prev = reader->list.prev;
3740
3741 /*
3742 * cpu_buffer->pages just needs to point to the buffer, it
3743 * has no specific buffer page to point to. Lets move it out
3744 * of our way so we don't accidentally swap it.
3745 */
3746 cpu_buffer->pages = reader->list.prev;
3747
3748 /* The reader page will be pointing to the new head */
3749 rb_set_list_to_head(cpu_buffer, &cpu_buffer->reader_page->list);
3750
3751 /*
3752 * We want to make sure we read the overruns after we set up our
3753 * pointers to the next object. The writer side does a
3754 * cmpxchg to cross pages which acts as the mb on the writer
3755 * side. Note, the reader will constantly fail the swap
3756 * while the writer is updating the pointers, so this
3757 * guarantees that the overwrite recorded here is the one we
3758 * want to compare with the last_overrun.
3759 */
3760 smp_mb();
3761 overwrite = local_read(&(cpu_buffer->overrun));
3762
3763 /*
3764 * Here's the tricky part.
3765 *
3766 * We need to move the pointer past the header page.
3767 * But we can only do that if a writer is not currently
3768 * moving it. The page before the header page has the
3769 * flag bit '1' set if it is pointing to the page we want.
3770 * but if the writer is in the process of moving it
3771 * than it will be '2' or already moved '0'.
3772 */
3773
3774 ret = rb_head_page_replace(reader, cpu_buffer->reader_page);
3775
3776 /*
3777 * If we did not convert it, then we must try again.
3778 */
3779 if (!ret)
3780 goto spin;
3781
3782 /*
3783 * Yay! We succeeded in replacing the page.
3784 *
3785 * Now make the new head point back to the reader page.
3786 */
3787 rb_list_head(reader->list.next)->prev = &cpu_buffer->reader_page->list;
3788 rb_inc_page(cpu_buffer, &cpu_buffer->head_page);
3789
3790 local_inc(&cpu_buffer->pages_read);
3791
3792 /* Finally update the reader page to the new head */
3793 cpu_buffer->reader_page = reader;
3794 cpu_buffer->reader_page->read = 0;
3795
3796 if (overwrite != cpu_buffer->last_overrun) {
3797 cpu_buffer->lost_events = overwrite - cpu_buffer->last_overrun;
3798 cpu_buffer->last_overrun = overwrite;
3799 }
3800
3801 goto again;
3802
3803 out:
3804 /* Update the read_stamp on the first event */
3805 if (reader && reader->read == 0)
3806 cpu_buffer->read_stamp = reader->page->time_stamp;
3807
3808 arch_spin_unlock(&cpu_buffer->lock);
3809 local_irq_restore(flags);
3810
3811 return reader;
3812}
3813
3814static void rb_advance_reader(struct ring_buffer_per_cpu *cpu_buffer)
3815{
3816 struct ring_buffer_event *event;
3817 struct buffer_page *reader;
3818 unsigned length;
3819
3820 reader = rb_get_reader_page(cpu_buffer);
3821
3822 /* This function should not be called when buffer is empty */
3823 if (