Root/kernel/trace/ring_buffer.c

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

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