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linux/kernel/trace/ring_buffer.c
Lai Jiangshan f7112949f6 ring-buffer: Synchronize resizing buffer with reader lock 
We got a sudden panic when we reduced the size of the
ringbuffer.

We can reproduce the panic by the following steps:

echo 1 > events/sched/enable
cat trace_pipe > /dev/null &

while ((1))
do
echo 12000 > buffer_size_kb
echo 512 > buffer_size_kb
done

(not more than 5 seconds, panic ...)

Reported-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
LKML-Reference: <4AF01735.9060409@cn.fujitsu.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2009-11-04 00:04:20 -05:00

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/*
* Generic ring buffer
*
* Copyright (C) 2008 Steven Rostedt <srostedt@redhat.com>
*/
#include <linux/ring_buffer.h>
#include <linux/trace_clock.h>
#include <linux/ftrace_irq.h>
#include <linux/spinlock.h>
#include <linux/debugfs.h>
#include <linux/uaccess.h>
#include <linux/hardirq.h>
#include <linux/kmemcheck.h>
#include <linux/module.h>
#include <linux/percpu.h>
#include <linux/mutex.h>
#include <linux/init.h>
#include <linux/hash.h>
#include <linux/list.h>
#include <linux/cpu.h>
#include <linux/fs.h>
#include "trace.h"
/*
* The ring buffer header is special. We must manually up keep it.
*/
int ring_buffer_print_entry_header(struct trace_seq *s)
{
int ret;
ret = trace_seq_printf(s, "# compressed entry header\n");
ret = trace_seq_printf(s, "\ttype_len : 5 bits\n");
ret = trace_seq_printf(s, "\ttime_delta : 27 bits\n");
ret = trace_seq_printf(s, "\tarray : 32 bits\n");
ret = trace_seq_printf(s, "\n");
ret = trace_seq_printf(s, "\tpadding : type == %d\n",
RINGBUF_TYPE_PADDING);
ret = trace_seq_printf(s, "\ttime_extend : type == %d\n",
RINGBUF_TYPE_TIME_EXTEND);
ret = trace_seq_printf(s, "\tdata max type_len == %d\n",
RINGBUF_TYPE_DATA_TYPE_LEN_MAX);
return ret;
}
/*
* The ring buffer is made up of a list of pages. A separate list of pages is
* allocated for each CPU. A writer may only write to a buffer that is
* associated with the CPU it is currently executing on. A reader may read
* from any per cpu buffer.
*
* The reader is special. For each per cpu buffer, the reader has its own
* reader page. When a reader has read the entire reader page, this reader
* page is swapped with another page in the ring buffer.
*
* Now, as long as the writer is off the reader page, the reader can do what
* ever it wants with that page. The writer will never write to that page
* again (as long as it is out of the ring buffer).
*
* Here's some silly ASCII art.
*
* +------+
* |reader| RING BUFFER
* |page |
* +------+ +---+ +---+ +---+
* | |-->| |-->| |
* +---+ +---+ +---+
* ^ |
* | |
* +---------------+
*
*
* +------+
* |reader| RING BUFFER
* |page |------------------v
* +------+ +---+ +---+ +---+
* | |-->| |-->| |
* +---+ +---+ +---+
* ^ |
* | |
* +---------------+
*
*
* +------+
* |reader| RING BUFFER
* |page |------------------v
* +------+ +---+ +---+ +---+
* ^ | |-->| |-->| |
* | +---+ +---+ +---+
* | |
* | |
* +------------------------------+
*
*
* +------+
* |buffer| RING BUFFER
* |page |------------------v
* +------+ +---+ +---+ +---+
* ^ | | | |-->| |
* | New +---+ +---+ +---+
* | Reader------^ |
* | page |
* +------------------------------+
*
*
* After we make this swap, the reader can hand this page off to the splice
* code and be done with it. It can even allocate a new page if it needs to
* and swap that into the ring buffer.
*
* We will be using cmpxchg soon to make all this lockless.
*
*/
/*
* A fast way to enable or disable all ring buffers is to
* call tracing_on or tracing_off. Turning off the ring buffers
* prevents all ring buffers from being recorded to.
* Turning this switch on, makes it OK to write to the
* ring buffer, if the ring buffer is enabled itself.
*
* There's three layers that must be on in order to write
* to the ring buffer.
*
* 1) This global flag must be set.
* 2) The ring buffer must be enabled for recording.
* 3) The per cpu buffer must be enabled for recording.
*
* In case of an anomaly, this global flag has a bit set that
* will permantly disable all ring buffers.
*/
/*
* Global flag to disable all recording to ring buffers
* This has two bits: ON, DISABLED
*
* ON DISABLED
* ---- ----------
* 0 0 : ring buffers are off
* 1 0 : ring buffers are on
* X 1 : ring buffers are permanently disabled
*/
enum {
RB_BUFFERS_ON_BIT = 0,
RB_BUFFERS_DISABLED_BIT = 1,
};
enum {
RB_BUFFERS_ON = 1 << RB_BUFFERS_ON_BIT,
RB_BUFFERS_DISABLED = 1 << RB_BUFFERS_DISABLED_BIT,
};
static unsigned long ring_buffer_flags __read_mostly = RB_BUFFERS_ON;
#define BUF_PAGE_HDR_SIZE offsetof(struct buffer_data_page, data)
/**
* tracing_on - enable all tracing buffers
*
* This function enables all tracing buffers that may have been
* disabled with tracing_off.
*/
void tracing_on(void)
{
set_bit(RB_BUFFERS_ON_BIT, &ring_buffer_flags);
}
EXPORT_SYMBOL_GPL(tracing_on);
/**
* tracing_off - turn off all tracing buffers
*
* This function stops all tracing buffers from recording data.
* It does not disable any overhead the tracers themselves may
* be causing. This function simply causes all recording to
* the ring buffers to fail.
*/
void tracing_off(void)
{
clear_bit(RB_BUFFERS_ON_BIT, &ring_buffer_flags);
}
EXPORT_SYMBOL_GPL(tracing_off);
/**
* tracing_off_permanent - permanently disable ring buffers
*
* This function, once called, will disable all ring buffers
* permanently.
*/
void tracing_off_permanent(void)
{
set_bit(RB_BUFFERS_DISABLED_BIT, &ring_buffer_flags);
}
/**
* tracing_is_on - show state of ring buffers enabled
*/
int tracing_is_on(void)
{
return ring_buffer_flags == RB_BUFFERS_ON;
}
EXPORT_SYMBOL_GPL(tracing_is_on);
#define RB_EVNT_HDR_SIZE (offsetof(struct ring_buffer_event, array))
#define RB_ALIGNMENT 4U
#define RB_MAX_SMALL_DATA (RB_ALIGNMENT * RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
#define RB_EVNT_MIN_SIZE 8U /* two 32bit words */
/* define RINGBUF_TYPE_DATA for 'case RINGBUF_TYPE_DATA:' */
#define RINGBUF_TYPE_DATA 0 ... RINGBUF_TYPE_DATA_TYPE_LEN_MAX
enum {
RB_LEN_TIME_EXTEND = 8,
RB_LEN_TIME_STAMP = 16,
};
static inline int rb_null_event(struct ring_buffer_event *event)
{
return event->type_len == RINGBUF_TYPE_PADDING && !event->time_delta;
}
static void rb_event_set_padding(struct ring_buffer_event *event)
{
/* padding has a NULL time_delta */
event->type_len = RINGBUF_TYPE_PADDING;
event->time_delta = 0;
}
static unsigned
rb_event_data_length(struct ring_buffer_event *event)
{
unsigned length;
if (event->type_len)
length = event->type_len * RB_ALIGNMENT;
else
length = event->array[0];
return length + RB_EVNT_HDR_SIZE;
}
/* inline for ring buffer fast paths */
static unsigned
rb_event_length(struct ring_buffer_event *event)
{
switch (event->type_len) {
case RINGBUF_TYPE_PADDING:
if (rb_null_event(event))
/* undefined */
return -1;
return event->array[0] + RB_EVNT_HDR_SIZE;
case RINGBUF_TYPE_TIME_EXTEND:
return RB_LEN_TIME_EXTEND;
case RINGBUF_TYPE_TIME_STAMP:
return RB_LEN_TIME_STAMP;
case RINGBUF_TYPE_DATA:
return rb_event_data_length(event);
default:
BUG();
}
/* not hit */
return 0;
}
/**
* ring_buffer_event_length - return the length of the event
* @event: the event to get the length of
*/
unsigned ring_buffer_event_length(struct ring_buffer_event *event)
{
unsigned length = rb_event_length(event);
if (event->type_len > RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
return length;
length -= RB_EVNT_HDR_SIZE;
if (length > RB_MAX_SMALL_DATA + sizeof(event->array[0]))
length -= sizeof(event->array[0]);
return length;
}
EXPORT_SYMBOL_GPL(ring_buffer_event_length);
/* inline for ring buffer fast paths */
static void *
rb_event_data(struct ring_buffer_event *event)
{
BUG_ON(event->type_len > RINGBUF_TYPE_DATA_TYPE_LEN_MAX);
/* If length is in len field, then array[0] has the data */
if (event->type_len)
return (void *)&event->array[0];
/* Otherwise length is in array[0] and array[1] has the data */
return (void *)&event->array[1];
}
/**
* ring_buffer_event_data - return the data of the event
* @event: the event to get the data from
*/
void *ring_buffer_event_data(struct ring_buffer_event *event)
{
return rb_event_data(event);
}
EXPORT_SYMBOL_GPL(ring_buffer_event_data);
#define for_each_buffer_cpu(buffer, cpu) \
for_each_cpu(cpu, buffer->cpumask)
#define TS_SHIFT 27
#define TS_MASK ((1ULL << TS_SHIFT) - 1)
#define TS_DELTA_TEST (~TS_MASK)
struct buffer_data_page {
u64 time_stamp; /* page time stamp */
local_t commit; /* write committed index */
unsigned char data[]; /* data of buffer page */
};
/*
* Note, the buffer_page list must be first. The buffer pages
* are allocated in cache lines, which means that each buffer
* page will be at the beginning of a cache line, and thus
* the least significant bits will be zero. We use this to
* add flags in the list struct pointers, to make the ring buffer
* lockless.
*/
struct buffer_page {
struct list_head list; /* list of buffer pages */
local_t write; /* index for next write */
unsigned read; /* index for next read */
local_t entries; /* entries on this page */
struct buffer_data_page *page; /* Actual data page */
};
/*
* The buffer page counters, write and entries, must be reset
* atomically when crossing page boundaries. To synchronize this
* update, two counters are inserted into the number. One is
* the actual counter for the write position or count on the page.
*
* The other is a counter of updaters. Before an update happens
* the update partition of the counter is incremented. This will
* allow the updater to update the counter atomically.
*
* The counter is 20 bits, and the state data is 12.
*/
#define RB_WRITE_MASK 0xfffff
#define RB_WRITE_INTCNT (1 << 20)
static void rb_init_page(struct buffer_data_page *bpage)
{
local_set(&bpage->commit, 0);
}
/**
* ring_buffer_page_len - the size of data on the page.
* @page: The page to read
*
* Returns the amount of data on the page, including buffer page header.
*/
size_t ring_buffer_page_len(void *page)
{
return local_read(&((struct buffer_data_page *)page)->commit)
+ BUF_PAGE_HDR_SIZE;
}
/*
* Also stolen from mm/slob.c. Thanks to Mathieu Desnoyers for pointing
* this issue out.
*/
static void free_buffer_page(struct buffer_page *bpage)
{
free_page((unsigned long)bpage->page);
kfree(bpage);
}
/*
* We need to fit the time_stamp delta into 27 bits.
*/
static inline int test_time_stamp(u64 delta)
{
if (delta & TS_DELTA_TEST)
return 1;
return 0;
}
#define BUF_PAGE_SIZE (PAGE_SIZE - BUF_PAGE_HDR_SIZE)
/* Max payload is BUF_PAGE_SIZE - header (8bytes) */
#define BUF_MAX_DATA_SIZE (BUF_PAGE_SIZE - (sizeof(u32) * 2))
/* Max number of timestamps that can fit on a page */
#define RB_TIMESTAMPS_PER_PAGE (BUF_PAGE_SIZE / RB_LEN_TIME_STAMP)
int ring_buffer_print_page_header(struct trace_seq *s)
{
struct buffer_data_page field;
int ret;
ret = trace_seq_printf(s, "\tfield: u64 timestamp;\t"
"offset:0;\tsize:%u;\n",
(unsigned int)sizeof(field.time_stamp));
ret = trace_seq_printf(s, "\tfield: local_t commit;\t"
"offset:%u;\tsize:%u;\n",
(unsigned int)offsetof(typeof(field), commit),
(unsigned int)sizeof(field.commit));
ret = trace_seq_printf(s, "\tfield: char data;\t"
"offset:%u;\tsize:%u;\n",
(unsigned int)offsetof(typeof(field), data),
(unsigned int)BUF_PAGE_SIZE);
return ret;
}
/*
* head_page == tail_page && head == tail then buffer is empty.
*/
struct ring_buffer_per_cpu {
int cpu;
struct ring_buffer *buffer;
spinlock_t reader_lock; /* serialize readers */
raw_spinlock_t lock;
struct lock_class_key lock_key;
struct list_head *pages;
struct buffer_page *head_page; /* read from head */
struct buffer_page *tail_page; /* write to tail */
struct buffer_page *commit_page; /* committed pages */
struct buffer_page *reader_page;
local_t commit_overrun;
local_t overrun;
local_t entries;
local_t committing;
local_t commits;
unsigned long read;
u64 write_stamp;
u64 read_stamp;
atomic_t record_disabled;
};
struct ring_buffer {
unsigned pages;
unsigned flags;
int cpus;
atomic_t record_disabled;
cpumask_var_t cpumask;
struct lock_class_key *reader_lock_key;
struct mutex mutex;
struct ring_buffer_per_cpu **buffers;
#ifdef CONFIG_HOTPLUG_CPU
struct notifier_block cpu_notify;
#endif
u64 (*clock)(void);
};
struct ring_buffer_iter {
struct ring_buffer_per_cpu *cpu_buffer;
unsigned long head;
struct buffer_page *head_page;
u64 read_stamp;
};
/* buffer may be either ring_buffer or ring_buffer_per_cpu */
#define RB_WARN_ON(b, cond) \
({ \
int _____ret = unlikely(cond); \
if (_____ret) { \
if (__same_type(*(b), struct ring_buffer_per_cpu)) { \
struct ring_buffer_per_cpu *__b = \
(void *)b; \
atomic_inc(&__b->buffer->record_disabled); \
} else \
atomic_inc(&b->record_disabled); \
WARN_ON(1); \
} \
_____ret; \
})
/* Up this if you want to test the TIME_EXTENTS and normalization */
#define DEBUG_SHIFT 0
static inline u64 rb_time_stamp(struct ring_buffer *buffer)
{
/* shift to debug/test normalization and TIME_EXTENTS */
return buffer->clock() << DEBUG_SHIFT;
}
u64 ring_buffer_time_stamp(struct ring_buffer *buffer, int cpu)
{
u64 time;
preempt_disable_notrace();
time = rb_time_stamp(buffer);
preempt_enable_no_resched_notrace();
return time;
}
EXPORT_SYMBOL_GPL(ring_buffer_time_stamp);
void ring_buffer_normalize_time_stamp(struct ring_buffer *buffer,
int cpu, u64 *ts)
{
/* Just stupid testing the normalize function and deltas */
*ts >>= DEBUG_SHIFT;
}
EXPORT_SYMBOL_GPL(ring_buffer_normalize_time_stamp);
/*
* Making the ring buffer lockless makes things tricky.
* Although writes only happen on the CPU that they are on,
* and they only need to worry about interrupts. Reads can
* happen on any CPU.
*
* The reader page is always off the ring buffer, but when the
* reader finishes with a page, it needs to swap its page with
* a new one from the buffer. The reader needs to take from
* the head (writes go to the tail). But if a writer is in overwrite
* mode and wraps, it must push the head page forward.
*
* Here lies the problem.
*
* The reader must be careful to replace only the head page, and
* not another one. As described at the top of the file in the
* ASCII art, the reader sets its old page to point to the next
* page after head. It then sets the page after head to point to
* the old reader page. But if the writer moves the head page
* during this operation, the reader could end up with the tail.
*
* We use cmpxchg to help prevent this race. We also do something
* special with the page before head. We set the LSB to 1.
*
* When the writer must push the page forward, it will clear the
* bit that points to the head page, move the head, and then set
* the bit that points to the new head page.
*
* We also don't want an interrupt coming in and moving the head
* page on another writer. Thus we use the second LSB to catch
* that too. Thus:
*
* head->list->prev->next bit 1 bit 0
* ------- -------
* Normal page 0 0
* Points to head page 0 1
* New head page 1 0
*
* Note we can not trust the prev pointer of the head page, because:
*
* +----+ +-----+ +-----+
* | |------>| T |---X--->| N |
* | |<------| | | |
* +----+ +-----+ +-----+
* ^ ^ |
* | +-----+ | |
* +----------| R |----------+ |
* | |<-----------+
* +-----+
*
* Key: ---X--> HEAD flag set in pointer
* T Tail page
* R Reader page
* N Next page
*
* (see __rb_reserve_next() to see where this happens)
*
* What the above shows is that the reader just swapped out
* the reader page with a page in the buffer, but before it
* could make the new header point back to the new page added
* it was preempted by a writer. The writer moved forward onto
* the new page added by the reader and is about to move forward
* again.
*
* You can see, it is legitimate for the previous pointer of
* the head (or any page) not to point back to itself. But only
* temporarially.
*/
#define RB_PAGE_NORMAL 0UL
#define RB_PAGE_HEAD 1UL
#define RB_PAGE_UPDATE 2UL
#define RB_FLAG_MASK 3UL
/* PAGE_MOVED is not part of the mask */
#define RB_PAGE_MOVED 4UL
/*
* rb_list_head - remove any bit
*/
static struct list_head *rb_list_head(struct list_head *list)
{
unsigned long val = (unsigned long)list;
return (struct list_head *)(val & ~RB_FLAG_MASK);
}
/*
* rb_is_head_page - test if the given page is the head page
*
* Because the reader may move the head_page pointer, we can
* not trust what the head page is (it may be pointing to
* the reader page). But if the next page is a header page,
* its flags will be non zero.
*/
static int inline
rb_is_head_page(struct ring_buffer_per_cpu *cpu_buffer,
struct buffer_page *page, struct list_head *list)
{
unsigned long val;
val = (unsigned long)list->next;
if ((val & ~RB_FLAG_MASK) != (unsigned long)&page->list)
return RB_PAGE_MOVED;
return val & RB_FLAG_MASK;
}
/*
* rb_is_reader_page
*
* The unique thing about the reader page, is that, if the
* writer is ever on it, the previous pointer never points
* back to the reader page.
*/
static int rb_is_reader_page(struct buffer_page *page)
{
struct list_head *list = page->list.prev;
return rb_list_head(list->next) != &page->list;
}
/*
* rb_set_list_to_head - set a list_head to be pointing to head.
*/
static void rb_set_list_to_head(struct ring_buffer_per_cpu *cpu_buffer,
struct list_head *list)
{
unsigned long *ptr;
ptr = (unsigned long *)&list->next;
*ptr |= RB_PAGE_HEAD;
*ptr &= ~RB_PAGE_UPDATE;
}
/*
* rb_head_page_activate - sets up head page
*/
static void rb_head_page_activate(struct ring_buffer_per_cpu *cpu_buffer)
{
struct buffer_page *head;
head = cpu_buffer->head_page;
if (!head)
return;
/*
* Set the previous list pointer to have the HEAD flag.
*/
rb_set_list_to_head(cpu_buffer, head->list.prev);
}
static void rb_list_head_clear(struct list_head *list)
{
unsigned long *ptr = (unsigned long *)&list->next;
*ptr &= ~RB_FLAG_MASK;
}
/*
* rb_head_page_dactivate - clears head page ptr (for free list)
*/
static void
rb_head_page_deactivate(struct ring_buffer_per_cpu *cpu_buffer)
{
struct list_head *hd;
/* Go through the whole list and clear any pointers found. */
rb_list_head_clear(cpu_buffer->pages);
list_for_each(hd, cpu_buffer->pages)
rb_list_head_clear(hd);
}
static int rb_head_page_set(struct ring_buffer_per_cpu *cpu_buffer,
struct buffer_page *head,
struct buffer_page *prev,
int old_flag, int new_flag)
{
struct list_head *list;
unsigned long val = (unsigned long)&head->list;
unsigned long ret;
list = &prev->list;
val &= ~RB_FLAG_MASK;
ret = cmpxchg((unsigned long *)&list->next,
val | old_flag, val | new_flag);
/* check if the reader took the page */
if ((ret & ~RB_FLAG_MASK) != val)
return RB_PAGE_MOVED;
return ret & RB_FLAG_MASK;
}
static int rb_head_page_set_update(struct ring_buffer_per_cpu *cpu_buffer,
struct buffer_page *head,
struct buffer_page *prev,
int old_flag)
{
return rb_head_page_set(cpu_buffer, head, prev,
old_flag, RB_PAGE_UPDATE);
}
static int rb_head_page_set_head(struct ring_buffer_per_cpu *cpu_buffer,
struct buffer_page *head,
struct buffer_page *prev,
int old_flag)
{
return rb_head_page_set(cpu_buffer, head, prev,
old_flag, RB_PAGE_HEAD);
}
static int rb_head_page_set_normal(struct ring_buffer_per_cpu *cpu_buffer,
struct buffer_page *head,
struct buffer_page *prev,
int old_flag)
{
return rb_head_page_set(cpu_buffer, head, prev,
old_flag, RB_PAGE_NORMAL);
}
static inline void rb_inc_page(struct ring_buffer_per_cpu *cpu_buffer,
struct buffer_page **bpage)
{
struct list_head *p = rb_list_head((*bpage)->list.next);
*bpage = list_entry(p, struct buffer_page, list);
}
static struct buffer_page *
rb_set_head_page(struct ring_buffer_per_cpu *cpu_buffer)
{
struct buffer_page *head;
struct buffer_page *page;
struct list_head *list;
int i;
if (RB_WARN_ON(cpu_buffer, !cpu_buffer->head_page))
return NULL;
/* sanity check */
list = cpu_buffer->pages;
if (RB_WARN_ON(cpu_buffer, rb_list_head(list->prev->next) != list))
return NULL;
page = head = cpu_buffer->head_page;
/*
* It is possible that the writer moves the header behind
* where we started, and we miss in one loop.
* A second loop should grab the header, but we'll do
* three loops just because I'm paranoid.
*/
for (i = 0; i < 3; i++) {
do {
if (rb_is_head_page(cpu_buffer, page, page->list.prev)) {
cpu_buffer->head_page = page;
return page;
}
rb_inc_page(cpu_buffer, &page);
} while (page != head);
}
RB_WARN_ON(cpu_buffer, 1);
return NULL;
}
static int rb_head_page_replace(struct buffer_page *old,
struct buffer_page *new)
{
unsigned long *ptr = (unsigned long *)&old->list.prev->next;
unsigned long val;
unsigned long ret;
val = *ptr & ~RB_FLAG_MASK;
val |= RB_PAGE_HEAD;
ret = cmpxchg(ptr, val, (unsigned long)&new->list);
return ret == val;
}
/*
* rb_tail_page_update - move the tail page forward
*
* Returns 1 if moved tail page, 0 if someone else did.
*/
static int rb_tail_page_update(struct ring_buffer_per_cpu *cpu_buffer,
struct buffer_page *tail_page,
struct buffer_page *next_page)
{
struct buffer_page *old_tail;
unsigned long old_entries;
unsigned long old_write;
int ret = 0;
/*
* The tail page now needs to be moved forward.
*
* We need to reset the tail page, but without messing
* with possible erasing of data brought in by interrupts
* that have moved the tail page and are currently on it.
*
* We add a counter to the write field to denote this.
*/
old_write = local_add_return(RB_WRITE_INTCNT, &next_page->write);
old_entries = local_add_return(RB_WRITE_INTCNT, &next_page->entries);
/*
* Just make sure we have seen our old_write and synchronize
* with any interrupts that come in.
*/
barrier();
/*
* If the tail page is still the same as what we think
* it is, then it is up to us to update the tail
* pointer.
*/
if (tail_page == cpu_buffer->tail_page) {
/* Zero the write counter */
unsigned long val = old_write & ~RB_WRITE_MASK;
unsigned long eval = old_entries & ~RB_WRITE_MASK;
/*
* This will only succeed if an interrupt did
* not come in and change it. In which case, we
* do not want to modify it.
*
* We add (void) to let the compiler know that we do not care
* about the return value of these functions. We use the
* cmpxchg to only update if an interrupt did not already
* do it for us. If the cmpxchg fails, we don't care.
*/
(void)local_cmpxchg(&next_page->write, old_write, val);
(void)local_cmpxchg(&next_page->entries, old_entries, eval);
/*
* No need to worry about races with clearing out the commit.
* it only can increment when a commit takes place. But that
* only happens in the outer most nested commit.
*/
local_set(&next_page->page->commit, 0);
old_tail = cmpxchg(&cpu_buffer->tail_page,
tail_page, next_page);
if (old_tail == tail_page)
ret = 1;
}
return ret;
}
static int rb_check_bpage(struct ring_buffer_per_cpu *cpu_buffer,
struct buffer_page *bpage)
{
unsigned long val = (unsigned long)bpage;
if (RB_WARN_ON(cpu_buffer, val & RB_FLAG_MASK))
return 1;
return 0;
}
/**
* rb_check_list - make sure a pointer to a list has the last bits zero
*/
static int rb_check_list(struct ring_buffer_per_cpu *cpu_buffer,
struct list_head *list)
{
if (RB_WARN_ON(cpu_buffer, rb_list_head(list->prev) != list->prev))
return 1;
if (RB_WARN_ON(cpu_buffer, rb_list_head(list->next) != list->next))
return 1;
return 0;
}
/**
* check_pages - integrity check of buffer pages
* @cpu_buffer: CPU buffer with pages to test
*
* As a safety measure we check to make sure the data pages have not
* been corrupted.
*/
static int rb_check_pages(struct ring_buffer_per_cpu *cpu_buffer)
{
struct list_head *head = cpu_buffer->pages;
struct buffer_page *bpage, *tmp;
rb_head_page_deactivate(cpu_buffer);
if (RB_WARN_ON(cpu_buffer, head->next->prev != head))
return -1;
if (RB_WARN_ON(cpu_buffer, head->prev->next != head))
return -1;
if (rb_check_list(cpu_buffer, head))
return -1;
list_for_each_entry_safe(bpage, tmp, head, list) {
if (RB_WARN_ON(cpu_buffer,
bpage->list.next->prev != &bpage->list))
return -1;
if (RB_WARN_ON(cpu_buffer,
bpage->list.prev->next != &bpage->list))
return -1;
if (rb_check_list(cpu_buffer, &bpage->list))
return -1;
}
rb_head_page_activate(cpu_buffer);
return 0;
}
static int rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
unsigned nr_pages)
{
struct buffer_page *bpage, *tmp;
unsigned long addr;
LIST_HEAD(pages);
unsigned i;
WARN_ON(!nr_pages);
for (i = 0; i < nr_pages; i++) {
bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
GFP_KERNEL, cpu_to_node(cpu_buffer->cpu));
if (!bpage)
goto free_pages;
rb_check_bpage(cpu_buffer, bpage);
list_add(&bpage->list, &pages);
addr = __get_free_page(GFP_KERNEL);
if (!addr)
goto free_pages;
bpage->page = (void *)addr;
rb_init_page(bpage->page);
}
/*
* The ring buffer page list is a circular list that does not
* start and end with a list head. All page list items point to
* other pages.
*/
cpu_buffer->pages = pages.next;
list_del(&pages);
rb_check_pages(cpu_buffer);
return 0;
free_pages:
list_for_each_entry_safe(bpage, tmp, &pages, list) {
list_del_init(&bpage->list);
free_buffer_page(bpage);
}
return -ENOMEM;
}
static struct ring_buffer_per_cpu *
rb_allocate_cpu_buffer(struct ring_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;
struct buffer_page *bpage;
unsigned long addr;
int ret;
cpu_buffer = kzalloc_node(ALIGN(sizeof(*cpu_buffer), cache_line_size()),
GFP_KERNEL, cpu_to_node(cpu));
if (!cpu_buffer)
return NULL;
cpu_buffer->cpu = cpu;
cpu_buffer->buffer = buffer;
spin_lock_init(&cpu_buffer->reader_lock);
lockdep_set_class(&cpu_buffer->reader_lock, buffer->reader_lock_key);
cpu_buffer->lock = (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;
bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
GFP_KERNEL, cpu_to_node(cpu));
if (!bpage)
goto fail_free_buffer;
rb_check_bpage(cpu_buffer, bpage);
cpu_buffer->reader_page = bpage;
addr = __get_free_page(GFP_KERNEL);
if (!addr)
goto fail_free_reader;
bpage->page = (void *)addr;
rb_init_page(bpage->page);
INIT_LIST_HEAD(&cpu_buffer->reader_page->list);
ret = rb_allocate_pages(cpu_buffer, buffer->pages);
if (ret < 0)
goto fail_free_reader;
cpu_buffer->head_page
= list_entry(cpu_buffer->pages, struct buffer_page, list);
cpu_buffer->tail_page = cpu_buffer->commit_page = cpu_buffer->head_page;
rb_head_page_activate(cpu_buffer);
return cpu_buffer;
fail_free_reader:
free_buffer_page(cpu_buffer->reader_page);
fail_free_buffer:
kfree(cpu_buffer);
return NULL;
}
static void rb_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
{
struct list_head *head = cpu_buffer->pages;
struct buffer_page *bpage, *tmp;
free_buffer_page(cpu_buffer->reader_page);
rb_head_page_deactivate(cpu_buffer);
if (head) {
list_for_each_entry_safe(bpage, tmp, head, list) {
list_del_init(&bpage->list);
free_buffer_page(bpage);
}
bpage = list_entry(head, struct buffer_page, list);
free_buffer_page(bpage);
}
kfree(cpu_buffer);
}
#ifdef CONFIG_HOTPLUG_CPU
static int rb_cpu_notify(struct notifier_block *self,
unsigned long action, void *hcpu);
#endif
/**
* ring_buffer_alloc - allocate a new ring_buffer
* @size: the size in bytes per cpu that is needed.
* @flags: attributes to set for the ring buffer.
*
* Currently the only flag that is available is the RB_FL_OVERWRITE
* flag. This flag means that the buffer will overwrite old data
* when the buffer wraps. If this flag is not set, the buffer will
* drop data when the tail hits the head.
*/
struct ring_buffer *__ring_buffer_alloc(unsigned long size, unsigned flags,
struct lock_class_key *key)
{
struct ring_buffer *buffer;
int bsize;
int cpu;
/* keep it in its own cache line */
buffer = kzalloc(ALIGN(sizeof(*buffer), cache_line_size()),
GFP_KERNEL);
if (!buffer)
return NULL;
if (!alloc_cpumask_var(&buffer->cpumask, GFP_KERNEL))
goto fail_free_buffer;
buffer->pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
buffer->flags = flags;
buffer->clock = trace_clock_local;
buffer->reader_lock_key = key;
/* need at least two pages */
if (buffer->pages < 2)
buffer->pages = 2;
/*
* In case of non-hotplug cpu, if the ring-buffer is allocated
* in early initcall, it will not be notified of secondary cpus.
* In that off case, we need to allocate for all possible cpus.
*/
#ifdef CONFIG_HOTPLUG_CPU
get_online_cpus();
cpumask_copy(buffer->cpumask, cpu_online_mask);
#else
cpumask_copy(buffer->cpumask, cpu_possible_mask);
#endif
buffer->cpus = nr_cpu_ids;
bsize = sizeof(void *) * nr_cpu_ids;
buffer->buffers = kzalloc(ALIGN(bsize, cache_line_size()),
GFP_KERNEL);
if (!buffer->buffers)
goto fail_free_cpumask;
for_each_buffer_cpu(buffer, cpu) {
buffer->buffers[cpu] =
rb_allocate_cpu_buffer(buffer, cpu);
if (!buffer->buffers[cpu])
goto fail_free_buffers;
}
#ifdef CONFIG_HOTPLUG_CPU
buffer->cpu_notify.notifier_call = rb_cpu_notify;
buffer->cpu_notify.priority = 0;
register_cpu_notifier(&buffer->cpu_notify);
#endif
put_online_cpus();
mutex_init(&buffer->mutex);
return buffer;
fail_free_buffers:
for_each_buffer_cpu(buffer, cpu) {
if (buffer->buffers[cpu])
rb_free_cpu_buffer(buffer->buffers[cpu]);
}
kfree(buffer->buffers);
fail_free_cpumask:
free_cpumask_var(buffer->cpumask);
put_online_cpus();
fail_free_buffer:
kfree(buffer);
return NULL;
}
EXPORT_SYMBOL_GPL(__ring_buffer_alloc);
/**
* ring_buffer_free - free a ring buffer.
* @buffer: the buffer to free.
*/
void
ring_buffer_free(struct ring_buffer *buffer)
{
int cpu;
get_online_cpus();
#ifdef CONFIG_HOTPLUG_CPU
unregister_cpu_notifier(&buffer->cpu_notify);
#endif
for_each_buffer_cpu(buffer, cpu)
rb_free_cpu_buffer(buffer->buffers[cpu]);
put_online_cpus();
kfree(buffer->buffers);
free_cpumask_var(buffer->cpumask);
kfree(buffer);
}
EXPORT_SYMBOL_GPL(ring_buffer_free);
void ring_buffer_set_clock(struct ring_buffer *buffer,
u64 (*clock)(void))
{
buffer->clock = clock;
}
static void rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer);
static void
rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned nr_pages)
{
struct buffer_page *bpage;
struct list_head *p;
unsigned i;
atomic_inc(&cpu_buffer->record_disabled);
synchronize_sched();
spin_lock_irq(&cpu_buffer->reader_lock);
rb_head_page_deactivate(cpu_buffer);
for (i = 0; i < nr_pages; i++) {
if (RB_WARN_ON(cpu_buffer, list_empty(cpu_buffer->pages)))
return;
p = cpu_buffer->pages->next;
bpage = list_entry(p, struct buffer_page, list);
list_del_init(&bpage->list);
free_buffer_page(bpage);
}
if (RB_WARN_ON(cpu_buffer, list_empty(cpu_buffer->pages)))
return;
rb_reset_cpu(cpu_buffer);
spin_unlock_irq(&cpu_buffer->reader_lock);
rb_check_pages(cpu_buffer);
atomic_dec(&cpu_buffer->record_disabled);
}
static void
rb_insert_pages(struct ring_buffer_per_cpu *cpu_buffer,
struct list_head *pages, unsigned nr_pages)
{
struct buffer_page *bpage;
struct list_head *p;
unsigned i;
atomic_inc(&cpu_buffer->record_disabled);
synchronize_sched();
spin_lock_irq(&cpu_buffer->reader_lock);
rb_head_page_deactivate(cpu_buffer);
for (i = 0; i < nr_pages; i++) {
if (RB_WARN_ON(cpu_buffer, list_empty(pages)))
return;
p = pages->next;
bpage = list_entry(p, struct buffer_page, list);
list_del_init(&bpage->list);
list_add_tail(&bpage->list, cpu_buffer->pages);
}
rb_reset_cpu(cpu_buffer);
spin_unlock_irq(&cpu_buffer->reader_lock);
rb_check_pages(cpu_buffer);
atomic_dec(&cpu_buffer->record_disabled);
}
/**
* ring_buffer_resize - resize the ring buffer
* @buffer: the buffer to resize.
* @size: the new size.
*
* The tracer is responsible for making sure that the buffer is
* not being used while changing the size.
* Note: We may be able to change the above requirement by using
* RCU synchronizations.
*
* Minimum size is 2 * BUF_PAGE_SIZE.
*
* Returns -1 on failure.
*/
int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size)
{
struct ring_buffer_per_cpu *cpu_buffer;
unsigned nr_pages, rm_pages, new_pages;
struct buffer_page *bpage, *tmp;
unsigned long buffer_size;
unsigned long addr;
LIST_HEAD(pages);
int i, cpu;
/*
* Always succeed at resizing a non-existent buffer:
*/
if (!buffer)
return size;
size = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
size *= BUF_PAGE_SIZE;
buffer_size = buffer->pages * BUF_PAGE_SIZE;
/* we need a minimum of two pages */
if (size < BUF_PAGE_SIZE * 2)
size = BUF_PAGE_SIZE * 2;
if (size == buffer_size)
return size;
mutex_lock(&buffer->mutex);
get_online_cpus();
nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
if (size < buffer_size) {
/* easy case, just free pages */
if (RB_WARN_ON(buffer, nr_pages >= buffer->pages))
goto out_fail;
rm_pages = buffer->pages - nr_pages;
for_each_buffer_cpu(buffer, cpu) {
cpu_buffer = buffer->buffers[cpu];
rb_remove_pages(cpu_buffer, rm_pages);
}
goto out;
}
/*
* This is a bit more difficult. We only want to add pages
* when we can allocate enough for all CPUs. We do this
* by allocating all the pages and storing them on a local
* link list. If we succeed in our allocation, then we
* add these pages to the cpu_buffers. Otherwise we just free
* them all and return -ENOMEM;
*/
if (RB_WARN_ON(buffer, nr_pages <= buffer->pages))
goto out_fail;
new_pages = nr_pages - buffer->pages;
for_each_buffer_cpu(buffer, cpu) {
for (i = 0; i < new_pages; i++) {
bpage = kzalloc_node(ALIGN(sizeof(*bpage),
cache_line_size()),
GFP_KERNEL, cpu_to_node(cpu));
if (!bpage)
goto free_pages;
list_add(&bpage->list, &pages);
addr = __get_free_page(GFP_KERNEL);
if (!addr)
goto free_pages;
bpage->page = (void *)addr;
rb_init_page(bpage->page);
}
}
for_each_buffer_cpu(buffer, cpu) {
cpu_buffer = buffer->buffers[cpu];
rb_insert_pages(cpu_buffer, &pages, new_pages);
}
if (RB_WARN_ON(buffer, !list_empty(&pages)))
goto out_fail;
out:
buffer->pages = nr_pages;
put_online_cpus();
mutex_unlock(&buffer->mutex);
return size;
free_pages:
list_for_each_entry_safe(bpage, tmp, &pages, list) {
list_del_init(&bpage->list);
free_buffer_page(bpage);
}
put_online_cpus();
mutex_unlock(&buffer->mutex);
return -ENOMEM;
/*
* Something went totally wrong, and we are too paranoid
* to even clean up the mess.
*/
out_fail:
put_online_cpus();
mutex_unlock(&buffer->mutex);
return -1;
}
EXPORT_SYMBOL_GPL(ring_buffer_resize);
static inline void *
__rb_data_page_index(struct buffer_data_page *bpage, unsigned index)
{
return bpage->data + index;
}
static inline void *__rb_page_index(struct buffer_page *bpage, unsigned index)
{
return bpage->page->data + index;
}
static inline struct ring_buffer_event *
rb_reader_event(struct ring_buffer_per_cpu *cpu_buffer)
{
return __rb_page_index(cpu_buffer->reader_page,
cpu_buffer->reader_page->read);
}
static inline struct ring_buffer_event *
rb_iter_head_event(struct ring_buffer_iter *iter)
{
return __rb_page_index(iter->head_page, iter->head);
}
static inline unsigned long rb_page_write(struct buffer_page *bpage)
{
return local_read(&bpage->write) & RB_WRITE_MASK;
}
static inline unsigned rb_page_commit(struct buffer_page *bpage)
{
return local_read(&bpage->page->commit);
}
static inline unsigned long rb_page_entries(struct buffer_page *bpage)
{
return local_read(&bpage->entries) & RB_WRITE_MASK;
}
/* Size is determined by what has been commited */
static inline unsigned rb_page_size(struct buffer_page *bpage)
{
return rb_page_commit(bpage);
}
static inline unsigned
rb_commit_index(struct ring_buffer_per_cpu *cpu_buffer)
{
return rb_page_commit(cpu_buffer->commit_page);
}
static inline unsigned
rb_event_index(struct ring_buffer_event *event)
{
unsigned long addr = (unsigned long)event;
return (addr & ~PAGE_MASK) - BUF_PAGE_HDR_SIZE;
}
static inline int
rb_event_is_commit(struct ring_buffer_per_cpu *cpu_buffer,
struct ring_buffer_event *event)
{
unsigned long addr = (unsigned long)event;
unsigned long index;
index = rb_event_index(event);
addr &= PAGE_MASK;
return cpu_buffer->commit_page->page == (void *)addr &&
rb_commit_index(cpu_buffer) == index;
}
static void
rb_set_commit_to_write(struct ring_buffer_per_cpu *cpu_buffer)
{
unsigned long max_count;
/*
* We only race with interrupts and NMIs on this CPU.
* If we own the commit event, then we can commit
* all others that interrupted us, since the interruptions
* are in stack format (they finish before they come
* back to us). This allows us to do a simple loop to
* assign the commit to the tail.
*/
again:
max_count = cpu_buffer->buffer->pages * 100;
while (cpu_buffer->commit_page != cpu_buffer->tail_page) {
if (RB_WARN_ON(cpu_buffer, !(--max_count)))
return;
if (RB_WARN_ON(cpu_buffer,
rb_is_reader_page(cpu_buffer->tail_page)))
return;
local_set(&cpu_buffer->commit_page->page->commit,
rb_page_write(cpu_buffer->commit_page));
rb_inc_page(cpu_buffer, &cpu_buffer->commit_page);
cpu_buffer->write_stamp =
cpu_buffer->commit_page->page->time_stamp;
/* add barrier to keep gcc from optimizing too much */
barrier();
}
while (rb_commit_index(cpu_buffer) !=
rb_page_write(cpu_buffer->commit_page)) {
local_set(&cpu_buffer->commit_page->page->commit,
rb_page_write(cpu_buffer->commit_page));
RB_WARN_ON(cpu_buffer,
local_read(&cpu_buffer->commit_page->page->commit) &
~RB_WRITE_MASK);
barrier();
}
/* again, keep gcc from optimizing */
barrier();
/*
* If an interrupt came in just after the first while loop
* and pushed the tail page forward, we will be left with
* a dangling commit that will never go forward.
*/
if (unlikely(cpu_buffer->commit_page != cpu_buffer->tail_page))
goto again;
}
static void rb_reset_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
{
cpu_buffer->read_stamp = cpu_buffer->reader_page->page->time_stamp;
cpu_buffer->reader_page->read = 0;
}
static void rb_inc_iter(struct ring_buffer_iter *iter)
{
struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
/*
* The iterator could be on the reader page (it starts there).
* But the head could have moved, since the reader was
* found. Check for this case and assign the iterator
* to the head page instead of next.
*/
if (iter->head_page == cpu_buffer->reader_page)
iter->head_page = rb_set_head_page(cpu_buffer);
else
rb_inc_page(cpu_buffer, &iter->head_page);
iter->read_stamp = iter->head_page->page->time_stamp;
iter->head = 0;
}
/**
* ring_buffer_update_event - update event type and data
* @event: the even to update
* @type: the type of event
* @length: the size of the event field in the ring buffer
*
* Update the type and data fields of the event. The length
* is the actual size that is written to the ring buffer,
* and with this, we can determine what to place into the
* data field.
*/
static void
rb_update_event(struct ring_buffer_event *event,
unsigned type, unsigned length)
{
event->type_len = type;
switch (type) {
case RINGBUF_TYPE_PADDING:
case RINGBUF_TYPE_TIME_EXTEND:
case RINGBUF_TYPE_TIME_STAMP:
break;
case 0:
length -= RB_EVNT_HDR_SIZE;
if (length > RB_MAX_SMALL_DATA)
event->array[0] = length;
else
event->type_len = DIV_ROUND_UP(length, RB_ALIGNMENT);
break;
default:
BUG();
}
}
/*
* rb_handle_head_page - writer hit the head page
*
* Returns: +1 to retry page
* 0 to continue
* -1 on error
*/
static int
rb_handle_head_page(struct ring_buffer_per_cpu *cpu_buffer,
struct buffer_page *tail_page,
struct buffer_page *next_page)
{
struct buffer_page *new_head;
int entries;
int type;
int ret;
entries = rb_page_entries(next_page);
/*
* The hard part is here. We need to move the head
* forward, and protect against both readers on
* other CPUs and writers coming in via interrupts.
*/
type = rb_head_page_set_update(cpu_buffer, next_page, tail_page,
RB_PAGE_HEAD);
/*
* type can be one of four:
* NORMAL - an interrupt already moved it for us
* HEAD - we are the first to get here.
* UPDATE - we are the interrupt interrupting
* a current move.
* MOVED - a reader on another CPU moved the next
* pointer to its reader page. Give up
* and try again.
*/
switch (type) {
case RB_PAGE_HEAD:
/*
* We changed the head to UPDATE, thus
* it is our responsibility to update
* the counters.
*/
local_add(entries, &cpu_buffer->overrun);
/*
* The entries will be zeroed out when we move the
* tail page.
*/
/* still more to do */
break;
case RB_PAGE_UPDATE:
/*
* This is an interrupt that interrupt the
* previous update. Still more to do.
*/
break;
case RB_PAGE_NORMAL:
/*
* An interrupt came in before the update
* and processed this for us.
* Nothing left to do.
*/
return 1;
case RB_PAGE_MOVED:
/*
* The reader is on another CPU and just did
* a swap with our next_page.
* Try again.
*/
return 1;
default:
RB_WARN_ON(cpu_buffer, 1); /* WTF??? */
return -1;
}
/*
* Now that we are here, the old head pointer is
* set to UPDATE. This will keep the reader from
* swapping the head page with the reader page.
* The reader (on another CPU) will spin till
* we are finished.
*
* We just need to protect against interrupts
* doing the job. We will set the next pointer
* to HEAD. After that, we set the old pointer
* to NORMAL, but only if it was HEAD before.
* otherwise we are an interrupt, and only
* want the outer most commit to reset it.
*/
new_head = next_page;
rb_inc_page(cpu_buffer, &new_head);
ret = rb_head_page_set_head(cpu_buffer, new_head, next_page,
RB_PAGE_NORMAL);
/*
* Valid returns are:
* HEAD - an interrupt came in and already set it.
* NORMAL - One of two things:
* 1) We really set it.
* 2) A bunch of interrupts came in and moved
* the page forward again.
*/
switch (ret) {
case RB_PAGE_HEAD:
case RB_PAGE_NORMAL:
/* OK */
break;
default:
RB_WARN_ON(cpu_buffer, 1);
return -1;
}
/*
* It is possible that an interrupt came in,
* set the head up, then more interrupts came in
* and moved it again. When we get back here,
* the page would have been set to NORMAL but we
* just set it back to HEAD.
*
* How do you detect this? Well, if that happened
* the tail page would have moved.
*/
if (ret == RB_PAGE_NORMAL) {
/*
* If the tail had moved passed next, then we need
* to reset the pointer.
*/
if (cpu_buffer->tail_page != tail_page &&
cpu_buffer->tail_page != next_page)
rb_head_page_set_normal(cpu_buffer, new_head,
next_page,
RB_PAGE_HEAD);
}
/*
* If this was the outer most commit (the one that
* changed the original pointer from HEAD to UPDATE),
* then it is up to us to reset it to NORMAL.
*/
if (type == RB_PAGE_HEAD) {
ret = rb_head_page_set_normal(cpu_buffer, next_page,
tail_page,
RB_PAGE_UPDATE);
if (RB_WARN_ON(cpu_buffer,
ret != RB_PAGE_UPDATE))
return -1;
}
return 0;
}
static unsigned rb_calculate_event_length(unsigned length)
{
struct ring_buffer_event event; /* Used only for sizeof array */
/* zero length can cause confusions */
if (!length)
length = 1;
if (length > RB_MAX_SMALL_DATA)
length += sizeof(event.array[0]);
length += RB_EVNT_HDR_SIZE;
length = ALIGN(length, RB_ALIGNMENT);
return length;
}
static inline void
rb_reset_tail(struct ring_buffer_per_cpu *cpu_buffer,
struct buffer_page *tail_page,
unsigned long tail, unsigned long length)
{
struct ring_buffer_event *event;
/*
* Only the event that crossed the page boundary
* must fill the old tail_page with padding.
*/
if (tail >= BUF_PAGE_SIZE) {
local_sub(length, &tail_page->write);
return;
}
event = __rb_page_index(tail_page, tail);
kmemcheck_annotate_bitfield(event, bitfield);
/*
* If this event is bigger than the minimum size, then
* we need to be careful that we don't subtract the
* write counter enough to allow another writer to slip
* in on this page.
* We put in a discarded commit instead, to make sure
* that this space is not used again.
*
* If we are less than the minimum size, we don't need to
* worry about it.
*/
if (tail > (BUF_PAGE_SIZE - RB_EVNT_MIN_SIZE)) {
/* No room for any events */
/* Mark the rest of the page with padding */
rb_event_set_padding(event);
/* Set the write back to the previous setting */
local_sub(length, &tail_page->write);
return;
}
/* Put in a discarded event */
event->array[0] = (BUF_PAGE_SIZE - tail) - RB_EVNT_HDR_SIZE;
event->type_len = RINGBUF_TYPE_PADDING;
/* time delta must be non zero */
event->time_delta = 1;
/* Set write to end of buffer */
length = (tail + length) - BUF_PAGE_SIZE;
local_sub(length, &tail_page->write);
}
static struct ring_buffer_event *
rb_move_tail(struct ring_buffer_per_cpu *cpu_buffer,
unsigned long length, unsigned long tail,
struct buffer_page *commit_page,
struct buffer_page *tail_page, u64 *ts)
{
struct ring_buffer *buffer = cpu_buffer->buffer;
struct buffer_page *next_page;
int ret;
next_page = tail_page;
rb_inc_page(cpu_buffer, &next_page);
/*
* If for some reason, we had an interrupt storm that made
* it all the way around the buffer, bail, and warn
* about it.
*/
if (unlikely(next_page == commit_page)) {
local_inc(&cpu_buffer->commit_overrun);
goto out_reset;
}
/*
* This is where the fun begins!
*
* We are fighting against races between a reader that
* could be on another CPU trying to swap its reader
* page with the buffer head.
*
* We are also fighting against interrupts coming in and
* moving the head or tail on us as well.
*
* If the next page is the head page then we have filled
* the buffer, unless the commit page is still on the
* reader page.
*/
if (rb_is_head_page(cpu_buffer, next_page, &tail_page->list)) {
/*
* If the commit is not on the reader page, then
* move the header page.
*/
if (!rb_is_reader_page(cpu_buffer->commit_page)) {
/*
* If we are not in overwrite mode,
* this is easy, just stop here.
*/
if (!(buffer->flags & RB_FL_OVERWRITE))
goto out_reset;
ret = rb_handle_head_page(cpu_buffer,
tail_page,
next_page);
if (ret < 0)
goto out_reset;
if (ret)
goto out_again;
} else {
/*
* We need to be careful here too. The
* commit page could still be on the reader
* page. We could have a small buffer, and
* have filled up the buffer with events
* from interrupts and such, and wrapped.
*
* Note, if the tail page is also the on the
* reader_page, we let it move out.
*/
if (unlikely((cpu_buffer->commit_page !=
cpu_buffer->tail_page) &&
(cpu_buffer->commit_page ==
cpu_buffer->reader_page))) {
local_inc(&cpu_buffer->commit_overrun);
goto out_reset;
}
}
}
ret = rb_tail_page_update(cpu_buffer, tail_page, next_page);
if (ret) {
/*
* Nested commits always have zero deltas, so
* just reread the time stamp
*/
*ts = rb_time_stamp(buffer);
next_page->page->time_stamp = *ts;
}
out_again:
rb_reset_tail(cpu_buffer, tail_page, tail, length);
/* fail and let the caller try again */
return ERR_PTR(-EAGAIN);
out_reset:
/* reset write */
rb_reset_tail(cpu_buffer, tail_page, tail, length);
return NULL;
}
static struct ring_buffer_event *
__rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
unsigned type, unsigned long length, u64 *ts)
{
struct buffer_page *tail_page, *commit_page;
struct ring_buffer_event *event;
unsigned long tail, write;
commit_page = cpu_buffer->commit_page;
/* we just need to protect against interrupts */
barrier();
tail_page = cpu_buffer->tail_page;
write = local_add_return(length, &tail_page->write);
/* set write to only the index of the write */
write &= RB_WRITE_MASK;
tail = write - length;
/* See if we shot pass the end of this buffer page */
if (write > BUF_PAGE_SIZE)
return rb_move_tail(cpu_buffer, length, tail,
commit_page, tail_page, ts);
/* We reserved something on the buffer */
event = __rb_page_index(tail_page, tail);
kmemcheck_annotate_bitfield(event, bitfield);
rb_update_event(event, type, length);
/* The passed in type is zero for DATA */
if (likely(!type))
local_inc(&tail_page->entries);
/*
* If this is the first commit on the page, then update
* its timestamp.
*/
if (!tail)
tail_page->page->time_stamp = *ts;
return event;
}
static inline int
rb_try_to_discard(struct ring_buffer_per_cpu *cpu_buffer,
struct ring_buffer_event *event)
{
unsigned long new_index, old_index;
struct buffer_page *bpage;
unsigned long index;
unsigned long addr;
new_index = rb_event_index(event);
old_index = new_index + rb_event_length(event);
addr = (unsigned long)event;
addr &= PAGE_MASK;
bpage = cpu_buffer->tail_page;
if (bpage->page == (void *)addr && rb_page_write(bpage) == old_index) {
unsigned long write_mask =
local_read(&bpage->write) & ~RB_WRITE_MASK;
/*
* This is on the tail page. It is possible that
* a write could come in and move the tail page
* and write to the next page. That is fine
* because we just shorten what is on this page.
*/
old_index += write_mask;
new_index += write_mask;
index = local_cmpxchg(&bpage->write, old_index, new_index);
if (index == old_index)
return 1;
}
/* could not discard */
return 0;
}
static int
rb_add_time_stamp(struct ring_buffer_per_cpu *cpu_buffer,
u64 *ts, u64 *delta)
{
struct ring_buffer_event *event;
static int once;
int ret;
if (unlikely(*delta > (1ULL << 59) && !once++)) {
printk(KERN_WARNING "Delta way too big! %llu"
" ts=%llu write stamp = %llu\n",
(unsigned long long)*delta,
(unsigned long long)*ts,
(unsigned long long)cpu_buffer->write_stamp);
WARN_ON(1);
}
/*
* The delta is too big, we to add a
* new timestamp.
*/
event = __rb_reserve_next(cpu_buffer,
RINGBUF_TYPE_TIME_EXTEND,
RB_LEN_TIME_EXTEND,
ts);
if (!event)
return -EBUSY;
if (PTR_ERR(event) == -EAGAIN)
return -EAGAIN;
/* Only a commited time event can update the write stamp */
if (rb_event_is_commit(cpu_buffer, event)) {
/*
* If this is the first on the page, then it was
* updated with the page itself. Try to discard it
* and if we can't just make it zero.
*/
if (rb_event_index(event)) {
event->time_delta = *delta & TS_MASK;
event->array[0] = *delta >> TS_SHIFT;
} else {
/* try to discard, since we do not need this */
if (!rb_try_to_discard(cpu_buffer, event)) {
/* nope, just zero it */
event->time_delta = 0;
event->array[0] = 0;
}
}
cpu_buffer->write_stamp = *ts;
/* let the caller know this was the commit */
ret = 1;
} else {
/* Try to discard the event */
if (!rb_try_to_discard(cpu_buffer, event)) {
/* Darn, this is just wasted space */
event->time_delta = 0;
event->array[0] = 0;
}
ret = 0;
}
*delta = 0;
return ret;
}
static void rb_start_commit(struct ring_buffer_per_cpu *cpu_buffer)
{
local_inc(&cpu_buffer->committing);
local_inc(&cpu_buffer->commits);
}
static void rb_end_commit(struct ring_buffer_per_cpu *cpu_buffer)
{
unsigned long commits;
if (RB_WARN_ON(cpu_buffer,
!local_read(&cpu_buffer->committing)))
return;
again:
commits = local_read(&cpu_buffer->commits);
/* synchronize with interrupts */
barrier();
if (local_read(&cpu_buffer->committing) == 1)
rb_set_commit_to_write(cpu_buffer);
local_dec(&cpu_buffer->committing);
/* synchronize with interrupts */
barrier();
/*
* Need to account for interrupts coming in between the
* updating of the commit page and the clearing of the
* committing counter.
*/
if (unlikely(local_read(&cpu_buffer->commits) != commits) &&
!local_read(&cpu_buffer->committing)) {
local_inc(&cpu_buffer->committing);
goto again;
}
}
static struct ring_buffer_event *
rb_reserve_next_event(struct ring_buffer *buffer,
struct ring_buffer_per_cpu *cpu_buffer,
unsigned long length)
{
struct ring_buffer_event *event;
u64 ts, delta = 0;
int commit = 0;
int nr_loops = 0;
rb_start_commit(cpu_buffer);
#ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
/*
* Due to the ability to swap a cpu buffer from a buffer
* it is possible it was swapped before we committed.
* (committing stops a swap). We check for it here and
* if it happened, we have to fail the write.
*/
barrier();
if (unlikely(ACCESS_ONCE(cpu_buffer->buffer) != buffer)) {
local_dec(&cpu_buffer->committing);
local_dec(&cpu_buffer->commits);
return NULL;
}
#endif
length = rb_calculate_event_length(length);
again:
/*
* We allow for interrupts to reenter here and do a trace.
* If one does, it will cause this original code to loop
* back here. Even with heavy interrupts happening, this
* should only happen a few times in a row. If this happens
* 1000 times in a row, there must be either an interrupt
* storm or we have something buggy.
* Bail!
*/
if (RB_WARN_ON(cpu_buffer, ++nr_loops > 1000))
goto out_fail;
ts = rb_time_stamp(cpu_buffer->buffer);
/*
* Only the first commit can update the timestamp.
* Yes there is a race here. If an interrupt comes in
* just after the conditional and it traces too, then it
* will also check the deltas. More than one timestamp may
* also be made. But only the entry that did the actual
* commit will be something other than zero.
*/
if (likely(cpu_buffer->tail_page == cpu_buffer->commit_page &&
rb_page_write(cpu_buffer->tail_page) ==
rb_commit_index(cpu_buffer))) {
u64 diff;
diff = ts - cpu_buffer->write_stamp;
/* make sure this diff is calculated here */
barrier();
/* Did the write stamp get updated already? */
if (unlikely(ts < cpu_buffer->write_stamp))
goto get_event;
delta = diff;
if (unlikely(test_time_stamp(delta))) {
commit = rb_add_time_stamp(cpu_buffer, &ts, &delta);
if (commit == -EBUSY)
goto out_fail;
if (commit == -EAGAIN)
goto again;
RB_WARN_ON(cpu_buffer, commit < 0);
}
}
get_event:
event = __rb_reserve_next(cpu_buffer, 0, length, &ts);
if (unlikely(PTR_ERR(event) == -EAGAIN))
goto again;
if (!event)
goto out_fail;
if (!rb_event_is_commit(cpu_buffer, event))
delta = 0;
event->time_delta = delta;
return event;
out_fail:
rb_end_commit(cpu_buffer);
return NULL;
}
#ifdef CONFIG_TRACING
#define TRACE_RECURSIVE_DEPTH 16
static int trace_recursive_lock(void)
{
current->trace_recursion++;
if (likely(current->trace_recursion < TRACE_RECURSIVE_DEPTH))
return 0;
/* Disable all tracing before we do anything else */
tracing_off_permanent();
printk_once(KERN_WARNING "Tracing recursion: depth[%ld]:"
"HC[%lu]:SC[%lu]:NMI[%lu]\n",
current->trace_recursion,
hardirq_count() >> HARDIRQ_SHIFT,
softirq_count() >> SOFTIRQ_SHIFT,
in_nmi());
WARN_ON_ONCE(1);
return -1;
}
static void trace_recursive_unlock(void)
{
WARN_ON_ONCE(!current->trace_recursion);
current->trace_recursion--;
}
#else
#define trace_recursive_lock() (0)
#define trace_recursive_unlock() do { } while (0)
#endif
static DEFINE_PER_CPU(int, rb_need_resched);
/**
* ring_buffer_lock_reserve - reserve a part of the buffer
* @buffer: the ring buffer to reserve from
* @length: the length of the data to reserve (excluding event header)
*
* Returns a reseverd event on the ring buffer to copy directly to.
* The user of this interface will need to get the body to write into
* and can use the ring_buffer_event_data() interface.
*
* The length is the length of the data needed, not the event length
* which also includes the event header.
*
* Must be paired with ring_buffer_unlock_commit, unless NULL is returned.
* If NULL is returned, then nothing has been allocated or locked.
*/
struct ring_buffer_event *
ring_buffer_lock_reserve(struct ring_buffer *buffer, unsigned long length)
{
struct ring_buffer_per_cpu *cpu_buffer;
struct ring_buffer_event *event;
int cpu, resched;
if (ring_buffer_flags != RB_BUFFERS_ON)
return NULL;
if (atomic_read(&buffer->record_disabled))
return NULL;
/* If we are tracing schedule, we don't want to recurse */
resched = ftrace_preempt_disable();
if (trace_recursive_lock())
goto out_nocheck;
cpu = raw_smp_processor_id();
if (!cpumask_test_cpu(cpu, buffer->cpumask))
goto out;
cpu_buffer = buffer->buffers[cpu];
if (atomic_read(&cpu_buffer->record_disabled))
goto out;
if (length > BUF_MAX_DATA_SIZE)
goto out;
event = rb_reserve_next_event(buffer, cpu_buffer, length);
if (!event)
goto out;
/*
* Need to store resched state on this cpu.
* Only the first needs to.
*/
if (preempt_count() == 1)
per_cpu(rb_need_resched, cpu) = resched;
return event;
out:
trace_recursive_unlock();
out_nocheck:
ftrace_preempt_enable(resched);
return NULL;
}
EXPORT_SYMBOL_GPL(ring_buffer_lock_reserve);
static void
rb_update_write_stamp(struct ring_buffer_per_cpu *cpu_buffer,
struct ring_buffer_event *event)
{
/*
* The event first in the commit queue updates the
* time stamp.
*/
if (rb_event_is_commit(cpu_buffer, event))
cpu_buffer->write_stamp += event->time_delta;
}
static void rb_commit(struct ring_buffer_per_cpu *cpu_buffer,
struct ring_buffer_event *event)
{
local_inc(&cpu_buffer->entries);
rb_update_write_stamp(cpu_buffer, event);
rb_end_commit(cpu_buffer);
}
/**
* ring_buffer_unlock_commit - commit a reserved
* @buffer: The buffer to commit to
* @event: The event pointer to commit.
*
* This commits the data to the ring buffer, and releases any locks held.
*
* Must be paired with ring_buffer_lock_reserve.
*/
int ring_buffer_unlock_commit(struct ring_buffer *buffer,
struct ring_buffer_event *event)
{
struct ring_buffer_per_cpu *cpu_buffer;
int cpu = raw_smp_processor_id();
cpu_buffer = buffer->buffers[cpu];
rb_commit(cpu_buffer, event);
trace_recursive_unlock();
/*
* Only the last preempt count needs to restore preemption.
*/
if (preempt_count() == 1)
ftrace_preempt_enable(per_cpu(rb_need_resched, cpu));
else
preempt_enable_no_resched_notrace();
return 0;
}
EXPORT_SYMBOL_GPL(ring_buffer_unlock_commit);
static inline void rb_event_discard(struct ring_buffer_event *event)
{
/* array[0] holds the actual length for the discarded event */
event->array[0] = rb_event_data_length(event) - RB_EVNT_HDR_SIZE;
event->type_len = RINGBUF_TYPE_PADDING;
/* time delta must be non zero */
if (!event->time_delta)
event->time_delta = 1;
}
/*
* Decrement the entries to the page that an event is on.
* The event does not even need to exist, only the pointer
* to the page it is on. This may only be called before the commit
* takes place.
*/
static inline void
rb_decrement_entry(struct ring_buffer_per_cpu *cpu_buffer,
struct ring_buffer_event *event)
{
unsigned long addr = (unsigned long)event;
struct buffer_page *bpage = cpu_buffer->commit_page;
struct buffer_page *start;
addr &= PAGE_MASK;
/* Do the likely case first */
if (likely(bpage->page == (void *)addr)) {
local_dec(&bpage->entries);
return;
}
/*
* Because the commit page may be on the reader page we
* start with the next page and check the end loop there.
*/
rb_inc_page(cpu_buffer, &bpage);
start = bpage;
do {
if (bpage->page == (void *)addr) {
local_dec(&bpage->entries);
return;
}
rb_inc_page(cpu_buffer, &bpage);
} while (bpage != start);
/* commit not part of this buffer?? */
RB_WARN_ON(cpu_buffer, 1);
}
/**
* ring_buffer_commit_discard - discard an event that has not been committed
* @buffer: the ring buffer
* @event: non committed event to discard
*
* Sometimes an event that is in the ring buffer needs to be ignored.
* This function lets the user discard an event in the ring buffer
* and then that event will not be read later.
*
* This function only works if it is called before the the item has been
* committed. It will try to free the event from the ring buffer
* if another event has not been added behind it.
*
* If another event has been added behind it, it will set the event
* up as discarded, and perform the commit.
*
* If this function is called, do not call ring_buffer_unlock_commit on
* the event.
*/
void ring_buffer_discard_commit(struct ring_buffer *buffer,
struct ring_buffer_event *event)
{
struct ring_buffer_per_cpu *cpu_buffer;
int cpu;
/* The event is discarded regardless */
rb_event_discard(event);
cpu = smp_processor_id();
cpu_buffer = buffer->buffers[cpu];
/*
* This must only be called if the event has not been
* committed yet. Thus we can assume that preemption
* is still disabled.
*/
RB_WARN_ON(buffer, !local_read(&cpu_buffer->committing));
rb_decrement_entry(cpu_buffer, event);
if (rb_try_to_discard(cpu_buffer, event))
goto out;
/*
* The commit is still visible by the reader, so we
* must still update the timestamp.
*/
rb_update_write_stamp(cpu_buffer, event);
out:
rb_end_commit(cpu_buffer);
trace_recursive_unlock();
/*
* Only the last preempt count needs to restore preemption.
*/
if (preempt_count() == 1)
ftrace_preempt_enable(per_cpu(rb_need_resched, cpu));
else
preempt_enable_no_resched_notrace();
}
EXPORT_SYMBOL_GPL(ring_buffer_discard_commit);
/**
* ring_buffer_write - write data to the buffer without reserving
* @buffer: The ring buffer to write to.
* @length: The length of the data being written (excluding the event header)
* @data: The data to write to the buffer.
*
* This is like ring_buffer_lock_reserve and ring_buffer_unlock_commit as
* one function. If you already have the data to write to the buffer, it
* may be easier to simply call this function.
*
* Note, like ring_buffer_lock_reserve, the length is the length of the data
* and not the length of the event which would hold the header.
*/
int ring_buffer_write(struct ring_buffer *buffer,
unsigned long length,
void *data)
{
struct ring_buffer_per_cpu *cpu_buffer;
struct ring_buffer_event *event;
void *body;
int ret = -EBUSY;
int cpu, resched;
if (ring_buffer_flags != RB_BUFFERS_ON)
return -EBUSY;
if (atomic_read(&buffer->record_disabled))
return -EBUSY;
resched = ftrace_preempt_disable();
cpu = raw_smp_processor_id();
if (!cpumask_test_cpu(cpu, buffer->cpumask))
goto out;
cpu_buffer = buffer->buffers[cpu];
if (atomic_read(&cpu_buffer->record_disabled))
goto out;
if (length > BUF_MAX_DATA_SIZE)
goto out;
event = rb_reserve_next_event(buffer, cpu_buffer, length);
if (!event)
goto out;
body = rb_event_data(event);
memcpy(body, data, length);
rb_commit(cpu_buffer, event);
ret = 0;
out:
ftrace_preempt_enable(resched);
return ret;
}
EXPORT_SYMBOL_GPL(ring_buffer_write);
static int rb_per_cpu_empty(struct ring_buffer_per_cpu *cpu_buffer)
{
struct buffer_page *reader = cpu_buffer->reader_page;
struct buffer_page *head = rb_set_head_page(cpu_buffer);
struct buffer_page *commit = cpu_buffer->commit_page;
/* In case of error, head will be NULL */
if (unlikely(!head))
return 1;
return reader->read == rb_page_commit(reader) &&
(commit == reader ||
(commit == head &&
head->read == rb_page_commit(commit)));
}
/**
* ring_buffer_record_disable - stop all writes into the buffer
* @buffer: The ring buffer to stop writes to.
*
* This prevents all writes to the buffer. Any attempt to write
* to the buffer after this will fail and return NULL.
*
* The caller should call synchronize_sched() after this.
*/
void ring_buffer_record_disable(struct ring_buffer *buffer)
{
atomic_inc(&buffer->record_disabled);
}
EXPORT_SYMBOL_GPL(ring_buffer_record_disable);
/**
* ring_buffer_record_enable - enable writes to the buffer
* @buffer: The ring buffer to enable writes
*
* Note, multiple disables will need the same number of enables
* to truely enable the writing (much like preempt_disable).
*/
void ring_buffer_record_enable(struct ring_buffer *buffer)
{
atomic_dec(&buffer->record_disabled);
}
EXPORT_SYMBOL_GPL(ring_buffer_record_enable);
/**
* ring_buffer_record_disable_cpu - stop all writes into the cpu_buffer
* @buffer: The ring buffer to stop writes to.
* @cpu: The CPU buffer to stop
*
* This prevents all writes to the buffer. Any attempt to write
* to the buffer after this will fail and return NULL.
*
* The caller should call synchronize_sched() after this.
*/
void ring_buffer_record_disable_cpu(struct ring_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return;
cpu_buffer = buffer->buffers[cpu];
atomic_inc(&cpu_buffer->record_disabled);
}
EXPORT_SYMBOL_GPL(ring_buffer_record_disable_cpu);
/**
* ring_buffer_record_enable_cpu - enable writes to the buffer
* @buffer: The ring buffer to enable writes
* @cpu: The CPU to enable.
*
* Note, multiple disables will need the same number of enables
* to truely enable the writing (much like preempt_disable).
*/
void ring_buffer_record_enable_cpu(struct ring_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return;
cpu_buffer = buffer->buffers[cpu];
atomic_dec(&cpu_buffer->record_disabled);
}
EXPORT_SYMBOL_GPL(ring_buffer_record_enable_cpu);
/**
* ring_buffer_entries_cpu - get the number of entries in a cpu buffer
* @buffer: The ring buffer
* @cpu: The per CPU buffer to get the entries from.
*/
unsigned long ring_buffer_entries_cpu(struct ring_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;
unsigned long ret;
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return 0;
cpu_buffer = buffer->buffers[cpu];
ret = (local_read(&cpu_buffer->entries) - local_read(&cpu_buffer->overrun))
- cpu_buffer->read;
return ret;
}
EXPORT_SYMBOL_GPL(ring_buffer_entries_cpu);
/**
* ring_buffer_overrun_cpu - get the number of overruns in a cpu_buffer
* @buffer: The ring buffer
* @cpu: The per CPU buffer to get the number of overruns from
*/
unsigned long ring_buffer_overrun_cpu(struct ring_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;
unsigned long ret;
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return 0;
cpu_buffer = buffer->buffers[cpu];
ret = local_read(&cpu_buffer->overrun);
return ret;
}
EXPORT_SYMBOL_GPL(ring_buffer_overrun_cpu);
/**
* ring_buffer_commit_overrun_cpu - get the number of overruns caused by commits
* @buffer: The ring buffer
* @cpu: The per CPU buffer to get the number of overruns from
*/
unsigned long
ring_buffer_commit_overrun_cpu(struct ring_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;
unsigned long ret;
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return 0;
cpu_buffer = buffer->buffers[cpu];
ret = local_read(&cpu_buffer->commit_overrun);
return ret;
}
EXPORT_SYMBOL_GPL(ring_buffer_commit_overrun_cpu);
/**
* ring_buffer_entries - get the number of entries in a buffer
* @buffer: The ring buffer
*
* Returns the total number of entries in the ring buffer
* (all CPU entries)
*/
unsigned long ring_buffer_entries(struct ring_buffer *buffer)
{
struct ring_buffer_per_cpu *cpu_buffer;
unsigned long entries = 0;
int cpu;
/* if you care about this being correct, lock the buffer */
for_each_buffer_cpu(buffer, cpu) {
cpu_buffer = buffer->buffers[cpu];
entries += (local_read(&cpu_buffer->entries) -
local_read(&cpu_buffer->overrun)) - cpu_buffer->read;
}
return entries;
}
EXPORT_SYMBOL_GPL(ring_buffer_entries);
/**
* ring_buffer_overruns - get the number of overruns in buffer
* @buffer: The ring buffer
*
* Returns the total number of overruns in the ring buffer
* (all CPU entries)
*/
unsigned long ring_buffer_overruns(struct ring_buffer *buffer)
{
struct ring_buffer_per_cpu *cpu_buffer;
unsigned long overruns = 0;
int cpu;
/* if you care about this being correct, lock the buffer */
for_each_buffer_cpu(buffer, cpu) {
cpu_buffer = buffer->buffers[cpu];
overruns += local_read(&cpu_buffer->overrun);
}
return overruns;
}
EXPORT_SYMBOL_GPL(ring_buffer_overruns);
static void rb_iter_reset(struct ring_buffer_iter *iter)
{
struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
/* Iterator usage is expected to have record disabled */
if (list_empty(&cpu_buffer->reader_page->list)) {
iter->head_page = rb_set_head_page(cpu_buffer);
if (unlikely(!iter->head_page))
return;
iter->head = iter->head_page->read;
} else {
iter->head_page = cpu_buffer->reader_page;
iter->head = cpu_buffer->reader_page->read;
}
if (iter->head)
iter->read_stamp = cpu_buffer->read_stamp;
else
iter->read_stamp = iter->head_page->page->time_stamp;
}
/**
* ring_buffer_iter_reset - reset an iterator
* @iter: The iterator to reset
*
* Resets the iterator, so that it will start from the beginning
* again.
*/
void ring_buffer_iter_reset(struct ring_buffer_iter *iter)
{
struct ring_buffer_per_cpu *cpu_buffer;
unsigned long flags;
if (!iter)
return;
cpu_buffer = iter->cpu_buffer;
spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
rb_iter_reset(iter);
spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
}
EXPORT_SYMBOL_GPL(ring_buffer_iter_reset);
/**
* ring_buffer_iter_empty - check if an iterator has no more to read
* @iter: The iterator to check
*/
int ring_buffer_iter_empty(struct ring_buffer_iter *iter)
{
struct ring_buffer_per_cpu *cpu_buffer;
cpu_buffer = iter->cpu_buffer;
return iter->head_page == cpu_buffer->commit_page &&
iter->head == rb_commit_index(cpu_buffer);
}
EXPORT_SYMBOL_GPL(ring_buffer_iter_empty);
static void
rb_update_read_stamp(struct ring_buffer_per_cpu *cpu_buffer,
struct ring_buffer_event *event)
{
u64 delta;
switch (event->type_len) {
case RINGBUF_TYPE_PADDING:
return;
case RINGBUF_TYPE_TIME_EXTEND:
delta = event->array[0];
delta <<= TS_SHIFT;
delta += event->time_delta;
cpu_buffer->read_stamp += delta;
return;
case RINGBUF_TYPE_TIME_STAMP:
/* FIXME: not implemented */
return;
case RINGBUF_TYPE_DATA:
cpu_buffer->read_stamp += event->time_delta;
return;
default:
BUG();
}
return;
}
static void
rb_update_iter_read_stamp(struct ring_buffer_iter *iter,
struct ring_buffer_event *event)
{
u64 delta;
switch (event->type_len) {
case RINGBUF_TYPE_PADDING:
return;
case RINGBUF_TYPE_TIME_EXTEND:
delta = event->array[0];
delta <<= TS_SHIFT;
delta += event->time_delta;
iter->read_stamp += delta;
return;
case RINGBUF_TYPE_TIME_STAMP:
/* FIXME: not implemented */
return;
case RINGBUF_TYPE_DATA:
iter->read_stamp += event->time_delta;
return;
default:
BUG();
}
return;
}
static struct buffer_page *
rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
{
struct buffer_page *reader = NULL;
unsigned long flags;
int nr_loops = 0;
int ret;
local_irq_save(flags);
__raw_spin_lock(&cpu_buffer->lock);
again:
/*
* This should normally only loop twice. But because the
* start of the reader inserts an empty page, it causes
* a case where we will loop three times. There should be no
* reason to loop four times (that I know of).
*/
if (RB_WARN_ON(cpu_buffer, ++nr_loops > 3)) {
reader = NULL;
goto out;
}
reader = cpu_buffer->reader_page;
/* If there's more to read, return this page */
if (cpu_buffer->reader_page->read < rb_page_size(reader))
goto out;
/* Never should we have an index greater than the size */
if (RB_WARN_ON(cpu_buffer,
cpu_buffer->reader_page->read > rb_page_size(reader)))
goto out;
/* check if we caught up to the tail */
reader = NULL;
if (cpu_buffer->commit_page == cpu_buffer->reader_page)
goto out;
/*
* Reset the reader page to size zero.
*/
local_set(&cpu_buffer->reader_page->write, 0);
local_set(&cpu_buffer->reader_page->entries, 0);
local_set(&cpu_buffer->reader_page->page->commit, 0);
spin:
/*
* Splice the empty reader page into the list around the head.
*/
reader = rb_set_head_page(cpu_buffer);
cpu_buffer->reader_page->list.next = reader->list.next;
cpu_buffer->reader_page->list.prev = reader->list.prev;
/*
* cpu_buffer->pages just needs to point to the buffer, it
* has no specific buffer page to point to. Lets move it out
* of our way so we don't accidently swap it.
*/
cpu_buffer->pages = reader->list.prev;
/* The reader page will be pointing to the new head */
rb_set_list_to_head(cpu_buffer, &cpu_buffer->reader_page->list);
/*
* Here's the tricky part.
*
* We need to move the pointer past the header page.
* But we can only do that if a writer is not currently
* moving it. The page before the header page has the
* flag bit '1' set if it is pointing to the page we want.
* but if the writer is in the process of moving it
* than it will be '2' or already moved '0'.
*/
ret = rb_head_page_replace(reader, cpu_buffer->reader_page);
/*
* If we did not convert it, then we must try again.
*/
if (!ret)
goto spin;
/*
* Yeah! We succeeded in replacing the page.
*
* Now make the new head point back to the reader page.
*/
reader->list.next->prev = &cpu_buffer->reader_page->list;
rb_inc_page(cpu_buffer, &cpu_buffer->head_page);
/* Finally update the reader page to the new head */
cpu_buffer->reader_page = reader;
rb_reset_reader_page(cpu_buffer);
goto again;
out:
__raw_spin_unlock(&cpu_buffer->lock);
local_irq_restore(flags);
return reader;
}
static void rb_advance_reader(struct ring_buffer_per_cpu *cpu_buffer)
{
struct ring_buffer_event *event;
struct buffer_page *reader;
unsigned length;
reader = rb_get_reader_page(cpu_buffer);
/* This function should not be called when buffer is empty */
if (RB_WARN_ON(cpu_buffer, !reader))
return;
event = rb_reader_event(cpu_buffer);
if (event->type_len <= RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
cpu_buffer->read++;
rb_update_read_stamp(cpu_buffer, event);
length = rb_event_length(event);
cpu_buffer->reader_page->read += length;
}
static void rb_advance_iter(struct ring_buffer_iter *iter)
{
struct ring_buffer *buffer;
struct ring_buffer_per_cpu *cpu_buffer;
struct ring_buffer_event *event;
unsigned length;
cpu_buffer = iter->cpu_buffer;
buffer = cpu_buffer->buffer;
/*
* Check if we are at the end of the buffer.
*/
if (iter->head >= rb_page_size(iter->head_page)) {
/* discarded commits can make the page empty */
if (iter->head_page == cpu_buffer->commit_page)
return;
rb_inc_iter(iter);
return;
}
event = rb_iter_head_event(iter);
length = rb_event_length(event);
/*
* This should not be called to advance the header if we are
* at the tail of the buffer.
*/
if (RB_WARN_ON(cpu_buffer,
(iter->head_page == cpu_buffer->commit_page) &&
(iter->head + length > rb_commit_index(cpu_buffer))))
return;
rb_update_iter_read_stamp(iter, event);
iter->head += length;
/* check for end of page padding */
if ((iter->head >= rb_page_size(iter->head_page)) &&
(iter->head_page != cpu_buffer->commit_page))
rb_advance_iter(iter);
}
static struct ring_buffer_event *
rb_buffer_peek(struct ring_buffer_per_cpu *cpu_buffer, u64 *ts)
{
struct ring_buffer_event *event;
struct buffer_page *reader;
int nr_loops = 0;
again:
/*
* We repeat when a timestamp is encountered. It is possible
* to get multiple timestamps from an interrupt entering just
* as one timestamp is about to be written, or from discarded
* commits. The most that we can have is the number on a single page.
*/
if (RB_WARN_ON(cpu_buffer, ++nr_loops > RB_TIMESTAMPS_PER_PAGE))
return NULL;
reader = rb_get_reader_page(cpu_buffer);
if (!reader)
return NULL;
event = rb_reader_event(cpu_buffer);
switch (event->type_len) {
case RINGBUF_TYPE_PADDING:
if (rb_null_event(event))
RB_WARN_ON(cpu_buffer, 1);
/*
* Because the writer could be discarding every
* event it creates (which would probably be bad)
* if we were to go back to "again" then we may never
* catch up, and will trigger the warn on, or lock
* the box. Return the padding, and we will release
* the current locks, and try again.
*/
return event;
case RINGBUF_TYPE_TIME_EXTEND:
/* Internal data, OK to advance */
rb_advance_reader(cpu_buffer);
goto again;
case RINGBUF_TYPE_TIME_STAMP:
/* FIXME: not implemented */
rb_advance_reader(cpu_buffer);
goto again;
case RINGBUF_TYPE_DATA:
if (ts) {
*ts = cpu_buffer->read_stamp + event->time_delta;
ring_buffer_normalize_time_stamp(cpu_buffer->buffer,
cpu_buffer->cpu, ts);
}
return event;
default:
BUG();
}
return NULL;
}
EXPORT_SYMBOL_GPL(ring_buffer_peek);
static struct ring_buffer_event *
rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
{
struct ring_buffer *buffer;
struct ring_buffer_per_cpu *cpu_buffer;
struct ring_buffer_event *event;
int nr_loops = 0;
if (ring_buffer_iter_empty(iter))
return NULL;
cpu_buffer = iter->cpu_buffer;
buffer = cpu_buffer->buffer;
again:
/*
* We repeat when a timestamp is encountered.
* We can get multiple timestamps by nested interrupts or also
* if filtering is on (discarding commits). Since discarding
* commits can be frequent we can get a lot of timestamps.
* But we limit them by not adding timestamps if they begin
* at the start of a page.
*/
if (RB_WARN_ON(cpu_buffer, ++nr_loops > RB_TIMESTAMPS_PER_PAGE))
return NULL;
if (rb_per_cpu_empty(cpu_buffer))
return NULL;
event = rb_iter_head_event(iter);
switch (event->type_len) {
case RINGBUF_TYPE_PADDING:
if (rb_null_event(event)) {
rb_inc_iter(iter);
goto again;
}
rb_advance_iter(iter);
return event;
case RINGBUF_TYPE_TIME_EXTEND:
/* Internal data, OK to advance */
rb_advance_iter(iter);
goto again;
case RINGBUF_TYPE_TIME_STAMP:
/* FIXME: not implemented */
rb_advance_iter(iter);
goto again;
case RINGBUF_TYPE_DATA:
if (ts) {
*ts = iter->read_stamp + event->time_delta;
ring_buffer_normalize_time_stamp(buffer,
cpu_buffer->cpu, ts);
}
return event;
default:
BUG();
}
return NULL;
}
EXPORT_SYMBOL_GPL(ring_buffer_iter_peek);
static inline int rb_ok_to_lock(void)
{
/*
* If an NMI die dumps out the content of the ring buffer
* do not grab locks. We also permanently disable the ring
* buffer too. A one time deal is all you get from reading
* the ring buffer from an NMI.
*/
if (likely(!in_nmi()))
return 1;
tracing_off_permanent();
return 0;
}
/**
* ring_buffer_peek - peek at the next event to be read
* @buffer: The ring buffer to read
* @cpu: The cpu to peak at
* @ts: The timestamp counter of this event.
*
* This will return the event that will be read next, but does
* not consume the data.
*/
struct ring_buffer_event *
ring_buffer_peek(struct ring_buffer *buffer, int cpu, u64 *ts)
{
struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
struct ring_buffer_event *event;
unsigned long flags;
int dolock;
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return NULL;
dolock = rb_ok_to_lock();
again:
local_irq_save(flags);
if (dolock)
spin_lock(&cpu_buffer->reader_lock);
event = rb_buffer_peek(cpu_buffer, ts);
if (event && event->type_len == RINGBUF_TYPE_PADDING)
rb_advance_reader(cpu_buffer);
if (dolock)
spin_unlock(&cpu_buffer->reader_lock);
local_irq_restore(flags);
if (event && event->type_len == RINGBUF_TYPE_PADDING)
goto again;
return event;
}
/**
* ring_buffer_iter_peek - peek at the next event to be read
* @iter: The ring buffer iterator
* @ts: The timestamp counter of this event.
*
* This will return the event that will be read next, but does
* not increment the iterator.
*/
struct ring_buffer_event *
ring_buffer_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
{
struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
struct ring_buffer_event *event;
unsigned long flags;
again:
spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
event = rb_iter_peek(iter, ts);
spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
if (event && event->type_len == RINGBUF_TYPE_PADDING)
goto again;
return event;
}
/**
* ring_buffer_consume - return an event and consume it
* @buffer: The ring buffer to get the next event from
*
* Returns the next event in the ring buffer, and that event is consumed.
* Meaning, that sequential reads will keep returning a different event,
* and eventually empty the ring buffer if the producer is slower.
*/
struct ring_buffer_event *
ring_buffer_consume(struct ring_buffer *buffer, int cpu, u64 *ts)
{
struct ring_buffer_per_cpu *cpu_buffer;
struct ring_buffer_event *event = NULL;
unsigned long flags;
int dolock;
dolock = rb_ok_to_lock();
again:
/* might be called in atomic */
preempt_disable();
if (!cpumask_test_cpu(cpu, buffer->cpumask))
goto out;
cpu_buffer = buffer->buffers[cpu];
local_irq_save(flags);
if (dolock)
spin_lock(&cpu_buffer->reader_lock);
event = rb_buffer_peek(cpu_buffer, ts);
if (event)
rb_advance_reader(cpu_buffer);
if (dolock)
spin_unlock(&cpu_buffer->reader_lock);
local_irq_restore(flags);
out:
preempt_enable();
if (event && event->type_len == RINGBUF_TYPE_PADDING)
goto again;
return event;
}
EXPORT_SYMBOL_GPL(ring_buffer_consume);
/**
* ring_buffer_read_start - start a non consuming read of the buffer
* @buffer: The ring buffer to read from
* @cpu: The cpu buffer to iterate over
*
* This starts up an iteration through the buffer. It also disables
* the recording to the buffer until the reading is finished.
* This prevents the reading from being corrupted. This is not
* a consuming read, so a producer is not expected.
*
* Must be paired with ring_buffer_finish.
*/
struct ring_buffer_iter *
ring_buffer_read_start(struct ring_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;
struct ring_buffer_iter *iter;
unsigned long flags;
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return NULL;
iter = kmalloc(sizeof(*iter), GFP_KERNEL);
if (!iter)
return NULL;
cpu_buffer = buffer->buffers[cpu];
iter->cpu_buffer = cpu_buffer;
atomic_inc(&cpu_buffer->record_disabled);
synchronize_sched();
spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
__raw_spin_lock(&cpu_buffer->lock);
rb_iter_reset(iter);
__raw_spin_unlock(&cpu_buffer->lock);
spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
return iter;
}
EXPORT_SYMBOL_GPL(ring_buffer_read_start);
/**
* ring_buffer_finish - finish reading the iterator of the buffer
* @iter: The iterator retrieved by ring_buffer_start
*
* This re-enables the recording to the buffer, and frees the
* iterator.
*/
void
ring_buffer_read_finish(struct ring_buffer_iter *iter)
{
struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
atomic_dec(&cpu_buffer->record_disabled);
kfree(iter);
}
EXPORT_SYMBOL_GPL(ring_buffer_read_finish);
/**
* ring_buffer_read - read the next item in the ring buffer by the iterator
* @iter: The ring buffer iterator
* @ts: The time stamp of the event read.
*
* This reads the next event in the ring buffer and increments the iterator.
*/
struct ring_buffer_event *
ring_buffer_read(struct ring_buffer_iter *iter, u64 *ts)
{
struct ring_buffer_event *event;
struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
unsigned long flags;
spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
again:
event = rb_iter_peek(iter, ts);
if (!event)
goto out;
if (event->type_len == RINGBUF_TYPE_PADDING)
goto again;
rb_advance_iter(iter);
out:
spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
return event;
}
EXPORT_SYMBOL_GPL(ring_buffer_read);
/**
* ring_buffer_size - return the size of the ring buffer (in bytes)
* @buffer: The ring buffer.
*/
unsigned long ring_buffer_size(struct ring_buffer *buffer)
{
return BUF_PAGE_SIZE * buffer->pages;
}
EXPORT_SYMBOL_GPL(ring_buffer_size);
static void
rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
{
rb_head_page_deactivate(cpu_buffer);
cpu_buffer->head_page
= list_entry(cpu_buffer->pages, struct buffer_page, list);
local_set(&cpu_buffer->head_page->write, 0);
local_set(&cpu_buffer->head_page->entries, 0);
local_set(&cpu_buffer->head_page->page->commit, 0);
cpu_buffer->head_page->read = 0;
cpu_buffer->tail_page = cpu_buffer->head_page;
cpu_buffer->commit_page = cpu_buffer->head_page;
INIT_LIST_HEAD(&cpu_buffer->reader_page->list);
local_set(&cpu_buffer->reader_page->write, 0);
local_set(&cpu_buffer->reader_page->entries, 0);
local_set(&cpu_buffer->reader_page->page->commit, 0);
cpu_buffer->reader_page->read = 0;
local_set(&cpu_buffer->commit_overrun, 0);
local_set(&cpu_buffer->overrun, 0);
local_set(&cpu_buffer->entries, 0);
local_set(&cpu_buffer->committing, 0);
local_set(&cpu_buffer->commits, 0);
cpu_buffer->read = 0;
cpu_buffer->write_stamp = 0;
cpu_buffer->read_stamp = 0;
rb_head_page_activate(cpu_buffer);
}
/**
* ring_buffer_reset_cpu - reset a ring buffer per CPU buffer
* @buffer: The ring buffer to reset a per cpu buffer of
* @cpu: The CPU buffer to be reset
*/
void ring_buffer_reset_cpu(struct ring_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
unsigned long flags;
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return;
atomic_inc(&cpu_buffer->record_disabled);
spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
if (RB_WARN_ON(cpu_buffer, local_read(&cpu_buffer->committing)))
goto out;
__raw_spin_lock(&cpu_buffer->lock);
rb_reset_cpu(cpu_buffer);
__raw_spin_unlock(&cpu_buffer->lock);
out:
spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
atomic_dec(&cpu_buffer->record_disabled);
}
EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu);
/**
* ring_buffer_reset - reset a ring buffer
* @buffer: The ring buffer to reset all cpu buffers
*/
void ring_buffer_reset(struct ring_buffer *buffer)
{
int cpu;
for_each_buffer_cpu(buffer, cpu)
ring_buffer_reset_cpu(buffer, cpu);
}
EXPORT_SYMBOL_GPL(ring_buffer_reset);
/**
* rind_buffer_empty - is the ring buffer empty?
* @buffer: The ring buffer to test
*/
int ring_buffer_empty(struct ring_buffer *buffer)
{
struct ring_buffer_per_cpu *cpu_buffer;
unsigned long flags;
int dolock;
int cpu;
int ret;
dolock = rb_ok_to_lock();
/* yes this is racy, but if you don't like the race, lock the buffer */
for_each_buffer_cpu(buffer, cpu) {
cpu_buffer = buffer->buffers[cpu];
local_irq_save(flags);
if (dolock)
spin_lock(&cpu_buffer->reader_lock);
ret = rb_per_cpu_empty(cpu_buffer);
if (dolock)
spin_unlock(&cpu_buffer->reader_lock);
local_irq_restore(flags);
if (!ret)
return 0;
}
return 1;
}
EXPORT_SYMBOL_GPL(ring_buffer_empty);
/**
* ring_buffer_empty_cpu - is a cpu buffer of a ring buffer empty?
* @buffer: The ring buffer
* @cpu: The CPU buffer to test
*/
int ring_buffer_empty_cpu(struct ring_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;
unsigned long flags;
int dolock;
int ret;
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return 1;
dolock = rb_ok_to_lock();
cpu_buffer = buffer->buffers[cpu];
local_irq_save(flags);
if (dolock)
spin_lock(&cpu_buffer->reader_lock);
ret = rb_per_cpu_empty(cpu_buffer);
if (dolock)
spin_unlock(&cpu_buffer->reader_lock);
local_irq_restore(flags);
return ret;
}
EXPORT_SYMBOL_GPL(ring_buffer_empty_cpu);
#ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
/**
* ring_buffer_swap_cpu - swap a CPU buffer between two ring buffers
* @buffer_a: One buffer to swap with
* @buffer_b: The other buffer to swap with
*
* This function is useful for tracers that want to take a "snapshot"
* of a CPU buffer and has another back up buffer lying around.
* it is expected that the tracer handles the cpu buffer not being
* used at the moment.
*/
int ring_buffer_swap_cpu(struct ring_buffer *buffer_a,
struct ring_buffer *buffer_b, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer_a;
struct ring_buffer_per_cpu *cpu_buffer_b;
int ret = -EINVAL;
if (!cpumask_test_cpu(cpu, buffer_a->cpumask) ||
!cpumask_test_cpu(cpu, buffer_b->cpumask))
goto out;
/* At least make sure the two buffers are somewhat the same */
if (buffer_a->pages != buffer_b->pages)
goto out;
ret = -EAGAIN;
if (ring_buffer_flags != RB_BUFFERS_ON)
goto out;
if (atomic_read(&buffer_a->record_disabled))
goto out;
if (atomic_read(&buffer_b->record_disabled))
goto out;
cpu_buffer_a = buffer_a->buffers[cpu];
cpu_buffer_b = buffer_b->buffers[cpu];
if (atomic_read(&cpu_buffer_a->record_disabled))
goto out;
if (atomic_read(&cpu_buffer_b->record_disabled))
goto out;
/*
* We can't do a synchronize_sched here because this
* function can be called in atomic context.
* Normally this will be called from the same CPU as cpu.
* If not it's up to the caller to protect this.
*/
atomic_inc(&cpu_buffer_a->record_disabled);
atomic_inc(&cpu_buffer_b->record_disabled);
ret = -EBUSY;
if (local_read(&cpu_buffer_a->committing))
goto out_dec;
if (local_read(&cpu_buffer_b->committing))
goto out_dec;
buffer_a->buffers[cpu] = cpu_buffer_b;
buffer_b->buffers[cpu] = cpu_buffer_a;
cpu_buffer_b->buffer = buffer_a;
cpu_buffer_a->buffer = buffer_b;
ret = 0;
out_dec:
atomic_dec(&cpu_buffer_a->record_disabled);
atomic_dec(&cpu_buffer_b->record_disabled);
out:
return ret;
}
EXPORT_SYMBOL_GPL(ring_buffer_swap_cpu);
#endif /* CONFIG_RING_BUFFER_ALLOW_SWAP */
/**
* ring_buffer_alloc_read_page - allocate a page to read from buffer
* @buffer: the buffer to allocate for.
*
* This function is used in conjunction with ring_buffer_read_page.
* When reading a full page from the ring buffer, these functions
* can be used to speed up the process. The calling function should
* allocate a few pages first with this function. Then when it
* needs to get pages from the ring buffer, it passes the result
* of this function into ring_buffer_read_page, which will swap
* the page that was allocated, with the read page of the buffer.
*
* Returns:
* The page allocated, or NULL on error.
*/
void *ring_buffer_alloc_read_page(struct ring_buffer *buffer)
{
struct buffer_data_page *bpage;
unsigned long addr;
addr = __get_free_page(GFP_KERNEL);
if (!addr)
return NULL;
bpage = (void *)addr;
rb_init_page(bpage);
return bpage;
}
EXPORT_SYMBOL_GPL(ring_buffer_alloc_read_page);
/**
* ring_buffer_free_read_page - free an allocated read page
* @buffer: the buffer the page was allocate for
* @data: the page to free
*
* Free a page allocated from ring_buffer_alloc_read_page.
*/
void ring_buffer_free_read_page(struct ring_buffer *buffer, void *data)
{
free_page((unsigned long)data);
}
EXPORT_SYMBOL_GPL(ring_buffer_free_read_page);
/**
* ring_buffer_read_page - extract a page from the ring buffer
* @buffer: buffer to extract from
* @data_page: the page to use allocated from ring_buffer_alloc_read_page
* @len: amount to extract
* @cpu: the cpu of the buffer to extract
* @full: should the extraction only happen when the page is full.
*
* This function will pull out a page from the ring buffer and consume it.
* @data_page must be the address of the variable that was returned
* from ring_buffer_alloc_read_page. This is because the page might be used
* to swap with a page in the ring buffer.
*
* for example:
* rpage = ring_buffer_alloc_read_page(buffer);
* if (!rpage)
* return error;
* ret = ring_buffer_read_page(buffer, &rpage, len, cpu, 0);
* if (ret >= 0)
* process_page(rpage, ret);
*
* When @full is set, the function will not return true unless
* the writer is off the reader page.
*
* Note: it is up to the calling functions to handle sleeps and wakeups.
* The ring buffer can be used anywhere in the kernel and can not
* blindly call wake_up. The layer that uses the ring buffer must be
* responsible for that.
*
* Returns:
* >=0 if data has been transferred, returns the offset of consumed data.
* <0 if no data has been transferred.
*/
int ring_buffer_read_page(struct ring_buffer *buffer,
void **data_page, size_t len, int cpu, int full)
{
struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
struct ring_buffer_event *event;
struct buffer_data_page *bpage;
struct buffer_page *reader;
unsigned long flags;
unsigned int commit;
unsigned int read;
u64 save_timestamp;
int ret = -1;
if (!cpumask_test_cpu(cpu, buffer->cpumask))
goto out;
/*
* If len is not big enough to hold the page header, then
* we can not copy anything.
*/
if (len <= BUF_PAGE_HDR_SIZE)
goto out;
len -= BUF_PAGE_HDR_SIZE;
if (!data_page)
goto out;
bpage = *data_page;
if (!bpage)
goto out;
spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
reader = rb_get_reader_page(cpu_buffer);
if (!reader)
goto out_unlock;
event = rb_reader_event(cpu_buffer);
read = reader->read;
commit = rb_page_commit(reader);
/*
* If this page has been partially read or
* if len is not big enough to read the rest of the page or
* a writer is still on the page, then
* we must copy the data from the page to the buffer.
* Otherwise, we can simply swap the page with the one passed in.
*/
if (read || (len < (commit - read)) ||
cpu_buffer->reader_page == cpu_buffer->commit_page) {
struct buffer_data_page *rpage = cpu_buffer->reader_page->page;
unsigned int rpos = read;
unsigned int pos = 0;
unsigned int size;
if (full)
goto out_unlock;
if (len > (commit - read))
len = (commit - read);
size = rb_event_length(event);
if (len < size)
goto out_unlock;
/* save the current timestamp, since the user will need it */
save_timestamp = cpu_buffer->read_stamp;
/* Need to copy one event at a time */
do {
memcpy(bpage->data + pos, rpage->data + rpos, size);
len -= size;
rb_advance_reader(cpu_buffer);
rpos = reader->read;
pos += size;
event = rb_reader_event(cpu_buffer);
size = rb_event_length(event);
} while (len > size);
/* update bpage */
local_set(&bpage->commit, pos);
bpage->time_stamp = save_timestamp;
/* we copied everything to the beginning */
read = 0;
} else {
/* update the entry counter */
cpu_buffer->read += rb_page_entries(reader);
/* swap the pages */
rb_init_page(bpage);
bpage = reader->page;
reader->page = *data_page;
local_set(&reader->write, 0);
local_set(&reader->entries, 0);
reader->read = 0;
*data_page = bpage;
}
ret = read;
out_unlock:
spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
out:
return ret;
}
EXPORT_SYMBOL_GPL(ring_buffer_read_page);
#ifdef CONFIG_TRACING
static ssize_t
rb_simple_read(struct file *filp, char __user *ubuf,
size_t cnt, loff_t *ppos)
{
unsigned long *p = filp->private_data;
char buf[64];
int r;
if (test_bit(RB_BUFFERS_DISABLED_BIT, p))
r = sprintf(buf, "permanently disabled\n");
else
r = sprintf(buf, "%d\n", test_bit(RB_BUFFERS_ON_BIT, p));
return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
}
static ssize_t
rb_simple_write(struct file *filp, const char __user *ubuf,
size_t cnt, loff_t *ppos)
{
unsigned long *p = filp->private_data;
char buf[64];
unsigned long val;
int ret;
if (cnt >= sizeof(buf))
return -EINVAL;
if (copy_from_user(&buf, ubuf, cnt))
return -EFAULT;
buf[cnt] = 0;
ret = strict_strtoul(buf, 10, &val);
if (ret < 0)
return ret;
if (val)
set_bit(RB_BUFFERS_ON_BIT, p);
else
clear_bit(RB_BUFFERS_ON_BIT, p);
(*ppos)++;
return cnt;
}
static const struct file_operations rb_simple_fops = {
.open = tracing_open_generic,
.read = rb_simple_read,
.write = rb_simple_write,
};
static __init int rb_init_debugfs(void)
{
struct dentry *d_tracer;
d_tracer = tracing_init_dentry();
trace_create_file("tracing_on", 0644, d_tracer,
&ring_buffer_flags, &rb_simple_fops);
return 0;
}
fs_initcall(rb_init_debugfs);
#endif
#ifdef CONFIG_HOTPLUG_CPU
static int rb_cpu_notify(struct notifier_block *self,
unsigned long action, void *hcpu)
{
struct ring_buffer *buffer =
container_of(self, struct ring_buffer, cpu_notify);
long cpu = (long)hcpu;
switch (action) {
case CPU_UP_PREPARE:
case CPU_UP_PREPARE_FROZEN:
if (cpumask_test_cpu(cpu, buffer->cpumask))
return NOTIFY_OK;
buffer->buffers[cpu] =
rb_allocate_cpu_buffer(buffer, cpu);
if (!buffer->buffers[cpu]) {
WARN(1, "failed to allocate ring buffer on CPU %ld\n",
cpu);
return NOTIFY_OK;
}
smp_wmb();
cpumask_set_cpu(cpu, buffer->cpumask);
break;
case CPU_DOWN_PREPARE:
case CPU_DOWN_PREPARE_FROZEN:
/*
* Do nothing.
* If we were to free the buffer, then the user would
* lose any trace that was in the buffer.
*/
break;
default:
break;
}
return NOTIFY_OK;
}
#endif
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