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tracing: Consolidate protection of reader access to the ring buffer 

At the beginning, access to the ring buffer was fully serialized
by trace_types_lock. Patch d7350c3f45 gives more freedom to readers,
and patch b04cc6b1f6 adds code to protect trace_pipe and cpu#/trace_pipe.

But actually it is not enough, ring buffer readers are not always
read-only, they may consume data.

This patch makes accesses to trace, trace_pipe, trace_pipe_raw
cpu#/trace, cpu#/trace_pipe and cpu#/trace_pipe_raw serialized.
And removes tracing_reader_cpumask which is used to protect trace_pipe.

Details:

Ring buffer serializes readers, but it is low level protection.
The validity of the events (which returns by ring_buffer_peek() ..etc)
are not protected by ring buffer.

The content of events may become garbage if we allow another process to consume
these events concurrently:
  A) the page of the consumed events may become a normal page
     (not reader page) in ring buffer, and this page will be rewritten
     by the events producer.
  B) The page of the consumed events may become a page for splice_read,
     and this page will be returned to system.

This patch adds trace_access_lock() and trace_access_unlock() primitives.

These primitives allow multi process access to different cpu ring buffers
concurrently.

These primitives don't distinguish read-only and read-consume access.
Multi read-only access is also serialized.

And we don't use these primitives when we open files,
we only use them when we read files.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
LKML-Reference: <4B447D52.1050602@cn.fujitsu.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Lai Jiangshan 2010-01-06 20:08:50 +08:00 committed by Steven Rostedt
parent 0fa0edaf32
commit 7e53bd42d1
1 changed files with 97 additions and 39 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

136
kernel/trace/trace.c
View File

@ -32,6 +32,7 @@
#include <linux/splice.h>
#include <linux/kdebug.h>
#include <linux/string.h>
#include <linux/rwsem.h>
#include <linux/ctype.h>
#include <linux/init.h>
#include <linux/poll.h>
@ -102,9 +103,6 @@ static inline void ftrace_enable_cpu(void)
static cpumask_var_t __read_mostly tracing_buffer_mask;
/* Define which cpu buffers are currently read in trace_pipe */
static cpumask_var_t tracing_reader_cpumask;
#define for_each_tracing_cpu(cpu) \
for_each_cpu(cpu, tracing_buffer_mask)
@ -243,12 +241,91 @@ static struct tracer *current_trace __read_mostly;
/*
* trace_types_lock is used to protect the trace_types list.
* This lock is also used to keep user access serialized.
* Accesses from userspace will grab this lock while userspace
* activities happen inside the kernel.
*/
static DEFINE_MUTEX(trace_types_lock);
/*
* serialize the access of the ring buffer
*
* ring buffer serializes readers, but it is low level protection.
* The validity of the events (which returns by ring_buffer_peek() ..etc)
* are not protected by ring buffer.
*
* The content of events may become garbage if we allow other process consumes
* these events concurrently:
* A) the page of the consumed events may become a normal page
* (not reader page) in ring buffer, and this page will be rewrited
* by events producer.
* B) The page of the consumed events may become a page for splice_read,
* and this page will be returned to system.
*
* These primitives allow multi process access to different cpu ring buffer
* concurrently.
*
* These primitives don't distinguish read-only and read-consume access.
* Multi read-only access are also serialized.
*/
#ifdef CONFIG_SMP
static DECLARE_RWSEM(all_cpu_access_lock);
static DEFINE_PER_CPU(struct mutex, cpu_access_lock);
static inline void trace_access_lock(int cpu)
{
if (cpu == TRACE_PIPE_ALL_CPU) {
/* gain it for accessing the whole ring buffer. */
down_write(&all_cpu_access_lock);
} else {
/* gain it for accessing a cpu ring buffer. */
/* Firstly block other trace_access_lock(TRACE_PIPE_ALL_CPU). */
down_read(&all_cpu_access_lock);
/* Secondly block other access to this @cpu ring buffer. */
mutex_lock(&per_cpu(cpu_access_lock, cpu));
}
}
static inline void trace_access_unlock(int cpu)
{
if (cpu == TRACE_PIPE_ALL_CPU) {
up_write(&all_cpu_access_lock);
} else {
mutex_unlock(&per_cpu(cpu_access_lock, cpu));
up_read(&all_cpu_access_lock);
}
}
static inline void trace_access_lock_init(void)
{
int cpu;
for_each_possible_cpu(cpu)
mutex_init(&per_cpu(cpu_access_lock, cpu));
}
#else
static DEFINE_MUTEX(access_lock);
static inline void trace_access_lock(int cpu)
{
(void)cpu;
mutex_lock(&access_lock);
}
static inline void trace_access_unlock(int cpu)
{
(void)cpu;
mutex_unlock(&access_lock);
}
static inline void trace_access_lock_init(void)
{
}
#endif
/* trace_wait is a waitqueue for tasks blocked on trace_poll */
static DECLARE_WAIT_QUEUE_HEAD(trace_wait);
@ -1580,12 +1657,6 @@ static void tracing_iter_reset(struct trace_iterator *iter, int cpu)
}
/*
* No necessary locking here. The worst thing which can
* happen is loosing events consumed at the same time
* by a trace_pipe reader.
* Other than that, we don't risk to crash the ring buffer
* because it serializes the readers.
*
* The current tracer is copied to avoid a global locking
* all around.
*/
@ -1640,12 +1711,16 @@ static void *s_start(struct seq_file *m, loff_t *pos)
}
trace_event_read_lock();
trace_access_lock(cpu_file);
return p;
}
static void s_stop(struct seq_file *m, void *p)
{
struct trace_iterator *iter = m->private;
atomic_dec(&trace_record_cmdline_disabled);
trace_access_unlock(iter->cpu_file);
trace_event_read_unlock();
}
@ -2836,22 +2911,6 @@ static int tracing_open_pipe(struct inode *inode, struct file *filp)
mutex_lock(&trace_types_lock);
/* We only allow one reader per cpu */
if (cpu_file == TRACE_PIPE_ALL_CPU) {
if (!cpumask_empty(tracing_reader_cpumask)) {
ret = -EBUSY;
goto out;
}
cpumask_setall(tracing_reader_cpumask);
} else {
if (!cpumask_test_cpu(cpu_file, tracing_reader_cpumask))
cpumask_set_cpu(cpu_file, tracing_reader_cpumask);
else {
ret = -EBUSY;
goto out;
}
}
/* create a buffer to store the information to pass to userspace */
iter = kzalloc(sizeof(*iter), GFP_KERNEL);
if (!iter) {
@ -2907,12 +2966,6 @@ static int tracing_release_pipe(struct inode *inode, struct file *file)
mutex_lock(&trace_types_lock);
if (iter->cpu_file == TRACE_PIPE_ALL_CPU)
cpumask_clear(tracing_reader_cpumask);
else
cpumask_clear_cpu(iter->cpu_file, tracing_reader_cpumask);
if (iter->trace->pipe_close)
iter->trace->pipe_close(iter);
@ -3074,6 +3127,7 @@ waitagain:
iter->pos = -1;
trace_event_read_lock();
trace_access_lock(iter->cpu_file);
while (find_next_entry_inc(iter) != NULL) {
enum print_line_t ret;
int len = iter->seq.len;
@ -3090,6 +3144,7 @@ waitagain:
if (iter->seq.len >= cnt)
break;
}
trace_access_unlock(iter->cpu_file);
trace_event_read_unlock();
/* Now copy what we have to the user */
@ -3215,6 +3270,7 @@ static ssize_t tracing_splice_read_pipe(struct file *filp,
}
trace_event_read_lock();
trace_access_lock(iter->cpu_file);
/* Fill as many pages as possible. */
for (i = 0, rem = len; i < PIPE_BUFFERS && rem; i++) {
@ -3238,6 +3294,7 @@ static ssize_t tracing_splice_read_pipe(struct file *filp,
trace_seq_init(&iter->seq);
}
trace_access_unlock(iter->cpu_file);
trace_event_read_unlock();
mutex_unlock(&iter->mutex);
@ -3539,10 +3596,12 @@ tracing_buffers_read(struct file *filp, char __user *ubuf,
info->read = 0;
trace_access_lock(info->cpu);
ret = ring_buffer_read_page(info->tr->buffer,
&info->spare,
count,
info->cpu, 0);
trace_access_unlock(info->cpu);
if (ret < 0)
return 0;
@ -3670,6 +3729,7 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos,
len &= PAGE_MASK;
}
trace_access_lock(info->cpu);
entries = ring_buffer_entries_cpu(info->tr->buffer, info->cpu);
for (i = 0; i < PIPE_BUFFERS && len && entries; i++, len -= PAGE_SIZE) {
@ -3717,6 +3777,7 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos,
entries = ring_buffer_entries_cpu(info->tr->buffer, info->cpu);
}
trace_access_unlock(info->cpu);
spd.nr_pages = i;
/* did we read anything? */
@ -4153,6 +4214,8 @@ static __init int tracer_init_debugfs(void)
struct dentry *d_tracer;
int cpu;
trace_access_lock_init();
d_tracer = tracing_init_dentry();
trace_create_file("tracing_enabled", 0644, d_tracer,
@ -4387,9 +4450,6 @@ __init static int tracer_alloc_buffers(void)
if (!alloc_cpumask_var(&tracing_cpumask, GFP_KERNEL))
goto out_free_buffer_mask;
if (!zalloc_cpumask_var(&tracing_reader_cpumask, GFP_KERNEL))
goto out_free_tracing_cpumask;
/* To save memory, keep the ring buffer size to its minimum */
if (ring_buffer_expanded)
ring_buf_size = trace_buf_size;
@ -4447,8 +4507,6 @@ __init static int tracer_alloc_buffers(void)
return 0;
out_free_cpumask:
free_cpumask_var(tracing_reader_cpumask);
out_free_tracing_cpumask:
free_cpumask_var(tracing_cpumask);
out_free_buffer_mask:
free_cpumask_var(tracing_buffer_mask);