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tracing/events: fix concurrent access to ftrace_events list

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A module will add/remove its trace events when it gets loaded/unloaded, so
the ftrace_events list is not "const", and concurrent access needs to be
protected.

This patch thus fixes races between loading/unloding modules and read
'available_events' or read/write 'set_event', etc.

Below shows how to reproduce the race:

 # for ((; ;)) { cat /mnt/tracing/available_events; } > /dev/null &
 # for ((; ;)) { insmod trace-events-sample.ko; rmmod sample; } &

After a while:

BUG: unable to handle kernel paging request at 0010011c
IP: [<c1080f27>] t_next+0x1b/0x2d
...
Call Trace:
 [<c10c90e6>] ? seq_read+0x217/0x30d
 [<c10c8ecf>] ? seq_read+0x0/0x30d
 [<c10b4c19>] ? vfs_read+0x8f/0x136
 [<c10b4fc3>] ? sys_read+0x40/0x65
 [<c1002a68>] ? sysenter_do_call+0x12/0x36

[ Impact: fix races when concurrent accessing ftrace_events list ]

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Tom Zanussi <tzanussi@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <4A00F709.3080800@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Li Zefan
2009-05-06 10:33:45 +08:00
committed by Ingo Molnar
parent 2df75e4157
commit 20c8928abe
4 changed files with 33 additions and 17 deletions
Download Patch File Download Diff File Expand all files Collapse all files

20
kernel/trace/trace_events.c
View File

@ -21,7 +21,7 @@
#define TRACE_SYSTEM "TRACE_SYSTEM"
static DEFINE_MUTEX(event_mutex);
DEFINE_MUTEX(event_mutex);
LIST_HEAD(ftrace_events);
@ -80,6 +80,7 @@ static void ftrace_clear_events(void)
{
struct ftrace_event_call *call;
mutex_lock(&event_mutex);
list_for_each_entry(call, &ftrace_events, list) {
if (call->enabled) {
@ -87,6 +88,7 @@ static void ftrace_clear_events(void)
call->unregfunc();
}
}
mutex_unlock(&event_mutex);
}
static void ftrace_event_enable_disable(struct ftrace_event_call *call,
@ -274,6 +276,9 @@ t_next(struct seq_file *m, void *v, loff_t *pos)
static void *t_start(struct seq_file *m, loff_t *pos)
{
mutex_lock(&event_mutex);
if (*pos == 0)
m->private = ftrace_events.next;
return t_next(m, NULL, pos);
}
@ -303,6 +308,9 @@ s_next(struct seq_file *m, void *v, loff_t *pos)
static void *s_start(struct seq_file *m, loff_t *pos)
{
mutex_lock(&event_mutex);
if (*pos == 0)
m->private = ftrace_events.next;
return s_next(m, NULL, pos);
}
@ -319,12 +327,12 @@ static int t_show(struct seq_file *m, void *v)
static void t_stop(struct seq_file *m, void *p)
{
mutex_unlock(&event_mutex);
}
static int
ftrace_event_seq_open(struct inode *inode, struct file *file)
{
int ret;
const struct seq_operations *seq_ops;
if ((file->f_mode & FMODE_WRITE) &&
@ -332,13 +340,7 @@ ftrace_event_seq_open(struct inode *inode, struct file *file)
ftrace_clear_events();
seq_ops = inode->i_private;
ret = seq_open(file, seq_ops);
if (!ret) {
struct seq_file *m = file->private_data;
m->private = ftrace_events.next;
}
return ret;
return seq_open(file, seq_ops);
}
static ssize_t