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tracing/events: Don't increment @pos in s_start()

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While testing syscall tracepoints posted by Jason, I found 3 entries
were missing when reading available_events. The output size of
available_events is < 4 pages, which means we lost 1 entry per page.

The cause is, it's wrong to increment @pos in s_start().

Actually there's another bug here -- reading avaiable_events/set_events
can race with module unload:

  # cat available_events               |
      s_start()                        |
      s_stop()                         |
                                       | # rmmod foo.ko
      s_start()                        |
        call = list_entry(m->private)  |

@call might be freed and accessing it will lead to crash.

Reviewed-by: Liming Wang <liming.wang@windriver.com>
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <4A4186DD.6090405@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Li Zefan 2009-06-24 09:52:29 +08:00 committed by Ingo Molnar
parent 4e8a2372f9
commit e1c7e2a6e6
1 changed files with 22 additions and 6 deletions
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28
kernel/trace/trace_events.c
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@ -300,10 +300,18 @@ t_next(struct seq_file *m, void *v, loff_t *pos)
static void *t_start(struct seq_file *m, loff_t *pos)
{
struct ftrace_event_call *call = NULL;
loff_t l;
mutex_lock(&event_mutex);
if (*pos == 0)
m->private = ftrace_events.next;
return t_next(m, NULL, pos);
m->private = ftrace_events.next;
for (l = 0; l <= *pos; ) {
call = t_next(m, NULL, &l);
if (!call)
break;
}
return call;
}
static void *
@ -332,10 +340,18 @@ s_next(struct seq_file *m, void *v, loff_t *pos)
static void *s_start(struct seq_file *m, loff_t *pos)
{
struct ftrace_event_call *call = NULL;
loff_t l;
mutex_lock(&event_mutex);
if (*pos == 0)
m->private = ftrace_events.next;
return s_next(m, NULL, pos);
m->private = ftrace_events.next;
for (l = 0; l <= *pos; ) {
call = s_next(m, NULL, &l);
if (!call)
break;
}
return call;
}
static int t_show(struct seq_file *m, void *v)