Commit e1c7e2a6 authored Jun 24, 2009 by Li Zefan Committed by Ingo Molnar Jun 24, 2009

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



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>

parent 4e8a2372

kernel/trace/trace_events.c

+22 −6

Original line number	Diff line number	Diff line
		@@ -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);
		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);
		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)

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