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Message-Id: <1237797183.7527.47.camel@charm-linux>
Date: Mon, 23 Mar 2009 03:33:03 -0500
From: Tom Zanussi <tzanussi@...il.com>
To: Frederic Weisbecker <fweisbec@...il.com>
Cc: Ingo Molnar <mingo@...e.hu>, Steven Rostedt <rostedt@...dmis.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] tracing/events: don't discard an event after commit
Hi Frederic,
On Mon, 2009-03-23 at 00:18 +0100, Frederic Weisbecker wrote:
> Note: depends on "tracing/events: don't use wake up for events"
>
> When we want to filter an event, the filter test is done after
> the event is commited to the ring-buffer to be discarded later if
> needed.
>
> But a reader could be reading this event while we are trying to discard
> it. Other kind of racy events can even happen because the event is
> commited and can be read and/or consumed.
>
> What we want is to discard the event before committing it.
>
Thanks for fixing this - I had intend on doing this, but it completely
slipped my mind.
Thanks for all your other comments and fixes too...
Tom
> v2: add a reported-by Steven Rostedt
>
> Reported-by: Steven Rostedt <rostedt@...dmis.org>
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> ---
> kernel/trace/trace_events_stage_3.h | 5 +++--
> 1 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/trace/trace_events_stage_3.h b/kernel/trace/trace_events_stage_3.h
> index 9a3bd49..9d2fa78 100644
> --- a/kernel/trace/trace_events_stage_3.h
> +++ b/kernel/trace/trace_events_stage_3.h
> @@ -222,10 +222,11 @@ static void ftrace_raw_event_##call(proto) \
> \
> assign; \
> \
> - trace_nowake_buffer_unlock_commit(event, irq_flags, pc); \
> - \
> if (call->preds && !filter_match_preds(call, entry)) \
> ring_buffer_event_discard(event); \
> + \
> + trace_nowake_buffer_unlock_commit(event, irq_flags, pc); \
> + \
> } \
> \
> static int ftrace_raw_reg_event_##call(void) \
--
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