linux-kernel - Re: [PATCH,RFC] perf: panic due to inclied cpu context task

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Date:	Sat, 26 Mar 2011 19:49:34 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Jiri Olsa <jolsa@...hat.com>, Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH,RFC] perf: panic due to inclied cpu context task_ctx
	value

On 03/26, Peter Zijlstra wrote:
>
> On Sat, 2011-03-26 at 18:35 +0100, Oleg Nesterov wrote:
> >
> > but probably we also need update_context_time().
>
> It looks like event_sched_out() relies on up-to-date ctx->time through
> perf_event_time() and most call-paths leading to event_sched_out() do
> indeed seem to update the ctx time, all except the move_group branch in
> perf_event_open() afaict.

OK, thanks...

> Sadly the reproducer doesn't seem to trigger the issue at all, its still
> running on a plain -tip kernel.

This test-case is not "perfect", the task should change its CPU after
it closes the last perf_even_fd and before it exits...

But to me, the main question is: I do not understand how this test-case
can ever trigger the problem with HAVE_JUMP_LABEL. But it does.

I didn't try to reproduce, my gcc is old and not-CC_HAVE_ASM_GOTO.

Oleg.

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