linux-kernel - Re: [PATCH 1/3] posix-timers: Correctly get dying task time sample in posix_cpu_timer

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Message-ID: <20130411152656.GG15699@somewhere>
Date:	Thu, 11 Apr 2013 17:26:59 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Chen Gang <gang.chen@...anux.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Stanislaw Gruszka <sgruszka@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>, Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH 1/3] posix-timers: Correctly get dying task time sample
 in posix_cpu_timer_schedule()

On Mon, Apr 01, 2013 at 08:07:59AM +0800, Chen Gang wrote:
> On 2013年03月30日 21:15, Frederic Weisbecker wrote:
> > In order to arm the next timer to schedule, we take a sample of the
> > current process or thread cputime.
> > 
> > If the task is dying though, we don't arm anything but we
> > cache the remaining timer expiration delta for further reads.
> > 
> > Something similar is performed in posix_cpu_timer_get() but
> > here we forget to take the process wide cputime sample
> > before caching it.
> > 
> > As a result we are storing random stack content, leading
> > every further reads of that timer to return junk values.
> > 
> > Fix this by taking the appropriate sample in the case of
> > process wide timers.
> > 
> > Reported-by: Andrew Morton <akpm@...ux-foundation.org>
> > Reported-by: Chen Gang <gang.chen@...anux.com>
> > Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> > Cc: Stanislaw Gruszka <sgruszka@...hat.com>
> > Cc: Thomas Gleixner <tglx@...utronix.de>
> > Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> > Cc: Ingo Molnar <mingo@...e.hu>
> > Cc: Oleg Nesterov <oleg@...hat.com>
> > Cc: Chen Gang <gang.chen@...anux.com>
> > ---
> 
>   thank you for mark me as reported by, although I reported too late
> (Andrew Morton is the first reporter).

Bug reporters simply deserve to be credited, no sorting is required ;)

> 
>   next, I should continue to try to find another issues about kernel.

I encourage you to do so :)

Thanks.
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