linux-kernel - Re: Possible bug introduced in commit 9b84cca

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Date:	Wed, 28 Dec 2011 22:07:24 +0100
From:	Denys Vlasenko <dvlasenk@...hat.com>
To:	Denys Vlasenko <vda.linux@...glemail.com>
CC:	Tejun Heo <tj@...nel.org>, Oleg Nesterov <oleg@...hat.com>,
	linux-kernel@...r.kernel.org,
	Łukasz Michalik <lmi@....uni.wroc.pl>,
	"Dmitry V. Levin" <ldv@...linux.org>
Subject: Re: Possible bug introduced in commit 9b84cca

On 12/28/2011 07:55 PM, Denys Vlasenko wrote:
> Hi Tejun, Oleg,
>
> Apologies if you are already informed about this bug
> by people who originally discovered it.
>
> Looks like after commit 9b84cca, waitpid under strace
> sometimes returns bogus ECHILD while child does exist.
>
> I did not yet confirm that the bug appeared exactly
> at this commit - Łukasz says that.
>
> I confirmed that bug exists on kernels 3.1.6 (in Fedora)
> and 3.1.0-rc4 (vanilla).

I tested it under a few more Fedora kernels.
On kernel-PAE-2.6.39-1.fc16.i686 bug does not trigger.
On next Fedora kernel, kernel-PAE-3.0-0.rc1.git0.2.fc16.i686,
it triggers.

And indeed, these kernels differ in kernel/exit.c::wait_consider_task()
only by commit 9b84cca.

Oleg, if you need to test it, I have the setup on my machine.

On Thu, Nov 17, 2011 at 10:25:26AM +0100, Łukasz Michalik wrote:
 > The bug only happens on recent linux.  I've bisected the kernel and
 > found that it was introduced by 9b84cca2564b9 [2] in linux.git, so
 > pretty much everything since 3.0-rc2 is affected.

Łukasz, looks like 3.0-rc1 is affected too.

-- 
vda
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