Re: Possible bug introduced in commit 9b84cca

From: Denys Vlasenko
Date: Wed Dec 28 2011 - 16:07:40 EST

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 - Åukasz 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, Åukasz 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.

Åukasz, looks like 3.0-rc1 is affected too.

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