Re: Possible bug introduced in commit 9b84cca

[Denys Vlasenko]

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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