wait: No child processes

[Dmitry V. Levin]

Hi,

On Thu, Nov 17, 2011 at 10:25:26AM +0100, Łukasz Michalik wrote:
> Hello,
> 
> I'm currently debugging an issue in sydbox wrt recent linux kernels.
> I initially thought strace wasn't affected by it, but then debian bug
> #622863 [1] made me investigate further, althought it's impossible to
> say what version was that user using.  It seems that unreleased code
> clean up in HEAD exposes the bug, namely the 19cdada5b commit.
> 
> 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, thanks for letting us aware of the issue.  I had a hope that
Denys as the author of that cleanup series would comment it, but
I haven't heard from him yet.

How do you suggest to deal with this bug?  Is there a chance to get it
fixed in the kernel soon enough?

> I'm attaching a testcase that makes strace -f fail within seconds
> (compile with g++ -std=c++0x -pthread); it just fires whole bunch of
> threads that fork and wait for exiting children.  The test case is
> perverse, but same would happen if one would try to compile say gcc
> under strace with considerable number of paraller jobs for long
> enough.
> 
> [1] http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=622863
> [2] https://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=commit;h=9b84cca2564b9a5b2d064fb44d2a55a5b44473a0


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