linux-kernel - Re: [PATCHSET] ptrace,signal: group stop / ptrace updates

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Date:	Fri, 28 Jan 2011 17:54:55 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Tejun Heo <tj@...nel.org>
Cc:	roland@...hat.com, oleg@...hat.com, jan.kratochvil@...hat.com,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>,
	Frédéric Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCHSET] ptrace,signal: group stop / ptrace updates

Hi,

I'm hijacking this thread, to report a signal handling bug that Linux and Bash has, 
and which has been there at least for 10 years since i started using SMP Linux 
systems ...

It's not easy to reproduce but today i found a reproducer - maybe you guys have an 
idea what's going on.

There's two very simple scripts, one calls the other in an infinite loop:

 $ cat test-signal
 #!/bin/bash

 while true; do ./test-signal2; done

 $ cat test-signal2
 #!/bin/bash

 true

The bug is that occasionally Ctrl-C does not get processed, and that the Ctrl-C is 
'lost'. It can be reproduced here by running ./test-signal several times, and 
Ctrl-C-ing it:

 $ ./test-signal
 ^C
 $ ./test-signal
 ^C^C
 $ ./test-signal
 ^C

See that '^C^C' line? That is where i had to do Ctrl-C twice.

It only fails here about once every 10 times, so it's very rare. I have a stock F14 
system running on that box, with the very latest .38 based kernel.

Any ideas what's going on?

Thanks,

	Ingo
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