linux-kernel - Re: Bash not reacting to Ctrl-C

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Message-ID: <20110128182947.GB20056@elte.hu>
Date:	Fri, 28 Jan 2011 19:29:47 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Tejun Heo <tj@...nel.org>, roland@...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: Bash not reacting to Ctrl-C


* Oleg Nesterov <oleg@...hat.com> wrote:

> On 01/28, Ingo Molnar wrote:
> >
> > 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.
> 
> Reproduced.
> 
> At first glance, /bin/sh should be blamed... Hmm, probably yes,
> I even reproduced this under strace, and this is what I see
> 
> 	wait4(-1, 0x7fff388431c4, 0, NULL) = ? ERESTARTSYS (To be restarted)
> 	--- SIGINT (Interrupt) @ 0 (0) ---
> 	rt_sigreturn(0)                         = -1 EINTR (Interrupted system call)
> 	wait4(-1, [{WIFEXITED(s) && WEXITSTATUS(s) == 0}], 0, NULL) = 9706
> 
> So, ^C is not lost, but ./test-signal doesn't want to exit.

Might be some Bash assumption or race that works under other OSs but somehow Linux 
does differently. IIRC Bash is being developed on MacOS-X.

But it's happening all the time (with yum for example - but also with makejobs, as 
Thomas has reported it) - this is simply the first time i managed to reproduce it 
with something really simple.

Thanks,

	Ingo
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