linux-kernel - Re: process 'stuck' at exit.

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Date:	Tue, 10 Dec 2013 13:06:23 -0800
From:	Darren Hart <dvhart@...ux.intel.com>
To:	Dave Jones <davej@...hat.com>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Mel Gorman <mgorman@...e.de>
Subject: Re: process 'stuck' at exit.

On Tue, 2013-12-10 at 15:49 -0500, Dave Jones wrote:
> On Tue, Dec 10, 2013 at 09:35:59PM +0100, Oleg Nesterov wrote:
>  > Dave, I must have missed something, help.
>  > 
>  > I am looking at the first message and I can't understand who stuck
>  > "at exit".
>  > 
>  > The trace shows that the task with pid=10818 called sys_futex() ?
>  >
>  > Perhaps "exit" means the userspace paths?
> 
> pid 1131 is wait()'ing for 10818 to exit
> 
> pid 1130 is periodically sending SIGKILL to 10818 because it's gotten
> tired of waiting. 10818 is ignoring these because it's stuck in a loop
> somewhere in the kernel.
> 
> I tried attaching to 10818 with gdb, and it just hangs.
> (possibly because its weird stack situation [see 1st post])
> 
> by inspecting the shared mapping that all processes have (by gdb'ing 1130)
> I can see that 10818 did all its full run without incident, and the
> "exit child" flag in the fuzzer had been in set.
> 
> The last 'random syscall' the fuzzer did was to sys_accept4, so the futex call
> must come from somewhere in libc maybe ?

If that is the case, then Linus' requeue_pi path is highly unlikely as
FUTEX_CMP_REQUEUE_PI is not used by glibc (yet). That gives me hope as
that way there be dragons. Knowing exactly what syscall was made would
be very useful, but I don't know if that information is even available
anymore.

-- 
Darren Hart
Intel Open Source Technology Center
Yocto Project - Linux Kernel


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