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

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Message-ID: <20131210213431.GA6342@redhat.com>
Date:	Tue, 10 Dec 2013 22:34:31 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Dave Jones <davej@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Darren Hart <dvhart@...ux.intel.com>,
	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 12/10, Dave Jones wrote:
>
> On Tue, Dec 10, 2013 at 09:35:59PM +0100, Oleg Nesterov wrote:
>  >
>  > 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.

OK, thanks. So it doesn't return to user-space.

could you do

	cd /sys/kernel/debug/tracing/
	echo 10818 >> set_ftrace_pid
	echo function_graph >> current_tracer
	echo 1 >> tracing_on

and look into "trace" file to find out how exactly it loops?

> I tried attaching to 10818 with gdb, and it just hangs.

This is clear, 10818 obviously can't stop.

Oleg.

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