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Date: Tue, 10 Dec 2013 22:34:31 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Dave Jones <davej@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Darren Hart <dvhart@linux.intel.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>, Mel Gorman <mgorman@suse.de>
Subject: Re: process 'stuck' at exit.
Message-ID: <20131210213431.GA6342@redhat.com>
References: <20131210154724.GA30020@redhat.com> <CA+55aFxgFAfcQKDoDhmJcCRb5pfxumxJ9OmpUhhNzs+CY_Yqqw@mail.gmail.com> <alpine.DEB.2.02.1312102001090.28330@ionos.tec.linutronix.de> <CA+55aFzLnheC6W+Db=-MVr6aR5UzP-c1Q1yk_aN-9gxSjUpANw@mail.gmail.com> <20131210203559.GA1209@redhat.com> <20131210204925.GB27373@redhat.com>
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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.