linux-kernel - Re: Zombie process when ptracing

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Date:	Mon, 23 Nov 2009 09:36:23 +0100
From:	Nick Piggin <npiggin@...e.de>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Roland McGrath <roland@...hat.com>
Subject: Re: Zombie process when ptracing

On Fri, Nov 20, 2009 at 02:29:30AM +0100, Oleg Nesterov wrote:
> Hi,
> 
> On 11/19, Nick Piggin wrote:
> >
> > Running recent git kernel, I have a process stuck in Z state
> >
> > bash          ? 0000000000000000     0  3188   3187 0x00000000
> >  ffff88012e24fec8 0000000000000046 0000000000000000 0000000000000012
> >  ffff88012e24fec8 ffff88012e24e000 ffff88012e24ffd8 ffff88012e24e000
> >  000000000000efc8 ffff88012e24e000 ffff88012ea82090 ffff88012ff78640
> > Call Trace:
> >  [<ffffffff8124baee>] ? proc_clear_tty+0x5e/0x70
> >  [<ffffffff810587a8>] ? exit_ptrace+0xb8/0x140
> >  [<ffffffff8105126a>] do_exit+0x58a/0x7c0
> >  [<ffffffff810514dd>] do_group_exit+0x3d/0xb0
> >  [<ffffffff81051562>] sys_exit_group+0x12/0x20
> >  [<ffffffff8100b3eb>] system_call_fastpath+0x16/0x1b
> >
> > This was after stracing a few test programs.
> >
> > It also seems to have lost job control (^C) at the same time.
> 
> This can happen if the tracer (strace) itself hangs, zombies
> should go away once the tracer is killed. Or its ->real_parent
> is stopped or hangs...
> 
> (I assume you didn't strace /sbin/init)

No, I straced something else, and all straces seemed to be
killed but bash remained. I was running a script that in
turn launched another process, so I ran it via
strace -ff bash ./script.sh


> But,
> 
> > Hmm, and the kernel just paniced with an nmi lockup while I was
> > trying to get more info.
> 
> this probably means we have a kernel bug ;)

Hmm sorry that seemed like it _may_ have been an unrelated issue
(with the ssh connection).

 
> If you see a zombie again, could you look at its /ptoc/pid/status?

OK, any other hints if I see it again?


> And of course, which programs did you trace and how? It would be
> great if we can reproduce the problem.

At this stage I have not reproduced it, and I can't share the program
which was being straced. If it does happen again and I cannot distil
a simple test case, I will ask permission to distribute it.

Thanks,
Nick
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