linux-kernel - Re: Zombie process when ptracing

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Date:	Mon, 23 Nov 2009 16:16:12 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Nick Piggin <npiggin@...e.de>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Roland McGrath <roland@...hat.com>
Subject: Re: Zombie process when ptracing

On 11/23, Nick Piggin wrote:
>
> 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

OK, thanks.

Hmm. Just noticed the state above == '?'. Looks like sched_show_task()
is buggy, it should check ->exit_state for "ZX" from TASK_STATE_TO_CHAR_STR.
But this is off-topic.

> > If you see a zombie again, could you look at its /ptoc/pid/status?
>
> OK, any other hints if I see it again?

Well, also the contents of /proc/PPid/status and /proc/TracerPid/status
may help. And sysrq-t ouput. Otherwise, currently I have no idea where
to start.

Oleg.

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