netdev - Re: [regression, 2.6.37-rc1] 'ip link tap0 up' stuck in do

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Message-ID: <20101208140822.GA18681@redhat.com>
Date:	Wed, 8 Dec 2010 15:08:22 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Florian Mickler <florian@...kler.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Américo Wang <xiyou.wangcong@...il.com>,
	Dave Chinner <david@...morbit.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [regression, 2.6.37-rc1] 'ip link tap0 up' stuck in do_exit()

On 12/08, Oleg Nesterov wrote:
>
> On 12/08, Oleg Nesterov wrote:
> >
> > On 12/08, Florian Mickler wrote:
> > >
> > > [ ccing Ingo and Oleg ] as suggested
> >
> > Well. Of course I can't explain this bug. But, looking at this email
> > I do not see amything strange in exit/schedule/etc.
> >
> > > > >> > > > This is resulting in the command 'ip link set tap0 up' hanging as a zombie:
> > > > >> > > >
> > > > >> > > > root      3005     1  0 16:53 pts/3    00:00:00 /bin/sh /vm-images/qemu-ifup tap0
> > > > >> > > > root      3011  3005  0 16:53 pts/3    00:00:00 /usr/bin/sudo /sbin/ip link set tap0 up
> > > > >> > > > root      3012  3011  0 16:53 pts/3    00:00:00 [ip] <defunct>
> >
> > That is. ip is a zombie.
>
> And. I do not know if this matters or not, but "the command 'ip link
> set tap0 up' hanging as a zombie" does not look right.
>
> This was spawned by
>
> > >> > > > if [ -n "$1" ];then
> > >> > > >         /usr/bin/sudo /sbin/ip link set $1 up
> > >> > > >         sleep 0.5s
> > >> > > >         /usr/bin/sudo /usr/sbin/brctl addif $switch $1
> > >> > > >      exit 0
> > >> > > > fi
>
> The command does not hang. But it forks the child with pid == 3012,
> this child exits.

Damn, sorry for noise, forgot to mention...

The parent's trace (pid == 3011) can be more useful. Say, if it
hangs in do_wait(), then the kernel is obviously wrong.

Oleg.

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