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

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Date:	Thu, 09 Dec 2010 18:59:48 +0100
From:	Jim Bos <jim876@...all.nl>
To:	Américo Wang <xiyou.wangcong@...il.com>
CC:	Oleg Nesterov <oleg@...hat.com>,
	Florian Mickler <florian@...kler.org>,
	Ingo Molnar <mingo@...e.hu>,
	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 12/09/2010 05:47 PM, Américo Wang wrote:
> On Wed, Dec 08, 2010 at 03:08:22PM +0100, Oleg Nesterov wrote:
>> 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.
>>
> 
> Yeah, there is no point that a zombie can trigger a BUG_ON in kenrel.
> But it is still interesting to know why it becomes a zombie...
> 
> --
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ip link tap0 up not working might be this issue:

   http://marc.info/?l=linux-netdev&m=128783852132311&w=2

( Latest Virtualbox 3.2.12 works around this issue )

Jim



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