netdev - Re: ipv6: tunnel: hang when destroying ipv6 tunnel

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Message-ID: <CA+1xoqcAXyh306=2=QKWyM3BE44=MT+nsuRQn5YLOLgbtZqicA@mail.gmail.com>
Date:	Sat, 31 Mar 2012 23:43:19 +0200
From:	Sasha Levin <levinsasha928@...il.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>, davem@...emloft.net,
	kuznet@....inr.ac.ru, jmorris@...ei.org, yoshfuji@...ux-ipv6.org,
	Patrick McHardy <kaber@...sh.net>, netdev@...r.kernel.org,
	"linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
	Dave Jones <davej@...hat.com>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Subject: Re: ipv6: tunnel: hang when destroying ipv6 tunnel

On Sat, Mar 31, 2012 at 11:34 PM, Oleg Nesterov <oleg@...hat.com> wrote:
> On 03/31, Eric Dumazet wrote:
>>
>> On Sat, 2012-03-31 at 19:51 +0200, Sasha Levin wrote:
>> > Hi all,
>> >
>> > It appears that a hang may occur when destroying an ipv6 tunnel, which
>> > I've reproduced several times in a KVM vm.
>
> kernel version?

latest linux-next

>> > [ 1561.564172] INFO: task kworker/u:2:3140 blocked for more than 120 seconds.
>
> And nobody else?

Some more messages follow a bit later which get stuck in vfs related code.

> It would be nice to know what sysrq-t says, in particular the trace
> of khelper thread is interesting.

Sure, I'll get one when it happens again.

>> Something is wrong here, call_usermodehelper_exec ( ... UMH_WAIT_EXEC)
>> should not block forever.
>
> Yes, unless it triggers another request_module()...
>
> Tetsuo, could you please take a look? Unlikely, but may be this
> is fixed by your kmod-avoid-deadlock-by-recursive-kmod-call.patch
> in -mm ?
>
> Oleg.
>
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