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

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Date:	Sat, 31 Mar 2012 23:34:23 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Sasha Levin <levinsasha928@...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 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?

> > [ 1561.564172] INFO: task kworker/u:2:3140 blocked for more than 120 seconds.

And nobody else?

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

> 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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