linux-kernel - Re: [PATCH v2] virtio-balloon: do not call blocking ops when !TASK

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Message-ID: <87mw3lk5h3.fsf@rustcorp.com.au>
Date:	Tue, 10 Mar 2015 11:56:32 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Thomas Huth <thuth@...ux.vnet.ibm.com>,
	Cornelia Huck <cornelia.huck@...ibm.com>
Cc:	"Michael S. Tsirkin" <mst@...hat.com>,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org
Subject: Re: [PATCH v2] virtio-balloon: do not call blocking ops when !TASK_RUNNING

Thomas Huth <thuth@...ux.vnet.ibm.com> writes:
> On Wed, 25 Feb 2015 16:11:27 +0100
> Cornelia Huck <cornelia.huck@...ibm.com> wrote:
>
>> On Wed, 25 Feb 2015 15:36:02 +0100
>> "Michael S. Tsirkin" <mst@...hat.com> wrote:
>> 
>> > virtio balloon has this code:
>> >         wait_event_interruptible(vb->config_change,
>> >                                  (diff = towards_target(vb)) != 0
>> >                                  || vb->need_stats_update
>> >                                  || kthread_should_stop()
>> >                                  || freezing(current));
>> > 
>> > Which is a problem because towards_target() call might block after
>> > wait_event_interruptible sets task state to TAST_INTERRUPTIBLE, causing
>> > the task_struct::state collision typical of nesting of sleeping
>> > primitives
>> > 
>> > See also http://lwn.net/Articles/628628/ or Thomas's
>> > bug report
>> > http://article.gmane.org/gmane.linux.kernel.virtualization/24846
>> > for a fuller explanation.
>> > 
>> > To fix, rewrite using wait_woken.
>> > 
>> > Cc: stable@...r.kernel.org
>> > Reported-by: Thomas Huth <thuth@...ux.vnet.ibm.com>
>> > Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
>> > ---
>> > 
>> > changes from v1:
>> > 	remove wait_event_interruptible
>> > 	noticed by Cornelia Huck <cornelia.huck@...ibm.com>
>> > 
>> >  drivers/virtio/virtio_balloon.c | 19 ++++++++++++++-----
>> >  1 file changed, 14 insertions(+), 5 deletions(-)
>> > 
>> 
>> I was able to reproduce Thomas' original problem and can confirm that
>> it is gone with this patch.
>> 
>> Reviewed-by: Cornelia Huck <cornelia.huck@...ibm.com>
>
> Right, I just applied the patch on my system, too, and the problem is
> indeed gone! Thanks for the quick fix!
>
> Tested-by: Thomas Huth <thuth@...ux.vnet.ibm.com>

Applied.

Thanks,
Rusty.
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