From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753169AbbBYOcW (ORCPT ); Wed, 25 Feb 2015 09:32:22 -0500 Received: from e06smtp10.uk.ibm.com ([195.75.94.106]:52847 "EHLO e06smtp10.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753091AbbBYOcR (ORCPT ); Wed, 25 Feb 2015 09:32:17 -0500 Date: Wed, 25 Feb 2015 15:32:08 +0100 From: Cornelia Huck To: "Michael S. Tsirkin" Cc: linux-kernel@vger.kernel.org, stable@vger.kernel.org, Thomas Huth , Rusty Russell , virtualization@lists.linux-foundation.org, kvm@vger.kernel.org Subject: Re: [PATCH] virtio-balloon: do not call blocking ops when !TASK_RUNNING Message-ID: <20150225153208.341b230f.cornelia.huck@de.ibm.com> In-Reply-To: <1424873603-16386-1-git-send-email-mst@redhat.com> References: <1424873603-16386-1-git-send-email-mst@redhat.com> Organization: IBM Deutschland Research & Development GmbH Vorsitzende des Aufsichtsrats: Martina Koederitz =?UTF-8?B?R2VzY2jDpGZ0c2bDvGhydW5nOg==?= Dirk Wittkopp Sitz der Gesellschaft: =?UTF-8?B?QsO2Ymxpbmdlbg==?= Registergericht: Amtsgericht Stuttgart, HRB 243294 X-Mailer: Claws Mail 3.8.0 (GTK+ 2.24.10; i686-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15022514-0041-0000-0000-0000035D9EFF Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 25 Feb 2015 15:14:36 +0100 "Michael S. Tsirkin" 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@vger.kernel.org > Reported-by: Thomas Huth > Signed-off-by: Michael S. Tsirkin > --- > drivers/virtio/virtio_balloon.c | 14 ++++++++++++++ > 1 file changed, 14 insertions(+) > > diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c > index 0413157..2f19f65 100644 > --- a/drivers/virtio/virtio_balloon.c > +++ b/drivers/virtio/virtio_balloon.c > @@ -29,6 +29,7 @@ > #include > #include > #include > +#include > > /* > * Balloon device works in 4K page units. So each page is pointed to by > @@ -334,12 +335,25 @@ static int virtballoon_oom_notify(struct notifier_block *self, > static int balloon(void *_vballoon) > { > struct virtio_balloon *vb = _vballoon; > + DEFINE_WAIT_FUNC(wait, woken_wake_function); > > set_freezable(); > while (!kthread_should_stop()) { > s64 diff; > > try_to_freeze(); > + > + add_wait_queue(&vb->config_change, &wait); > + for (;;) { > + if ((diff = towards_target(vb)) != 0 || > + vb->need_stats_update || > + kthread_should_stop() || > + freezing(current)) > + break; > + wait_woken(&wait, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT); > + } > + remove_wait_queue(&vb->config_change, &wait); > + > wait_event_interruptible(vb->config_change, > (diff = towards_target(vb)) != 0 > || vb->need_stats_update Forgot to remove the wait_event_interruptible()?