[PATCH v2] virtio-balloon: do not call blocking ops when !TASK_RUNNING

Thomas Huth
Wed, 25 Feb 2015 15:37:56 -0000

On Wed, 25 Feb 2015 16:11:27 +0100
Cornelia Huck <cornelia.huck at de.ibm.com> wrote:

> On Wed, 25 Feb 2015 15:36:02 +0100
> "Michael S. Tsirkin" <mst at redhat.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 at vger.kernel.org
> > Reported-by: Thomas Huth <thuth at linux.vnet.ibm.com>
> > Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
> > ---
> >
> > changes from v1:
> > 	remove wait_event_interruptible
> > 	noticed by Cornelia Huck <cornelia.huck at de.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 at de.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 at linux.vnet.ibm.com>