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SubjectRe: [PATCH] virtio-balloon: do not call blocking ops when !TASK_RUNNING
On Wed, Feb 25, 2015 at 03:32:08PM +0100, Cornelia Huck wrote:
> On Wed, 25 Feb 2015 15:14:36 +0100
> "Michael S. Tsirkin" <mst@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@vger.kernel.org
> > Reported-by: Thomas Huth <thuth@linux.vnet.ibm.com>
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > ---
> > 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 <linux/module.h>
> > #include <linux/balloon_compaction.h>
> > #include <linux/oom.h>
> > +#include <linux/wait.h>
> >
> > /*
> > * 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()?

Ugh. Forgot to commit :(
Will resend.



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