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

Thomas Huth [off-list ref] writes:

On Wed, 25 Feb 2015 16:11:27 +0100
Cornelia Huck [off-list ref] wrote:

quoted

On Wed, 25 Feb 2015 15:36:02 +0100
"Michael S. Tsirkin" [off-list ref] wrote:

quoted

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 <redacted>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---

changes from v1:
	remove wait_event_interruptible
	noticed by Cornelia Huck [off-list ref]

 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 <redacted>

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 <redacted>

Applied.

Thanks,
Rusty.