virtio: Avoid possible kernel panic if DEBUG is enabled.

The virtqueue_add() calls START_USE() upon entry. The virtqueue_kick() is
called if vq->num_added == (1 << 16) - 1 before calling END_USE().
The virtqueue_kick_prepare() called via virtqueue_kick() calls START_USE()
upon entry, and will call panic() if DEBUG is enabled.
Move this virtqueue_kick() call to after END_USE() call.

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 95b9661554d14b8160cd298df3a005eb631398a1..096b857e7b75abad526f487c84392d863c3c6b06 100644 (file)
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -244,14 +244,14 @@ static inline int virtqueue_add(struct virtqueue *_vq,
        vq->vring.avail->idx = cpu_to_virtio16(_vq->vdev, virtio16_to_cpu(_vq->vdev, vq->vring.avail->idx) + 1);
        vq->num_added++;
 
+       pr_debug("Added buffer head %i to %p\n", head, vq);
+       END_USE(vq);
+
        /* This is very unlikely, but theoretically possible.  Kick
         * just in case. */
        if (unlikely(vq->num_added == (1 << 16) - 1))
                virtqueue_kick(_vq);
 
-       pr_debug("Added buffer head %i to %p\n", head, vq);
-       END_USE(vq);
-
        return 0;
 }