>From 11fd997d724f520ca628615e7ffbfd7901c40b62 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-ker...@i-love.sakura.ne.jp>
Date: Fri, 6 Feb 2015 13:28:38 +0900
Subject: [PATCH] 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-ker...@i-love.sakura.ne.jp>
---
 drivers/virtio/virtio_ring.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 00ec6b3..596735b 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -245,14 +245,14 @@ 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;
 }
 
-- 
1.8.3.1
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