From 8499a89ac3ab9a7799266815f270f6d5c85b3fa1 Mon Sep 17 00:00:00 2001 From: Jason Wang Date: Fri, 20 Jan 2012 16:17:08 +0800 Subject: [PATCH] virtio: correct the memory barrier in virtqueue_kick_prepare() Use virtio_mb() to make sure the available index to be exposed before checking the the avail event. Otherwise we may get stale value of avail event in guest and never kick the host after. Note: this fixes a bug introduced by 14c47ea6caaa7c30ae2b6b2116f3c5366536be72. Signed-off-by: Jason Wang Acked-by: Michael S. Tsirkin Signed-off-by: Rusty Russell Cc: stable@kernel.org --- 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 78428a863b469..5aa43c3392a2a 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -308,9 +308,9 @@ bool virtqueue_kick_prepare(struct virtqueue *_vq) bool needs_kick; START_USE(vq); - /* Descriptors and available array need to be set before we expose the - * new available array entries. */ - virtio_wmb(vq); + /* We need to expose available array entries before checking avail + * event. */ + virtio_mb(vq); old = vq->vring.avail->idx - vq->num_added; new = vq->vring.avail->idx; -- 2.39.5