From 65433ab2cf634b8cfed28a70ed552fb6877b4349 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 91c29160a2c6187ce938c9f235f1c2dd06e519e0. 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