Re: [PATCH 2/2] virtio: correct the memory barrier in virtqueue_kick_prepare()
From: "Michael S. Tsirkin" <mst@redhat.com>
Date: 2012-01-22 11:46:13
Also in:
kvm, lkml, virtualization
On Fri, Jan 20, 2012 at 04:17:08PM +0800, Jason Wang wrote:
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. Signed-off-by: Jason Wang <redacted>
Good catch. Note: this fixes a bug introduced by ee7cd8981e15bcb365fc762afe3fc47b8242f630. Acked-by: Michael S. Tsirkin <mst@redhat.com>
quoted hunk ↗ jump to hunk
--- drivers/virtio/virtio_ring.c | 6 +++--- 1 files changed, 3 insertions(+), 3 deletions(-)diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index 78428a8..07d9360 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 expose available array entries before checking avail
Nit: We need expose -> Need to expose
+ * event. */ + virtio_mb(vq); old = vq->vring.avail->idx - vq->num_added; new = vq->vring.avail->idx;