| Message ID | 20120120081708.50747.60241.stgit@amd-6168-8-1.englab.nay.redhat.com |
|---|---|
| State | Not Applicable, archived |
| Delegated to: | David Miller |
| Headers | show |
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 <jasowang@redhat.com> Good catch. Note: this fixes a bug introduced by ee7cd8981e15bcb365fc762afe3fc47b8242f630. Acked-by: Michael S. Tsirkin <mst@redhat.com> > --- > 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; -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Sun, 22 Jan 2012 13:47:57 +0200, "Michael S. Tsirkin" <mst@redhat.com> wrote: > 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 <jasowang@redhat.com> > > Good catch. > Note: this fixes a bug introduced by ee7cd8981e15bcb365fc762afe3fc47b8242f630. Indeed, great catch. It replaces the missing barrier, and after some careful thought I've convinced myself that it is necessary for both the avail index and flag cases. > > 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); Fixed typo and applied. Thanks, Rusty. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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 + * event. */ + virtio_mb(vq); old = vq->vring.avail->idx - vq->num_added; new = vq->vring.avail->idx;
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 <jasowang@redhat.com> --- drivers/virtio/virtio_ring.c | 6 +++--- 1 files changed, 3 insertions(+), 3 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html