* [PATCH 1/2] virtio: fix typos of memory barriers
@ 2012-01-20 8:16 Jason Wang
2012-01-20 8:17 ` [PATCH 2/2] virtio: correct the memory barrier in virtqueue_kick_prepare() Jason Wang
2012-01-22 11:47 ` [PATCH 1/2] virtio: fix typos of memory barriers Michael S. Tsirkin
0 siblings, 2 replies; 6+ messages in thread
From: Jason Wang @ 2012-01-20 8:16 UTC (permalink / raw)
To: rusty, virtualization, linux-kernel, mst; +Cc: netdev, kvm
Signed-off-by: Jason Wang <jasowang@redhat.com>
---
drivers/virtio/virtio_ring.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 79e1b29..78428a8 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -35,7 +35,7 @@
#define virtio_rmb(vq) \
do { if ((vq)->weak_barriers) smp_rmb(); else rmb(); } while(0)
#define virtio_wmb(vq) \
- do { if ((vq)->weak_barriers) smp_rmb(); else rmb(); } while(0)
+ do { if ((vq)->weak_barriers) smp_wmb(); else wmb(); } while(0)
#else
/* We must force memory ordering even if guest is UP since host could be
* running on another CPU, but SMP barriers are defined to barrier() in that
^ permalink raw reply related [flat|nested] 6+ messages in thread* [PATCH 2/2] virtio: correct the memory barrier in virtqueue_kick_prepare()
2012-01-20 8:16 [PATCH 1/2] virtio: fix typos of memory barriers Jason Wang
@ 2012-01-20 8:17 ` Jason Wang
2012-01-22 11:47 ` Michael S. Tsirkin
2012-01-22 11:47 ` [PATCH 1/2] virtio: fix typos of memory barriers Michael S. Tsirkin
1 sibling, 1 reply; 6+ messages in thread
From: Jason Wang @ 2012-01-20 8:17 UTC (permalink / raw)
To: rusty, virtualization, linux-kernel, mst; +Cc: netdev, kvm
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(-)
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;
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH 2/2] virtio: correct the memory barrier in virtqueue_kick_prepare()
2012-01-20 8:17 ` [PATCH 2/2] virtio: correct the memory barrier in virtqueue_kick_prepare() Jason Wang
@ 2012-01-22 11:47 ` Michael S. Tsirkin
2012-01-22 23:34 ` Rusty Russell
0 siblings, 1 reply; 6+ messages in thread
From: Michael S. Tsirkin @ 2012-01-22 11:47 UTC (permalink / raw)
To: Jason Wang; +Cc: rusty, virtualization, linux-kernel, netdev, kvm
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;
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH 2/2] virtio: correct the memory barrier in virtqueue_kick_prepare()
2012-01-22 11:47 ` Michael S. Tsirkin
@ 2012-01-22 23:34 ` Rusty Russell
0 siblings, 0 replies; 6+ messages in thread
From: Rusty Russell @ 2012-01-22 23:34 UTC (permalink / raw)
To: Michael S. Tsirkin, Jason Wang; +Cc: virtualization, linux-kernel, netdev, kvm
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.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH 1/2] virtio: fix typos of memory barriers
2012-01-20 8:16 [PATCH 1/2] virtio: fix typos of memory barriers Jason Wang
2012-01-20 8:17 ` [PATCH 2/2] virtio: correct the memory barrier in virtqueue_kick_prepare() Jason Wang
@ 2012-01-22 11:47 ` Michael S. Tsirkin
2012-01-22 23:07 ` Rusty Russell
1 sibling, 1 reply; 6+ messages in thread
From: Michael S. Tsirkin @ 2012-01-22 11:47 UTC (permalink / raw)
To: Jason Wang; +Cc: rusty, virtualization, linux-kernel, netdev, kvm
On Fri, Jan 20, 2012 at 04:16:59PM +0800, Jason Wang wrote:
> Signed-off-by: Jason Wang <jasowang@redhat.com>
Good catch.
Note: this fixes a bug introduced by
7b21e34fd1c272e3a8c3846168f2f6287a4cd72b.
It's probably a good idea to mention
this is the commit log.
Acked-by: Michael S. Tsirkin <mst@redhat.com>
> ---
> drivers/virtio/virtio_ring.c | 2 +-
> 1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 79e1b29..78428a8 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -35,7 +35,7 @@
> #define virtio_rmb(vq) \
> do { if ((vq)->weak_barriers) smp_rmb(); else rmb(); } while(0)
> #define virtio_wmb(vq) \
> - do { if ((vq)->weak_barriers) smp_rmb(); else rmb(); } while(0)
> + do { if ((vq)->weak_barriers) smp_wmb(); else wmb(); } while(0)
> #else
> /* We must force memory ordering even if guest is UP since host could be
> * running on another CPU, but SMP barriers are defined to barrier() in that
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH 1/2] virtio: fix typos of memory barriers
2012-01-22 11:47 ` [PATCH 1/2] virtio: fix typos of memory barriers Michael S. Tsirkin
@ 2012-01-22 23:07 ` Rusty Russell
0 siblings, 0 replies; 6+ messages in thread
From: Rusty Russell @ 2012-01-22 23:07 UTC (permalink / raw)
To: Michael S. Tsirkin, Jason Wang; +Cc: virtualization, linux-kernel, netdev, kvm
On Sun, 22 Jan 2012 13:47:46 +0200, "Michael S. Tsirkin" <mst@redhat.com> wrote:
> On Fri, Jan 20, 2012 at 04:16:59PM +0800, Jason Wang wrote:
> > Signed-off-by: Jason Wang <jasowang@redhat.com>
>
> Good catch.
> Note: this fixes a bug introduced by
> 7b21e34fd1c272e3a8c3846168f2f6287a4cd72b.
> It's probably a good idea to mention
> this is the commit log.
>
> Acked-by: Michael S. Tsirkin <mst@redhat.com>
Thanks, applied!
Cheers,
Rusty.
^ permalink raw reply [flat|nested] 6+ messages in thread
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2012-01-20 8:16 [PATCH 1/2] virtio: fix typos of memory barriers Jason Wang
2012-01-20 8:17 ` [PATCH 2/2] virtio: correct the memory barrier in virtqueue_kick_prepare() Jason Wang
2012-01-22 11:47 ` Michael S. Tsirkin
2012-01-22 23:34 ` Rusty Russell
2012-01-22 11:47 ` [PATCH 1/2] virtio: fix typos of memory barriers Michael S. Tsirkin
2012-01-22 23:07 ` Rusty Russell
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