Re: [Xen-devel] [PATCH v2 32/32] virtio_ring: use virt_store_mb

["Michael S. Tsirkin" <mst@xxxxxxxxxx>]

On Fri, Jan 01, 2016 at 08:23:46PM +0300, Sergei Shtylyov wrote:
> Hello.
> 
> On 12/31/2015 10:09 PM, Michael S. Tsirkin wrote:
> 
> >We need a full barrier after writing out event index, using
> >virt_store_mb there seems better than open-coding.  As usual, we need a
> >wrapper to account for strong barriers.
> >
> >It's tempting to use this in vhost as well, for that, we'll
> >need a variant of smp_store_mb that works on __user pointers.
> >
> >Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> >---
> >  include/linux/virtio_ring.h  | 12 ++++++++++++
> >  drivers/virtio/virtio_ring.c | 15 +++++++++------
> >  2 files changed, 21 insertions(+), 6 deletions(-)
> >
> >diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h
> >index f3fa55b..3a74d91 100644
> >--- a/include/linux/virtio_ring.h
> >+++ b/include/linux/virtio_ring.h
> >@@ -45,6 +45,18 @@ static inline void virtio_wmb(bool weak_barriers)
> >             wmb();
> >  }
> >
> >+static inline void virtio_store_mb(bool weak_barriers,
> >+                               __virtio16 *p, __virtio16 v)
> >+{
> >+    if (weak_barriers)
> >+            virt_store_mb(*p, v);
> >+    else
> >+    {
> 
>    The kernel coding style dictates:
> 
>       if (weak_barriers) {
>               virt_store_mb(*p, v);
>       } else {
> 
> >+            WRITE_ONCE(*p, v);
> >+            mb();
> >+    }
> >+}
> >+
> [...]
> 
> MBR, Sergei

Will fix, thanks!

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