Re: [Xen-devel] [PATCH 31/34] xenbus: use __smp_XXX barriers

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Wed, 30 Dec 2015, Michael S. Tsirkin wrote:
> drivers/xen/xenbus/xenbus_comms.c uses
> full memory barriers to communicate with the other side.
> 
> For guests compiled with CONFIG_SMP, smp_wmb and smp_mb
> would be sufficient, so mb() and wmb() here are only needed if
> a non-SMP guest runs on an SMP host.
> 
> Switch to __smp_XXX barriers which serve this exact purpose.
> 
> Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>

Reviewed-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>


> This is straight-forward, but untested.
> I can either merge this patchset through my tree if this is
> acked, or defer this and merge the patchset first,
> and xen bits through xen tree afterwards.
> 
> Pls let me know.

I think it can go via your tree. However you have missed a few Xen
source files which need the same mb/__smb_mb conversions:

drivers/xen/grant-table.c
drivers/xen/evtchn.c
drivers/xen/events/events_fifo.c
drivers/xen/xen-scsiback.c
drivers/xen/tmem.c
drivers/xen/xen-pciback/pci_stub.c
drivers/xen/xen-pciback/pciback_ops.c


>  drivers/xen/xenbus/xenbus_comms.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/xen/xenbus/xenbus_comms.c 
> b/drivers/xen/xenbus/xenbus_comms.c
> index fdb0f33..09b17c7 100644
> --- a/drivers/xen/xenbus/xenbus_comms.c
> +++ b/drivers/xen/xenbus/xenbus_comms.c
> @@ -123,14 +123,14 @@ int xb_write(const void *data, unsigned len)
>                       avail = len;
>  
>               /* Must write data /after/ reading the consumer index. */
> -             mb();
> +             __smp_mb();
>  
>               memcpy(dst, data, avail);
>               data += avail;
>               len -= avail;
>  
>               /* Other side must not see new producer until data is there. */
> -             wmb();
> +             __smp_wmb();
>               intf->req_prod += avail;
>  
>               /* Implies mb(): other side will see the updated producer. */
> @@ -180,14 +180,14 @@ int xb_read(void *data, unsigned len)
>                       avail = len;
>  
>               /* Must read data /after/ reading the producer index. */
> -             rmb();
> +             __smp_rmb();
>  
>               memcpy(data, src, avail);
>               data += avail;
>               len -= avail;
>  
>               /* Other side must not see free space until we've copied out */
> -             mb();
> +             __smp_mb();
>               intf->rsp_cons += avail;
>  
>               pr_debug("Finished read of %i bytes (%i to go)\n", avail, len);
> -- 
> MST
> 

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel