Re: [PATCH] tcm_vhost: Use ACCESS_ONCE for vs->vs_tpg[target] access

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Apr 02, 2013 at 11:31:37PM +0800, Asias He wrote:
> In vhost_scsi_handle_vq:
> 
>       tv_tpg = vs->vs_tpg[target];
>       if (!tv_tpg) {
>               ....
>               return
>       }
> 
>       tv_cmd = vhost_scsi_allocate_cmd(tv_tpg, &v_req,
> 
> 1) vs->vs_tpg[target] might change after the NULL check and 2) the above
> line might access tv_tpg from vs->vs_tpg[target]. To prevent 2), use
> ACCESS_ONCE. Thanks mst for catching this up!
> 
> Signed-off-by: Asias He <asias@redhat.com>

OK this might be ok for 3.9.

Acked-by: Michael S. Tsirkin <mst@redhat.com>

Nicholas can you pick this up pls?

For 3.10 I still think it's best to get rid of it
and stick vs->vs_tpg in vq->private_data.

> ---
>  drivers/vhost/tcm_vhost.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/vhost/tcm_vhost.c b/drivers/vhost/tcm_vhost.c
> index 0524267..32d95e3 100644
> --- a/drivers/vhost/tcm_vhost.c
> +++ b/drivers/vhost/tcm_vhost.c
> @@ -668,7 +668,7 @@ static void vhost_scsi_handle_vq(struct vhost_scsi *vs,
>  
>  		/* Extract the tpgt */
>  		target = v_req.lun[1];
> -		tv_tpg = vs->vs_tpg[target];
> +		tv_tpg = ACCESS_ONCE(vs->vs_tpg[target]);
>  
>  		/* Target does not exist, fail the request */
>  		if (unlikely(!tv_tpg)) {
> -- 
> 1.8.1.4