From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Michael S. Tsirkin" <mst@redhat.com>
Subject: Re: [PATCH 3/4] tcm_vhost: Fix vs->vs_endpoint checking in
	vhost_scsi_handle_vq()
Date: Tue, 12 Mar 2013 13:11:19 +0200
Message-ID: <20130312111119.GA6788@redhat.com>
References: <1363056171-5854-1-git-send-email-asias@redhat.com>
	<1363056171-5854-4-git-send-email-asias@redhat.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Return-path: <virtualization-bounces@lists.linux-foundation.org>
Content-Disposition: inline
In-Reply-To: <1363056171-5854-4-git-send-email-asias@redhat.com>
List-Unsubscribe: <https://lists.linuxfoundation.org/mailman/options/virtualization>,
	<mailto:virtualization-request@lists.linux-foundation.org?subject=unsubscribe>
List-Archive: <http://lists.linuxfoundation.org/pipermail/virtualization/>
List-Post: <mailto:virtualization@lists.linux-foundation.org>
List-Help: <mailto:virtualization-request@lists.linux-foundation.org?subject=help>
List-Subscribe: <https://lists.linuxfoundation.org/mailman/listinfo/virtualization>,
	<mailto:virtualization-request@lists.linux-foundation.org?subject=subscribe>
Sender: virtualization-bounces@lists.linux-foundation.org
Errors-To: virtualization-bounces@lists.linux-foundation.org
To: Asias He <asias@redhat.com>
Cc: kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, target-devel@vger.kernel.org, Stefan Hajnoczi <stefanha@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>
List-Id: virtualization@lists.linuxfoundation.org

On Tue, Mar 12, 2013 at 10:42:50AM +0800, Asias He wrote:
> vs->vs_endpoint is protected by the vs->dev.mutex. Use
> tcm_vhost_check_endpoint() to do check. The helper does the needed
> locking for us.
> 
> Signed-off-by: Asias He <asias@redhat.com>
> Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

This takes dev mutex on data path which will introduce
contention esp for multiqueue.
How about storing the endpoint as part of vq
private data and protecting with vq mutex?

> ---
>  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 29612bc..61093d1 100644
> --- a/drivers/vhost/tcm_vhost.c
> +++ b/drivers/vhost/tcm_vhost.c
> @@ -594,7 +594,7 @@ static void vhost_scsi_handle_vq(struct vhost_scsi *vs,
>  	u8 target;
>  
>  	/* Must use ioctl VHOST_SCSI_SET_ENDPOINT */
> -	if (unlikely(!vs->vs_endpoint))
> +	if (!tcm_vhost_check_endpoint(vs))
>  		return;
>  
>  	mutex_lock(&vq->mutex);
> -- 
> 1.8.1.4