Linux Virtualization - Feb 2011 - [PATCH] virtio_net: Add schedule check to napi_enable call

From: "Bruce Rogers" <brogers at novell.com>

Under harsh testing conditions, including low memory, the guest would
stop receiving packets. With this patch applied we no longer see any
problems in the driver while performing these tests for extended periods
of time.

Make sure napi is scheduled subsequent to each napi_enable.

Signed-off-by: Bruce Rogers <brogers at novell.com>
Signed-off-by: Olaf Kirch <okir at suse.de>
Cc: stable at kernel.org
Signed-off-by: Rusty Russell <rusty at rustcorp.com.au>
---
 drivers/net/virtio_net.c |   27 ++++++++++++++++-----------
 1 file changed, 16 insertions(+), 11 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -446,6 +446,20 @@ static void skb_recv_done(struct virtque
 	}
 }
 
+static void virtnet_napi_enable(struct virtnet_info *vi)
+{
+	napi_enable(&vi->napi);
+
+	/* If all buffers were filled by other side before we napi_enabled, we
+	 * won't get another interrupt, so process any outstanding packets
+	 * now.  virtnet_poll wants re-enable the queue, so we disable here.
+	 * We synchronize against interrupts via NAPI_STATE_SCHED */
+	if (napi_schedule_prep(&vi->napi)) {
+		virtqueue_disable_cb(vi->rvq);
+		__napi_schedule(&vi->napi);
+	}
+}
+
 static void refill_work(struct work_struct *work)
 {
 	struct virtnet_info *vi;
@@ -454,7 +468,7 @@ static void refill_work(struct work_stru
 	vi = container_of(work, struct virtnet_info, refill.work);
 	napi_disable(&vi->napi);
 	still_empty = !try_fill_recv(vi, GFP_KERNEL);
-	napi_enable(&vi->napi);
+	virtnet_napi_enable(vi);
 
 	/* In theory, this can happen: if we don't get any buffers in
 	 * we will *never* try to fill again. */
@@ -638,16 +652,7 @@ static int virtnet_open(struct net_devic
 {
 	struct virtnet_info *vi = netdev_priv(dev);
 
-	napi_enable(&vi->napi);
-
-	/* If all buffers were filled by other side before we napi_enabled, we
-	 * won't get another interrupt, so process any outstanding packets
-	 * now.  virtnet_poll wants re-enable the queue, so we disable here.
-	 * We synchronize against interrupts via NAPI_STATE_SCHED */
-	if (napi_schedule_prep(&vi->napi)) {
-		virtqueue_disable_cb(vi->rvq);
-		__napi_schedule(&vi->napi);
-	}
+	virtnet_napi_enable(vi);
 	return 0;
 }

On Thu, Feb 10, 2011 at 12:32:50PM +1030, Rusty Russell
wrote:
> From: "Bruce Rogers" <brogers at novell.com>
> 
> Under harsh testing conditions, including low memory, the guest would
> stop receiving packets. With this patch applied we no longer see any
> problems in the driver while performing these tests for extended periods
> of time.
> 
> Make sure napi is scheduled subsequent to each napi_enable.
> 
> Signed-off-by: Bruce Rogers <brogers at novell.com>
> Signed-off-by: Olaf Kirch <okir at suse.de>
> Cc: stable at kernel.org
> Signed-off-by: Rusty Russell <rusty at rustcorp.com.au>
Rusty, so this is 2.6.38 material - you'll send this to Linus? Or DaveM?
> ---
>  drivers/net/virtio_net.c |   27 ++++++++++++++++-----------
>  1 file changed, 16 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -446,6 +446,20 @@ static void skb_recv_done(struct virtque
>  	}
>  }
>  
> +static void virtnet_napi_enable(struct virtnet_info *vi)
> +{
> +	napi_enable(&vi->napi);
> +
> +	/* If all buffers were filled by other side before we napi_enabled, we
> +	 * won't get another interrupt, so process any outstanding packets
> +	 * now.  virtnet_poll wants re-enable the queue, so we disable here.
> +	 * We synchronize against interrupts via NAPI_STATE_SCHED */
> +	if (napi_schedule_prep(&vi->napi)) {
> +		virtqueue_disable_cb(vi->rvq);
> +		__napi_schedule(&vi->napi);
> +	}
> +}
> +
>  static void refill_work(struct work_struct *work)
>  {
>  	struct virtnet_info *vi;
> @@ -454,7 +468,7 @@ static void refill_work(struct work_stru
>  	vi = container_of(work, struct virtnet_info, refill.work);
>  	napi_disable(&vi->napi);
>  	still_empty = !try_fill_recv(vi, GFP_KERNEL);
> -	napi_enable(&vi->napi);
> +	virtnet_napi_enable(vi);
>  
>  	/* In theory, this can happen: if we don't get any buffers in
>  	 * we will *never* try to fill again. */
> @@ -638,16 +652,7 @@ static int virtnet_open(struct net_devic
>  {
>  	struct virtnet_info *vi = netdev_priv(dev);
>  
> -	napi_enable(&vi->napi);
> -
> -	/* If all buffers were filled by other side before we napi_enabled, we
> -	 * won't get another interrupt, so process any outstanding packets
> -	 * now.  virtnet_poll wants re-enable the queue, so we disable here.
> -	 * We synchronize against interrupts via NAPI_STATE_SCHED */
> -	if (napi_schedule_prep(&vi->napi)) {
> -		virtqueue_disable_cb(vi->rvq);
> -		__napi_schedule(&vi->napi);
> -	}
> +	virtnet_napi_enable(vi);
>  	return 0;
>  }
>  
> --
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From: Rusty Russell <rusty at rustcorp.com.au>
Date: Thu, 10 Feb 2011 12:32:50 +1030
> From: "Bruce Rogers" <brogers at novell.com>
> 
> Under harsh testing conditions, including low memory, the guest would
> stop receiving packets. With this patch applied we no longer see any
> problems in the driver while performing these tests for extended periods
> of time.
> 
> Make sure napi is scheduled subsequent to each napi_enable.
> 
> Signed-off-by: Bruce Rogers <brogers at novell.com>
> Signed-off-by: Olaf Kirch <okir at suse.de>
> Cc: stable at kernel.org
> Signed-off-by: Rusty Russell <rusty at rustcorp.com.au>
Applied, thanks everyone.