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Jason Wang

2022-Jul-25 07:21 UTC

[PATCH V6] virtio-net: fix the race between refill work and close

We try using cancel_delayed_work_sync() to prevent the work from
enabling NAPI. This is insufficient since we don't disable the source
of the refill work scheduling. This means an NAPI poll callback after
cancel_delayed_work_sync() can schedule the refill work then can
re-enable the NAPI that leads to use-after-free [1].

Since the work can enable NAPI, we can't simply disable NAPI before
calling cancel_delayed_work_sync(). So fix this by introducing a
dedicated boolean to control whether or not the work could be
scheduled from NAPI.

[1]
=================================================================BUG: KASAN:
use-after-free in refill_work+0x43/0xd4
Read of size 2 at addr ffff88810562c92e by task kworker/2:1/42

CPU: 2 PID: 42 Comm: kworker/2:1 Not tainted 5.19.0-rc1+ #480
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS
rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
Workqueue: events refill_work
Call Trace:
 <TASK>
 dump_stack_lvl+0x34/0x44
 print_report.cold+0xbb/0x6ac
 ? _printk+0xad/0xde
 ? refill_work+0x43/0xd4
 kasan_report+0xa8/0x130
 ? refill_work+0x43/0xd4
 refill_work+0x43/0xd4
 process_one_work+0x43d/0x780
 worker_thread+0x2a0/0x6f0
 ? process_one_work+0x780/0x780
 kthread+0x167/0x1a0
 ? kthread_exit+0x50/0x50
 ret_from_fork+0x22/0x30
 </TASK>
...

Fixes: b2baed69e605c ("virtio_net: set/cancel work on
ndo_open/ndo_stop")
Signed-off-by: Jason Wang <jasowang at redhat.com>
---
 drivers/net/virtio_net.c | 37 ++++++++++++++++++++++++++++++++++---
 1 file changed, 34 insertions(+), 3 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 356cf8dd4164..ec8e1b3108c3 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -242,9 +242,15 @@ struct virtnet_info {
 	/* Packet virtio header size */
 	u8 hdr_len;
 
-	/* Work struct for refilling if we run low on memory. */
+	/* Work struct for delayed refilling if we run low on memory. */
 	struct delayed_work refill;
 
+	/* Is delayed refill enabled? */
+	bool refill_enabled;
+
+	/* The lock to synchronize the access to refill_enabled */
+	spinlock_t refill_lock;
+
 	/* Work struct for config space updates */
 	struct work_struct config_work;
 
@@ -348,6 +354,20 @@ static struct page *get_a_page(struct receive_queue *rq,
gfp_t gfp_mask)
 	return p;
 }
 
+static void enable_delayed_refill(struct virtnet_info *vi)
+{
+	spin_lock_bh(&vi->refill_lock);
+	vi->refill_enabled = true;
+	spin_unlock_bh(&vi->refill_lock);
+}
+
+static void disable_delayed_refill(struct virtnet_info *vi)
+{
+	spin_lock_bh(&vi->refill_lock);
+	vi->refill_enabled = false;
+	spin_unlock_bh(&vi->refill_lock);
+}
+
 static void virtqueue_napi_schedule(struct napi_struct *napi,
 				    struct virtqueue *vq)
 {
@@ -1527,8 +1547,12 @@ static int virtnet_receive(struct receive_queue *rq, int
budget,
 	}
 
 	if (rq->vq->num_free > min((unsigned int)budget,
virtqueue_get_vring_size(rq->vq)) / 2) {
-		if (!try_fill_recv(vi, rq, GFP_ATOMIC))
-			schedule_delayed_work(&vi->refill, 0);
+		if (!try_fill_recv(vi, rq, GFP_ATOMIC)) {
+			spin_lock(&vi->refill_lock);
+			if (vi->refill_enabled)
+				schedule_delayed_work(&vi->refill, 0);
+			spin_unlock(&vi->refill_lock);
+		}
 	}
 
 	u64_stats_update_begin(&rq->stats.syncp);
@@ -1651,6 +1675,8 @@ static int virtnet_open(struct net_device *dev)
 	struct virtnet_info *vi = netdev_priv(dev);
 	int i, err;
 
+	enable_delayed_refill(vi);
+
 	for (i = 0; i < vi->max_queue_pairs; i++) {
 		if (i < vi->curr_queue_pairs)
 			/* Make sure we have some buffers: if oom use wq. */
@@ -2033,6 +2059,8 @@ static int virtnet_close(struct net_device *dev)
 	struct virtnet_info *vi = netdev_priv(dev);
 	int i;
 
+	/* Make sure NAPI doesn't schedule refill work */
+	disable_delayed_refill(vi);
 	/* Make sure refill_work doesn't re-enable napi! */
 	cancel_delayed_work_sync(&vi->refill);
 
@@ -2792,6 +2820,8 @@ static int virtnet_restore_up(struct virtio_device *vdev)
 
 	virtio_device_ready(vdev);
 
+	enable_delayed_refill(vi);
+
 	if (netif_running(vi->dev)) {
 		err = virtnet_open(vi->dev);
 		if (err)
@@ -3535,6 +3565,7 @@ static int virtnet_probe(struct virtio_device *vdev)
 	vdev->priv = vi;
 
 	INIT_WORK(&vi->config_work, virtnet_config_changed_work);
+	spin_lock_init(&vi->refill_lock);
 
 	/* If we can receive ANY GSO packets, we must allocate large ones. */
 	if (virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO4) ||
-- 
2.25.1

Jason Wang

2022-Jul-25 07:23 UTC

head link

[PATCH V6] virtio-net: fix the race between refill work and close

On Mon, Jul 25, 2022 at 3:22 PM Jason Wang <jasowang at redhat.com>
wrote:>
> We try using cancel_delayed_work_sync() to prevent the work from
> enabling NAPI. This is insufficient since we don't disable the source
> of the refill work scheduling. This means an NAPI poll callback after
> cancel_delayed_work_sync() can schedule the refill work then can
> re-enable the NAPI that leads to use-after-free [1].
>
> Since the work can enable NAPI, we can't simply disable NAPI before
> calling cancel_delayed_work_sync(). So fix this by introducing a
> dedicated boolean to control whether or not the work could be
> scheduled from NAPI.
In case this is not too late, the patch is for -net. (otherwise i can repost).

Thanks
>
> [1]
> =================================================================> BUG:
KASAN: use-after-free in refill_work+0x43/0xd4
> Read of size 2 at addr ffff88810562c92e by task kworker/2:1/42
>
> CPU: 2 PID: 42 Comm: kworker/2:1 Not tainted 5.19.0-rc1+ #480
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS
rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
> Workqueue: events refill_work
> Call Trace:
>  <TASK>
>  dump_stack_lvl+0x34/0x44
>  print_report.cold+0xbb/0x6ac
>  ? _printk+0xad/0xde
>  ? refill_work+0x43/0xd4
>  kasan_report+0xa8/0x130
>  ? refill_work+0x43/0xd4
>  refill_work+0x43/0xd4
>  process_one_work+0x43d/0x780
>  worker_thread+0x2a0/0x6f0
>  ? process_one_work+0x780/0x780
>  kthread+0x167/0x1a0
>  ? kthread_exit+0x50/0x50
>  ret_from_fork+0x22/0x30
>  </TASK>
> ...
>
> Fixes: b2baed69e605c ("virtio_net: set/cancel work on
ndo_open/ndo_stop")
> Signed-off-by: Jason Wang <jasowang at redhat.com>
> ---
>  drivers/net/virtio_net.c | 37 ++++++++++++++++++++++++++++++++++---
>  1 file changed, 34 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 356cf8dd4164..ec8e1b3108c3 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -242,9 +242,15 @@ struct virtnet_info {
>         /* Packet virtio header size */
>         u8 hdr_len;
>
> -       /* Work struct for refilling if we run low on memory. */
> +       /* Work struct for delayed refilling if we run low on memory. */
>         struct delayed_work refill;
>
> +       /* Is delayed refill enabled? */
> +       bool refill_enabled;
> +
> +       /* The lock to synchronize the access to refill_enabled */
> +       spinlock_t refill_lock;
> +
>         /* Work struct for config space updates */
>         struct work_struct config_work;
>
> @@ -348,6 +354,20 @@ static struct page *get_a_page(struct receive_queue
*rq, gfp_t gfp_mask)
>         return p;
>  }
>
> +static void enable_delayed_refill(struct virtnet_info *vi)
> +{
> +       spin_lock_bh(&vi->refill_lock);
> +       vi->refill_enabled = true;
> +       spin_unlock_bh(&vi->refill_lock);
> +}
> +
> +static void disable_delayed_refill(struct virtnet_info *vi)
> +{
> +       spin_lock_bh(&vi->refill_lock);
> +       vi->refill_enabled = false;
> +       spin_unlock_bh(&vi->refill_lock);
> +}
> +
>  static void virtqueue_napi_schedule(struct napi_struct *napi,
>                                     struct virtqueue *vq)
>  {
> @@ -1527,8 +1547,12 @@ static int virtnet_receive(struct receive_queue *rq,
int budget,
>         }
>
>         if (rq->vq->num_free > min((unsigned int)budget,
virtqueue_get_vring_size(rq->vq)) / 2) {
> -               if (!try_fill_recv(vi, rq, GFP_ATOMIC))
> -                       schedule_delayed_work(&vi->refill, 0);
> +               if (!try_fill_recv(vi, rq, GFP_ATOMIC)) {
> +                       spin_lock(&vi->refill_lock);
> +                       if (vi->refill_enabled)
> +                               schedule_delayed_work(&vi->refill,
0);
> +                       spin_unlock(&vi->refill_lock);
> +               }
>         }
>
>         u64_stats_update_begin(&rq->stats.syncp);
> @@ -1651,6 +1675,8 @@ static int virtnet_open(struct net_device *dev)
>         struct virtnet_info *vi = netdev_priv(dev);
>         int i, err;
>
> +       enable_delayed_refill(vi);
> +
>         for (i = 0; i < vi->max_queue_pairs; i++) {
>                 if (i < vi->curr_queue_pairs)
>                         /* Make sure we have some buffers: if oom use wq.
*/
> @@ -2033,6 +2059,8 @@ static int virtnet_close(struct net_device *dev)
>         struct virtnet_info *vi = netdev_priv(dev);
>         int i;
>
> +       /* Make sure NAPI doesn't schedule refill work */
> +       disable_delayed_refill(vi);
>         /* Make sure refill_work doesn't re-enable napi! */
>         cancel_delayed_work_sync(&vi->refill);
>
> @@ -2792,6 +2820,8 @@ static int virtnet_restore_up(struct virtio_device
*vdev)
>
>         virtio_device_ready(vdev);
>
> +       enable_delayed_refill(vi);
> +
>         if (netif_running(vi->dev)) {
>                 err = virtnet_open(vi->dev);
>                 if (err)
> @@ -3535,6 +3565,7 @@ static int virtnet_probe(struct virtio_device *vdev)
>         vdev->priv = vi;
>
>         INIT_WORK(&vi->config_work, virtnet_config_changed_work);
> +       spin_lock_init(&vi->refill_lock);
>
>         /* If we can receive ANY GSO packets, we must allocate large ones.
*/
>         if (virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO4) ||
> --
> 2.25.1
>

Michael S. Tsirkin

2022-Jul-25 07:46 UTC

head link

[PATCH V6] virtio-net: fix the race between refill work and close

On Mon, Jul 25, 2022 at 03:21:59PM +0800, Jason Wang
wrote:> We try using cancel_delayed_work_sync() to prevent the work from
> enabling NAPI. This is insufficient since we don't disable the source
> of the refill work scheduling. This means an NAPI poll callback after
> cancel_delayed_work_sync() can schedule the refill work then can
> re-enable the NAPI that leads to use-after-free [1].
> 
> Since the work can enable NAPI, we can't simply disable NAPI before
> calling cancel_delayed_work_sync(). So fix this by introducing a
> dedicated boolean to control whether or not the work could be
> scheduled from NAPI.
> 
> [1]
> =================================================================> BUG:
KASAN: use-after-free in refill_work+0x43/0xd4
> Read of size 2 at addr ffff88810562c92e by task kworker/2:1/42
> 
> CPU: 2 PID: 42 Comm: kworker/2:1 Not tainted 5.19.0-rc1+ #480
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS
rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
> Workqueue: events refill_work
> Call Trace:
>  <TASK>
>  dump_stack_lvl+0x34/0x44
>  print_report.cold+0xbb/0x6ac
>  ? _printk+0xad/0xde
>  ? refill_work+0x43/0xd4
>  kasan_report+0xa8/0x130
>  ? refill_work+0x43/0xd4
>  refill_work+0x43/0xd4
>  process_one_work+0x43d/0x780
>  worker_thread+0x2a0/0x6f0
>  ? process_one_work+0x780/0x780
>  kthread+0x167/0x1a0
>  ? kthread_exit+0x50/0x50
>  ret_from_fork+0x22/0x30
>  </TASK>
> ...
> 
> Fixes: b2baed69e605c ("virtio_net: set/cancel work on
ndo_open/ndo_stop")
> Signed-off-by: Jason Wang <jasowang at redhat.com>
That's very clean, thanks!

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


> ---
>  drivers/net/virtio_net.c | 37 ++++++++++++++++++++++++++++++++++---
>  1 file changed, 34 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 356cf8dd4164..ec8e1b3108c3 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -242,9 +242,15 @@ struct virtnet_info {
>  	/* Packet virtio header size */
>  	u8 hdr_len;
>  
> -	/* Work struct for refilling if we run low on memory. */
> +	/* Work struct for delayed refilling if we run low on memory. */
>  	struct delayed_work refill;
>  
> +	/* Is delayed refill enabled? */
> +	bool refill_enabled;
> +
> +	/* The lock to synchronize the access to refill_enabled */
> +	spinlock_t refill_lock;
> +
>  	/* Work struct for config space updates */
>  	struct work_struct config_work;
>  
> @@ -348,6 +354,20 @@ static struct page *get_a_page(struct receive_queue
*rq, gfp_t gfp_mask)
>  	return p;
>  }
>  
> +static void enable_delayed_refill(struct virtnet_info *vi)
> +{
> +	spin_lock_bh(&vi->refill_lock);
> +	vi->refill_enabled = true;
> +	spin_unlock_bh(&vi->refill_lock);
> +}
> +
> +static void disable_delayed_refill(struct virtnet_info *vi)
> +{
> +	spin_lock_bh(&vi->refill_lock);
> +	vi->refill_enabled = false;
> +	spin_unlock_bh(&vi->refill_lock);
> +}
> +
>  static void virtqueue_napi_schedule(struct napi_struct *napi,
>  				    struct virtqueue *vq)
>  {
> @@ -1527,8 +1547,12 @@ static int virtnet_receive(struct receive_queue *rq,
int budget,
>  	}
>  
>  	if (rq->vq->num_free > min((unsigned int)budget,
virtqueue_get_vring_size(rq->vq)) / 2) {
> -		if (!try_fill_recv(vi, rq, GFP_ATOMIC))
> -			schedule_delayed_work(&vi->refill, 0);
> +		if (!try_fill_recv(vi, rq, GFP_ATOMIC)) {
> +			spin_lock(&vi->refill_lock);
> +			if (vi->refill_enabled)
> +				schedule_delayed_work(&vi->refill, 0);
> +			spin_unlock(&vi->refill_lock);
> +		}
>  	}
>  
>  	u64_stats_update_begin(&rq->stats.syncp);
> @@ -1651,6 +1675,8 @@ static int virtnet_open(struct net_device *dev)
>  	struct virtnet_info *vi = netdev_priv(dev);
>  	int i, err;
>  
> +	enable_delayed_refill(vi);
> +
>  	for (i = 0; i < vi->max_queue_pairs; i++) {
>  		if (i < vi->curr_queue_pairs)
>  			/* Make sure we have some buffers: if oom use wq. */
> @@ -2033,6 +2059,8 @@ static int virtnet_close(struct net_device *dev)
>  	struct virtnet_info *vi = netdev_priv(dev);
>  	int i;
>  
> +	/* Make sure NAPI doesn't schedule refill work */
> +	disable_delayed_refill(vi);
>  	/* Make sure refill_work doesn't re-enable napi! */
>  	cancel_delayed_work_sync(&vi->refill);
>  
> @@ -2792,6 +2820,8 @@ static int virtnet_restore_up(struct virtio_device
*vdev)
>  
>  	virtio_device_ready(vdev);
>  
> +	enable_delayed_refill(vi);
> +
>  	if (netif_running(vi->dev)) {
>  		err = virtnet_open(vi->dev);
>  		if (err)
> @@ -3535,6 +3565,7 @@ static int virtnet_probe(struct virtio_device *vdev)
>  	vdev->priv = vi;
>  
>  	INIT_WORK(&vi->config_work, virtnet_config_changed_work);
> +	spin_lock_init(&vi->refill_lock);
>  
>  	/* If we can receive ANY GSO packets, we must allocate large ones. */
>  	if (virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO4) ||
> -- 
> 2.25.1

Xuan Zhuo

2022-Jul-25 09:39 UTC

head link

[PATCH V6] virtio-net: fix the race between refill work and close

On Mon, 25 Jul 2022 15:21:59 +0800, Jason Wang <jasowang at redhat.com>
wrote:> We try using cancel_delayed_work_sync() to prevent the work from
> enabling NAPI. This is insufficient since we don't disable the source
> of the refill work scheduling. This means an NAPI poll callback after
> cancel_delayed_work_sync() can schedule the refill work then can
> re-enable the NAPI that leads to use-after-free [1].
>
> Since the work can enable NAPI, we can't simply disable NAPI before
> calling cancel_delayed_work_sync(). So fix this by introducing a
> dedicated boolean to control whether or not the work could be
> scheduled from NAPI.
>
> [1]
> =================================================================> BUG:
KASAN: use-after-free in refill_work+0x43/0xd4
> Read of size 2 at addr ffff88810562c92e by task kworker/2:1/42
>
> CPU: 2 PID: 42 Comm: kworker/2:1 Not tainted 5.19.0-rc1+ #480
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS
rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
> Workqueue: events refill_work
> Call Trace:
>  <TASK>
>  dump_stack_lvl+0x34/0x44
>  print_report.cold+0xbb/0x6ac
>  ? _printk+0xad/0xde
>  ? refill_work+0x43/0xd4
>  kasan_report+0xa8/0x130
>  ? refill_work+0x43/0xd4
>  refill_work+0x43/0xd4
>  process_one_work+0x43d/0x780
>  worker_thread+0x2a0/0x6f0
>  ? process_one_work+0x780/0x780
>  kthread+0x167/0x1a0
>  ? kthread_exit+0x50/0x50
>  ret_from_fork+0x22/0x30
>  </TASK>
> ...
>
> Fixes: b2baed69e605c ("virtio_net: set/cancel work on
ndo_open/ndo_stop")
> Signed-off-by: Jason Wang <jasowang at redhat.com>
Reviewed-by: Xuan Zhuo <xuanzhuo at linux.alibaba.com>
> ---
>  drivers/net/virtio_net.c | 37 ++++++++++++++++++++++++++++++++++---
>  1 file changed, 34 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 356cf8dd4164..ec8e1b3108c3 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -242,9 +242,15 @@ struct virtnet_info {
>  	/* Packet virtio header size */
>  	u8 hdr_len;
>
> -	/* Work struct for refilling if we run low on memory. */
> +	/* Work struct for delayed refilling if we run low on memory. */
>  	struct delayed_work refill;
>
> +	/* Is delayed refill enabled? */
> +	bool refill_enabled;
> +
> +	/* The lock to synchronize the access to refill_enabled */
> +	spinlock_t refill_lock;
> +
>  	/* Work struct for config space updates */
>  	struct work_struct config_work;
>
> @@ -348,6 +354,20 @@ static struct page *get_a_page(struct receive_queue
*rq, gfp_t gfp_mask)
>  	return p;
>  }
>
> +static void enable_delayed_refill(struct virtnet_info *vi)
> +{
> +	spin_lock_bh(&vi->refill_lock);
> +	vi->refill_enabled = true;
> +	spin_unlock_bh(&vi->refill_lock);
> +}
> +
> +static void disable_delayed_refill(struct virtnet_info *vi)
> +{
> +	spin_lock_bh(&vi->refill_lock);
> +	vi->refill_enabled = false;
> +	spin_unlock_bh(&vi->refill_lock);
> +}
> +
>  static void virtqueue_napi_schedule(struct napi_struct *napi,
>  				    struct virtqueue *vq)
>  {
> @@ -1527,8 +1547,12 @@ static int virtnet_receive(struct receive_queue *rq,
int budget,
>  	}
>
>  	if (rq->vq->num_free > min((unsigned int)budget,
virtqueue_get_vring_size(rq->vq)) / 2) {
> -		if (!try_fill_recv(vi, rq, GFP_ATOMIC))
> -			schedule_delayed_work(&vi->refill, 0);
> +		if (!try_fill_recv(vi, rq, GFP_ATOMIC)) {
> +			spin_lock(&vi->refill_lock);
> +			if (vi->refill_enabled)
> +				schedule_delayed_work(&vi->refill, 0);
> +			spin_unlock(&vi->refill_lock);
> +		}
>  	}
>
>  	u64_stats_update_begin(&rq->stats.syncp);
> @@ -1651,6 +1675,8 @@ static int virtnet_open(struct net_device *dev)
>  	struct virtnet_info *vi = netdev_priv(dev);
>  	int i, err;
>
> +	enable_delayed_refill(vi);
> +
>  	for (i = 0; i < vi->max_queue_pairs; i++) {
>  		if (i < vi->curr_queue_pairs)
>  			/* Make sure we have some buffers: if oom use wq. */
> @@ -2033,6 +2059,8 @@ static int virtnet_close(struct net_device *dev)
>  	struct virtnet_info *vi = netdev_priv(dev);
>  	int i;
>
> +	/* Make sure NAPI doesn't schedule refill work */
> +	disable_delayed_refill(vi);
>  	/* Make sure refill_work doesn't re-enable napi! */
>  	cancel_delayed_work_sync(&vi->refill);
>
> @@ -2792,6 +2820,8 @@ static int virtnet_restore_up(struct virtio_device
*vdev)
>
>  	virtio_device_ready(vdev);
>
> +	enable_delayed_refill(vi);
> +
>  	if (netif_running(vi->dev)) {
>  		err = virtnet_open(vi->dev);
>  		if (err)
> @@ -3535,6 +3565,7 @@ static int virtnet_probe(struct virtio_device *vdev)
>  	vdev->priv = vi;
>
>  	INIT_WORK(&vi->config_work, virtnet_config_changed_work);
> +	spin_lock_init(&vi->refill_lock);
>
>  	/* If we can receive ANY GSO packets, we must allocate large ones. */
>  	if (virtio_has_feature(vdev, VIRTIO_NET_F_GUEST_TSO4) ||
> --
> 2.25.1
>

Virtualization - Jul 2022 - [PATCH V6] virtio-net: fix the race between refill work and close

[PATCH V6] virtio-net: fix the race between refill work and close

[PATCH V6] virtio-net: fix the race between refill work and close

[PATCH V6] virtio-net: fix the race between refill work and close

[PATCH V6] virtio-net: fix the race between refill work and close