[PATCH V2] virtio-net: fix the race between refill work and close

[PATCH V2] virtio-net: fix the race between refill work and close

[Jason Wang]

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@redhat.com>
---
 drivers/net/virtio_net.c | 38 ++++++++++++++++++++++++++++++++++++--
 1 file changed, 36 insertions(+), 2 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index db05b5e930be..21bf1e5c81ef 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -251,6 +251,12 @@ struct virtnet_info {
 	/* Does the affinity hint is set for virtqueues? */
 	bool affinity_hint_set;
 
+	/* Is refill work enabled? */
+	bool refill_work_enabled;
+
+	/* The lock to synchronize the access to refill_work_enabled */
+	spinlock_t refill_lock;
+
 	/* CPU hotplug instances for online & dead */
 	struct hlist_node node;
 	struct hlist_node node_dead;
@@ -348,6 +354,20 @@ static struct page *get_a_page(struct receive_queue *rq, gfp_t gfp_mask)
 	return p;
 }
 
+static void enable_refill_work(struct virtnet_info *vi)
+{
+	spin_lock(&vi->refill_lock);
+	vi->refill_work_enabled = true;
+	spin_unlock(&vi->refill_lock);
+}
+
+static void disable_refill_work(struct virtnet_info *vi)
+{
+	spin_lock(&vi->refill_lock);
+	vi->refill_work_enabled = false;
+	spin_unlock(&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_work_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_refill_work(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_refill_work(vi);
 	/* Make sure refill_work doesn't re-enable napi! */
 	cancel_delayed_work_sync(&vi->refill);
 
@@ -2776,6 +2804,9 @@ static void virtnet_freeze_down(struct virtio_device *vdev)
 	netif_tx_lock_bh(vi->dev);
 	netif_device_detach(vi->dev);
 	netif_tx_unlock_bh(vi->dev);
+	/* Make sure NAPI doesn't schedule refill work */
+	disable_refill_work(vi);
+	/* Make sure refill_work doesn't re-enable napi! */
 	cancel_delayed_work_sync(&vi->refill);
 
 	if (netif_running(vi->dev)) {
@@ -2799,6 +2830,8 @@ static int virtnet_restore_up(struct virtio_device *vdev)
 
 	virtio_device_ready(vdev);
 
+	enable_refill_work(vi);
+
 	if (netif_running(vi->dev)) {
 		for (i = 0; i < vi->curr_queue_pairs; i++)
 			if (!try_fill_recv(vi, &vi->rq[i], GFP_KERNEL))
@@ -3548,6 +3581,7 @@ 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

[PATCH V2] virtio-net: fix the race between refill work and close

[Jason Wang]

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@redhat.com>
---
 drivers/net/virtio_net.c | 38 ++++++++++++++++++++++++++++++++++++--
 1 file changed, 36 insertions(+), 2 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index db05b5e930be..21bf1e5c81ef 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -251,6 +251,12 @@ struct virtnet_info {
 	/* Does the affinity hint is set for virtqueues? */
 	bool affinity_hint_set;
 
+	/* Is refill work enabled? */
+	bool refill_work_enabled;
+
+	/* The lock to synchronize the access to refill_work_enabled */
+	spinlock_t refill_lock;
+
 	/* CPU hotplug instances for online & dead */
 	struct hlist_node node;
 	struct hlist_node node_dead;
@@ -348,6 +354,20 @@ static struct page *get_a_page(struct receive_queue *rq, gfp_t gfp_mask)
 	return p;
 }
 
+static void enable_refill_work(struct virtnet_info *vi)
+{
+	spin_lock(&vi->refill_lock);
+	vi->refill_work_enabled = true;
+	spin_unlock(&vi->refill_lock);
+}
+
+static void disable_refill_work(struct virtnet_info *vi)
+{
+	spin_lock(&vi->refill_lock);
+	vi->refill_work_enabled = false;
+	spin_unlock(&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_work_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_refill_work(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_refill_work(vi);
 	/* Make sure refill_work doesn't re-enable napi! */
 	cancel_delayed_work_sync(&vi->refill);
 
@@ -2776,6 +2804,9 @@ static void virtnet_freeze_down(struct virtio_device *vdev)
 	netif_tx_lock_bh(vi->dev);
 	netif_device_detach(vi->dev);
 	netif_tx_unlock_bh(vi->dev);
+	/* Make sure NAPI doesn't schedule refill work */
+	disable_refill_work(vi);
+	/* Make sure refill_work doesn't re-enable napi! */
 	cancel_delayed_work_sync(&vi->refill);
 
 	if (netif_running(vi->dev)) {
@@ -2799,6 +2830,8 @@ static int virtnet_restore_up(struct virtio_device *vdev)
 
 	virtio_device_ready(vdev);
 
+	enable_refill_work(vi);
+
 	if (netif_running(vi->dev)) {
 		for (i = 0; i < vi->curr_queue_pairs; i++)
 			if (!try_fill_recv(vi, &vi->rq[i], GFP_KERNEL))
@@ -3548,6 +3581,7 @@ 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

Re: [PATCH V2] virtio-net: fix the race between refill work and close

[Xuan Zhuo]

On Thu, 30 Jun 2022 10:08:04 +0800, Jason Wang <jasowang@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].


Can you explain in more detail how this happened?

napi_disable() is normally called after cancel_delayed_work_sync(). This ensures
that all napi callbacks will end, and the new napi_disable() will wait.
There will be no re-enable napi.

So I guess the use-after-free is caused by refill_work being called after
dev/vi/napi is released. In this way, we can just call
cancel_delayed_work_sync() after napi_disalbe().

Thanks.

>
> 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@redhat.com>
> ---
>  drivers/net/virtio_net.c | 38 ++++++++++++++++++++++++++++++++++++--
>  1 file changed, 36 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index db05b5e930be..21bf1e5c81ef 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -251,6 +251,12 @@ struct virtnet_info {
>  	/* Does the affinity hint is set for virtqueues? */
>  	bool affinity_hint_set;
>
> +	/* Is refill work enabled? */
> +	bool refill_work_enabled;
> +
> +	/* The lock to synchronize the access to refill_work_enabled */
> +	spinlock_t refill_lock;
> +
>  	/* CPU hotplug instances for online & dead */
>  	struct hlist_node node;
>  	struct hlist_node node_dead;
> @@ -348,6 +354,20 @@ static struct page *get_a_page(struct receive_queue *rq, gfp_t gfp_mask)
>  	return p;
>  }
>
> +static void enable_refill_work(struct virtnet_info *vi)
> +{
> +	spin_lock(&vi->refill_lock);
> +	vi->refill_work_enabled = true;
> +	spin_unlock(&vi->refill_lock);
> +}
> +
> +static void disable_refill_work(struct virtnet_info *vi)
> +{
> +	spin_lock(&vi->refill_lock);
> +	vi->refill_work_enabled = false;
> +	spin_unlock(&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_work_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_refill_work(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_refill_work(vi);
>  	/* Make sure refill_work doesn't re-enable napi! */
>  	cancel_delayed_work_sync(&vi->refill);
>
> @@ -2776,6 +2804,9 @@ static void virtnet_freeze_down(struct virtio_device *vdev)
>  	netif_tx_lock_bh(vi->dev);
>  	netif_device_detach(vi->dev);
>  	netif_tx_unlock_bh(vi->dev);
> +	/* Make sure NAPI doesn't schedule refill work */
> +	disable_refill_work(vi);
> +	/* Make sure refill_work doesn't re-enable napi! */
>  	cancel_delayed_work_sync(&vi->refill);
>
>  	if (netif_running(vi->dev)) {
> @@ -2799,6 +2830,8 @@ static int virtnet_restore_up(struct virtio_device *vdev)
>
>  	virtio_device_ready(vdev);
>
> +	enable_refill_work(vi);
> +
>  	if (netif_running(vi->dev)) {
>  		for (i = 0; i < vi->curr_queue_pairs; i++)
>  			if (!try_fill_recv(vi, &vi->rq[i], GFP_KERNEL))
> @@ -3548,6 +3581,7 @@ 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
>

Re: [PATCH V2] virtio-net: fix the race between refill work and close

[Jason Wang]

On Thu, Jun 30, 2022 at 10:22 AM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote:
>
> On Thu, 30 Jun 2022 10:08:04 +0800, Jason Wang <jasowang@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].
>
>
> Can you explain in more detail how this happened?
>
> napi_disable() is normally called after cancel_delayed_work_sync(). This ensures
> that all napi callbacks will end, and the new napi_disable() will wait.
> There will be no re-enable napi.

An rx interrupt that may come between after the cancel_delayed_work()
but before the napi_disable(). It schedules a refill_work that may run
after the napi_disable() in virtnet_close().

>
> So I guess the use-after-free is caused by refill_work being called after
> dev/vi/napi is released. In this way, we can just call
> cancel_delayed_work_sync() after napi_disalbe().

So the refill_work can re-enable the NAPI when it is run after
napi_disable() in this case.

Thanks


>
> Thanks.
>
> >
> > 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@redhat.com>
> > ---
> >  drivers/net/virtio_net.c | 38 ++++++++++++++++++++++++++++++++++++--
> >  1 file changed, 36 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index db05b5e930be..21bf1e5c81ef 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -251,6 +251,12 @@ struct virtnet_info {
> >       /* Does the affinity hint is set for virtqueues? */
> >       bool affinity_hint_set;
> >
> > +     /* Is refill work enabled? */
> > +     bool refill_work_enabled;
> > +
> > +     /* The lock to synchronize the access to refill_work_enabled */
> > +     spinlock_t refill_lock;
> > +
> >       /* CPU hotplug instances for online & dead */
> >       struct hlist_node node;
> >       struct hlist_node node_dead;
> > @@ -348,6 +354,20 @@ static struct page *get_a_page(struct receive_queue *rq, gfp_t gfp_mask)
> >       return p;
> >  }
> >
> > +static void enable_refill_work(struct virtnet_info *vi)
> > +{
> > +     spin_lock(&vi->refill_lock);
> > +     vi->refill_work_enabled = true;
> > +     spin_unlock(&vi->refill_lock);
> > +}
> > +
> > +static void disable_refill_work(struct virtnet_info *vi)
> > +{
> > +     spin_lock(&vi->refill_lock);
> > +     vi->refill_work_enabled = false;
> > +     spin_unlock(&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_work_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_refill_work(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_refill_work(vi);
> >       /* Make sure refill_work doesn't re-enable napi! */
> >       cancel_delayed_work_sync(&vi->refill);
> >
> > @@ -2776,6 +2804,9 @@ static void virtnet_freeze_down(struct virtio_device *vdev)
> >       netif_tx_lock_bh(vi->dev);
> >       netif_device_detach(vi->dev);
> >       netif_tx_unlock_bh(vi->dev);
> > +     /* Make sure NAPI doesn't schedule refill work */
> > +     disable_refill_work(vi);
> > +     /* Make sure refill_work doesn't re-enable napi! */
> >       cancel_delayed_work_sync(&vi->refill);
> >
> >       if (netif_running(vi->dev)) {
> > @@ -2799,6 +2830,8 @@ static int virtnet_restore_up(struct virtio_device *vdev)
> >
> >       virtio_device_ready(vdev);
> >
> > +     enable_refill_work(vi);
> > +
> >       if (netif_running(vi->dev)) {
> >               for (i = 0; i < vi->curr_queue_pairs; i++)
> >                       if (!try_fill_recv(vi, &vi->rq[i], GFP_KERNEL))
> > @@ -3548,6 +3581,7 @@ 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
> >
>

Re: [PATCH V2] virtio-net: fix the race between refill work and close

[Xuan Zhuo]

On Thu, 30 Jun 2022 14:07:52 +0800, Jason Wang <jasowang@redhat.com> wrote:
> On Thu, Jun 30, 2022 at 10:22 AM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote:
> >
> > On Thu, 30 Jun 2022 10:08:04 +0800, Jason Wang <jasowang@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].
> >
> >
> > Can you explain in more detail how this happened?
> >
> > napi_disable() is normally called after cancel_delayed_work_sync(). This ensures
> > that all napi callbacks will end, and the new napi_disable() will wait.
> > There will be no re-enable napi.
>
> An rx interrupt that may come between after the cancel_delayed_work()
> but before the napi_disable(). It schedules a refill_work that may run
> after the napi_disable() in virtnet_close().

Yes


>
> >
> > So I guess the use-after-free is caused by refill_work being called after
> > dev/vi/napi is released. In this way, we can just call
> > cancel_delayed_work_sync() after napi_disalbe().
>
> So the refill_work can re-enable the NAPI when it is run after
> napi_disable() in this case.


Since napi_disable() has been called in virtnet_close(), it will get stuck when
napi_disable() in refill_work(). I think use-after-free is because vi/napi etc.
have been released, refill_work() going to access again causes an exception.

napi will not be re-enable.

I would like to call cancel_delayed_work_sync() after napi_disable()
to solve this problem. But this also has a problem, refill_work() can get stuck
on napi_disable() and cannot exit. In this way, we want napi_disable() to check
that the current state is disabled and exit directly.

Thanks.


>
> Thanks
>
>
> >
> > Thanks.
> >
> > >
> > > 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@redhat.com>
> > > ---
> > >  drivers/net/virtio_net.c | 38 ++++++++++++++++++++++++++++++++++++--
> > >  1 file changed, 36 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > index db05b5e930be..21bf1e5c81ef 100644
> > > --- a/drivers/net/virtio_net.c
> > > +++ b/drivers/net/virtio_net.c
> > > @@ -251,6 +251,12 @@ struct virtnet_info {
> > >       /* Does the affinity hint is set for virtqueues? */
> > >       bool affinity_hint_set;
> > >
> > > +     /* Is refill work enabled? */
> > > +     bool refill_work_enabled;
> > > +
> > > +     /* The lock to synchronize the access to refill_work_enabled */
> > > +     spinlock_t refill_lock;
> > > +
> > >       /* CPU hotplug instances for online & dead */
> > >       struct hlist_node node;
> > >       struct hlist_node node_dead;
> > > @@ -348,6 +354,20 @@ static struct page *get_a_page(struct receive_queue *rq, gfp_t gfp_mask)
> > >       return p;
> > >  }
> > >
> > > +static void enable_refill_work(struct virtnet_info *vi)
> > > +{
> > > +     spin_lock(&vi->refill_lock);
> > > +     vi->refill_work_enabled = true;
> > > +     spin_unlock(&vi->refill_lock);
> > > +}
> > > +
> > > +static void disable_refill_work(struct virtnet_info *vi)
> > > +{
> > > +     spin_lock(&vi->refill_lock);
> > > +     vi->refill_work_enabled = false;
> > > +     spin_unlock(&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_work_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_refill_work(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_refill_work(vi);
> > >       /* Make sure refill_work doesn't re-enable napi! */
> > >       cancel_delayed_work_sync(&vi->refill);
> > >
> > > @@ -2776,6 +2804,9 @@ static void virtnet_freeze_down(struct virtio_device *vdev)
> > >       netif_tx_lock_bh(vi->dev);
> > >       netif_device_detach(vi->dev);
> > >       netif_tx_unlock_bh(vi->dev);
> > > +     /* Make sure NAPI doesn't schedule refill work */
> > > +     disable_refill_work(vi);
> > > +     /* Make sure refill_work doesn't re-enable napi! */
> > >       cancel_delayed_work_sync(&vi->refill);
> > >
> > >       if (netif_running(vi->dev)) {
> > > @@ -2799,6 +2830,8 @@ static int virtnet_restore_up(struct virtio_device *vdev)
> > >
> > >       virtio_device_ready(vdev);
> > >
> > > +     enable_refill_work(vi);
> > > +
> > >       if (netif_running(vi->dev)) {
> > >               for (i = 0; i < vi->curr_queue_pairs; i++)
> > >                       if (!try_fill_recv(vi, &vi->rq[i], GFP_KERNEL))
> > > @@ -3548,6 +3581,7 @@ 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
> > >
> >
>

Re: [PATCH V2] virtio-net: fix the race between refill work and close

[Jason Wang]

On Thu, Jun 30, 2022 at 2:26 PM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote:
>
> On Thu, 30 Jun 2022 14:07:52 +0800, Jason Wang <jasowang@redhat.com> wrote:
> > On Thu, Jun 30, 2022 at 10:22 AM Xuan Zhuo <xuanzhuo@linux.alibaba.com> wrote:
> > >
> > > On Thu, 30 Jun 2022 10:08:04 +0800, Jason Wang <jasowang@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].
> > >
> > >
> > > Can you explain in more detail how this happened?
> > >
> > > napi_disable() is normally called after cancel_delayed_work_sync(). This ensures
> > > that all napi callbacks will end, and the new napi_disable() will wait.
> > > There will be no re-enable napi.
> >
> > An rx interrupt that may come between after the cancel_delayed_work()
> > but before the napi_disable(). It schedules a refill_work that may run
> > after the napi_disable() in virtnet_close().
>
> Yes
>
>
> >
> > >
> > > So I guess the use-after-free is caused by refill_work being called after
> > > dev/vi/napi is released. In this way, we can just call
> > > cancel_delayed_work_sync() after napi_disalbe().
> >
> > So the refill_work can re-enable the NAPI when it is run after
> > napi_disable() in this case.
>
>
> Since napi_disable() has been called in virtnet_close(), it will get stuck when
> napi_disable() in refill_work().

Right because e.g NAPIF_STATE_SCHED has been set by napi_disable() before.

> I think use-after-free is because vi/napi etc.
> have been released, refill_work() going to access again causes an exception.

Yes, this is the use-after-free I mentioned above.

>
> napi will not be re-enable.
>
> I would like to call cancel_delayed_work_sync() after napi_disable()
> to solve this problem. But this also has a problem, refill_work() can get stuck
> on napi_disable() and cannot exit. In this way, we want napi_disable() to check
> that the current state is disabled and exit directly.

Not sure this is a good design and it doesn't fit for -stable.

I think the design of NAPI is to pair napi_enable() and napi_disable()
instead of allowing napi_disable() to be called twice.

Thanks

>
> Thanks.
>
>
> >
> > Thanks
> >
> >
> > >
> > > Thanks.
> > >
> > > >
> > > > 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@redhat.com>
> > > > ---
> > > >  drivers/net/virtio_net.c | 38 ++++++++++++++++++++++++++++++++++++--
> > > >  1 file changed, 36 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > > index db05b5e930be..21bf1e5c81ef 100644
> > > > --- a/drivers/net/virtio_net.c
> > > > +++ b/drivers/net/virtio_net.c
> > > > @@ -251,6 +251,12 @@ struct virtnet_info {
> > > >       /* Does the affinity hint is set for virtqueues? */
> > > >       bool affinity_hint_set;
> > > >
> > > > +     /* Is refill work enabled? */
> > > > +     bool refill_work_enabled;
> > > > +
> > > > +     /* The lock to synchronize the access to refill_work_enabled */
> > > > +     spinlock_t refill_lock;
> > > > +
> > > >       /* CPU hotplug instances for online & dead */
> > > >       struct hlist_node node;
> > > >       struct hlist_node node_dead;
> > > > @@ -348,6 +354,20 @@ static struct page *get_a_page(struct receive_queue *rq, gfp_t gfp_mask)
> > > >       return p;
> > > >  }
> > > >
> > > > +static void enable_refill_work(struct virtnet_info *vi)
> > > > +{
> > > > +     spin_lock(&vi->refill_lock);
> > > > +     vi->refill_work_enabled = true;
> > > > +     spin_unlock(&vi->refill_lock);
> > > > +}
> > > > +
> > > > +static void disable_refill_work(struct virtnet_info *vi)
> > > > +{
> > > > +     spin_lock(&vi->refill_lock);
> > > > +     vi->refill_work_enabled = false;
> > > > +     spin_unlock(&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_work_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_refill_work(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_refill_work(vi);
> > > >       /* Make sure refill_work doesn't re-enable napi! */
> > > >       cancel_delayed_work_sync(&vi->refill);
> > > >
> > > > @@ -2776,6 +2804,9 @@ static void virtnet_freeze_down(struct virtio_device *vdev)
> > > >       netif_tx_lock_bh(vi->dev);
> > > >       netif_device_detach(vi->dev);
> > > >       netif_tx_unlock_bh(vi->dev);
> > > > +     /* Make sure NAPI doesn't schedule refill work */
> > > > +     disable_refill_work(vi);
> > > > +     /* Make sure refill_work doesn't re-enable napi! */
> > > >       cancel_delayed_work_sync(&vi->refill);
> > > >
> > > >       if (netif_running(vi->dev)) {
> > > > @@ -2799,6 +2830,8 @@ static int virtnet_restore_up(struct virtio_device *vdev)
> > > >
> > > >       virtio_device_ready(vdev);
> > > >
> > > > +     enable_refill_work(vi);
> > > > +
> > > >       if (netif_running(vi->dev)) {
> > > >               for (i = 0; i < vi->curr_queue_pairs; i++)
> > > >                       if (!try_fill_recv(vi, &vi->rq[i], GFP_KERNEL))
> > > > @@ -3548,6 +3581,7 @@ 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
> > > >
> > >
> >
>

Re: [PATCH V2] virtio-net: fix the race between refill work and close

[Jakub Kicinski]

On Thu, 30 Jun 2022 10:08:04 +0800 Jason Wang wrote:
> +static void enable_refill_work(struct virtnet_info *vi)
> +{
> +	spin_lock(&vi->refill_lock);
> +	vi->refill_work_enabled = true;
> +	spin_unlock(&vi->refill_lock);
> +}
> +
> +static void disable_refill_work(struct virtnet_info *vi)
> +{
> +	spin_lock(&vi->refill_lock);
> +	vi->refill_work_enabled = false;
> +	spin_unlock(&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_work_enabled)
> +				schedule_delayed_work(&vi->refill, 0);
> +			spin_unlock(&vi->refill_lock);

Are you sure you can use the basic spin_lock() flavor in all cases?
Isn't the disable/enable called from a different context than this
thing here?

The entire delayed work construct seems a little risky because the work
may go to sleep after disabling napi, causing large latency spikes.
I guess you must have a good reason no to simply reschedule the NAPI
and keep retrying with GFP_ATOMIC...

Please add the target tree name to the subject.

Re: [PATCH V2] virtio-net: fix the race between refill work and close

[Jason Wang]

On Thu, Jun 30, 2022 at 10:51 AM Jakub Kicinski <kuba@kernel.org> wrote:
>
> On Thu, 30 Jun 2022 10:08:04 +0800 Jason Wang wrote:
> > +static void enable_refill_work(struct virtnet_info *vi)
> > +{
> > +     spin_lock(&vi->refill_lock);
> > +     vi->refill_work_enabled = true;
> > +     spin_unlock(&vi->refill_lock);
> > +}
> > +
> > +static void disable_refill_work(struct virtnet_info *vi)
> > +{
> > +     spin_lock(&vi->refill_lock);
> > +     vi->refill_work_enabled = false;
> > +     spin_unlock(&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_work_enabled)
> > +                             schedule_delayed_work(&vi->refill, 0);
> > +                     spin_unlock(&vi->refill_lock);
>
> Are you sure you can use the basic spin_lock() flavor in all cases?
> Isn't the disable/enable called from a different context than this
> thing here?

This function will only be called in bh so it's safe.

>
> The entire delayed work construct seems a little risky because the work
> may go to sleep after disabling napi, causing large latency spikes.

Yes, but it only happens on OOM.

> I guess you must have a good reason no to simply reschedule the NAPI
> and keep retrying with GFP_ATOMIC...

Less pressure on the memory allocator on OOM probably, but it looks
like an independent issue that might be optimized in the future.

>
> Please add the target tree name to the subject.

Ok

Thanks

>

Re: [PATCH V2] virtio-net: fix the race between refill work and close

[Jason Wang]

On Thu, Jun 30, 2022 at 2:07 PM Jason Wang <jasowang@redhat.com> wrote:
>
> On Thu, Jun 30, 2022 at 10:51 AM Jakub Kicinski <kuba@kernel.org> wrote:
> >
> > On Thu, 30 Jun 2022 10:08:04 +0800 Jason Wang wrote:
> > > +static void enable_refill_work(struct virtnet_info *vi)
> > > +{
> > > +     spin_lock(&vi->refill_lock);
> > > +     vi->refill_work_enabled = true;
> > > +     spin_unlock(&vi->refill_lock);
> > > +}
> > > +
> > > +static void disable_refill_work(struct virtnet_info *vi)
> > > +{
> > > +     spin_lock(&vi->refill_lock);
> > > +     vi->refill_work_enabled = false;
> > > +     spin_unlock(&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_work_enabled)
> > > +                             schedule_delayed_work(&vi->refill, 0);
> > > +                     spin_unlock(&vi->refill_lock);
> >
> > Are you sure you can use the basic spin_lock() flavor in all cases?
> > Isn't the disable/enable called from a different context than this
> > thing here?
>
> This function will only be called in bh so it's safe.

Ok, so it looks like we should use the bh variant in close. Otherwise
we may have a deadlock. Will fix it.

Thanks

>
> >
> > The entire delayed work construct seems a little risky because the work
> > may go to sleep after disabling napi, causing large latency spikes.
>
> Yes, but it only happens on OOM.
>
> > I guess you must have a good reason no to simply reschedule the NAPI
> > and keep retrying with GFP_ATOMIC...
>
> Less pressure on the memory allocator on OOM probably, but it looks
> like an independent issue that might be optimized in the future.
>
> >
> > Please add the target tree name to the subject.
>
> Ok
>
> Thanks
>
> >