Commit 1e20324b authored by Jakub Kicinski's avatar Jakub Kicinski
Browse files

virtio-net: don't re-enable refill work too early when NAPI is disabled 



Commit 4bc12818 ("virtio-net: disable delayed refill when pausing rx")
fixed a deadlock between reconfig paths and refill work trying to disable
the same NAPI instance. The refill work can't run in parallel with reconfig
because trying to double-disable a NAPI instance causes a stall under the
instance lock, which the reconfig path needs to re-enable the NAPI and
therefore unblock the stalled thread.

There are two cases where we re-enable refill too early. One is in the
virtnet_set_queues() handler. We call it when installing XDP:

   virtnet_rx_pause_all(vi);
   ...
   virtnet_napi_tx_disable(..);
   ...
   virtnet_set_queues(..);
   ...
   virtnet_rx_resume_all(..);

We want the work to be disabled until we call virtnet_rx_resume_all(),
but virtnet_set_queues() kicks it before NAPIs were re-enabled.

The other case is a more trivial case of mis-ordering in
__virtnet_rx_resume() found by code inspection.

Taking the spin lock in virtnet_set_queues() (requested during review)
may be unnecessary as we are under rtnl_lock and so are all paths writing
to ->refill_enabled.

Acked-by: default avatarMichael S. Tsirkin <mst@redhat.com>
Reviewed-by: default avatarBui Quang Minh <minhquangbui99@gmail.com>
Fixes: 4bc12818 ("virtio-net: disable delayed refill when pausing rx")
Fixes: 413f0271 ("net: protect NAPI enablement with netdev_lock()")
Link: https://patch.msgid.link/20250430163758.3029367-1-kuba@kernel.org


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent 75dbdaad

drivers/net/virtio_net.c

+8 −3
Original line number Diff line number Diff line
@@ -3383,12 +3383,15 @@ static void __virtnet_rx_resume(struct virtnet_info *vi, 
				bool refill)

{

	bool running = netif_running(vi->dev);

	bool schedule_refill = false;



	if (refill && !try_fill_recv(vi, rq, GFP_KERNEL))

		schedule_delayed_work(&vi->refill, 0);



		schedule_refill = true;

	if (running)

		virtnet_napi_enable(rq);



	if (schedule_refill)

		schedule_delayed_work(&vi->refill, 0);

}



static void virtnet_rx_resume_all(struct virtnet_info *vi)
@@ -3728,8 +3731,10 @@ static int virtnet_set_queues(struct virtnet_info *vi, u16 queue_pairs) 
succ:

	vi->curr_queue_pairs = queue_pairs;

	/* virtnet_open() will refill when device is going to up. */

	if (dev->flags & IFF_UP)

	spin_lock_bh(&vi->refill_lock);

	if (dev->flags & IFF_UP && vi->refill_enabled)

		schedule_delayed_work(&vi->refill, 0);

	spin_unlock_bh(&vi->refill_lock);



	return 0;

}