Commit 4bc12818b363 ("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.

Reviewed-by: Bui Quang Minh <minhquangbu...@gmail.com>
Fixes: 4bc12818b363 ("virtio-net: disable delayed refill when pausing rx")
Fixes: 413f0271f396 ("net: protect NAPI enablement with netdev_lock()")
Signed-off-by: Jakub Kicinski <k...@kernel.org>
---
v2:
 - wrap schedule under the spin lock
v1: https://lore.kernel.org/20250429143104.2576553-1-k...@kernel.org

CC: m...@redhat.com
CC: jasow...@redhat.com
CC: xuanz...@linux.alibaba.com
CC: epere...@redhat.com
CC: minhquangbu...@gmail.com
CC: rom...@fr.zoreil.com
CC: kun...@amazon.com
CC: virtualizat...@lists.linux.dev
---
 drivers/net/virtio_net.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index c107916b685e..f9e3e628ec4d 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -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;
 }
-- 
2.49.0


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