[PATCH net v2 0/3] virtio-net: fix the deadlock when disabling rx NAPI

[Bui Quang Minh <minhquangbui99@gmail.com>]

Calling napi_disable() on an already disabled napi can cause the
deadlock. In commit 4bc12818b363 ("virtio-net: disable delayed refill
when pausing rx"), to avoid the deadlock, when pausing the RX in
virtnet_rx_pause[_all](), we disable and cancel the delayed refill work.
However, in the virtnet_rx_resume_all(), we enable the delayed refill
work too early before enabling all the receive queue napis.

The deadlock can be reproduced by running
selftests/drivers/net/hw/xsk_reconfig.py with multiqueue virtio-net
device and inserting a cond_resched() inside the for loop in
virtnet_rx_resume_all() to increase the success rate. Because the worker
processing the delayed refilled work runs on the same CPU as
virtnet_rx_resume_all(), a reschedule is needed to cause the deadlock.
In real scenario, the contention on netdev_lock can cause the
reschedule.

Due to the complexity of delayed refill worker, in this series, we remove
it. When we fail to refill the receive buffer, we will retry in the next
NAPI poll instead.
- Patch 1: removes delayed refill worker schedule and retry refill in next
NAPI
- Patch 2, 3: removes and clean up unused delayed refill worker code

For testing, I've run the following tests with no issue so far
- selftests/drivers/net/hw/xsk_reconfig.py which sets up the XDP zerocopy
without providing any descriptors to the fill ring. As a result,
try_fill_recv will always fail.
- Send TCP packets from host to guest while guest is nearly OOM and some
try_fill_recv calls fail.

Changes in v2:
- Remove the delayed refill worker to simplify the logic instead of trying
to fix it
- Link to v1:
https://lore.kernel.org/netdev/20251223152533.24364-1-minhquangbui99@gmail.com/

Link to the previous approach and discussion:
https://lore.kernel.org/netdev/20251212152741.11656-1-minhquangbui99@gmail.com/

Thanks,
Quang Minh.

Bui Quang Minh (3):
  virtio-net: don't schedule delayed refill worker
  virtio-net: remove unused delayed refill worker
  virtio-net: clean up __virtnet_rx_pause/resume

 drivers/net/virtio_net.c | 171 +++++++++------------------------------
 1 file changed, 40 insertions(+), 131 deletions(-)

-- 
2.43.0