From: Longjun Tang <redacted>

When busy-poll is active, napi_schedule_prep() returns false in
virtqueue_napi_schedule(), so virtqueue_disable_cb() is skipped.
The device may keep firing irqs until reaches virtqueue_napi_complete().
Under load (received == budget), it will lead to a large number
of spurious interrupts.

Fix it by disabling the callback at the virtnet_poll() entry.
This keeps the callback off while we poll and it is re-enabled by
virtqueue_napi_complete() when going idle.

Fixes: ceef438d613f ("virtio_net: remove custom busy_poll")
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Longjun Tang <redacted>

---
V4 -> V5: Guard disable_cb with budget to avoid netpoll stall
V3 -> V4: Update commit message and remove some comments
V2 -> V3: Add fixes tag
V1 -> V2: Remain agnostic to busy polling
---
 drivers/net/virtio_net.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 7d2eeb9b1226..0b3f1bb227d2 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c

@@ -3008,6 +3008,9 @@ static int virtnet_poll(struct napi_struct *napi, int budget)
 	unsigned int xdp_xmit = 0;
 	bool napi_complete;
 
+	if (budget)
+		virtqueue_disable_cb(rq->vq);
+
 	virtnet_poll_cleantx(rq, budget);
 
 	received = virtnet_receive(rq, budget, &xdp_xmit);

-- 
2.43.0