[PATCH net 2/2] virtio_net: mask callbacks before releasing NAPI ownership

[Congjie Zhou]

virtqueue_napi_complete() prepares callbacks before calling
napi_complete_done(), then disables them if completion returns false.
On the hard IRQ deferral path, completion can release NAPI ownership
and arm the watchdog before returning false.

A successor poll can rearm callbacks and complete before the old caller
executes virtqueue_disable_cb(). The stale mask then disables
notifications again. If the one-shot watchdog has already run, no NAPI
owner or timer remains to consume later used entries, causing a
persistent RX stall.

Use napi_complete_done_with_irq_mask() to disable callbacks before
completion can hand NAPI to a successor, and remove the stale mask after
a false return. Keep virtqueue_enable_cb_prepare() before completion:
moving it after ownership release would reintroduce the RX virtqueue
race fixed by commit cbdadbbf0c79 ("virtio_net: fix race in RX VQ
processing").

Signed-off-by: Congjie Zhou <zcjie0802@xxxxxx>
---
 drivers/net/virtio_net.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index dd2c41ef6..0de6bd95a 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -727,19 +727,23 @@ static void virtqueue_napi_schedule(struct napi_struct *napi,
 	}
 }
 
+static void virtqueue_napi_mask(void *data)
+{
+	virtqueue_disable_cb(data);
+}
+
 static bool virtqueue_napi_complete(struct napi_struct *napi,
 				    struct virtqueue *vq, int processed)
 {
 	int opaque;
 
 	opaque = virtqueue_enable_cb_prepare(vq);
-	if (napi_complete_done(napi, processed)) {
+	if (napi_complete_done_with_irq_mask(napi, processed,
+					     virtqueue_napi_mask, vq)) {
 		if (unlikely(virtqueue_poll(vq, opaque)))
 			virtqueue_napi_schedule(napi, vq);
 		else
 			return true;
-	} else {
-		virtqueue_disable_cb(vq);
 	}
 
 	return false;
-- 
2.43.0