virtio-net: correctly enable callback during start_xmit

[ Upstream commit 2ea20770c6f8c8ffddaf960d26b054f1ab1a6646 ]

Commit 3d651258564f("virtio_net: disable cb aggressively") enables
virtqueue callback via the following statement:

        do {
		if (use_napi)
			virtqueue_disable_cb(sq->vq);

		free_old_xmit_skbs(sq, false);

	} while (use_napi && kick &&
               unlikely(!virtqueue_enable_cb_delayed(sq->vq)));

When NAPI is used and kick is false, the callback won't be enabled
here. And when the virtqueue is about to be full, the tx will be
disabled, but we still don't enable tx interrupt which will cause a TX
hang. This could be observed when using pktgen with burst enabled.

TO be consistent with the logic that tries to disable cb only for
NAPI, fixing this by trying to enable delayed callback only when NAPI
is enabled when the queue is about to be full.

Fixes: 3d651258564f ("virtio_net: disable cb aggressively")
Signed-off-by: Jason Wang <jasowang@redhat.com>
Tested-by: Laurent Vivier <lvivier@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 86e52454b5b5c550c0ebdf7c1d65c8a9f087e515..3cd15f16090f17f1d6bb7a8e8c955108f99705ae 100644 (file)
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -1873,8 +1873,10 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
         */
        if (sq->vq->num_free < 2+MAX_SKB_FRAGS) {
                netif_stop_subqueue(dev, qnum);
-               if (!use_napi &&
-                   unlikely(!virtqueue_enable_cb_delayed(sq->vq))) {
+               if (use_napi) {
+                       if (unlikely(!virtqueue_enable_cb_delayed(sq->vq)))
+                               virtqueue_napi_schedule(&sq->napi, sq->vq);
+               } else if (unlikely(!virtqueue_enable_cb_delayed(sq->vq))) {
                        /* More just got used, free them then recheck. */
                        free_old_xmit_skbs(sq, false);
                        if (sq->vq->num_free >= 2+MAX_SKB_FRAGS) {