vhost-net: flush batched before enabling notifications

commit e430451613c7a27beeadd00d707bcf7ceec6328e upstream.

Commit 8c2e6b26ffe2 ("vhost/net: Defer TX queue re-enable until after
sendmsg") tries to defer the notification enabling by moving the logic
out of the loop after the vhost_tx_batch() when nothing new is spotted.
This caused unexpected side effects as the new logic is reused for
several other error conditions.

A previous patch reverted 8c2e6b26ffe2. Now, bring the performance
back up by flushing batched buffers before enabling notifications.

Reported-by: Jon Kohler <jon@nutanix.com>
Cc: stable@vger.kernel.org
Fixes: 8c2e6b26ffe2 ("vhost/net: Defer TX queue re-enable until after sendmsg")
Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Message-Id: <20250917063045.2042-3-jasowang@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 2c780950b39d531bfebe6396b7947270c50a071c..c5902cc261e5b00edd0e9f9fa83e82720dc59a08 100644 (file)
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -774,6 +774,11 @@ static void handle_tx_copy(struct vhost_net *net, struct socket *sock)
                        break;
                /* Nothing new?  Wait for eventfd to tell us they refilled. */
                if (head == vq->num) {
+                       /* Flush batched packets to handle pending RX
+                        * work (if busyloop_intr is set) and to avoid
+                        * unnecessary virtqueue kicks.
+                        */
+                       vhost_tx_batch(net, nvq, sock, &msg);
                        if (unlikely(busyloop_intr)) {
                                vhost_poll_queue(&vq->poll);
                        } else if (unlikely(vhost_enable_notify(&net->dev,