hv_netvsc: fix race that may miss tx queue wakeup

When the ring buffer is almost full due to RX completion messages, a
TX packet may reach the "low watermark" and cause the queue stopped.
If the TX completion arrives earlier than queue stopping, the wakeup
may be missed.

This patch moves the check for the last pending packet to cover both
EAGAIN and success cases, so the queue will be reliably waked up when
necessary.

Reported-and-tested-by: Stephan Klein <stephan.klein@wegfinder.at>
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/hyperv/netvsc.c b/drivers/net/hyperv/netvsc.c
index e0dce373cdd9d875ded78bff545d76b32920f69c..3d4a166a49d58f7ce5909f51d27c64a0fb6a6ce3 100644 (file)
--- a/drivers/net/hyperv/netvsc.c
+++ b/drivers/net/hyperv/netvsc.c
@@ -875,12 +875,6 @@ static inline int netvsc_send_pkt(
        } else if (ret == -EAGAIN) {
                netif_tx_stop_queue(txq);
                ndev_ctx->eth_stats.stop_queue++;
-               if (atomic_read(&nvchan->queue_sends) < 1 &&
-                   !net_device->tx_disable) {
-                       netif_tx_wake_queue(txq);
-                       ndev_ctx->eth_stats.wake_queue++;
-                       ret = -ENOSPC;
-               }
        } else {
                netdev_err(ndev,
                           "Unable to send packet pages %u len %u, ret %d\n",
@@ -888,6 +882,15 @@ static inline int netvsc_send_pkt(
                           ret);
        }
 
+       if (netif_tx_queue_stopped(txq) &&
+           atomic_read(&nvchan->queue_sends) < 1 &&
+           !net_device->tx_disable) {
+               netif_tx_wake_queue(txq);
+               ndev_ctx->eth_stats.wake_queue++;
+               if (ret == -EAGAIN)
+                       ret = -ENOSPC;
+       }
+
        return ret;
 }