From: Haiyang Zhang <haiyangz@microsoft.com>
Date: Tue, 30 Apr 2019 19:29:07 +0000
Patch-mainline: v5.2-rc1
References: fate#321895
Subject: hv_netvsc: fix race that may miss tx queue wakeup
Git-commit: 93aa4792c3908eac87ddd368ee0fe0564148232b

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>
Acked-by: Olaf Hering <ohering@suse.de>
---
 drivers/net/hyperv/netvsc.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/drivers/net/hyperv/netvsc.c b/drivers/net/hyperv/netvsc.c
--- 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;
 }