Subject: [PATCH AUTOSEL 5.1 024/375] hv_netvsc: fix race that may miss tx queue wakeup

From: Sasha Levin <[email-masked]>
Date: Wed, 22 May 2019 15:15:24 -0400

From: Haiyang Zhang <[email-masked]>

[ Upstream 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 <[email-masked]>
Signed-off-by: Haiyang Zhang <[email-masked]>
Signed-off-by: David S. Miller <[email-masked]>
Signed-off-by: Sasha Levin <[email-masked]>
---
 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
index e0dce373cdd9d..3d4a166a49d58 100644
--- 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;
 }
 
-- 
2.20.1