From ab4e577ee31a052ec2a95c00cdc14fa18b4a214d Mon Sep 17 00:00:00 2001
From: Esben Haabendal <esben@geanix.com>
Date: Fri, 21 Feb 2020 07:47:21 +0100
Subject: [PATCH 2/3] net: ll_temac: Fix race condition causing TX hang
References: git-fixes
Git-commit: 84823ff80f7403752b59e00bb198724100dc611c
Patch-mainline: v5.6-rc4

It is possible that the interrupt handler fires and frees up space in
the TX ring in between checking for sufficient TX ring space and
stopping the TX queue in temac_start_xmit. If this happens, the
queue wake from the interrupt handler will occur before the queue is
stopped, causing a lost wakeup and the adapter's transmit hanging.

To avoid this, after stopping the queue, check again whether there is
sufficient space in the TX ring. If so, wake up the queue again.

This is a port of the similar fix in axienet driver,
commit 7de44285c1f6 ("net: axienet: Fix race condition causing TX hang").

Fixes: 23ecc4bde21f ("net: ll_temac: fix checksum offload logic")
Signed-off-by: Esben Haabendal <esben@geanix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Denis Kirjanov <denis.kirjanov@suse.com>
---
 drivers/net/ethernet/xilinx/ll_temac_main.c | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/xilinx/ll_temac_main.c b/drivers/net/ethernet/xilinx/ll_temac_main.c
index 83a1b46bafb7..1fbebdeb513f 100644
--- a/drivers/net/ethernet/xilinx/ll_temac_main.c
+++ b/drivers/net/ethernet/xilinx/ll_temac_main.c
@@ -678,6 +678,9 @@ static void temac_start_xmit_done(struct
 		stat = be32_to_cpu(cur_p->app0);
 	}
 
+	/* Matches barrier in temac_start_xmit */
+	smp_mb();
+
 	netif_wake_queue(ndev);
 }
 
@@ -689,9 +692,19 @@ static int temac_start_xmit(struct sk_buff *skb, struct net_device *ndev)
 	cur_p = &lp->tx_bd_v[lp->tx_bd_tail];
 
 	if (temac_check_tx_bd_space(lp, num_frag + 1)) {
-		if (!netif_queue_stopped(ndev))
-			netif_stop_queue(ndev);
-		return NETDEV_TX_BUSY;
+		if (netif_queue_stopped(ndev))
+			return NETDEV_TX_BUSY;
+
+		netif_stop_queue(ndev);
+
+		/* Matches barrier in temac_start_xmit_done */
+		smp_mb();
+
+		/* Space might have just been freed - check again */
+		if (temac_check_tx_bd_space(lp, num_frag))
+			return NETDEV_TX_BUSY;
+
+		netif_wake_queue(ndev);
 	}
 
 	cur_p->app0 = 0;
-- 
2.16.4