net: ll_temac: Fix race condition causing TX hang

BugLink: https://bugs.launchpad.net/bugs/1868538
[ Upstream commit 84823ff80f7403752b59e00bb198724100dc611c ]

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: Sasha Levin <sashal@kernel.org>
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>

diff --git a/drivers/net/ethernet/xilinx/ll_temac_main.c b/drivers/net/ethernet/xilinx/ll_temac_main.c
index 21c1b4322ea78941d0ee58801dbe62f3442f1acc..fd578568b3bff728f7b0b84000ab35bb4acd19c7 100644 (file)
--- a/drivers/net/ethernet/xilinx/ll_temac_main.c
+++ b/drivers/net/ethernet/xilinx/ll_temac_main.c
@@ -788,6 +788,9 @@ static void temac_start_xmit_done(struct net_device *ndev)
                stat = be32_to_cpu(cur_p->app0);
        }
 
+       /* Matches barrier in temac_start_xmit */
+       smp_mb();
+
        netif_wake_queue(ndev);
 }
 
@@ -830,9 +833,19 @@ 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;