[PATCH 1/8] net: ll_temac: Fix race condition causing TX hang

[PATCH 1/8] net: ll_temac: Fix race condition causing TX hang

[Esben Haabendal]

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").

Signed-off-by: Esben Haabendal <esben@geanix.com>
Cc: stable@vger.kernel.org
---
 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 6f11f52c9a9e..996004ef8bd4 100644
--- 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;
-- 
2.25.0


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Re: [PATCH 1/8] net: ll_temac: Fix race condition causing TX hang

[Sasha Levin]

Hi,

[This is an automated email]

This commit has been processed because it contains a -stable tag.
The stable tag indicates that it's relevant for the following trees: all

The bot has tested the following trees: v5.5.4, v5.4.20, v4.19.104, v4.14.171, v4.9.214, v4.4.214.

v5.5.4: Build OK!
v5.4.20: Build OK!
v4.19.104: Failed to apply! Possible dependencies:
    2c9938e738a2 ("net: ll_temac: Fix bug causing buffer descriptor overrun")

v4.14.171: Failed to apply! Possible dependencies:
    2c9938e738a2 ("net: ll_temac: Fix bug causing buffer descriptor overrun")

v4.9.214: Failed to apply! Possible dependencies:
    2c9938e738a2 ("net: ll_temac: Fix bug causing buffer descriptor overrun")

v4.4.214: Failed to apply! Possible dependencies:
    2c9938e738a2 ("net: ll_temac: Fix bug causing buffer descriptor overrun")


NOTE: The patch will not be queued to stable trees until it is upstream.

How should we proceed with this patch?

-- 
Thanks,
Sasha

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