[PATCH net 2/3] igb: skip reset in igb_tx_timeout() during XDP transition

[Alex Dvoretsky <advoretsky@gmail.com>]

When igb_xdp_setup() transitions between XDP and non-XDP mode on a
running device, it calls igb_close() followed by igb_open(). During
this window the adapter is down while trans_start still contains the
timestamp from before igb_close(), so the TX watchdog can fire a
spurious timeout.

The resulting schedule_work(&adapter->reset_task) races with the
igb_open() path: the reset task may run while the device is being
brought back up, or immediately after, causing unexpected ring
reinitialisation and register writes.

Fix this by checking __IGB_DOWN at the top of igb_tx_timeout(). A
reset is unnecessary because the device will be fully reinitialised
by the subsequent igb_open().

Fixes: 9cbc948b5a20 ("igb: add XDP support")
Cc: stable@vger.kernel.org
Signed-off-by: Alex Dvoretsky <advoretsky@gmail.com>
---
 drivers/net/ethernet/intel/igb/igb_main.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/net/ethernet/intel/igb/igb_main.c b/drivers/net/ethernet/intel/igb/igb_main.c
index 223a10cae4a9..ddb7ce9e97bf 100644
--- a/drivers/net/ethernet/intel/igb/igb_main.c
+++ b/drivers/net/ethernet/intel/igb/igb_main.c
@@ -6651,6 +6651,10 @@ static void igb_tx_timeout(struct net_device *netdev, unsigned int __always_unus
 	struct igb_adapter *adapter = netdev_priv(netdev);
 	struct e1000_hw *hw = &adapter->hw;
 
+	/* Ignore timeout if the adapter is going down. */
+	if (test_bit(__IGB_DOWN, &adapter->state))
+		return;
+
 	/* Do the reset outside of interrupt context */
 	adapter->tx_timeout_count++;
 
-- 
2.51.0