netdev - [PATCH net 1/3] ibmvnic: don't stop queue in xmit

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Date:   Fri, 29 Oct 2021 15:03:14 -0700
From:   Sukadev Bhattiprolu <sukadev@...ux.ibm.com>
To:     netdev@...r.kernel.org
Cc:     Brian King <brking@...ux.ibm.com>, Dany Madden <drt@...ux.ibm.com>,
        abdhalee@...ibm.com, vaish123@...ibm.com
Subject: [PATCH net 1/3] ibmvnic: don't stop queue in xmit

If adapter's resetting bit is on, discard the packet but don't stop the
transmit queue - instead leave that to the reset code. With this change,
it is possible that we may get several calls to ibmvnic_xmit() that simply
discard packets and return.

But if we stop the queue here, we might end up doing so just after
__ibmvnic_open() started the queues (during a hard/soft reset) and before
the ->resetting bit was cleared. If that happens, there will be no one to
restart queue and transmissions will be blocked indefinitely.

This can cause a TIMEOUT reset and with auto priority failover enabled,
an unnecessary FAILOVER reset to less favored backing device and then a
FAILOVER back to the most favored backing device. If we hit the window
repeatedly, we can get stuck in a loop of TIMEOUT, FAILOVER, FAILOVER
resets leaving the adapter unusable for extended periods of time.

Fixes: 7f5b030830fe ("ibmvnic: Free skb's in cases of failure in transmit")
Reported-by: Abdul Haleem <abdhalee@...ibm.com>
Reported-by: Vaishnavi Bhat <vaish123@...ibm.com>
Signed-off-by: Sukadev Bhattiprolu <sukadev@...ux.ibm.com>
---
 drivers/net/ethernet/ibm/ibmvnic.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/drivers/net/ethernet/ibm/ibmvnic.c b/drivers/net/ethernet/ibm/ibmvnic.c
index 8f17096e614d..a1533979c670 100644
--- a/drivers/net/ethernet/ibm/ibmvnic.c
+++ b/drivers/net/ethernet/ibm/ibmvnic.c
@@ -1914,8 +1914,6 @@ static netdev_tx_t ibmvnic_xmit(struct sk_buff *skb, struct net_device *netdev)
 	ind_bufp = &tx_scrq->ind_buf;

 	if (test_bit(0, &adapter->resetting)) {
-		if (!netif_subqueue_stopped(netdev, skb))
-			netif_stop_subqueue(netdev, queue_num);
 		dev_kfree_skb_any(skb);

 		tx_send_failed++;
-- 
2.26.2