netdev - [PATCH net v2] ibmvnic: Properly dispose of all skbs during a failover.

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Message-Id: <20220702103711.4036357-1-ricklind@us.ibm.com>
Date:   Sat,  2 Jul 2022 03:37:12 -0700
From:   Rick Lindsley <ricklind@...ibm.com>
To:     netdev@...r.kernel.org
Cc:     bjking1@...ux.ibm.com, haren@...ux.ibm.com, nnac123@...ux.ibm.com,
        mmc@...ux.ibm.com, ricklind@...ux.ibm.com
Subject: [PATCH net v2] ibmvnic: Properly dispose of all skbs during a failover.

During a reset, there may have been transmits in flight that are no
longer valid and cannot be fulfilled.  Resetting and clearing the
queues is insufficient; each skb also needs to be explicitly freed
so that upper levels are not left waiting for confirmation of a
transmit that will never happen.  If this happens frequently enough,
the apparent backlog will cause TCP to begin "congestion control"
unnecessarily, culminating in permanently decreased throughput.

Fixes: d7c0ef36bde03 ("ibmvnic: Free and re-allocate scrqs when tx/rx scrqs change")
Tested-by: Nick Child <nnac123@...ux.ibm.com>
Reviewed-by: Brian King <brking@...ux.vnet.ibm.com>
Signed-off-by: Rick Lindsley <ricklind@...ibm.com>
---
 drivers/net/ethernet/ibm/ibmvnic.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/net/ethernet/ibm/ibmvnic.c b/drivers/net/ethernet/ibm/ibmvnic.c
index 7e7fe5bdf1f8..5ab7c0f81e9a 100644
--- a/drivers/net/ethernet/ibm/ibmvnic.c
+++ b/drivers/net/ethernet/ibm/ibmvnic.c
@@ -5981,6 +5981,15 @@ static int ibmvnic_reset_init(struct ibmvnic_adapter *adapter, bool reset)
 			release_sub_crqs(adapter, 0);
 			rc = init_sub_crqs(adapter);
 		} else {
+			/* no need to reinitialize completely, but we do
+			 * need to clean up transmits that were in flight
+			 * when we processed the reset.  Failure to do so
+			 * will confound the upper layer, usually TCP, by
+			 * creating the illusion of transmits that are
+			 * awaiting completion.
+			 */
+			clean_tx_pools(adapter);
+
 			rc = reset_sub_crq_queues(adapter);
 		}
 	} else {
-- 
2.31.1