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

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Message-Id: <20220630000317.2509347-1-ricklind@us.ibm.com>
Date:   Wed, 29 Jun 2022 17:03:17 -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
Subject: [PATCH]     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    During a reset, there may have been transmits in flight that are no
    longer valid and cannot be fulfilled.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.

    This was noted during testing of heavy data transfers in
    conjunction with multiple consecutive device failovers.

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 {
-- 
2.27.0