From: Ganji Aravind <ganji.aravind@chelsio.com>
Date: Tue, 18 Aug 2020 21:10:58 +0530
Subject: cxgb4: Fix race between loopback and normal Tx path
Patch-mainline: v5.9-rc2
Git-commit: c650e04898072e4b579cbf8d9dd5b86bcdbe9b00
References: jsc#SLE-15131

Even after Tx queues are marked stopped, there exists a
small window where the current packet in the normal Tx
path is still being sent out and loopback selftest ends
up corrupting the same Tx ring. So, ensure selftest takes
the Tx lock to synchronize access the Tx ring.

Fixes: 7235ffae3d2c ("cxgb4: add loopback ethtool self-test")
Signed-off-by: Ganji Aravind <ganji.aravind@chelsio.com>
Reviewed-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 drivers/net/ethernet/chelsio/cxgb4/sge.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

--- a/drivers/net/ethernet/chelsio/cxgb4/sge.c
+++ b/drivers/net/ethernet/chelsio/cxgb4/sge.c
@@ -2561,11 +2561,14 @@ int cxgb4_selftest_lb_pkt(struct net_dev
 	lb->loopback = 1;
 
 	q = &adap->sge.ethtxq[pi->first_qset];
+	__netif_tx_lock(q->txq, smp_processor_id());
 
 	reclaim_completed_tx(adap, &q->q, -1, true);
 	credits = txq_avail(&q->q) - ndesc;
-	if (unlikely(credits < 0))
+	if (unlikely(credits < 0)) {
+		__netif_tx_unlock(q->txq);
 		return -ENOMEM;
+	}
 
 	wr = (void *)&q->q.desc[q->q.pidx];
 	memset(wr, 0, sizeof(struct tx_desc));
@@ -2598,6 +2601,7 @@ int cxgb4_selftest_lb_pkt(struct net_dev
 	init_completion(&lb->completion);
 	txq_advance(&q->q, ndesc);
 	cxgb4_ring_tx_db(adap, &q->q, ndesc);
+	__netif_tx_unlock(q->txq);
 
 	/* wait for the pkt to return */
 	ret = wait_for_completion_timeout(&lb->completion, 10 * HZ);