netdev - [PATCH RFC tip/core/rcu 03/15] drivers/net/ethernet/qlogic/qed: Fix __qed_spq

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Date:   Mon,  9 Oct 2017 17:22:37 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     linux-kernel@...r.kernel.org
Cc:     mingo@...nel.org, torvalds@...ux-foundation.org,
        mark.rutland@....com, dhowells@...hat.com,
        linux-arch@...r.kernel.org, peterz@...radead.org,
        will.deacon@....com,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Ariel Elior <Ariel.Elior@...ium.com>,
        <everest-linux-l2@...ium.com>, <netdev@...r.kernel.org>
Subject: [PATCH RFC tip/core/rcu 03/15] drivers/net/ethernet/qlogic/qed: Fix __qed_spq_block() ordering

The __qed_spq_block() function expects an smp_read_barrier_depends()
to order a prior READ_ONCE() against a later load that does not depend
on the prior READ_ONCE(), an expectation that can fail to be met.
This commit therefore replaces the READ_ONCE() with smp_load_acquire()
and removes the smp_read_barrier_depends().

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Ariel Elior <Ariel.Elior@...ium.com>
Cc: <everest-linux-l2@...ium.com>
Cc: <netdev@...r.kernel.org>
---
 drivers/net/ethernet/qlogic/qed/qed_spq.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/qlogic/qed/qed_spq.c b/drivers/net/ethernet/qlogic/qed/qed_spq.c
index be48d9abd001..c1237ec58b6c 100644
--- a/drivers/net/ethernet/qlogic/qed/qed_spq.c
+++ b/drivers/net/ethernet/qlogic/qed/qed_spq.c
@@ -97,9 +97,7 @@ static int __qed_spq_block(struct qed_hwfn *p_hwfn,
 
 	while (iter_cnt--) {
 		/* Validate we receive completion update */
-		if (READ_ONCE(comp_done->done) == 1) {
-			/* Read updated FW return value */
-			smp_read_barrier_depends();
+		if (smp_load_acquire(&comp_done->done) == 1) { /* ^^^ */
 			if (p_fw_ret)
 				*p_fw_ret = comp_done->fw_return_code;
 			return 0;
-- 
2.5.2