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Message-Id: <20180626171048.2181-6-paulmck@linux.vnet.ibm.com>
Date:   Tue, 26 Jun 2018 10:10:32 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     linux-kernel@...r.kernel.org
Cc:     mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
        rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
        fweisbec@...il.com, oleg@...hat.com, joel@...lfernandes.org,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 06/22] rcu: Replace smp_wmb() with smp_store_release() for stall check

This commit gets rid of the smp_wmb() in record_gp_stall_check_time()
in favor of an smp_store_release().

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 kernel/rcu/tree.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index d526c2125564..78dd96e8ce3e 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1246,9 +1246,9 @@ static void record_gp_stall_check_time(struct rcu_state *rsp)
 	unsigned long j1;
 
 	rsp->gp_start = j;
-	smp_wmb(); /* Record start time before stall time. */
 	j1 = rcu_jiffies_till_stall_check();
-	WRITE_ONCE(rsp->jiffies_stall, j + j1);
+	/* Record ->gp_start before ->jiffies_stall. */
+	smp_store_release(&rsp->jiffies_stall, j + j1); /* ^^^ */
 	rsp->jiffies_resched = j + j1 / 2;
 	rsp->n_force_qs_gpstart = READ_ONCE(rsp->n_force_qs);
 }
-- 
2.17.1

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