linux-kernel - [PATCH tip/core/rcu 6/9] rcu: Upgrade sync_exp_work_done() to smp

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Message-Id: <20190530150015.30995-6-paulmck@linux.ibm.com>
Date:   Thu, 30 May 2019 08:00:12 -0700
From:   "Paul E. McKenney" <paulmck@...ux.ibm.com>
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, 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.ibm.com>
Subject: [PATCH tip/core/rcu 6/9] rcu: Upgrade sync_exp_work_done() to smp_mb()

The sync_exp_work_done() function uses smp_mb__before_atomic(), but
there is no obvious atomic in the ensuing code.  The ordering is
absolutely required for grace periods to work correctly, so this
commit upgrades the smp_mb__before_atomic() to smp_mb().

Reported-by: Andrea Parri <andrea.parri@...rulasolutions.com>
Signed-off-by: Paul E. McKenney <paulmck@...ux.ibm.com>
---
 kernel/rcu/tree_exp.h | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 9c990df880d1..d969650a72c6 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -259,8 +259,7 @@ static bool sync_exp_work_done(unsigned long s)
 {
 	if (rcu_exp_gp_seq_done(s)) {
 		trace_rcu_exp_grace_period(rcu_state.name, s, TPS("done"));
-		/* Ensure test happens before caller kfree(). */
-		smp_mb__before_atomic(); /* ^^^ */
+		smp_mb(); /* Ensure test happens before caller kfree(). */
 		return true;
 	}
 	return false;
-- 
2.17.1