[PATCH tip/core/rcu 6/9] rcu: Upgrade sync_exp_work_done() to smp_mb()

[Paul E. McKenney]

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@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxx>
---
 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