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().

Fixes: 6fba2b3767ea ("rcu: Remove deprecated RCU debugfs tracing code")
Reported-by: Andrea Parri <andrea.parri@amarulasolutions.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>

1 files changed, 1 insertions, 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;