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>

diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 9c990df880d113f2468ba118ca1979d391fcf0d8..d969650a72c6349667f0b1adc3f835d6c3999f53 100644 (file)
--- 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;