rcu/exp: Remove full barrier upon main thread wakeup

When an expedited grace period is ending, care must be taken so that all
the quiescent states propagated up to the root are correctly ordered
against the wake up of the main expedited grace period workqueue.

This ordering is already carried through the root rnp locking augmented
by an smp_mb__after_unlock_lock() barrier.

Therefore the explicit smp_mb() placed before the wake up is not needed
and can be removed.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>

diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 2ac440bc7e10bc8e1248eae47a661eb017768cee..014ddf672165d33548351955ec8cbcd6253fbd53 100644 (file)
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -198,10 +198,9 @@ static void __rcu_report_exp_rnp(struct rcu_node *rnp,
                }
                if (rnp->parent == NULL) {
                        raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
-                       if (wake) {
-                               smp_mb(); /* EGP done before wake_up(). */
+                       if (wake)
                                swake_up_one_online(&rcu_state.expedited_wq);
-                       }
+
                        break;
                }
                mask = rnp->grpmask;