rcu: Protect rcu_boost() lockless accesses with ACCESS_ONCE()

This commit prevents random compiler optimizations by applying
ACCESS_ONCE() to lockless accesses.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 3ec85cb5d544b8588fd574a80e19bd564079533f..d59913ef8360073d670068dc7ebce9061a4f4cf8 100644 (file)
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1127,7 +1127,8 @@ static int rcu_boost(struct rcu_node *rnp)
        struct task_struct *t;
        struct list_head *tb;
 
-       if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL)
+       if (ACCESS_ONCE(rnp->exp_tasks) == NULL &&
+           ACCESS_ONCE(rnp->boost_tasks) == NULL)
                return 0;  /* Nothing left to boost. */
 
        raw_spin_lock_irqsave(&rnp->lock, flags);