rcu: Apply ACCESS_ONCE() to rcu_boost() return value

Both TINY_RCU's and TREE_RCU's implementations of rcu_boost() access
the ->boost_tasks and ->exp_tasks fields without preventing concurrent
changes to these fields.  This commit therefore applies ACCESS_ONCE in
order to prevent compiler mischief.

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

1 files changed, 2 insertions, 1 deletions

diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index f55f10ba01f5..8bb35d73e1f9 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -1232,7 +1232,8 @@ static int rcu_boost(struct rcu_node *rnp)
         rt_mutex_lock(&mtx);  /* Side effect: boosts task t's priority. */
         rt_mutex_unlock(&mtx);  /* Keep lockdep happy. */
 
-        return rnp->exp_tasks != NULL || rnp->boost_tasks != NULL;
+        return ACCESS_ONCE(rnp->exp_tasks) != NULL ||
+               ACCESS_ONCE(rnp->boost_tasks) != NULL;
 }
 
 /*