[PATCH tip/core/rcu 02/10] rcu: Protect rcu_boost() lockless accesses with ACCESS_ONCE()

From: Paul E. McKenney
Date: Wed Nov 05 2014 - 12:41:53 EST


From: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>

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

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---
kernel/rcu/tree_plugin.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 3ec85cb5d544..d59913ef8360 100644
--- 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);
--
1.8.1.5

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