From: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
Because preemptible RCU's __rcu_read_unlock() is an external function,
the rough equivalent of an implicit barrier() is inserted by the compiler.
Except that there is a direct call to __rcu_read_unlock() in that same
file, and compilers are getting to the point where they might choose to
inline the fastpath of the __rcu_read_unlock() function.
This commit therefore adds an explicit barrier() to the very beginning
of __rcu_read_unlock().
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
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 36212de..d9495de 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -393,8 +393,9 @@ void __rcu_read_unlock(void)
{
struct task_struct *t = current;
+ barrier(); // critical section before exit code.
if (rcu_preempt_read_exit() == 0) {
- barrier(); /* critical section before exit code. */
+ barrier(); // critical-section exit before .s check.
if (unlikely(READ_ONCE(t->rcu_read_unlock_special.s)))
rcu_read_unlock_special(t);
}
--
2.9.5
