rcu: Move __rcu_read_unlock()'s barrier() within if-statement

We only need to constrain the compiler if we are actually exiting
the top-level RCU read-side critical section.  This commit therefore
moves the first barrier() cal in __rcu_read_unlock() to inside the
"if" statement, thus avoiding needless register flushes for inner
rcu_read_unlock() calls.

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

1 files changed, 1 insertions, 1 deletions

diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 4bac5a29fb69..ed70f6bf4c31 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -415,10 +415,10 @@ void __rcu_read_unlock(void)
 {
         struct task_struct *t = current;
 
-        barrier();  /* needed if we ever invoke rcu_read_unlock in rcutree.c */
         if (t->rcu_read_lock_nesting != 1)
                 --t->rcu_read_lock_nesting;
         else {
+                barrier();  /* critical section before exit code. */
                 t->rcu_read_lock_nesting = INT_MIN;
                 barrier();  /* assign before ->rcu_read_unlock_special load */
                 if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))