rcu: apply TINY_PREEMPT_RCU read-side speedup to TREE_PREEMPT_RCU
Replace one of the ACCESS_ONCE() calls in each of __rcu_read_lock()
and __rcu_read_unlock() with barrier() as suggested by Steve Rostedt in
order to avoid the potential compiler-optimization-induced bug noted by
Mathieu Desnoyers.
Located-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 87f60f0..e9e0bc74 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -201,7 +201,7 @@
*/
void __rcu_read_lock(void)
{
- ACCESS_ONCE(current->rcu_read_lock_nesting)++;
+ current->rcu_read_lock_nesting++;
barrier(); /* needed if we ever invoke rcu_read_lock in rcutree.c */
}
EXPORT_SYMBOL_GPL(__rcu_read_lock);
@@ -344,7 +344,9 @@
struct task_struct *t = current;
barrier(); /* needed if we ever invoke rcu_read_unlock in rcutree.c */
- if (--ACCESS_ONCE(t->rcu_read_lock_nesting) == 0 &&
+ --t->rcu_read_lock_nesting;
+ barrier(); /* decrement before load of ->rcu_read_unlock_special */
+ if (t->rcu_read_lock_nesting == 0 &&
unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
rcu_read_unlock_special(t);
#ifdef CONFIG_PROVE_LOCKING