Commit-ID: 80dcf60e6b97c7363971e7a0a788d8484d35f8a6
Gitweb: http://git.kernel.org/tip/80dcf60e6b97c7363971e7a0a788d8484d35f8a6
Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
AuthorDate: Thu, 19 Aug 2010 16:57:45 -0700
Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
CommitDate: Fri, 20 Aug 2010 09:00:17 -0700
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@xxxxxxxxxx>
Suggested-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---
kernel/rcutree_plugin.h | 6 ++++--
1 files changed, 4 insertions(+), 2 deletions(-)
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 87f60f0..e9e0bc7 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -201,7 +201,7 @@ static void rcu_preempt_note_context_switch(int cpu)
*/
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 @@ void __rcu_read_unlock(void)
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
--
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