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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2010-08-19 16:57:45 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2010-08-20 09:00:17 -0700
commit80dcf60e6b97c7363971e7a0a788d8484d35f8a6 (patch)
tree2f493fdf6a7a52675733ac74daa9e1cd9342a030 /kernel/rcutree_plugin.h
parent7b0b759b65247cbc66384a912be9acf8d4800636 (diff)
downloadop-kernel-dev-80dcf60e6b97c7363971e7a0a788d8484d35f8a6.zip
op-kernel-dev-80dcf60e6b97c7363971e7a0a788d8484d35f8a6.tar.gz
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>
Diffstat (limited to 'kernel/rcutree_plugin.h')
-rw-r--r--kernel/rcutree_plugin.h6
1 files changed, 4 insertions, 2 deletions
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 @@ 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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