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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>
This commit is contained in:
Paul E. McKenney 2010-08-19 16:57:45 -07:00
parent 7b0b759b65
commit 80dcf60e6b
1 changed files with 4 additions and 2 deletions
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6
kernel/rcutree_plugin.h
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@ -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