[PATCH RFC v3] sched: completion: locks should not be needed for reading completion state

[Nicholas Mc Guire]

Signed-off-by: Nicholas Mc Guire <der.herr@xxxxxxx>
---

v2: proper subsystem tag in subject line
v3: typo in return fixed

Sorry for this resend - just noticed that I had - carelessly lost the
second inversion somehow - logic should be correct now.

The ACCESS_ONCE is needed for calls in a loop that, if inlined, could
optimize out the re-fetching of x->done. An explicit memory barrier is 
not needed as complete() and complete_all() imply a barrier.

 kernel/sched/completion.c |    9 +--------
 1 file changed, 1 insertion(+), 8 deletions(-)

diff --git a/kernel/sched/completion.c b/kernel/sched/completion.c
index 607f852..7c5cd70 100644
--- a/kernel/sched/completion.c
+++ b/kernel/sched/completion.c
@@ -288,13 +288,6 @@ EXPORT_SYMBOL(try_wait_for_completion);
  */
 bool completion_done(struct completion *x)
 {
-	unsigned long flags;
-	int ret = 1;
-
-	spin_lock_irqsave(&x->wait.lock, flags);
-	if (!x->done)
-		ret = 0;
-	spin_unlock_irqrestore(&x->wait.lock, flags);
-	return ret;
+	return !!ACCESS_ONCE(x->done);
 }
 EXPORT_SYMBOL(completion_done);
-- 
1.7.10.4

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/