[PATCH 4/7] ipc/sem.c: optimize if semops fail

[manfred@colorfullife.com]

From: Manfred Spraul <manfred@colorfullife.com>

Reduce the amount of scanning of the list of pending semaphore operations:
If try_atomic_semop failed, then no changes were applied. Thus no need to
restart.
Additionally, this patch correct an incorrect comment:
It's possible to wait for arbitrary semaphore values (do a dec by <x>,
wait-for-zero, inc by <x> in one atomic operation)

Both changes are from Nick Piggin, the patch is the result of a different
split of the individual changes.

Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
---
 ipc/sem.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/ipc/sem.c b/ipc/sem.c
index 3629ef8..9425817 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -444,13 +444,13 @@ again:
 		 * of the completed operation:
 		 * - if the operation modified the array, then restart from the
 		 *   head of the queue and check for threads that might be
-		 *   waiting for semaphore values to become 0.
+		 *   waiting for the new semaphore values.
 		 * - if the operation didn't modify the array, then just
 		 *   continue.
 		 */
 		alter = q->alter;
 		wake_up_sem_queue(q, error);
-		if (alter)
+		if (alter && !error)
 			goto again;
 	}
 }
-- 
1.6.2.5