ipc/sem.c: optimize if semops fail
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>
Cc: Nick Piggin <npiggin@suse.de>
Cc: Pierre Peiffer <peifferp@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/ipc/sem.c b/ipc/sem.c
index 2705fbb..eac3f46 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -445,13 +445,13 @@
* 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;
}
}