ipc/sem: do not call wake_sem_queue_do() prematurely

... as this call should obviously be paired with its _prepare()
counterpart. At least whenever possible, as there is no harm in
calling it bogusly as we do now in a few places. Immediate error
semop(2) paths that are far from ever having the task block can
be simplified and avoid a few unnecessary loads on their way out
of the call as it is not deeply nested.

Link: http://lkml.kernel.org/r/1474225896-10066-2-git-send-email-dave@stgolabs.net
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

ipc/sem.c

@@ -1904,16 +1904,22 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
 	}
 
 	error = -EFBIG;
-	if (max >= sma->sem_nsems)
-		goto out_rcu_wakeup;
+	if (max >= sma->sem_nsems) {
+		rcu_read_unlock();
+		goto out_free;
+	}
 
 	error = -EACCES;
-	if (ipcperms(ns, &sma->sem_perm, alter ? S_IWUGO : S_IRUGO))
-		goto out_rcu_wakeup;
+	if (ipcperms(ns, &sma->sem_perm, alter ? S_IWUGO : S_IRUGO)) {
+		rcu_read_unlock();
+		goto out_free;
+	}
 
 	error = security_sem_semop(sma, sops, nsops, alter);
-	if (error)
-		goto out_rcu_wakeup;
+	if (error) {
+		rcu_read_unlock();
+		goto out_free;
+	}
 
 	error = -EIDRM;
 	locknum = sem_lock(sma, sops, nsops);
@@ -2056,7 +2062,6 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
 
 out_unlock_free:
 	sem_unlock(sma, locknum);
-out_rcu_wakeup:
 	rcu_read_unlock();
 	wake_up_sem_queue_do(&tasks);
 out_free: