ipc/sem.c: fix return code race with semop vs. semop +semctl(IPC_RMID)

sys_semtimedop() may return -EIDRM although the semaphore operation
completed successfully:

thread 1: thread 2:
semtimedop(), sleeps
semop():
* acquires sem_lock()
semtimedop() woken up due to timeout
sem_lock() loops
* notices that thread 2 could be completed.
* performs the operations that thread 2 is sleeping on.
* marks the semaphore operation as IN_WAKEUP
* drops sem_lock(), does wakeup, sets return code to 0
* thread delayed due to interrupt, whatever
* returns to user space
* thread still delayed
semctl(IPC_RMID)
* acquires sem_lock()
* ipc_rmid(), ipcp->deleted=1
* drops sem_lock()
* thread finally continues - but seem_lock()
now fails due to ipcp->deleted == 1
* returns -EIDRM instead of 0

The fix is trivial: Always use the return code in queue.status.

In real world, the race probably doesn't matter:
If the semaphore array is destroyed, the app is probably not interested
if the last operation succeeded or was already cancelled.

Signed-off-by: Manfred Spraul <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: Mike Galbraith <[e-mail]>
Acked-by: Peter Zijlstra <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

ipc/sem.c

···
 	 * Array removed? If yes, leave without sem_unlock().
 	 */
 	if (IS_ERR(sma)) {
-		error = -EIDRM;
 		goto out_free;
 	}