ipc/sem.c: handle spurious wakeups

semtimedop() does not handle spurious wakeups, it returns -EINTR to user
space.  Most other schedule() users would just loop and not return to user
space.  The patch adds such a loop to semtimedop()
Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Reported-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Mike Galbraith <efault@gmx.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

ipc/sem.c

@@ -1426,6 +1426,8 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
 
 	queue.status = -EINTR;
 	queue.sleeper = current;
+
+sleep_again:
 	current->state = TASK_INTERRUPTIBLE;
 	sem_unlock(sma);
 
@@ -1478,6 +1480,13 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
 	 */
 	if (timeout && jiffies_left == 0)
 		error = -EAGAIN;
+
+	/*
+	 * If the wakeup was spurious, just retry
+	 */
+	if (error == -EINTR && !signal_pending(current))
+		goto sleep_again;
+
 	unlink_queue(sma, &queue);
 
 out_unlock_free: