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Commit 9cad200c authored by Nick Piggin's avatar Nick Piggin Committed by Linus Torvalds
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ipc/sem.c: sem use list operations 



Replace the handcoded list operations in update_queue() with the standard
list_for_each_entry macros.

list_for_each_entry_safe() must be used, because list entries can
disappear immediately uppon the wakeup event.

Signed-off-by: default avatarNick Piggin <npiggin@suse.de>
Signed-off-by: default avatarManfred Spraul <manfred@colorfullife.com>
Cc: Pierre Peiffer <peifferp@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent bf17bb71

ipc/sem.c

+31 −44
Original line number Diff line number Diff line
@@ -403,44 +403,32 @@ static int try_atomic_semop (struct sem_array * sma, struct sembuf * sops, 
 */

static void update_queue (struct sem_array * sma)

{

	struct sem_queue *q, *tq;



again:

	list_for_each_entry_safe(q, tq, &sma->sem_pending, list) {

		int error;

	struct sem_queue * q;

		int alter;



	q = list_entry(sma->sem_pending.next, struct sem_queue, list);

	while (&q->list != &sma->sem_pending) {

		error = try_atomic_semop(sma, q->sops, q->nsops,

					 q->undo, q->pid);



		/* Does q->sleeper still need to sleep? */

		if (error <= 0) {

			struct sem_queue *n;

		if (error > 0)

			continue;



		list_del(&q->list);



		/*

			 * Continue scanning. The next operation

			 * that must be checked depends on the type 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.

			 * - if the operation didn't modify the array,

			 *   then just continue.

			 * The order of list_del() and reading ->next

			 * is crucial: In the former case, the list_del()

			 * must be done first [because we might be the

			 * first entry in ->sem_pending], in the latter

			 * case the list_del() must be done last

			 * [because the list is invalid after the list_del()]

		 * The next operation that must be checked depends on the type

		 * 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.

		 * - if the operation didn't modify the array, then just

		 *   continue.

		 */

			if (q->alter) {

				list_del(&q->list);

				n = list_entry(sma->sem_pending.next,

						struct sem_queue, list);

			} else {

				n = list_entry(q->list.next, struct sem_queue,

						list);

				list_del(&q->list);

			}

		alter = q->alter;



		/* wake up the waiting thread */

		q->status = IN_WAKEUP;
@@ -451,10 +439,9 @@ static void update_queue (struct sem_array * sma) 
		 */

		smp_wmb();

		q->status = error;

			q = n;

		} else {

			q = list_entry(q->list.next, struct sem_queue, list);

		}



		if (alter)

			goto again;

	}

}