From 9cad200c7686708b326520a45dd680a4147568a6 Mon Sep 17 00:00:00 2001 From: Nick Piggin Date: Tue, 15 Dec 2009 16:47:29 -0800 Subject: 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: Nick Piggin Signed-off-by: Manfred Spraul Cc: Pierre Peiffer Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- ipc/sem.c | 75 ++++++++++++++++++++++++++------------------------------------- 1 file changed, 31 insertions(+), 44 deletions(-) (limited to 'ipc') diff --git a/ipc/sem.c b/ipc/sem.c index cb0070ecf5b..d377b3adfc3 100644 --- a/ipc/sem.c +++ b/ipc/sem.c @@ -403,58 +403,45 @@ undo: */ static void update_queue (struct sem_array * sma) { - int error; - struct sem_queue * q; + struct sem_queue *q, *tq; + +again: + list_for_each_entry_safe(q, tq, &sma->sem_pending, list) { + int error; + 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; - /* - * 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()] - */ - 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); - } + list_del(&q->list); - /* wake up the waiting thread */ - q->status = IN_WAKEUP; + /* + * 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. + */ + alter = q->alter; + + /* wake up the waiting thread */ + q->status = IN_WAKEUP; - wake_up_process(q->sleeper); - /* hands-off: q will disappear immediately after - * writing q->status. - */ - smp_wmb(); - q->status = error; - q = n; - } else { - q = list_entry(q->list.next, struct sem_queue, list); - } + wake_up_process(q->sleeper); + /* hands-off: q will disappear immediately after + * writing q->status. + */ + smp_wmb(); + q->status = error; + + if (alter) + goto again; } } -- cgit v1.2.3