[patch 2/4] ipc: sem use list operations

npiggin
2009-08-11T11:54:37Z

[-- Attachment #1: ipc-sem-use-list-ops.patch --]
[-- Type: text/plain, Size: 2838 bytes --]

Signed-off-by: Nick Piggin <npiggin@suse.de>
---
ipc/sem.c | 79 +++++++++++++++++++++++++-------------------------------------
1 file changed, 33 insertions(+), 46 deletions(-)

Index: linux-2.6/ipc/sem.c
===================================================================
--- linux-2.6.orig/ipc/sem.c
+++ linux-2.6/ipc/sem.c
@@ -402,58 +402,45 @@ 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;
+
+ list_del(&q->list);
+
+ /*
+ * 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;

- /*
- * 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);
- }
-
- /* 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);
- }
+ if (alter)
+ goto again;
}
}