Commit ab465df9 authored May 26, 2013 by Manfred Spraul Committed by Linus Torvalds May 26, 2013

ipc/sem.c: Fix missing wakeups in do_smart_update_queue()



do_smart_update_queue() is called when an operation (semop,
semctl(SETVAL), semctl(SETALL), ...) modified the array.  It must check
which of the sleeping tasks can proceed.

do_smart_update_queue() missed a few wakeups:
 - if a sleeping complex op was completed, then all per-semaphore queues
   must be scanned - not only those that were modified by *sops
 - if a sleeping simple op proceeded, then the global queue must be
   scanned again

And:
 - the test for "|sops == NULL) before scanning the global queue is not
   required: If the global queue is empty, then it doesn't need to be
   scanned - regardless of the reason for calling do_smart_update_queue()

The patch is not optimized, i.e.  even completing a wait-for-zero
operation causes a rescan.  This is done to keep the patch as simple as
possible.

Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Acked-by: Davidlohr Bueso <davidlohr.bueso@hp.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 89ff7783

ipc/sem.c

+22 −5

Original line number	Diff line number	Diff line
		@@ -752,19 +752,29 @@ static void do_smart_update(struct sem_array sma, struct sembuf sops, int nsop
		int otime, struct list_head *pt)
		{
		int i;
		int progress;

		if (sma->complex_count \|\| sops == NULL) {
		if (update_queue(sma, -1, pt))
		progress = 1;
		retry_global:
		if (sma->complex_count) {
		if (update_queue(sma, -1, pt)) {
		progress = 1;
		otime = 1;
		sops = NULL;
		}
		}
		if (!progress)
		goto done;

		if (!sops) {
		/* No semops; something special is going on. */
		for (i = 0; i < sma->sem_nsems; i++) {
		if (update_queue(sma, i, pt))
		if (update_queue(sma, i, pt)) {
		otime = 1;
		progress = 1;
		}
		goto done;
		}
		goto done_checkretry;
		}

		/* Check the semaphores that were modified. */
		@@ -772,8 +782,15 @@ static void do_smart_update(struct sem_array sma, struct sembuf sops, int nsop
		if (sops[i].sem_op > 0 \|\|
		(sops[i].sem_op < 0 &&
		sma->sem_base[sops[i].sem_num].semval == 0))
		if (update_queue(sma, sops[i].sem_num, pt))
		if (update_queue(sma, sops[i].sem_num, pt)) {
		otime = 1;
		progress = 1;
		}
		}
		done_checkretry:
		if (progress) {
		progress = 0;
		goto retry_global;
		}
		done:
		if (otime)