Subject: remove woken threads from the runqueue early
From: Christoph Hellwig <hch@lst.de>

A single context should only be woken once, and we should not have
more wakeups for a given priority than the number of contexts on
that runqueue position.

Also add some asserts to trap future problems in this area more
easily.


Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>

Index: linux-2.6/arch/powerpc/platforms/cell/spufs/sched.c
===================================================================
--- linux-2.6.orig/arch/powerpc/platforms/cell/spufs/sched.c
+++ linux-2.6/arch/powerpc/platforms/cell/spufs/sched.c
@@ -245,6 +245,14 @@ static void spu_add_to_rq(struct spu_con
 	spin_unlock(&spu_prio->runq_lock);
 }
 
+static void __spu_del_from_rq(struct spu_context *ctx, int prio)
+{
+	if (!list_empty(&ctx->rq))
+		list_del_init(&ctx->rq);
+	if (list_empty(&spu_prio->runq[prio]))
+		clear_bit(ctx->prio, spu_prio->bitmap);
+}
+
 /**
  * spu_del_from_rq - remove a context from the runqueue
  * @ctx:       context to remove
@@ -252,33 +260,10 @@ static void spu_add_to_rq(struct spu_con
 static void spu_del_from_rq(struct spu_context *ctx)
 {
 	spin_lock(&spu_prio->runq_lock);
-	list_del_init(&ctx->rq);
-	if (list_empty(&spu_prio->runq[ctx->prio]))
-		clear_bit(ctx->prio, spu_prio->bitmap);
+	__spu_del_from_rq(ctx, ctx->prio);
 	spin_unlock(&spu_prio->runq_lock);
 }
 
-/**
- * spu_grab_context - remove one context from the runqueue
- * @prio:      priority of the context to be removed
- *
- * This function removes one context from the runqueue for priority @prio.
- * If there is more than one context with the given priority the first
- * task on the runqueue will be taken.
- *
- * Returns the spu_context it just removed.
- *
- * Must be called with spu_prio->runq_lock held.
- */
-static struct spu_context *spu_grab_context(int prio)
-{
-	struct list_head *rq = &spu_prio->runq[prio];
-
-	if (list_empty(rq))
-		return NULL;
-	return list_entry(rq->next, struct spu_context, rq);
-}
-
 static void spu_prio_wait(struct spu_context *ctx)
 {
 	DEFINE_WAIT(wait);
@@ -309,9 +294,14 @@ static void spu_reschedule(struct spu *s
 	spin_lock(&spu_prio->runq_lock);
 	best = sched_find_first_bit(spu_prio->bitmap);
 	if (best < MAX_PRIO) {
-		struct spu_context *ctx = spu_grab_context(best);
-		if (ctx)
-			wake_up(&ctx->stop_wq);
+		struct list_head *rq = &spu_prio->runq[best];
+		struct spu_context *ctx;
+
+		BUG_ON(list_empty(rq));
+
+		ctx = list_entry(rq->next, struct spu_context, rq);
+		__spu_del_from_rq(ctx, best);
+		wake_up(&ctx->stop_wq);
 	}
 	spin_unlock(&spu_prio->runq_lock);
 }
Index: linux-2.6/arch/powerpc/platforms/cell/spufs/context.c
===================================================================
--- linux-2.6.orig/arch/powerpc/platforms/cell/spufs/context.c
+++ linux-2.6/arch/powerpc/platforms/cell/spufs/context.c
@@ -52,6 +52,7 @@ struct spu_context *alloc_spu_context(st
 	ctx->state = SPU_STATE_SAVED;
 	ctx->ops = &spu_backing_ops;
 	ctx->owner = get_task_mm(current);
+	INIT_LIST_HEAD(&ctx->rq);
 	if (gang)
 		spu_gang_add_ctx(gang, ctx);
 	ctx->rt_priority = current->rt_priority;
@@ -76,6 +77,7 @@ void destroy_spu_context(struct kref *kr
 	spu_fini_csa(&ctx->csa);
 	if (ctx->gang)
 		spu_gang_remove_ctx(ctx->gang, ctx);
+	BUG_ON(!list_empty(&ctx->rq));
 	kfree(ctx);
 }