Message-ID: <49B7CF67.5070604@davidnewall.com>
Date: Thu, 12 Mar 2009 01:19:11 +1030
From: David Newall <davidn@davidnewall.com>
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To: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: [PATCH] fix off-by-one in __iterator_load_balance
Sender: linux-kernel-owner@vger.kernel.org
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An off-by-one bug in __iterator_load_balance causes it to erroneously
return NULL if the next task on the list is also the last entry in the
list.  This patch corrects that fault.

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 filename="sched_fair.patch"

--- sched_fair.c	2009-02-21 09:09:34.000000000 +1030
+++ sched_fair.c.dn	2009-03-12 01:09:46.000000000 +1030
@@ -1439,27 +1439,18 @@
 static struct task_struct *
 __load_balance_iterator(struct cfs_rq *cfs_rq, struct list_head *next)
 {
-	struct task_struct *p = NULL;
 	struct sched_entity *se;
-
-	if (next == &cfs_rq->tasks)
-		return NULL;
-
-	/* Skip over entities that are not tasks */
-	do {
+	while (next != &cfs_rq->tasks)
+	{
 		se = list_entry(next, struct sched_entity, group_node);
 		next = next->next;
-	} while (next != &cfs_rq->tasks && !entity_is_task(se));
-
-	if (next == &cfs_rq->tasks)
-		return NULL;
-
-	cfs_rq->balance_iterator = next;
-
-	if (entity_is_task(se))
-		p = task_of(se);
-
-	return p;
+		if (entity_is_task(se))
+		{
+			cfs_rq->balance_iterator = next;
+			return task_of(se);
+		}
+	}
+	return NULL;
 }
 
 static struct task_struct *load_balance_start_fair(void *arg)

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