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sched: fix __load_balance_iterator() for cfq with only one task

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The __load_balance_iterator() returns a NULL when there's only one
sched_entity which is a task. It is caused by the following code-path.

	/* Skip over entities that are not tasks */
	do {
		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;
	^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      This will return NULL even when se is a task.

As a side-effect, there was a regression in sched_mc behavior since 2.6.25,
since iter_move_one_task() when it calls load_balance_start_fair(),
would not get any tasks to move!

Fix this by checking if the last entity was a task or not.

Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Gautham R Shenoy 2008-09-06 14:50:23 +05:30 committed by Ingo Molnar
parent 7f79d852ed
commit 38736f4750
1 changed files with 1 additions and 1 deletions
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2
kernel/sched_fair.c
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@ -1458,7 +1458,7 @@ __load_balance_iterator(struct cfs_rq *cfs_rq, struct list_head *next)
next = next->next;
} while (next != &cfs_rq->tasks && !entity_is_task(se));
if (next == &cfs_rq->tasks)
if (next == &cfs_rq->tasks && !entity_is_task(se))
return NULL;
cfs_rq->balance_iterator = next;