src/patches/suse-2.6.27.39/patches.fixes/sched-fix-__load_balance_iterator-for-cfs-with-on.patch

   1 Subject: fix __load_balance_iterator() for cfs with only one task
   2 From: Gautham R Shenoy <ego@in.ibm.com>
   3 References: 457594 - LTC50544
   4
   5 The __load_balance_iterator() returns a NULL when there's only one
   6 sched_entity which is a task. It is caused by the following code-path.
   7
   8         /* Skip over entities that are not tasks */
   9         do {
  10                 se = list_entry(next, struct sched_entity, group_node);
  11                 next = next->next;
  12         } while (next != &cfs_rq->tasks && !entity_is_task(se));
  13
  14         if (next == &cfs_rq->tasks)
  15                 return NULL;
  16         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  17       This will return NULL even when se is a task.
  18
  19 As a side-effect, there was a regression in sched_mc behavior since 2.6.25,
  20 since iter_move_one_task() when it calls load_balance_start_fair(),
  21 would not get any tasks to move!
  22
  23 Fix this by checking if the last entity was a task or not.
  24
  25 Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>
  26 Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
  27 Signed-off-by: Ingo Molnar <mingo@elte.hu>
  28 Signed-off-by: Olaf Hering <olh@suse.de>
  29 ---
  30  kernel/sched_fair.c |    2 +-
  31  1 file changed, 1 insertion(+), 1 deletion(-)
  32
  33 --- a/kernel/sched_fair.c
  34 +++ b/kernel/sched_fair.c
  35 @@ -1410,7 +1410,7 @@ __load_balance_iterator(struct cfs_rq *c
  36                 next = next->next;
  37         } while (next != &cfs_rq->tasks && !entity_is_task(se));
  38
  39 -       if (next == &cfs_rq->tasks)
  40 +       if (next == &cfs_rq->tasks && !entity_is_task(se))
  41                 return NULL;
  42
  43         cfs_rq->balance_iterator = next;