[34-longterm 087/247] sched, cgroup: Fixup broken cgroup movement

Paul Gortmaker
2011-06-23T17:36:16Z

From: Peter Zijlstra <a.p.zijlstra@chello.nl>

-------------------
This is a commit scheduled for the next v2.6.34 longterm release.
If you see a problem with using this for longterm, please comment.
-------------------

commit b2b5ce022acf5e9f52f7b78c5579994fdde191d4 upstream.

Dima noticed that we fail to correct the ->vruntime of sleeping tasks
when we move them between cgroups.

Reported-by: Dima Zavin <dima@android.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Tested-by: Mike Galbraith <efault@gmx.de>
LKML-Reference: <1287150604.29097.1513.camel@twins>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
---
include/linux/sched.h | 2 +-
kernel/sched.c | 8 ++++----
kernel/sched_fair.c | 25 +++++++++++++++++++------
3 files changed, 24 insertions(+), 11 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 89e0fee..03e34c5 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1071,7 +1071,7 @@ struct sched_class {
struct task_struct *task);

#ifdef CONFIG_FAIR_GROUP_SCHED
- void (*moved_group) (struct task_struct *p, int on_rq);
+ void (*task_move_group) (struct task_struct *p, int on_rq);
#endif
};

diff --git a/kernel/sched.c b/kernel/sched.c
index f7bc764..39456fc 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -8275,12 +8275,12 @@ void sched_move_task(struct task_struct *tsk)
if (unlikely(running))
tsk->sched_class->put_prev_task(rq, tsk);

- set_task_rq(tsk, task_cpu(tsk));
-
#ifdef CONFIG_FAIR_GROUP_SCHED
- if (tsk->sched_class->moved_group)
- tsk->sched_class->moved_group(tsk, on_rq);
+ if (tsk->sched_class->task_move_group)
+ tsk->sched_class->task_move_group(tsk, on_rq);
+ else
#endif
+ set_task_rq(tsk, task_cpu(tsk));

if (unlikely(running))
tsk->sched_class->set_curr_task(rq);
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index b0f68035..f060583 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -3668,13 +3668,26 @@ static void set_curr_task_fair(struct rq *rq)
}

#ifdef CONFIG_FAIR_GROUP_SCHED
-static void moved_group_fair(struct task_struct *p, int on_rq)
+static void task_move_group_fair(struct task_struct *p, int on_rq)
{
- struct cfs_rq *cfs_rq = task_cfs_rq(p);
-
- update_curr(cfs_rq);
+ /*
+ * If the task was not on the rq at the time of this cgroup movement
+ * it must have been asleep, sleeping tasks keep their ->vruntime
+ * absolute on their old rq until wakeup (needed for the fair sleeper
+ * bonus in place_entity()).
+ *
+ * If it was on the rq, we've just 'preempted' it, which does convert
+ * ->vruntime to a relative base.
+ *
+ * Make sure both cases convert their relative position when migrating
+ * to another cgroup's rq. This does somewhat interfere with the
+ * fair sleeper stuff for the first placement, but who cares.
+ */
+ if (!on_rq)
+ p->se.vruntime -= cfs_rq_of(&p->se)->min_vruntime;
+ set_task_rq(p, task_cpu(p));
if (!on_rq)
- place_entity(cfs_rq, &p->se, 1);
+ p->se.vruntime += cfs_rq_of(&p->se)->min_vruntime;
}
#endif

@@ -3726,7 +3739,7 @@ static const struct sched_class fair_sched_class = {
.get_rr_interval = get_rr_interval_fair,

#ifdef CONFIG_FAIR_GROUP_SCHED
- .moved_group = moved_group_fair,
+ .task_move_group = task_move_group_fair,
#endif
};

--
1.7.4.4