sched, cgroup: Fixup broken cgroup movement

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>

2 files changed, 23 insertions, 10 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 5998222f901c..3fe253e6a6e9 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -8498,12 +8498,12 @@ 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 74cccfae87a8..3acc2a487c18 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -3866,13 +3866,26 @@ 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
 
@@ -3924,7 +3937,7 @@ 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
 };