Messages in this thread Patch in this message | | | Date | Tue, 13 Dec 2011 15:59:33 +0900 | From | Daisuke Nishimura <> | Subject | [PATCH 3/3] sched: fix cgroup movement of waking process |
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There is a small race between try_to_wake_up() and sched_move_task(), which is trying to move the process being woken up.
try_to_wake_up() on CPU0 sched_move_task() on CPU1 --------------------------------+--------------------------------- raw_spin_lock_irqsave(p->pi_lock) task_waking_fair() ->p.se.vruntime -= cfs_rq->min_vruntime ttwu_queue() ->send reschedule IPI to another CPU1 raw_spin_unlock_irqsave(p->pi_lock) task_rq_lock() -> tring to aquire both p->pi_lock and rq->lock with IRQ disabled task_move_group_fair() ->p.se.vruntime -= (old)cfs_rq->min_vruntime ->p.se.vruntime += (new)cfs_rq->min_vruntime task_rq_unlock()
(via IPI) sched_ttwu_pending() raw_spin_lock(rq->lock) ttwu_do_activate() ... enqueue_entity() child.se->vruntime += cfs_rq->min_vruntime raw_spin_unlock(rq->lock)
As a result, vruntime of the process becomes far bigger than min_vruntime, if (new)cfs_rq->min_vruntime >> (old)cfs_rq->min_vruntime.
This patch fixes this problem by just ignoring such process in task_move_group_fair(), because the vruntime has already been normalized in task_waking_fair().
Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> --- kernel/sched_fair.c | 4 ++-- 1 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c index bdaa4ab..3feb3a2 100644 --- a/kernel/sched_fair.c +++ b/kernel/sched_fair.c @@ -4925,10 +4925,10 @@ static void task_move_group_fair(struct task_struct *p, int on_rq) * 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->state != TASK_RUNNING) + if (!on_rq && p->state != TASK_RUNNING && p->state != TASK_WAKING) p->se.vruntime -= cfs_rq_of(&p->se)->min_vruntime; set_task_rq(p, task_cpu(p)); - if (!on_rq && p->state != TASK_RUNNING) + if (!on_rq && p->state != TASK_RUNNING && p->state != TASK_WAKING) p->se.vruntime += cfs_rq_of(&p->se)->min_vruntime; } #endif -- 1.7.1
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