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 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
+= (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@xxxxxxxxxxxxxxxxx>
---
kernel/sched/fair.c | 4 +++-
1 files changed, 3 insertions(+), 1 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index b1db01b..afd13a5 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5345,11 +5345,13 @@ static void task_move_group_fair(struct task_struct *p, int on_rq)
*
* - Moving a forked child which is waiting for being woken up by
* wake_up_new_task().
+ * - Moving a task which has been woken up by try_to_wake_up() and
+ * waiting for actually being woken up by sched_ttwu_pending().
*
* To prevent boost or penalty in the new cfs_rq caused by delta
* min_vruntime between the two cfs_rqs, we skip vruntime adjustment.
*/
- if (!on_rq && !p->se.sum_exec_runtime)
+ if (!on_rq && (!p->se.sum_exec_runtime || p->state == TASK_WAKING))
on_rq = 1;
if (!on_rq)
--
1.7.1
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