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authorDaisuke Nishimura <nishimura@mxp.nes.nec.co.jp>2011-12-15 14:36:07 +0900
committerIngo Molnar <mingo@elte.hu>2011-12-21 10:34:51 +0100
commit7ceff013c43c0f38f0d26c79507889c6791c0ea0 (patch)
treef4e164fcb0b75b3d559e644d41fd4c6c29990bef /kernel/sched
parent4fc420c91f53e0a9f95665c6b14a1983716081e7 (diff)
sched: Fix cgroup movement of newly created process
There is a small race between do_fork() and sched_move_task(), which is trying to move the child. do_fork() sched_move_task() --------------------------------+--------------------------------- copy_process() sched_fork() task_fork_fair() -> vruntime of the child is initialized based on that of the parent. -> we can see the child in "tasks" file now. task_rq_lock() task_move_group_fair() -> child.se.vruntime -= (old)cfs_rq->min_vruntime += (new)cfs_rq->min_vruntime task_rq_unlock() wake_up_new_task() ... enqueue_entity() child.se.vruntime += cfs_rq->min_vruntime As a result, vruntime of the child 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_fork_fair(). Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Tejun Heo <tj@kernel.org> Link: http://lkml.kernel.org/r/20111215143607.2ee12c5d.nishimura@mxp.nes.nec.co.jp Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/sched')
-rw-r--r--kernel/sched/fair.c13
1 files changed, 13 insertions, 0 deletions
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 525d69e5fb78..2d1ac6e2386d 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5338,6 +5338,19 @@ 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.
*/
+ /*
+ * When !on_rq, vruntime of the task has usually NOT been normalized.
+ * But there are some cases where it has already been normalized:
+ *
+ * - Moving a forked child which is waiting for being woken up by
+ * wake_up_new_task().
+ *
+ * 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)
+ on_rq = 1;
+
if (!on_rq)
p->se.vruntime -= cfs_rq_of(&p->se)->min_vruntime;
set_task_rq(p, task_cpu(p));