From 4fc420c91f53e0a9f95665c6b14a1983716081e7 Mon Sep 17 00:00:00 2001 From: Daisuke Nishimura Date: Thu, 15 Dec 2011 14:36:55 +0900 Subject: [PATCH] sched: Fix cgroup movement of forking process There is a small race between task_fork_fair() and sched_move_task(), which is trying to move the parent. task_fork_fair() sched_move_task() --------------------------------+--------------------------------- cfs_rq = task_cfs_rq(current) -> cfs_rq is the "old" one. curr = cfs_rq->curr -> curr is set to the parent. task_rq_lock() dequeue_task() ->parent.se.vruntime -= (old)cfs_rq->min_vruntime enqueue_task() ->parent.se.vruntime += (new)cfs_rq->min_vruntime task_rq_unlock() raw_spin_lock_irqsave(rq->lock) se->vruntime = curr->vruntime -> vruntime of the child is set to that of the parent which has already been updated by sched_move_task(). se->vruntime -= (old)cfs_rq->min_vruntime. raw_spin_unlock_irqrestore(rq->lock) As a result, vruntime of the child becomes far bigger than expected, if (new)cfs_rq->min_vruntime >> (old)cfs_rq->min_vruntime. This patch fixes this problem by setting "cfs_rq" and "curr" after holding the rq->lock. Signed-off-by: Daisuke Nishimura Acked-by: Paul Turner Signed-off-by: Peter Zijlstra Cc: Tejun Heo Link: http://lkml.kernel.org/r/20111215143655.662676b0.nishimura@mxp.nes.nec.co.jp Signed-off-by: Ingo Molnar --- kernel/sched/fair.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index cea2fa853274..525d69e5fb78 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -5190,8 +5190,8 @@ static void task_tick_fair(struct rq *rq, struct task_struct *curr, int queued) */ static void task_fork_fair(struct task_struct *p) { - struct cfs_rq *cfs_rq = task_cfs_rq(current); - struct sched_entity *se = &p->se, *curr = cfs_rq->curr; + struct cfs_rq *cfs_rq; + struct sched_entity *se = &p->se, *curr; int this_cpu = smp_processor_id(); struct rq *rq = this_rq(); unsigned long flags; @@ -5200,6 +5200,9 @@ static void task_fork_fair(struct task_struct *p) update_rq_clock(rq); + cfs_rq = task_cfs_rq(current); + curr = cfs_rq->curr; + if (unlikely(task_cpu(p) != this_cpu)) { rcu_read_lock(); __set_task_cpu(p, this_cpu);