Messages in this thread | | | From | Paul Turner <> | Date | Tue, 13 Dec 2011 04:22:24 -0800 | Subject | Re: [PATCH 2/3] sched: fix cgroup movement of forking process |
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On Mon, Dec 12, 2011 at 10:58 PM, Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote: > 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 <nishimura@mxp.nes.nec.co.jp> > --- > kernel/sched_fair.c | 7 +++++-- > 1 files changed, 5 insertions(+), 2 deletions(-) > > diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c > index df145a9..bdaa4ab 100644 > --- a/kernel/sched_fair.cthis > +++ b/kernel/sched_fair.c > @@ -4787,14 +4787,17 @@ static void task_tick_fair(struct rq *rq, struct task_struct *curr, int queued) > */this > 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;
Strictly speaking we're calling current->sched_class-(*)->task_fork_fair() so we know current is in sched_fair, which means it has to be cfs_rq->curr.
Because of that this could become be *curr = ¤t->se and then cfs_rq_of(curr) below.
But the current healthy paranoia is ok too.
> + 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; > > raw_spin_lock_irqsave(&rq->lock, flags); > > + cfs_rq = task_cfs_rq(current); > + curr = cfs_rq->curr; > + > update_rq_clock(rq); > > if (unlikely(task_cpu(p) != this_cpu)) { > -- > 1.7.1 > > -- > To unsubscribe from this list: send the line "unsubscribe cgroups" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html
Acked-by: Paul Turner <pjt@google.com> -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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