lkml.org 
[lkml]   [2011]   [Dec]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [tip:sched/core] sched: Fix cgroup movement of forking process
Hello, guys.

On Wed, Dec 21, 2011 at 03:44:14AM -0800, tip-bot for Daisuke Nishimura wrote:
> 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.

The race shouldn't happen with threadgroup locking scheduled to be
merged for the coming merge window. sched_fork() and cgroup migration
become exclusive and won't happen concurrently. Would still make
sense for -stable tho.

Thanks.

--
tejun


\
 
 \ /
  Last update: 2011-12-21 18:29    [from the cache]
©2003-2011 Jasper Spaans