linux-kernel - Re: [tip:sched/core] sched: Fix cgroup movement of forking process

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Wed, 21 Dec 2011 09:26:32 -0800
From:	Tejun Heo <tj@...nel.org>
To:	tip-bot for Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Cc:	linux-tip-commits@...r.kernel.org, linux-kernel@...r.kernel.org,
	hpa@...or.com, mingo@...hat.com, a.p.zijlstra@...llo.nl,
	pjt@...gle.com, tglx@...utronix.de, mingo@...e.hu
Subject: Re: [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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/