Re: [PATCH] sched: Fix race between task_group and sched_task_group

From: Peter Zijlstra <peterz@infradead.org>
To: Kirill Tkhai <ktkhai@parallels.com>
Cc: linux-kernel@vger.kernel.org, Oleg Nesterov <oleg@redhat.com>,
	Ingo Molnar <mingo@redhat.com>,
	Burke Libbey <burke.libbey@shopify.com>,
	Vladimir Davydov <vdavydov@parallels.com>,
	Kirill Tkhai <tkhai@yandex.ru>
Subject: Re: [PATCH] sched: Fix race between task_group and sched_task_group
Date: Mon, 27 Oct 2014 13:21:46 +0100	[thread overview]
Message-ID: <20141027122146.GC3337@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <1414405105.19914.169.camel@tkhai>

On Mon, Oct 27, 2014 at 02:18:25PM +0400, Kirill Tkhai wrote:
> 
> The race may happen when somebody is changing task_group of a forking task.
> Child's cgroup is the same as parent's after dup_task_struct() (there just
> memory copying). Also, cfs_rq and rt_rq are the same as parent's.
> 
> But if parent changes its task_group before it's called cgroup_post_fork(),
> we do not reflect this situation on child. Child's cfs_rq and rt_rq remain
> the same, while child's task_group changes in cgroup_post_fork().
> 
> To fix this we introduce fork() method, which calls sched_move_task() directly.
> This function changes sched_task_group on appropriate (also its logic has
> no problem with freshly created tasks, so we shouldn't introduce something
> special; we are able just to use it).

Right, I read some of that cgroup.c stuff and this is indeed possible,
yucky. Applied, thanks!