linux-kernel - Re: [PATCH 1/3] sched, cgroup: reorganize threadgroup locking

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Date:	Thu, 14 May 2015 11:17:42 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:	lizefan@...wei.com, cgroups@...r.kernel.org, mingo@...hat.com,
	peterz@...radead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] sched, cgroup: reorganize threadgroup locking

Hello, Sergey.

On Thu, May 14, 2015 at 10:09:13AM +0900, Sergey Senozhatsky wrote:
> > +static inline void threadgroup_change_begin(struct task_struct *tsk)
> >  {
> > -	down_write(&tsk->signal->group_rwsem);
> > +	might_sleep();
> 
> I think cgroup_threadgroup_change_begin()->down_read() already does
> might_sleep() check.

Sure but it's a layering thing.  threadgroup_change_begin() should be
called from a blockable context whether the hook users actually make
use of it or not.  e.g. We want might_sleep() even when
!CONFIG_CGROUP.

Thanks.

-- 
tejun
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