linux-kernel - Re: [PATCH 1/7] cgroup: cgroup_subsys->fork() should be called after the task is added to css

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Message-ID: <20121022211631.GE5951@atj.dyndns.org>
Date:	Mon, 22 Oct 2012 17:16:31 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	rjw@...k.pl, linux-kernel@...r.kernel.org, lizefan@...wei.com,
	containers@...ts.linux-foundation.org, cgroups@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH 1/7] cgroup: cgroup_subsys->fork() should be called after
 the task is added to css_set

Hey,

On Mon, Oct 22, 2012 at 08:04:45PM +0200, Oleg Nesterov wrote:
> > * Clear ->cgroup to %NULL during copy_process().
> 
> I completely agree. new_child->cgroups copied from parent looks simply
> strange until post_fork. If nothing else, the new task is still under
> construction by the time cgroup_fork() is called.

Yeah, and it's just nasty to have cgroup->fork() and ->attach() racing
each other.  As far as cgroup is concerned, the new task should be
completely idle till ->fork() is complete.

> > > I am starting to think again about a big-rw-lock around copy_process.
> > > Recently I tried to add one around dup_mmap for uprobes, but perhaps
> > > cgroups can use it too...
> >
> > If some other subsystems need it, maybe just make threadgroup locking
> > coarser?
> 
> What do you mean?

I probabl have misunderstood you but If you're gonna add big-rw-lock
around copy-process which is always gonna be grabbed, I was suggesting
maybe we could simply repurpose the existing threadgroup locking.  Or
are the requirements too different?

Thanks.

--
tejun
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