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

[Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>]

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