linux-kernel - Re: [RFC] [PATCH v3 1/2] cgroups: read-write lock CLONE

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Message-ID: <20100728082953.GA15455@ghc01.ghc.andrew.cmu.edu>
Date:	Wed, 28 Jul 2010 04:29:53 -0400
From:	Ben Blum <bblum@...rew.cmu.edu>
To:	Ben Blum <bblum@...rew.cmu.edu>
Cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-kernel@...r.kernel.org,
	containers@...ts.linux-foundation.org, akpm@...ux-foundation.org,
	ebiederm@...ssion.com, lizf@...fujitsu.com, matthltc@...ibm.com,
	menage@...gle.com, oleg@...hat.com
Subject: Re: [RFC] [PATCH v3 1/2] cgroups: read-write lock CLONE_THREAD
 forking per threadgroup

On Mon, Jun 28, 2010 at 11:43:59AM -0400, Ben Blum wrote:
> On Mon, Jun 28, 2010 at 04:10:31PM +0900, KAMEZAWA Hiroyuki wrote:
> > By the way, IMHO, hiding lock in cgroup_fork() and cgroup_post_fork() doesn't
> > seem good idea. How about a code like this ?
> > 
> >   read_lock_thread_clone(current);
> >   cgroup_fork();
> >  .....
> >   cgroup_post_fork();
> >   read_unlock_thrad_clone(current);
> > 
> > We may have chances to move these lock to better position if cgroup is
> > an only user.
> 
> I didn't do that out of a desire to change fork.c as little as possible,
> but that does look better than what I've got. Those two functions should
> be in fork.c under #ifdef CONFIG_CGROUPS.

I'm looking at this now and am not sure where the best place to put
these is:

1) Don't make new functions, just put:

    #ifdef CONFIG_CGROUPS
        if (clone_flags & CLONE_THREAD)
            down/up_read(...);
    #endif

directly in copy_process() in fork.c. Simplest, but uglifies the code.

2) Make static helper functions in fork.c. Good, but not consistent with
directly using the lock in write-side (attach_proc).

3) Define inline functions under #ifdef CONFIG_CGROUPS in sched.h, just
under the declaration of the lock. Most robust, but I'm hesitant to add
unneeded stuff to such a popular header file.

Any opinions?

-- Ben

> 
> > 
> > Thanks,
> > -Kame
> 
> Thanks,
> -- Ben
> 
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