Re: [PATCH 2/2] cgroup: Walk task list under tasklist_lock incgroup_enable_task_cg_list

[Tejun Heo]

On Wed, Feb 22, 2012 at 01:55:28AM +0100, Frederic Weisbecker wrote:
> > > +	 * We need tasklist_lock because RCU is not safe against
> > > +	 * while_each_thread(). Besides, a forking task that has passed
> > > +	 * cgroup_post_fork() without seeing use_task_css_set_links = 1
> > > +	 * is not guaranteed to have its child immediately visible in the
> > > +	 * tasklist if we walk through it with RCU.
> > > +	 */
> > 
> > Maybe add TODO to remove the lock once do_each_thread()/while_each_thread()
> > is made rcu safe. On a large system, it could take a while to iterate
> > over every thread in the system. Thats a long time to hold a spinlock.
> > But it only happens once so probably not that big a deal.
> 
> I think that even if while_each_thread() was RCU safe, that wouldn't
> work here.

Guys, this is one time thing.  It happens *once* after boot and we're
already holding exclusive lock.  There's no reason to optimize this at
all.  Let's just keep it simple.

Thanks.

-- 
tejun
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