Re: [PATCH 05/12] blkcg: update blkg get functions takeblkio_cgroup as parameter

[Tejun Heo]

On Thu, Jan 19, 2012 at 06:21:02AM -0500, Vivek Goyal wrote:
> On Wed, Jan 18, 2012 at 05:11:23PM -0800, Tejun Heo wrote:
> 
> [..]
> > -static struct throtl_grp * throtl_get_tg(struct throtl_data *td)
> > +static struct throtl_grp *throtl_get_tg(struct throtl_data *td,
> > +					struct blkio_cgroup *blkcg)
> >  {
> >  	struct throtl_grp *tg = NULL, *__tg = NULL;
> > -	struct blkio_cgroup *blkcg;
> >  	struct request_queue *q = td->queue;
> >  
> >  	/* no throttling for dead queue */
> >  	if (unlikely(blk_queue_dead(q)))
> >  		return NULL;
> >  
> > -	blkcg = task_blkio_cgroup(current);
> >  	tg = throtl_find_tg(td, blkcg);
> >  	if (tg)
> >  		return tg;
> >  
> > +	if (!css_tryget(&blkcg->css))
> > +		return NULL;
> > +
> 
> This reference is to make sure that blkcg does not go away while we drop
> the rcu lock and do the group allocation?

Yeah, for now but later patch will make blkg's hold onto the
associated blkcg and this reference will be dropped on blkg
destruction.

Thanks.

-- 
tejun
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