Re: [PATCH block/for-3.4/core] cfq: fix cfqg ref handling when BLK_CGROUP && !CFQ_GROUP_IOSCHED

Vivek Goyal
2012-03-15T17:01:30Z

On Thu, Mar 15, 2012 at 09:50:57AM -0700, Tejun Heo wrote:

> > [..]
> > > @@ -3533,7 +3551,7 @@ static int cfq_init_queue(struct request
> > >
> > > spin_lock_irq(q->queue_lock);
> > > cfq_link_cfqq_cfqg(&cfqd->oom_cfqq, cfqd->root_group);
> > > - blkg_put(cfqg_to_blkg(cfqd->root_group));
> > > + cfqg_put(cfqd->root_group);
> >
> > This seems to be a spurious cfqg_put()? Which reference we are putting
> > down here?
>
> The extra ref from cfq_link_cfqq_cfqg() for oom_cfqq; otherwise, we
> need an extra cfq_put() in cfq_exit_queue(). I thought I wrote
> comment about that somewhere. Hmmm.... apparently not. The thing is
> that oom_cfqq doesn't go through proper cfqq destruction and thus
> never puts the extra ref to root cfqg.

Ok. Is cfq_exit_queue() a better place to put down this reference
explicitly with a comment. Even if you keep it here, atleast a comment
is required. It is not obvious at all (atleast to me).

Thanks
Vivek