Re: [PATCH] block: don't allow the same type rq_qos add more than once

[hanjinke]

Thanks for your review. I have saw this review just after the send of 
patch v2

在 2022/7/19 下午2:53, Muchun Song 写道:
> On Mon, Jul 18, 2022 at 4:37 PM Jinke Han <hanjinke.666@xxxxxxxxxxxxx> wrote:
> > From: hanjinke <hanjinke.666@xxxxxxxxxxxxx>
> >
> > In our test of iocost, we encounttered some list add/del corrutions of
> > inner_walk list in ioc_timer_fn.
> > The resean can be descripted as follow:
> >
> > cpu 0                                           cpu 1
> > ioc_qos_write                                   ioc_qos_write
> >
> > ioc = q_to_ioc(bdev_get_queue(bdev));
> > if (!ioc) {
> >          ioc = kzalloc();                        ioc = q_to_ioc(bdev_get_queue(bdev));
> >                                                          if (!ioc) {
> >                                                                  ioc = kzalloc();
> >                                                                  ...
> >                                                                  rq_qos_add(q, rqos);
> >                                                           }
> >          ...
> >          rq_qos_add(q, rqos);
> >          ...
> > }
> >
> > When the io.cost.qos file is written by two cpu concurrently, rq_qos may
> > be added to one disk twice. In that case, there will be two iocs enabled
> > and running on one disk. They own different iocgs on their active list.
> > In the ioc_timer_fn function, because of the iocgs from two ioc have the
> > same root iocg, the root iocg's walk_list may be overwritten by each
> > other and this lead to list add/del corrutions in building or destorying
> > the inner_walk list.
> >
> > And so far, the blk-rq-qos framework works in case that one instance for
> > one type rq_qos per queue by default. This patch make this explicit and
> > also fix the crash above.
> >
> > Signed-off-by: hanjinke <hanjinke.666@xxxxxxxxxxxxx>
>
> The change LGTM. Maybe it is better to add a Fixes tag here so that
> others can easily know what Linux versions should be backported.
>
> Reviewed-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
>
> Thanks.