Re: [PATCH v5 1/3] blkcg: Introduce blkg_root_lookup()

[Jens Axboe <axboe@kernel.dk>]

On 8/9/18 2:17 PM, Bart Van Assche wrote:
> On Thu, 2018-08-09 at 12:56 -0700, Tejun Heo wrote:
>> Hello,
>>
>> On Thu, Aug 09, 2018 at 07:53:36AM -0700, Bart Van Assche wrote:
>>> +/**
>>> + * blkg_lookup - look up blkg for the specified request queue
>>> + * @q: request_queue of interest
>>> + *
>>> + * Lookup blkg for @q at the root level. See also blkg_lookup().
>>> + */
>>> +static inline struct blkcg_gq *blkg_root_lookup(struct request_queue *q)
>>> +{
>>> +	struct blkcg_gq *blkg;
>>> +
>>> +	rcu_read_lock();
>>> +	blkg = blkg_lookup(&blkcg_root, q);
>>> +	rcu_read_unlock();
>>> +
>>> +	return blkg;
>>> +}
>>
>> So, root blkg is always available as long as the request_queue is
>> alive.  Sth like the following would be simpler?
>>
>> static inline struct blkcg_gq *blk_queue_root_blkg(struct request_queue *q)
>> {
>> 	return q->root_blkg;
>> }
> 
> That would not only be simpler, it would also avoid that blk_queue_root_blkg()
> returns NULL if bypass mode is enabled and the request queue is still associated
> with the block cgroup controller. How do you want to proceed with this change?

Do a followup patch?

-- 
Jens Axboe