On 03/11/2017 03:42 PM, Jens Axboe wrote:
>> @@ -185,31 +187,53 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg,
>> goto err_free_blkg;
>> }
>>
>> + if (drop_locks) {
>> + spin_unlock_irq(q->queue_lock);
>> + rcu_read_unlock();
>> + }
>
> I have a general dislike for code like that, where you conditionally
> drop locks. And this one seems even worse, since the knowledge of
> whether the locks should/could be dropped or not is embedded in the gfp
> flags.
Talked to Tejun about this as well, and we both agree that the splitting
this into separate init/alloc paths would be much cleaner. I can't
apply the current patch, sorry, it's just too ugly to live.
>> +/**
>> + * blkg_lookup_create - lookup blkg, try to create one if not there
>> + *
>> + * Performs an initial queue bypass check and then passes control to
>> + * __blkg_lookup_create().
>> + */
>> +struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg,
>> + struct request_queue *q, gfp_t gfp,
>> + const struct blkcg_policy *pol)
>> +{
>> + WARN_ON_ONCE(!rcu_read_lock_held());
>> + lockdep_assert_held(q->queue_lock);
>
> This seems problematic, as blkcg_bio_issue_check() calls with the rcu
> read lock held.
Brain fart, that part is fine.
--
Jens Axboe
