On 1/4/22 6:42 AM, Ming Lei wrote:
> Commit cc9c884dd7f4 ("block: call submit_bio_checks under q_usage_counter")
> uses q_usage_counter to protect submit_bio_checks for avoiding IO after
> disk is deleted by del_gendisk().
>
> Turns out the protection isn't necessary, because once
> blk_mq_freeze_queue_wait() in del_gendisk() returns:
>
> 1) all in-flight IO has been done
>
> 2) all new IO will be failed in __bio_queue_enter() because
> q_usage_counter is dead, and GD_DEAD is set
>
> 3) both disk and request queue instance are safe since caller of
> submit_bio() guarantees that the disk can't be closed.
>
> Once submit_bio_checks() needn't the protection of q_usage_counter, we can
> move submit_bio_checks before calling blk_mq_submit_bio() and
> ->submit_bio(). With this change, we needn't to throttle queue with
> holding one allocated request, then precise driver tag or request won't be
> wasted in throttling. Meantime we can unify the bio check for both bio
> based and request based driver.
If you're now convinced it's fine, then I have no problems with it. This
basically reverts to the earlier version of what I had anyway.
--
Jens Axboe
