linux-kernel - Re: [PATCH 1/2] blk-mq: add two interfaces to lock/unlock blk_mq

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Date:   Sun, 8 Aug 2021 09:44:40 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Yu Kuai <yukuai3@...wei.com>, axboe@...nel.dk,
        josef@...icpanda.com, ming.lei@...hat.com
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        nbd@...er.debian.org, yi.zhang@...wei.com
Subject: Re: [PATCH 1/2] blk-mq: add two interfaces to lock/unlock
 blk_mq_tags->lock

On 8/7/21 8:17 PM, Yu Kuai wrote:
> +void blk_mq_tags_lock(struct blk_mq_tags *tags, unsigned long *flags)
> +{
> +	spin_lock_irqsave(&tags->lock, *flags);
> +}
> +EXPORT_SYMBOL(blk_mq_tags_lock);
> +
> +void blk_mq_tags_unlock(struct blk_mq_tags *tags, unsigned long *flags)
> +{
> +	spin_unlock_irqrestore(&tags->lock, *flags);
> +}
> +EXPORT_SYMBOL(blk_mq_tags_unlock);

The tag map lock is an implementation detail and hence this lock must
not be used directly by block drivers. I propose to introduce and export
a new function to block drivers that does the following:
* Lock tags->lock.
* Call blk_mq_tag_to_rq().
* Check whether the request is in the started state. If so, increment
its reference count.
* Unlock tags->lock.

Thanks,

Bart.