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.