[PATCH 1/2] blk-mq: add two interfaces to lock/unlock blk_mq_tags->lock

[Yu Kuai]

Ming Lei had fixed the request UAF while iterating tags, however
some drivers is calling blk_mq_tag_to_rq() directly to get request
through tag. So the problem might still exist since that
blk_mq_tags->lock should be held.

Thus add blk_mq_tags_lock() and blk_mq_tags_unlock() so that drivers
can lock and unlock blk_mq_tags->lock if they are not sure that the
request is valid.

Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
---
 block/blk-mq-tag.c     | 12 ++++++++++++
 include/linux/blk-mq.h |  2 ++
 2 files changed, 14 insertions(+)

diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index 86f87346232a..388d447c993a 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -652,3 +652,15 @@ u32 blk_mq_unique_tag(struct request *rq)
 		(rq->tag & BLK_MQ_UNIQUE_TAG_MASK);
 }
 EXPORT_SYMBOL(blk_mq_unique_tag);
+
+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);
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 1d18447ebebc..b4bad4d6a3a8 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -635,4 +635,6 @@ blk_qc_t blk_mq_submit_bio(struct bio *bio);
 void blk_mq_hctx_set_fq_lock_class(struct blk_mq_hw_ctx *hctx,
 		struct lock_class_key *key);
 
+void blk_mq_tags_lock(struct blk_mq_tags *tags, unsigned long *flags);
+void blk_mq_tags_unlock(struct blk_mq_tags *tags, unsigned long *flags);
 #endif
-- 
2.31.1