[PATCH v4 1/6] blk-mq: export two symbols to get request by tag

[Yu Kuai <yukuai3@huawei.com>]

nbd has a defect that blk_mq_tag_to_rq() might return a freed
request in nbd_read_stat(). We need a new mechanism if we want to
fix this in nbd driver, which is rather complicated.

Thus use blk_mq_find_and_get_req() to replace blk_mq_tag_to_rq(),
which can make sure the returned request is not freed, and then we
can do more checking while 'cmd->lock' is hold.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
 block/blk-mq-tag.c     | 5 +++--
 block/blk-mq.c         | 1 +
 include/linux/blk-mq.h | 3 +++
 3 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index 86f87346232a..b4f66b75b4d1 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -200,8 +200,8 @@ struct bt_iter_data {
 	bool reserved;
 };
 
-static struct request *blk_mq_find_and_get_req(struct blk_mq_tags *tags,
-		unsigned int bitnr)
+struct request *blk_mq_find_and_get_req(struct blk_mq_tags *tags,
+					unsigned int bitnr)
 {
 	struct request *rq;
 	unsigned long flags;
@@ -213,6 +213,7 @@ static struct request *blk_mq_find_and_get_req(struct blk_mq_tags *tags,
 	spin_unlock_irqrestore(&tags->lock, flags);
 	return rq;
 }
+EXPORT_SYMBOL(blk_mq_find_and_get_req);
 
 static bool bt_iter(struct sbitmap *bitmap, unsigned int bitnr, void *data)
 {
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 08626cb0534c..5113aa3788a2 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -916,6 +916,7 @@ void blk_mq_put_rq_ref(struct request *rq)
 	else if (refcount_dec_and_test(&rq->ref))
 		__blk_mq_free_request(rq);
 }
+EXPORT_SYMBOL(blk_mq_put_rq_ref);
 
 static bool blk_mq_check_expired(struct blk_mq_hw_ctx *hctx,
 		struct request *rq, void *priv, bool reserved)
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 13ba1861e688..03e02990609d 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -637,4 +637,7 @@ 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_put_rq_ref(struct request *rq);
+struct request *blk_mq_find_and_get_req(struct blk_mq_tags *tags,
+					unsigned int bitnr);
 #endif
-- 
2.31.1