blk-mq: fix "bad unlock balance detected" on q->srcu in __blk_mq_run_dispatch_ops

The 'q' parameter of the macro __blk_mq_run_dispatch_ops may not be one
local variable, such as, it is rq->q, then request queue pointed by
this variable could be changed to another queue in case of
BLK_MQ_F_TAG_QUEUE_SHARED after 'dispatch_ops' returns, then
'bad unlock balance' is triggered.

Fixes the issue by adding one local variable for doing srcu lock/unlock.

Fixes: 2a904d0 ("blk-mq: remove hctx_lock and hctx_unlock")
Cc: Marco Patalano <[email protected]>
Signed-off-by: Chris Leech <[email protected]>
Signed-off-by: Ming Lei <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

Author: cleech

block/blk-mq.h

@@ -378,12 +378,13 @@ static inline bool hctx_may_queue(struct blk_mq_hw_ctx *hctx,
 #define __blk_mq_run_dispatch_ops(q, check_sleep, dispatch_ops)	\
 do {								\
 	if ((q)->tag_set->flags & BLK_MQ_F_BLOCKING) {		\
+		struct blk_mq_tag_set *__tag_set = (q)->tag_set; \
 		int srcu_idx;					\
 								\
 		might_sleep_if(check_sleep);			\
-		srcu_idx = srcu_read_lock((q)->tag_set->srcu);	\
+		srcu_idx = srcu_read_lock(__tag_set->srcu);	\
 		(dispatch_ops);					\
-		srcu_read_unlock((q)->tag_set->srcu, srcu_idx);	\
+		srcu_read_unlock(__tag_set->srcu, srcu_idx);	\
 	} else {						\
 		rcu_read_lock();				\
 		(dispatch_ops);					\