Revert "block: Fix a lockdep complaint triggered by request queue flushing"

This reverts commit b3c6a59.

Now we can avoid nvme-loop lockdep warning of 'lockdep possible recursive locking'
by nvme-loop's lock class, no need to apply dynamically allocated lock class key,
so revert commit b3c6a59("block: Fix a lockdep complaint triggered by request
queue flushing").

This way fixes horrible SCSI probe delay issue on megaraid_sas, and it is reported
the whole probe may take more than half an hour.

Tested-by: Kashyap Desai <[email protected]>
Reported-by: Qian Cai <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Cc: Sumit Saxena <[email protected]>
Cc: John Garry <[email protected]>
Cc: Kashyap Desai <[email protected]>
Cc: Bart Van Assche <[email protected]>
Cc: Hannes Reinecke <[email protected]>
Signed-off-by: Ming Lei <[email protected]>
Reviewed-by: Hannes Reinecke <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>

Author: Ming Lei

block/blk-flush.c

@@ -69,7 +69,6 @@
 #include <linux/blkdev.h>
 #include <linux/gfp.h>
 #include <linux/blk-mq.h>
-#include <linux/lockdep.h>
 
 #include "blk.h"
 #include "blk-mq.h"
@@ -469,9 +468,6 @@ struct blk_flush_queue *blk_alloc_flush_queue(int node, int cmd_size,
 	INIT_LIST_HEAD(&fq->flush_queue[1]);
 	INIT_LIST_HEAD(&fq->flush_data_in_flight);
 
-	lockdep_register_key(&fq->key);
-	lockdep_set_class(&fq->mq_flush_lock, &fq->key);
-
 	return fq;
 
  fail_rq:
@@ -486,7 +482,6 @@ void blk_free_flush_queue(struct blk_flush_queue *fq)
 	if (!fq)
 		return;
 
-	lockdep_unregister_key(&fq->key);
 	kfree(fq->flush_rq);
 	kfree(fq);
 }

block/blk.h

@@ -25,7 +25,6 @@ struct blk_flush_queue {
 	struct list_head	flush_data_in_flight;
 	struct request		*flush_rq;
 
-	struct lock_class_key	key;
 	spinlock_t		mq_flush_lock;
 };