block: cache request queue in bdev

There are tons of places where we need to get a request_queue only
having bdev, which turns into bdev->bd_disk->queue. There are probably a
hundred of such places considering inline helpers, and enough of them
are in hot paths.

Cache queue pointer in struct block_device and make use of it in
bdev_get_queue().
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/a3bfaecdd28956f03629d0ca5c63ebc096e1c809.1634219547.git.asml.silence@gmail.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

block/bdev.c

@@ -493,6 +493,7 @@ struct block_device *bdev_alloc(struct gendisk *disk, u8 partno)
 	spin_lock_init(&bdev->bd_size_lock);
 	bdev->bd_partno = partno;
 	bdev->bd_inode = inode;
+	bdev->bd_queue = disk->queue;
 	bdev->bd_stats = alloc_percpu(struct disk_stats);
 	if (!bdev->bd_stats) {
 		iput(inode);

block/genhd.c

@@ -1267,6 +1267,9 @@ struct gendisk *__alloc_disk_node(struct request_queue *q, int node_id,
 	if (!disk->bdi)
 		goto out_free_disk;
 
+	/* bdev_alloc() might need the queue, set before the first call */
+	disk->queue = q;
+
 	disk->part0 = bdev_alloc(disk, 0);
 	if (!disk->part0)
 		goto out_free_bdi;
@@ -1282,7 +1285,6 @@ struct gendisk *__alloc_disk_node(struct request_queue *q, int node_id,
 	disk_to_dev(disk)->type = &disk_type;
 	device_initialize(disk_to_dev(disk));
 	inc_diskseq(disk);
-	disk->queue = q;
 	q->disk = disk;
 	lockdep_init_map(&disk->lockdep_map, "(bio completion)", lkclass, 0);
 #ifdef CONFIG_BLOCK_HOLDER_DEPRECATED

include/linux/blk_types.h

@@ -38,6 +38,7 @@ struct block_device {
 	u8			bd_partno;
 	spinlock_t		bd_size_lock; /* for bd_inode->i_size updates */
 	struct gendisk *	bd_disk;
+	struct request_queue *	bd_queue;
 
 	/* The counter of freeze processes */
 	int			bd_fsfreeze_count;

include/linux/blkdev.h

@@ -574,7 +574,7 @@ int iocb_bio_iopoll(struct kiocb *kiocb, unsigned int flags);
 
 static inline struct request_queue *bdev_get_queue(struct block_device *bdev)
 {
-	return bdev->bd_disk->queue;	/* this is never NULL */
+	return bdev->bd_queue;	/* this is never NULL */
 }
 
 /*