block: add a flag to make put_disk on partially initalized disks safer

Add a flag to indicate that __device_add_disk did grab a queue reference
so that disk_release only drops it if we actually had it.  This sort
out one of the major pitfals with partially initialized gendisk that
a lot of drivers did get wrong or still do.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20210521055116.1053587-5-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

block/genhd.c

@@ -539,7 +539,10 @@ static void __device_add_disk(struct device *parent, struct gendisk *disk,
 	 * Take an extra ref on queue which will be put on disk_release()
 	 * so that it sticks around as long as @disk is there.
 	 */
-	WARN_ON_ONCE(!blk_get_queue(disk->queue));
+	if (blk_get_queue(disk->queue))
+		set_bit(GD_QUEUE_REF, &disk->state);
+	else
+		WARN_ON_ONCE(1);
 
 	disk_add_events(disk);
 	blk_integrity_add(disk);
@@ -1107,7 +1110,7 @@ static void disk_release(struct device *dev)
 	kfree(disk->random);
 	xa_destroy(&disk->part_tbl);
 	bdput(disk->part0);
-	if (disk->queue)
+	if (test_bit(GD_QUEUE_REF, &disk->state) && disk->queue)
 		blk_put_queue(disk->queue);
 	kfree(disk);
 }

include/linux/genhd.h

@@ -153,6 +153,7 @@ struct gendisk {
 	unsigned long state;
 #define GD_NEED_PART_SCAN		0
 #define GD_READ_ONLY			1
+#define GD_QUEUE_REF			2
 	struct kobject *slave_dir;
 
 	struct timer_rand_state *random;