ublk: defer disk allocation

Defer allocating the gendisk and request_queue until UBLK_CMD_START_DEV
is called.  This avoids funky life times where a disk is allocated
and then can be added and removed multiple times, which has never been
supported by the block layer.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20220721130916.1869719-9-hch@lst.deSigned-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/ublk_drv.c

@@ -112,7 +112,6 @@ struct ublk_queue {
 
 struct ublk_device {
 	struct gendisk		*ub_disk;
-	struct request_queue	*ub_queue;
 
 	char	*__queues;
 
@@ -126,6 +125,7 @@ struct ublk_device {
 	struct device		cdev_dev;
 
 #define UB_STATE_OPEN		(1 << 0)
+#define UB_STATE_USED		(1 << 1)
 	unsigned long		state;
 	int			ub_number;
 
@@ -156,8 +156,6 @@ static DEFINE_MUTEX(ublk_ctl_mutex);
 
 static struct miscdevice ublk_misc;
 
-static struct lock_class_key ublk_bio_compl_lkclass;
-
 static inline bool ublk_can_use_task_work(const struct ublk_queue *ubq)
 {
 	if (IS_BUILTIN(CONFIG_BLK_DEV_UBLK) &&
@@ -209,8 +207,17 @@ static inline int ublk_queue_cmd_buf_size(struct ublk_device *ub, int q_id)
 			PAGE_SIZE);
 }
 
+static void ublk_free_disk(struct gendisk *disk)
+{
+	struct ublk_device *ub = disk->private_data;
+
+	clear_bit(UB_STATE_USED, &ub->state);
+	put_device(&ub->cdev_dev);
+}
+
 static const struct block_device_operations ub_fops = {
 	.owner =	THIS_MODULE,
+	.free_disk =	ublk_free_disk,
 };
 
 #define UBLK_MAX_PIN_PAGES	32
@@ -801,13 +808,15 @@ static void ublk_cancel_dev(struct ublk_device *ub)
 static void ublk_stop_dev(struct ublk_device *ub)
 {
 	mutex_lock(&ub->mutex);
-	if (!disk_live(ub->ub_disk))
+	if (ub->dev_info.state != UBLK_S_DEV_LIVE)
 		goto unlock;
 
 	del_gendisk(ub->ub_disk);
 	ub->dev_info.state = UBLK_S_DEV_DEAD;
 	ub->dev_info.ublksrv_pid = -1;
 	ublk_cancel_dev(ub);
+	put_disk(ub->ub_disk);
+	ub->ub_disk = NULL;
  unlock:
 	mutex_unlock(&ub->mutex);
 	cancel_delayed_work_sync(&ub->monitor_work);
@@ -1033,12 +1042,7 @@ static void ublk_cdev_rel(struct device *dev)
 {
 	struct ublk_device *ub = container_of(dev, struct ublk_device, cdev_dev);
 
-	blk_mq_destroy_queue(ub->ub_queue);
-
-	put_disk(ub->ub_disk);
-
 	blk_mq_free_tag_set(&ub->tag_set);
-
 	ublk_deinit_queues(ub);
 
 	__ublk_destroy_dev(ub);
@@ -1078,31 +1082,24 @@ static void ublk_stop_work_fn(struct work_struct *work)
 	ublk_stop_dev(ub);
 }
 
-static void ublk_update_capacity(struct ublk_device *ub)
+/* align maximum I/O size to PAGE_SIZE */
+static void ublk_align_max_io_size(struct ublk_device *ub)
 {
-	unsigned int max_rq_bytes;
+	unsigned int max_rq_bytes = ub->dev_info.rq_max_blocks << ub->bs_shift;
 
-	/* make max request buffer size aligned with PAGE_SIZE */
-	max_rq_bytes = round_down(ub->dev_info.rq_max_blocks <<
-			ub->bs_shift, PAGE_SIZE);
-	ub->dev_info.rq_max_blocks = max_rq_bytes >> ub->bs_shift;
-
-	set_capacity(ub->ub_disk, ub->dev_info.dev_blocks << (ub->bs_shift - 9));
+	ub->dev_info.rq_max_blocks =
+		round_down(max_rq_bytes, PAGE_SIZE) >> ub->bs_shift;
 }
 
-/* add disk & cdev, cleanup everything in case of failure */
+/* add tag_set & cdev, cleanup everything in case of failure */
 static int ublk_add_dev(struct ublk_device *ub)
 {
-	struct gendisk *disk;
 	int err = -ENOMEM;
-	int bsize;
 
 	/* We are not ready to support zero copy */
 	ub->dev_info.flags[0] &= ~UBLK_F_SUPPORT_ZERO_COPY;
 
-	bsize = ub->dev_info.block_size;
-	ub->bs_shift = ilog2(bsize);
-
+	ub->bs_shift = ilog2(ub->dev_info.block_size);
 	ub->dev_info.nr_hw_queues = min_t(unsigned int,
 			ub->dev_info.nr_hw_queues, nr_cpu_ids);
 
@@ -1119,59 +1116,16 @@ static int ublk_add_dev(struct ublk_device *ub)
 	ub->tag_set.cmd_size = sizeof(struct ublk_rq_data);
 	ub->tag_set.flags = BLK_MQ_F_SHOULD_MERGE;
 	ub->tag_set.driver_data = ub;
-
 	err = blk_mq_alloc_tag_set(&ub->tag_set);
 	if (err)
 		goto out_deinit_queues;
 
-	ub->ub_queue = blk_mq_init_queue(&ub->tag_set);
-	if (IS_ERR(ub->ub_queue)) {
-		err = PTR_ERR(ub->ub_queue);
-		goto out_cleanup_tags;
-	}
-	ub->ub_queue->queuedata = ub;
-
-	disk = ub->ub_disk = blk_mq_alloc_disk_for_queue(ub->ub_queue,
-						 &ublk_bio_compl_lkclass);
-	if (!disk) {
-		err = -ENOMEM;
-		goto out_free_request_queue;
-	}
-
-	blk_queue_logical_block_size(ub->ub_queue, bsize);
-	blk_queue_physical_block_size(ub->ub_queue, bsize);
-	blk_queue_io_min(ub->ub_queue, bsize);
-
-	blk_queue_max_hw_sectors(ub->ub_queue, ub->dev_info.rq_max_blocks <<
-			(ub->bs_shift - 9));
-
-	ub->ub_queue->limits.discard_granularity = PAGE_SIZE;
-
-	blk_queue_max_discard_sectors(ub->ub_queue, UINT_MAX >> 9);
-	blk_queue_max_write_zeroes_sectors(ub->ub_queue, UINT_MAX >> 9);
-
-	ublk_update_capacity(ub);
-
-	disk->fops		= &ub_fops;
-	disk->private_data	= ub;
-	disk->queue		= ub->ub_queue;
-	sprintf(disk->disk_name, "ublkb%d", ub->ub_number);
-
+	ublk_align_max_io_size(ub);
 	mutex_init(&ub->mutex);
 
 	/* add char dev so that ublksrv daemon can be setup */
-	err = ublk_add_chdev(ub);
-	if (err)
-		return err;
-
-	/* don't expose disk now until we got start command from cdev */
+	return ublk_add_chdev(ub);
 
-	return 0;
-
-out_free_request_queue:
-	blk_mq_destroy_queue(ub->ub_queue);
-out_cleanup_tags:
-	blk_mq_free_tag_set(&ub->tag_set);
 out_deinit_queues:
 	ublk_deinit_queues(ub);
 out_destroy_dev:
@@ -1209,6 +1163,7 @@ static int ublk_ctrl_start_dev(struct io_uring_cmd *cmd)
 	int ublksrv_pid = (int)header->data[0];
 	unsigned long dev_blocks = header->data[1];
 	struct ublk_device *ub;
+	struct gendisk *disk;
 	int ret = -EINVAL;
 
 	if (ublksrv_pid <= 0)
@@ -1223,21 +1178,45 @@ static int ublk_ctrl_start_dev(struct io_uring_cmd *cmd)
 	schedule_delayed_work(&ub->monitor_work, UBLK_DAEMON_MONITOR_PERIOD);
 
 	mutex_lock(&ub->mutex);
-	if (disk_live(ub->ub_disk)) {
+	if (ub->dev_info.state == UBLK_S_DEV_LIVE ||
+	    test_bit(UB_STATE_USED, &ub->state)) {
 		ret = -EEXIST;
 		goto out_unlock;
 	}
 
 	/* We may get disk size updated */
-	if (dev_blocks) {
+	if (dev_blocks)
 		ub->dev_info.dev_blocks = dev_blocks;
-		ublk_update_capacity(ub);
+
+	disk = blk_mq_alloc_disk(&ub->tag_set, ub);
+	if (IS_ERR(disk)) {
+		ret = PTR_ERR(disk);
+		goto out_unlock;
 	}
+	sprintf(disk->disk_name, "ublkb%d", ub->ub_number);
+	disk->fops = &ub_fops;
+	disk->private_data = ub;
+
+	blk_queue_logical_block_size(disk->queue, ub->dev_info.block_size);
+	blk_queue_physical_block_size(disk->queue, ub->dev_info.block_size);
+	blk_queue_io_min(disk->queue, ub->dev_info.block_size);
+	blk_queue_max_hw_sectors(disk->queue,
+		ub->dev_info.rq_max_blocks << (ub->bs_shift - 9));
+	disk->queue->limits.discard_granularity = PAGE_SIZE;
+	blk_queue_max_discard_sectors(disk->queue, UINT_MAX >> 9);
+	blk_queue_max_write_zeroes_sectors(disk->queue, UINT_MAX >> 9);
+
+	set_capacity(disk, ub->dev_info.dev_blocks << (ub->bs_shift - 9));
+
 	ub->dev_info.ublksrv_pid = ublksrv_pid;
-	ret = add_disk(ub->ub_disk);
-	if (ret)
+	ub->ub_disk = disk;
+	get_device(&ub->cdev_dev);
+	ret = add_disk(disk);
+	if (ret) {
+		put_disk(disk);
 		goto out_unlock;
-
+	}
+	set_bit(UB_STATE_USED, &ub->state);
 	ub->dev_info.state = UBLK_S_DEV_LIVE;
 out_unlock:
 	mutex_unlock(&ub->mutex);