block2mtd: prevent direct access of bd_inode

All we need is size, and that can be obtained via bdev_nr_bytes()

Signed-off-by: Yu Kuai <[e-mail]>
Reviewed-by: Christoph Hellwig <[e-mail]>
Reviewed-by: Jan Kara <[e-mail]>
Signed-off-by: Al Viro <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Christian Brauner <[e-mail]>

drivers/mtd/devices/block2mtd.c

···
 	struct file *bdev_file;
 	struct block_device *bdev;
 	struct block2mtd_dev *dev;
+	loff_t size;
 	char *name;
 
 	if (!devname)
···
 		goto err_free_block2mtd;
 	}
 
-	if ((long)bdev->bd_inode->i_size % erase_size) {
+	size = bdev_nr_bytes(bdev);
+	if ((long)size % erase_size) {
 		pr_err("erasesize must be a divisor of device size\n");
 		goto err_free_block2mtd;
 	}
···
 
 	dev->mtd.name = name;
 
-	dev->mtd.size = bdev->bd_inode->i_size & PAGE_MASK;
+	dev->mtd.size = size & PAGE_MASK;
 	dev->mtd.erasesize = erase_size;
 	dev->mtd.writesize = 1;
 	dev->mtd.writebufsize = PAGE_SIZE;