btrfs: free btrfs_path before copying subvol info to userspace

btrfs_ioctl_get_subvol_info() frees the search path after the userspace
copy from the temp buffer @subvol_info. This can lead to a lock splat
warning.

Fix this by freeing the path before we copy it to userspace.

CC: stable@vger.kernel.org # 4.19+
Signed-off-by: NAnand Jain <anand.jain@oracle.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs/btrfs/ioctl.c

@@ -3105,6 +3105,8 @@ static int btrfs_ioctl_get_subvol_info(struct inode *inode, void __user *argp)
 		}
 	}
 
+	btrfs_free_path(path);
+	path = NULL;
 	if (copy_to_user(argp, subvol_info, sizeof(*subvol_info)))
 		ret = -EFAULT;