btrfs: ioctl: reorder exclusive op check in RM_DEV

Move the op exclusivity check before the other code (same as in
ADD_DEV).
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ioctl.c

@@ -2689,32 +2689,31 @@ static long btrfs_ioctl_rm_dev(struct file *file, void __user *arg)
 	if (ret)
 		return ret;
 
-	vol_args = memdup_user(arg, sizeof(*vol_args));
-	if (IS_ERR(vol_args)) {
-		ret = PTR_ERR(vol_args);
-		goto err_drop;
-	}
-
-	vol_args->name[BTRFS_PATH_NAME_MAX] = '\0';
-
 	if (atomic_xchg(&root->fs_info->mutually_exclusive_operation_running,
 			1)) {
 		ret = BTRFS_ERROR_DEV_EXCL_RUN_IN_PROGRESS;
+		goto out_drop_write;
+	}
+
+	vol_args = memdup_user(arg, sizeof(*vol_args));
+	if (IS_ERR(vol_args)) {
+		ret = PTR_ERR(vol_args);
 		goto out;
 	}
 
+	vol_args->name[BTRFS_PATH_NAME_MAX] = '\0';
 	mutex_lock(&root->fs_info->volume_mutex);
 	ret = btrfs_rm_device(root, vol_args->name);
 	mutex_unlock(&root->fs_info->volume_mutex);
-	atomic_set(&root->fs_info->mutually_exclusive_operation_running, 0);
 
 	if (!ret)
 		btrfs_info(root->fs_info, "disk deleted %s",vol_args->name);
-
-out:
 	kfree(vol_args);
-err_drop:
+out:
+	atomic_set(&root->fs_info->mutually_exclusive_operation_running, 0);
+out_drop_write:
 	mnt_drop_write_file(file);
+
 	return ret;
 }