Commit 18f687d5 authored by Wang Shilong's avatar Wang Shilong Committed by Chris Mason
Browse files

Btrfs: fix protection between send and root deletion 



We should gurantee that parent and clone roots can not be destroyed
during send, for this we have two ideas.

1.by holding @subvol_sem, this might be a nightmare, because it will
block all subvolumes deletion for a long time.

2.Miao pointed out we can reuse @send_in_progress, that mean we will
skip snapshot deletion if root sending is in progress.

Here we adopt the second approach since it won't block other subvolumes
deletion for a long time.

Besides in btrfs_clean_one_deleted_snapshot(), we only check first root
, if this root is involved in send, we return directly rather than
continue to check.There are several reasons about it:

1.this case happen seldomly.
2.after sending,cleaner thread can continue to drop that root.
3.make code simple

Cc: David Sterba <dsterba@suse.cz>
Signed-off-by: default avatarWang Shilong <wangsl.fnst@cn.fujitsu.com>
Reviewed-by: default avatarMiao Xie <miaox@cn.fujitsu.com>
Signed-off-by: default avatarJosef Bacik <jbacik@fb.com>
Signed-off-by: default avatarChris Mason <clm@fb.com>
parent 896c14f9

fs/btrfs/send.c

+16 −0
Original line number Diff line number Diff line
@@ -4753,6 +4753,7 @@ long btrfs_ioctl_send(struct file *mnt_file, void __user *arg_) 
	u64 *clone_sources_tmp = NULL;

	int clone_sources_to_rollback = 0;

	int sort_clone_roots = 0;

	int index;



	if (!capable(CAP_SYS_ADMIN))

		return -EPERM;
@@ -4893,8 +4894,12 @@ long btrfs_ioctl_send(struct file *mnt_file, void __user *arg_) 
			key.objectid = clone_sources_tmp[i];

			key.type = BTRFS_ROOT_ITEM_KEY;

			key.offset = (u64)-1;



			index = srcu_read_lock(&fs_info->subvol_srcu);



			clone_root = btrfs_read_fs_root_no_name(fs_info, &key);

			if (IS_ERR(clone_root)) {

				srcu_read_unlock(&fs_info->subvol_srcu, index);

				ret = PTR_ERR(clone_root);

				goto out;

			}
@@ -4903,10 +4908,13 @@ long btrfs_ioctl_send(struct file *mnt_file, void __user *arg_) 
			clone_root->send_in_progress++;

			if (!btrfs_root_readonly(clone_root)) {

				spin_unlock(&clone_root->root_item_lock);

				srcu_read_unlock(&fs_info->subvol_srcu, index);

				ret = -EPERM;

				goto out;

			}

			spin_unlock(&clone_root->root_item_lock);

			srcu_read_unlock(&fs_info->subvol_srcu, index);



			sctx->clone_roots[i].root = clone_root;

		}

		vfree(clone_sources_tmp);
@@ -4917,19 +4925,27 @@ long btrfs_ioctl_send(struct file *mnt_file, void __user *arg_) 
		key.objectid = arg->parent_root;

		key.type = BTRFS_ROOT_ITEM_KEY;

		key.offset = (u64)-1;



		index = srcu_read_lock(&fs_info->subvol_srcu);



		sctx->parent_root = btrfs_read_fs_root_no_name(fs_info, &key);

		if (IS_ERR(sctx->parent_root)) {

			srcu_read_unlock(&fs_info->subvol_srcu, index);

			ret = PTR_ERR(sctx->parent_root);

			goto out;

		}



		spin_lock(&sctx->parent_root->root_item_lock);

		sctx->parent_root->send_in_progress++;

		if (!btrfs_root_readonly(sctx->parent_root)) {

			spin_unlock(&sctx->parent_root->root_item_lock);

			srcu_read_unlock(&fs_info->subvol_srcu, index);

			ret = -EPERM;

			goto out;

		}

		spin_unlock(&sctx->parent_root->root_item_lock);



		srcu_read_unlock(&fs_info->subvol_srcu, index);

	}



	/*

fs/btrfs/transaction.c

+13 −0
Original line number Diff line number Diff line
@@ -1972,6 +1972,19 @@ int btrfs_clean_one_deleted_snapshot(struct btrfs_root *root) 
	}

	root = list_first_entry(&fs_info->dead_roots,

			struct btrfs_root, root_list);

	/*

	 * Make sure root is not involved in send,

	 * if we fail with first root, we return

	 * directly rather than continue.

	 */

	spin_lock(&root->root_item_lock);

	if (root->send_in_progress) {

		spin_unlock(&fs_info->trans_lock);

		spin_unlock(&root->root_item_lock);

		return 0;

	}

	spin_unlock(&root->root_item_lock);



	list_del_init(&root->root_list);

	spin_unlock(&fs_info->trans_lock);

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