Re: [PATCH 10/13] btrfs-progs: check: fix bug in find_possible_backrefs

["Su Yanjun <suyj.fnst@xxxxxxxxxxxxxx>" <suyj.fnst@xxxxxxxxxxxxxx>]

On 10/24/2018 8:34 AM, Qu Wenruo wrote:
> On 2018/10/23 下午5:41, Su Yue wrote:
> > From: Su Yanjun <suyj.fnst@xxxxxxxxxxxxxx>
> >
> > It may cost more time to search all extent data of correspond files but
> > should not influence total speed too much cause that only corrupted
> > extent items are participated in.
> Sorry, I didn't really get the point of the modification from the commit
> message.
>
> Would you please explain the purpose of this patch first?
>
> Thanks,
> Qu

In find_possible_backrefs() function:

	key.objectid = dback->owner;
	key.type = BTRFS_EXTENT_DATA_KEY;
	key.offset = dback->offset;//
	ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);

'dback->offset' is not the offset in file range, we'll find wrong file extent.

Thanks,

Su

> > Signed-off-by: Su Yanjun <suyj.fnst@xxxxxxxxxxxxxx>
> > ---
> >   check/main.c | 110 ++++++++++++++++++++++++++++++++++++++++++---------
> >   1 file changed, 92 insertions(+), 18 deletions(-)
> >
> > diff --git a/check/main.c b/check/main.c
> > index bd1f322e0f12..90d9fd570287 100644
> > --- a/check/main.c
> > +++ b/check/main.c
> > @@ -7015,6 +7015,89 @@ out:
> >   	return ret ? ret : nr_del;
> >   }
> >   
> > +/*
> > + * Based extent backref item, we find all file extent items in the fs tree. By
> > + * the info we can rebuild the extent backref item
> > + */
> > +static int __find_possible_backrefs(struct btrfs_root *root,
> > +		u64 owner, u64 offset, u64 bytenr, u64 *refs_ret,
> > +		u64 *bytes_ret)
> > +{
> > +	int ret = 0;
> > +	struct btrfs_path path;
> > +	struct btrfs_key key;
> > +	struct btrfs_key found_key;
> > +	struct btrfs_file_extent_item *fi;
> > +	struct extent_buffer *leaf;
> > +	u64 backref_offset, disk_bytenr;
> > +	int slot;
> > +
> > +	btrfs_init_path(&path);
> > +
> > +	key.objectid = owner;
> > +	key.type = BTRFS_INODE_ITEM_KEY;
> > +	key.offset = 0;
> > +
> > +	ret = btrfs_search_slot(NULL, root, &key, &path, 0, 0);
> > +	if (ret > 0)
> > +		ret = -ENOENT;
> > +	if (ret) {
> > +		btrfs_release_path(&path);
> > +		return ret;
> > +	}
> > +
> > +	btrfs_release_path(&path);
> > +
> > +	key.objectid = owner;
> > +	key.type = BTRFS_EXTENT_DATA_KEY;
> > +	key.offset = 0;
> > +
> > +	ret = btrfs_search_slot(NULL, root, &key, &path, 0, 0);
> > +	if (ret < 0) {
> > +		btrfs_release_path(&path);
> > +		return ret;
> > +	}
> > +
> > +	while (1) {
> > +		leaf = path.nodes[0];
> > +		slot = path.slots[0];
> > +
> > +		if (slot >= btrfs_header_nritems(leaf)) {
> > +			ret = btrfs_next_leaf(root, &path);
> > +			if (ret) {
> > +				if (ret > 0)
> > +					ret = 0;
> > +				break;
> > +			}
> > +
> > +			leaf = path.nodes[0];
> > +			slot = path.slots[0];
> > +		}
> > +
> > +		btrfs_item_key_to_cpu(leaf, &found_key, slot);
> > +		if ((found_key.objectid != owner) ||
> > +			(found_key.type != BTRFS_EXTENT_DATA_KEY))
> > +			break;
> > +
> > +		fi = btrfs_item_ptr(leaf, slot,
> > +				struct btrfs_file_extent_item);
> > +
> > +		backref_offset = found_key.offset -
> > +			btrfs_file_extent_offset(leaf, fi);
> > +		disk_bytenr = btrfs_file_extent_disk_bytenr(leaf, fi);
> > +		*bytes_ret = btrfs_file_extent_disk_num_bytes(leaf,
> > +								fi);
> > +		if ((disk_bytenr == bytenr) &&
> > +			(backref_offset == offset)) {
> > +			(*refs_ret)++;
> > +		}
> > +		path.slots[0]++;
> > +	}
> > +
> > +	btrfs_release_path(&path);
> > +	return ret;
> > +}
> > +
> >   static int find_possible_backrefs(struct btrfs_fs_info *info,
> >   				  struct btrfs_path *path,
> >   				  struct cache_tree *extent_cache,
> > @@ -7024,9 +7107,9 @@ static int find_possible_backrefs(struct btrfs_fs_info *info,
> >   	struct extent_backref *back, *tmp;
> >   	struct data_backref *dback;
> >   	struct cache_extent *cache;
> > -	struct btrfs_file_extent_item *fi;
> >   	struct btrfs_key key;
> >   	u64 bytenr, bytes;
> > +	u64 refs;
> >   	int ret;
> >   
> >   	rbtree_postorder_for_each_entry_safe(back, tmp,
> > @@ -7054,24 +7137,15 @@ static int find_possible_backrefs(struct btrfs_fs_info *info,
> >   		if (IS_ERR(root))
> >   			return PTR_ERR(root);
> >   
> > -		key.objectid = dback->owner;
> > -		key.type = BTRFS_EXTENT_DATA_KEY;
> > -		key.offset = dback->offset;
> > -		ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
> > -		if (ret) {
> > -			btrfs_release_path(path);
> > -			if (ret < 0)
> > -				return ret;
> > -			/* Didn't find it, we can carry on */
> > -			ret = 0;
> > +		refs = 0;
> > +		bytes = 0;
> > +		ret = __find_possible_backrefs(root, dback->owner,
> > +				dback->offset, rec->start, &refs, &bytes);
> > +		if (ret)
> >   			continue;
> > -		}
> >   
> > -		fi = btrfs_item_ptr(path->nodes[0], path->slots[0],
> > -				    struct btrfs_file_extent_item);
> > -		bytenr = btrfs_file_extent_disk_bytenr(path->nodes[0], fi);
> > -		bytes = btrfs_file_extent_disk_num_bytes(path->nodes[0], fi);
> > -		btrfs_release_path(path);
> > +		bytenr = rec->start;
> > +
> >   		cache = lookup_cache_extent(extent_cache, bytenr, 1);
> >   		if (cache) {
> >   			struct extent_record *tmp;
> > @@ -7090,7 +7164,7 @@ static int find_possible_backrefs(struct btrfs_fs_info *info,
> >   				continue;
> >   		}
> >   
> > -		dback->found_ref += 1;
> > +		dback->found_ref += refs;
> >   		dback->disk_bytenr = bytenr;
> >   		dback->bytes = bytes;
> >