[10/13] btrfs-progs: check: fix bug in find_possible_backrefs
diff mbox series

Message ID 20181023094147.7906-11-suy.fnst@cn.fujitsu.com
State New
Headers show
Series
  • btrfs-progs: fixes of file extent in original and lowmem check
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Commit Message

Su Yue Oct. 23, 2018, 9:41 a.m. UTC
From: Su Yanjun <suyj.fnst@cn.fujitsu.com>

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.

Signed-off-by: Su Yanjun <suyj.fnst@cn.fujitsu.com>
---
 check/main.c | 110 ++++++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 92 insertions(+), 18 deletions(-)

Comments

Qu Wenruo Oct. 24, 2018, 12:34 a.m. UTC | #1
On 2018/10/23 下午5:41, Su Yue wrote:
> From: Su Yanjun <suyj.fnst@cn.fujitsu.com>
> 
> 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

> 
> Signed-off-by: Su Yanjun <suyj.fnst@cn.fujitsu.com>
> ---
>  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;
>  
>
Su Yanjun Nov. 7, 2018, 6:28 a.m. UTC | #2
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@cn.fujitsu.com>
>>
>> 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@cn.fujitsu.com>
>> ---
>>   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;
>>   
>>
>
Qu Wenruo Nov. 7, 2018, 6:40 a.m. UTC | #3
On 2018/11/7 下午2:28, Su Yanjun <suyj.fnst@cn.fujitsu.com> wrote:
> 
> 
> 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@cn.fujitsu.com>
>>>
>>> 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.

Now this makes sense.

The original commit message doesn't touch this part, and focused on the
side effect, not the problem itself.

Please update the commit message.

Thanks,
Qu

> 
> Thanks,
> 
> Su
> 
>>> Signed-off-by: Su Yanjun <suyj.fnst@cn.fujitsu.com>
>>> ---
>>>   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;
>>>  
>>
> 
> 
>

Patch
diff mbox series

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;