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

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

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;
>>>  
>>
> 
> 
>