On 2018年02月28日 18:13, Lu Fengqi wrote:
> Btrfs lowmem check reports the following false alert:
> ------
> ERROR: file extent[267 2162688] root 256 owner 5 backref lost
> ------
>
> The file extent is in the leaf which is shared by file tree 256 and fs
> tree.
> ------
> leaf 30605312 items 46 free space 4353 generation 7 owner 5
> ......
> item 45 key (267 EXTENT_DATA 2162688) itemoff 5503 itemsize 53
> generation 7 type 2 (prealloc)
> prealloc data disk byte 13631488 nr 65536
> prealloc data offset 32768 nr 32768
> ------
>
> And there is the corresponding extent_data_ref item in the extent tree.
> ------
> item 1 key (13631488 EXTENT_DATA_REF 1007496934287921081) itemoff
> 15274 itemsize 28
> extent data backref root 5 objectid 267 offset 2129920 count 1
> ------
>
> The offset of EXTENT_DATA_REF which is the hash of the owner root objectid,
> the inode number and the calculated offset (file offset - extent offset).
>
> What caused the false alert is the code mix up the owner root objectid and
> the file tree objectid.
>
> Fixes: b0d360b541f0 ("btrfs-progs: check: introduce function to check data
> backref in extent tree")
> Signed-off-by: Lu Fengqi <lufq.f...@cn.fujitsu.com>Looks good. Reviewed-by: Qu Wenruo <w...@suse.com> Thanks, Qu > --- > check/mode-lowmem.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/check/mode-lowmem.c b/check/mode-lowmem.c > index f37b1b2c1571..6f1ea8db341d 100644 > --- a/check/mode-lowmem.c > +++ b/check/mode-lowmem.c > @@ -2689,8 +2689,8 @@ static int check_extent_data_item(struct btrfs_root > *root, > /* Didn't find inlined data backref, try EXTENT_DATA_REF_KEY */ > dbref_key.objectid = btrfs_file_extent_disk_bytenr(eb, fi); > dbref_key.type = BTRFS_EXTENT_DATA_REF_KEY; > - dbref_key.offset = hash_extent_data_ref(root->objectid, > - fi_key.objectid, fi_key.offset - offset); > + dbref_key.offset = hash_extent_data_ref(owner, fi_key.objectid, > + fi_key.offset - offset); > > ret = btrfs_search_slot(NULL, root->fs_info->extent_root, > &dbref_key, &path, 0, 0); >
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