[PATCH] Btrfs: correctly get tree level in tree_backref_for_extent

[PATCH] Btrfs: correctly get tree level in tree_backref_for_extent

[Filipe Manana]

If we are using skinny metadata, the block's tree level is in the offset
of the key and not in a btrfs_tree_block_info structure following the
extent item (it doesn't exist). Therefore fix it.

Besides returning the correct level in the tree, this also prevents reading
past the leaf's end in the case where the extent item is the last item in
the leaf (eb) and it has only 1 inline reference - this is because
sizeof(struct btrfs_tree_block_info) is greater than
sizeof(struct btrfs_extent_inline_ref).

Got it while running a scrub which produced the following warning:

    BTRFS: checksum error at logical 42123264 on dev /dev/sde, sector 15840: metadata node (level 24) in tree 5

Signed-off-by: Filipe Manana <fdmanana@suse.com>
---
 fs/btrfs/backref.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
index 2d3e32e..8729cf6 100644
--- a/fs/btrfs/backref.c
+++ b/fs/btrfs/backref.c
@@ -1552,7 +1552,6 @@ int tree_backref_for_extent(unsigned long *ptr, struct extent_buffer *eb,
 {
 	int ret;
 	int type;
-	struct btrfs_tree_block_info *info;
 	struct btrfs_extent_inline_ref *eiref;
 
 	if (*ptr == (unsigned long)-1)
@@ -1573,9 +1572,17 @@ int tree_backref_for_extent(unsigned long *ptr, struct extent_buffer *eb,
 	}
 
 	/* we can treat both ref types equally here */
-	info = (struct btrfs_tree_block_info *)(ei + 1);
 	*out_root = btrfs_extent_inline_ref_offset(eb, eiref);
-	*out_level = btrfs_tree_block_level(eb, info);
+
+	if (key->type == BTRFS_EXTENT_ITEM_KEY) {
+		struct btrfs_tree_block_info *info;
+
+		info = (struct btrfs_tree_block_info *)(ei + 1);
+		*out_level = btrfs_tree_block_level(eb, info);
+	} else {
+		ASSERT(key->type == BTRFS_METADATA_ITEM_KEY);
+		*out_level = (u8)key->offset;
+	}
 
 	if (ret == 1)
 		*ptr = (unsigned long)-1;
-- 
2.1.3

Re: [PATCH] Btrfs: correctly get tree level in tree_backref_for_extent

[Satoru Takeuchi]

(2014/12/16 1:04), Filipe Manana wrote:
> If we are using skinny metadata, the block's tree level is in the offset
> of the key and not in a btrfs_tree_block_info structure following the
> extent item (it doesn't exist). Therefore fix it.

Yes, this key type is introduced by commit 3173a18.

fs/btrfs/ctree.h
======================
/*
 * The same as the BTRFS_EXTENT_ITEM_KEY, except it's metadata we already know
 * the length, so we save the level in key->offset instead of the length.
 */
#define BTRFS_METADATA_ITEM_KEY        169
======================

> 
> Besides returning the correct level in the tree, this also prevents reading
> past the leaf's end in the case where the extent item is the last item in
> the leaf (eb) and it has only 1 inline reference - this is because
> sizeof(struct btrfs_tree_block_info) is greater than
> sizeof(struct btrfs_extent_inline_ref).
> 
> Got it while running a scrub which produced the following warning:
> 
>      BTRFS: checksum error at logical 42123264 on dev /dev/sde, sector 15840: metadata node (level 24) in tree 5
> 
> Signed-off-by: Filipe Manana <fdmanana@suse.com>

Reviewed-by: Satoru Takeuchi <takeuchi_satoru@jp.fujitsu.com>

In addition, build v3.18 + this patch succeeded without any warning.

Thanks,
Satoru

> ---
>   fs/btrfs/backref.c | 13 ++++++++++---
>   1 file changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
> index 2d3e32e..8729cf6 100644
> --- a/fs/btrfs/backref.c
> +++ b/fs/btrfs/backref.c
> @@ -1552,7 +1552,6 @@ int tree_backref_for_extent(unsigned long *ptr, struct extent_buffer *eb,
>   {
>   	int ret;
>   	int type;
> -	struct btrfs_tree_block_info *info;
>   	struct btrfs_extent_inline_ref *eiref;
>   
>   	if (*ptr == (unsigned long)-1)
> @@ -1573,9 +1572,17 @@ int tree_backref_for_extent(unsigned long *ptr, struct extent_buffer *eb,
>   	}
>   
>   	/* we can treat both ref types equally here */
> -	info = (struct btrfs_tree_block_info *)(ei + 1);
>   	*out_root = btrfs_extent_inline_ref_offset(eb, eiref);
> -	*out_level = btrfs_tree_block_level(eb, info);
> +
> +	if (key->type == BTRFS_EXTENT_ITEM_KEY) {
> +		struct btrfs_tree_block_info *info;
> +
> +		info = (struct btrfs_tree_block_info *)(ei + 1);
> +		*out_level = btrfs_tree_block_level(eb, info);
> +	} else {
> +		ASSERT(key->type == BTRFS_METADATA_ITEM_KEY);
> +		*out_level = (u8)key->offset;
> +	}
>   
>   	if (ret == 1)
>   		*ptr = (unsigned long)-1;
>