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btrfs: clear 'ret' in btrfs_check_shared() loop

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btrfs_check_shared() is leaking a return value of '1' from
find_parent_nodes(). As a result, callers (in this case, extent_fiemap())
are told extents are shared when they are not. This in turn broke fiemap on
btrfs for kernels v3.18 and up.

The fix is simple - we just have to clear 'ret' after we are done processing
the results of find_parent_nodes().

It wasn't clear to me at first what was happening with return values in
btrfs_check_shared() and find_parent_nodes() - thanks to Josef for the help
on irc. I added documentation to both functions to make things more clear
for the next hacker who might come across them.

If we could queue this up for -stable too that would be great.

Signed-off-by: Mark Fasheh <mfasheh@suse.de>
Reviewed-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>
This commit is contained in:
Mark Fasheh 2015-05-19 12:49:50 -07:00 committed by Chris Mason
parent 062c19e9dd
commit 2c2ed5aa01
1 changed files with 17 additions and 0 deletions
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17
fs/btrfs/backref.c
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@ -880,6 +880,8 @@ static int __add_keyed_refs(struct btrfs_fs_info *fs_info,
* indirect refs to their parent bytenr.
* When roots are found, they're added to the roots list
*
* NOTE: This can return values > 0
*
* FIXME some caching might speed things up
*/
static int find_parent_nodes(struct btrfs_trans_handle *trans,
@ -1198,6 +1200,19 @@ int btrfs_find_all_roots(struct btrfs_trans_handle *trans,
return ret;
}
/**
* btrfs_check_shared - tell us whether an extent is shared
*
* @trans: optional trans handle
*
* btrfs_check_shared uses the backref walking code but will short
* circuit as soon as it finds a root or inode that doesn't match the
* one passed in. This provides a significant performance benefit for
* callers (such as fiemap) which want to know whether the extent is
* shared but do not need a ref count.
*
* Return: 0 if extent is not shared, 1 if it is shared, < 0 on error.
*/
int btrfs_check_shared(struct btrfs_trans_handle *trans,
struct btrfs_fs_info *fs_info, u64 root_objectid,
u64 inum, u64 bytenr)
@ -1226,11 +1241,13 @@ int btrfs_check_shared(struct btrfs_trans_handle *trans,
ret = find_parent_nodes(trans, fs_info, bytenr, elem.seq, tmp,
roots, NULL, root_objectid, inum);
if (ret == BACKREF_FOUND_SHARED) {
/* this is the only condition under which we return 1 */
ret = 1;
break;
}
if (ret < 0 && ret != -ENOENT)
break;
ret = 0;
node = ulist_next(tmp, &uiter);
if (!node)
break;