From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from cantor2.suse.de ([195.135.220.15]:60377 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750865AbbESTtw (ORCPT ); Tue, 19 May 2015 15:49:52 -0400 Date: Tue, 19 May 2015 12:49:50 -0700 From: Mark Fasheh To: linux-btrfs@vger.kernel.org Cc: Josef Bacik , Chris Mason Subject: [PATCH][RESEND] btrfs: clear 'ret' in btrfs_check_shared() loop Message-ID: <20150519194950.GE18148@wotan.suse.de> Reply-To: Mark Fasheh MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-btrfs-owner@vger.kernel.org List-ID: 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 --- fs/btrfs/backref.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c index f55721f..8d47380 100644 --- a/fs/btrfs/backref.c +++ b/fs/btrfs/backref.c @@ -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; -- 2.1.2