From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from aserp1040.oracle.com ([141.146.126.69]:26465 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932706AbbG1J6f (ORCPT ); Tue, 28 Jul 2015 05:58:35 -0400 Date: Tue, 28 Jul 2015 17:58:28 +0800 From: Liu Bo To: Filipe David Manana Cc: "linux-btrfs@vger.kernel.org" Subject: Re: [PATCH] Btrfs: fix warning in backref walking Message-ID: <20150728095828.GD1338@localhost.localdomain> Reply-To: bo.li.liu@oracle.com References: <1437984953-453-1-git-send-email-bo.li.liu@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: Sender: linux-btrfs-owner@vger.kernel.org List-ID: On Mon, Jul 27, 2015 at 10:03:44AM +0100, Filipe David Manana wrote: > On Mon, Jul 27, 2015 at 9:15 AM, Liu Bo wrote: > > When we do backref walking, we search firstly in queued delayed refs > > and then the on-disk backrefs, but we parse differently for shared > > references, for delayed refs we also add 'ref->root' while for on-disk > > backrefs we don't, this can prevent us from merging refs indexed > > by the same bytenr and cause find_parent_nodes() to throw a warning at > > 'WARN_ON(ref->count < 0)', for example, when we have a shared data extent > > with 'ref_cnt=1' and a delayed shared data with a BTRFS_DROP_DELAYED_REF, > > that happens. > > > > For shared references, no matter if it's delayed or on-disk, ref->root is > > not at all used, instead it's ref->parent that really matters, so this has > > delayed refs handled as the same way as on-disk refs. > > > > Signed-off-by: Liu Bo > > --- > > fs/btrfs/backref.c | 5 ++--- > > 1 file changed, 2 insertions(+), 3 deletions(-) > > > > diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c > > index 802fabb..2485b868 100644 > > --- a/fs/btrfs/backref.c > > +++ b/fs/btrfs/backref.c > > @@ -632,7 +632,7 @@ static int __add_delayed_refs(struct btrfs_delayed_ref_head *head, u64 seq, > > struct btrfs_delayed_tree_ref *ref; > > > > ref = btrfs_delayed_node_to_tree_ref(node); > > - ret = __add_prelim_ref(prefs, ref->root, NULL, > > + ret = __add_prelim_ref(prefs, 0, NULL, > > ref->level + 1, ref->parent, > > node->bytenr, > > node->ref_mod * sgn, GFP_ATOMIC); > > @@ -665,10 +665,9 @@ static int __add_delayed_refs(struct btrfs_delayed_ref_head *head, u64 seq, > > > > ref = btrfs_delayed_node_to_data_ref(node); > > > > - key.objectid = ref->objectid; > > Why remove only this line and not the following 2 as well if key isn't > used anymore? Urr, this looks like a typo, thanks for pointing it out. > > > key.type = BTRFS_EXTENT_DATA_KEY; > > key.offset = ref->offset; > > - ret = __add_prelim_ref(prefs, ref->root, &key, 0, > > + ret = __add_prelim_ref(prefs, 0, NULL, 0, > > ref->parent, node->bytenr, > > node->ref_mod * sgn, GFP_ATOMIC); > > break; > > Do you have any reproducer to turn into an fstest? Would be nice, > since this is a rather critical part of the code. I do have a reproducer, but it cannot be integrated in fstests since it's snapshot-aware defrag that helps me find this warning but right now it's hard-code turned off. Thanks, -liubo > > thanks > > > -- > > 2.1.0 > > > > -- > > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > > the body of a message to majordomo@vger.kernel.org > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > > > -- > Filipe David Manana, > > "Reasonable men adapt themselves to the world. > Unreasonable men adapt the world to themselves. > That's why all progress depends on unreasonable men."