linux-kernel - Re: [PATCH] ocfs2: fix lock acquisition order in refcounttree

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Message-ID: <dee1a0fe-7846-466a-a08b-4967929b5f6e@I-love.SAKURA.ne.jp>
Date: Mon, 21 Jul 2025 19:40:58 +0900
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To: Diogo Jahchan Koike <djahchankoike@...il.com>,
        Mark Fasheh <mark@...heh.com>, Joel Becker <jlbec@...lplan.org>,
        Joseph Qi <joseph.qi@...ux.alibaba.com>, ocfs2-devel@...ts.linux.dev
Cc: syzbot+1fed2de07d8e11a3ec1b@...kaller.appspotmail.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ocfs2: fix lock acquisition order in refcounttree

On 2025/07/18 22:54, Tetsuo Handa wrote:
> On 2025/07/15 11:51, Tetsuo Handa wrote:
>> On 2025/07/15 7:15, Diogo Jahchan Koike wrote:
>>> Acquiring the locks in refcounttree should follow
>>> the ip_alloc --> ip_xattr ordering, as done by multiple
>>> code paths in ocfs2; otherwise, we risk an ABBA deadlock
>>> (i.e in the start transaction path).
>>
>> I noticed that ocfs2_reflink() in the same file wants similar change.
>>
>> 	down_write(&OCFS2_I(inode)->ip_xattr_sem);
>> 	down_write(&OCFS2_I(inode)->ip_alloc_sem);
>> 	error = __ocfs2_reflink(old_dentry, old_bh,
>> 				new_orphan_inode, preserve);
>> 	up_write(&OCFS2_I(inode)->ip_alloc_sem);
>> 	up_write(&OCFS2_I(inode)->ip_xattr_sem);
>>
> 
> Moreover, I noticed that e.g. ocfs2_xattr_set_handle() firstly acquires
> ip_xatr_sem and then ocfs2_xattr_ibody_find() might acquire ip_alloc_sem.
> 
> Diogo, where do you see the ip_alloc --> ip_xattr ordering?
> 
> Unless we unify to either ip_alloc --> ip_xattr ordering or
> ip_xattr --> ip_alloc ordering (or replace ip_xattr with ip_alloc),
> this patch simply changes the location of lockdep warning?
> 

Since I couldn't find direct ip_alloc --> ip_xattr ordering,
I tried effectively replacing ip_xattr with ip_alloc at
https://lkml.kernel.org/r/687be24a.a70a0220.693ce.0092.GAE@google.com
and got sb_internal --> ip_alloc v.s. ip_alloc --> sb_internal
ordering problem, as with other lockdep reports in ocfs2 subsystem
at https://syzkaller.appspot.com/upstream/s/ocfs2 .

In the team network driver, this kind of ordering issues has been
addressed by simplifying locking dependency at
https://lkml.kernel.org/r/20250623153147.3413631-1-sdf@fomichev.me .

ocfs2 developers, can you simplify locking dependency in ocfs2, by
killing several locks and reordering the locks?