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

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Message-ID: <6e49d04a-4069-4cce-9f49-fd63983ae658@I-love.SAKURA.ne.jp>
Date: Fri, 18 Jul 2025 22:54:15 +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>
Cc: syzbot+1fed2de07d8e11a3ec1b@...kaller.appspotmail.com,
        ocfs2-devel@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ocfs2: fix lock acquisition order in refcounttree

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?