Date: Tue, 26 Jun 2007 11:35:20 +0200
From: Jarek Poplawski <jarkao2@o2.pl>
To: David Chinner <dgc@sgi.com>
Cc: Ingo Molnar <mingo@elte.hu>, Satyam Sharma <satyam.sharma@gmail.com>,
       Johannes Weiner <hannes-kernel@saeurebad.de>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       xfs-masters@oss.sgi.com
Subject: Re: [BUG] Lockdep warning with XFS on 2.6.22-rc6
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On 26-06-2007 04:16, David Chinner wrote:
> On Mon, Jun 25, 2007 at 11:01:11PM +0200, Ingo Molnar wrote:
>> * Satyam Sharma <satyam.sharma@gmail.com> wrote:
>>
>>> [ Ok, so we know that XFS wants to lock inodes in ascending inode 
>>> number order and not strictly the parent-first-child-second order that 
>>> rest of the fs/ code does, so that makes it difficult to teach lockdep 
>>> about this kind of lock ordering ... ]
> 
> It does both - parent-first/child-second and ascending inode # order,
> which is where the problem is. standing alone, these seem fine, but
> they don't appear to work when the child has a lower inode number
> than the parent.
...

>From xfs_inode.h:

/*
 * Flags for lockdep annotations.
 *
 * XFS_I[O]LOCK_PARENT - for operations that require locking two inodes
 * (ie directory operations that require locking a directory inode and
 * an entry inode).  The first inode gets locked with this flag so it
 * gets a lockdep subclass of 1 and the second lock will have a lockdep
 * subclass of 0.
 *
 * XFS_I[O]LOCK_INUMORDER - for locking several inodes at the some time
 * with xfs_lock_inodes().  This flag is used as the starting subclass
 * and each subsequent lock acquired will increment the subclass by one.
 * So the first lock acquired will have a lockdep subclass of 2, the
 * second lock will have a lockdep subclass of 3, and so on.
 */

I don't know xfs code, and probably miss something, but it seems
there could be some inconsistency: lockdep warning shows mr_lock/1
taken both before and after mr_lock (i.e. /0). According to the
above comment there should be always 1 before 0...

Cheers,
Jarek P.  
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