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Message-ID: <468206C0.90009@sgi.com>
Date: Wed, 27 Jun 2007 16:42:08 +1000
From: Tim Shimmin <tes@....com>
To: xfs-masters@....sgi.com
CC: Jarek Poplawski <jarkao2@...pl>, David Chinner <dgc@....com>,
Ingo Molnar <mingo@...e.hu>,
Satyam Sharma <satyam.sharma@...il.com>,
Johannes Weiner <hannes-kernel@...urebad.de>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [xfs-masters] Re: [BUG] Lockdep warning with XFS on 2.6.22-rc6
Patch looks good, Dave.
(though, I stuffed up reviewing that bit of code previously:-)
Oh, previous typo: s/inodes at the some time/inodes at the same time/
--Tim
David Chinner wrote:
> On Tue, Jun 26, 2007 at 11:35:20AM +0200, Jarek Poplawski wrote:
>> On 26-06-2007 04:16, David Chinner wrote:
>>> 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...
>
> That just fired some rusty neurons.
>
> #define XFS_IOLOCK_SHIFT 16
> #define XFS_IOLOCK_PARENT (1 << XFS_IOLOCK_SHIFT)
> #define XFS_IOLOCK_INUMORDER (2 << XFS_IOLOCK_SHIFT)
>
> #define XFS_ILOCK_SHIFT 24
> #define XFS_ILOCK_PARENT (1 << XFS_ILOCK_SHIFT)
> #define XFS_ILOCK_INUMORDER (2 << XFS_ILOCK_SHIFT)
>
> So, in a lock_mode parameter, the upper 8 bits are for the ILOCK lockdep
> subclass, and the 16..23 bits are for the IOLOCK lockdep subclass.
>
> Where do we add them?
>
> static inline int
> xfs_lock_inumorder(int lock_mode, int subclass)
> {
> if (lock_mode & (XFS_IOLOCK_SHARED|XFS_IOLOCK_EXCL))
> lock_mode |= (subclass + XFS_IOLOCK_INUMORDER) << XFS_IOLOCK_SHIFT;
> if (lock_mode & (XFS_ILOCK_SHARED|XFS_ILOCK_EXCL))
> lock_mode |= (subclass + XFS_ILOCK_INUMORDER) << XFS_ILOCK_SHIFT;
>
> return lock_mode;
> }
>
>
> OH, look at those nice overflow bugs in that in that code. We shift
> the XFS_IOLOCK_INUMORDER and XFS_ILOCK_INUMORDER bits out the far
> side of the lock_mode variable result in lock subclasses of 0-3 instead
> of 2-5....
>
> Bugger, eh?
>
> Patch below should fix this (untested).
>
> Jarek - thanks for pointing what I should have seen earlier.
>
> Cheers,
>
> Dave.
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