lkml.org 
[lkml]   [2007]   [Jun]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [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.

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2007-06-27 08:45    [W:0.050 / U:0.384 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site