On 26-06-2007 04:16, David Chinner wrote:
> On Mon, Jun 25, 2007 at 11:01:11PM +0200, Ingo Molnar wrote:
>> * Satyam Sharma <[email protected]> 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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