Re: [LOCKDEP] xfs: possible recursive locking detected

[Ingo Molnar <mingo@elte.hu>]

* Nathan Scott <nathans@sgi.com> wrote:

> > > While trying to remove 2 small files, 2 empty dirs and 1 empty dir 
> > > on xfs partition
> > 
> > Probably spurious.  xfs_ilock can be called on both the parent and 
> > child, which wouldn't be a deadlock.
> 
> Hmm... they'd be different inodes though, so different lock addresses 
> in memory - is lockdep taking that into account?  Would we need to go 
> annotate xfs_ilock somehow to give better hints to the lockdep code?

correct, lockdep has to be taught about relations between locks within 
the same lock-class. (it detects relations between different 
lock-classes automatically) It's usually a straightforward process.

In this particular case we probably need to do something similar to the 
VFS's 'enum inode_i_mutex_lock_class' subclass categorizations: we need 
xfs_ilock_nested(.., subclass), where in xfs_lock_dir_and_entry() we'd 
pass in ILOCK_PARENT. [normal locking calls have a default subclass ID 
of 0]

I suspect simply creating an XFS filesystem and doing a couple of VFS 
ops on it should trigger these locking patterns?

	Ingo