Re: [RT] Lockdep warning on boot with 2.6.31-rc5-rt1.1

[Peter Zijlstra <peterz@infradead.org>]

On Fri, 2009-08-07 at 12:45 -0400, Alan Stern wrote:
> On Fri, 7 Aug 2009, Peter Zijlstra wrote:

> > The other proposal was creating a fixed list of classes and register
> > each device at a class corresponding to its depth in the tree. I can't
> > remember what was wrong with that, but I seem to have been persuaded
> > that that was hard too.
> 
> It probably would work for the most part.  However a possible scenario
> involves first locking a parent and then locking all its children.  (I
> don't know if this ever happens anywhere, but it might.)  This can't
> cause a deadlock but it would run into trouble with depth-based
> classes.

If you know which parent is locked, we can solve that with
mutex_lock_nest_lock() [ doesn't currently exist, but is analogous to
spin_lock_nest_lock() ] and together with
http://lkml.org/lkml/2009/7/23/222 that would allow you to lock up to
2048 children.

Would something like that work?