Tracking down problems with vm

I'm working on tracking down the problems I've found running FreeBSD on
XEN's full virtualization. I'm looking at fixing a page fault in kernel
when INVARIANTS is enabled.

The problem is in uma_dbg_alloc slab->us_data is NULL. This means freei
is set to a value that is too large for the slabref->us_freelist array.

I've placed extra debugging code in the uma functions to try to find
where us_data is set to NULL. The point I found is in the call to
uma_dbg_getslab from uma_dbg_alloc. I've not managed to track down
where it was set to NULL however.

Can anyone give me a hint as to where to look to track down why the
us_data is NULL?

Andrew

-- 
Andrew Turner
http://fubar.geek.nz/blog/