panic after acpi suspend/resume 9.1, 9.2rc3

[J.R. Oldroyd]

On Mon, 9 Sep 2013 16:54:27 -0400 John Baldwin <jhb at freebsd.org> wrote:
>
> > > 
> > > > (kgdb) list *0xffffffff80ceddcd
> > > > 0xffffffff80ceddcd is in pmap_enter (../../../amd64/amd64/pmap.c:3577).
> > > > 3572            if ((m->oflags & VPO_UNMANAGED) == 0) {
> > > > 3573                    newpte |= PG_MANAGED;
> > > > 3574                    pv = get_pv_entry(pmap, &lock);
> > > > 3575                    pv->pv_va = va;
> > > > 3576                    CHANGE_PV_LIST_LOCK_TO_PHYS(&lock, pa);
> > > > 3577                    TAILQ_INSERT_TAIL(&m->md.pv_list, pv, pv_list);
> > > > 3578                    if ((newpte & PG_RW) != 0)
> > > > 3579                            vm_page_aflag_set(m, PGA_WRITEABLE);
> > > > 3580            }
> > > > 3581
> > > 
> > > So it seems like pv_list of a page might be busted?  Can you try looking at
> > > the disassembly to see if you can find 'm' in one of the registers?
> > > 
> > 
> > Sure, here you go...
> > 
> > (kgdb) print m
> > $1 = 0xfffffe00b260b430
> > (kgdb) print m->md.pv_list
> > $4 = {tqh_first = 0x0, tqh_last = 0x0}
> 
> Eh, tqh_last shouldn't bmd.pv_liste NULL here IIRC.  I think it should point at
> &tqh_first.
> 

I had a quick look at the code for this list.

md.pv_list is initialized in pmap_page_init() and there's also a
similar piece of init in pmap_init(), both in sys/amd64/amd64/pmap.c
and also in the other arch's.

But I have little background on how the VM code is supposed to be
initialized or saved on suspend and re-inited on resume.  It'd take
me ages to work out what should be going on here.

What's the best course of action here...?  Open a PR and hand-over to
someone with more background in these areas?

	-jr
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