From owner-freebsd-current  Tue Sep 17 10:44: 1 2002
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Date: Tue, 17 Sep 2002 10:42:14 -0700
From: Terry Lambert <tlambert2@mindspring.com>
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To: Nate Lawson <nate@root.org>
Cc: Martin Blapp <mb@imp.ch>, current@freebsd.org, peter@freebsd.org
Subject: Re: Crashdumps available for download ... please help
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Nate Lawson wrote:
> > 0xc02fd315 is in pmap_remove_pages (/usr/src/sys/i386/i386/pmap.c:2941).
> > 2936    #ifdef PMAP_REMOVE_PAGES_CURPROC_ONLY
> > 2937                    pte = vtopte(pv->pv_va);
> > 2938    #else
> > 2939                    pte = pmap_pte_quick(pv->pv_pmap, pv->pv_va);
> > 2940    #endif
> > 2941                    tpte = *pte;
> > 2942
> > 2943                    if (tpte == 0) {
> > 2944                            printf("TPTE at %p  IS ZERO @ VA %08x\n",
> > 2945                                    pte, pv->pv_va);
> 
> Try building your kernel with "options PMAP_REMOVE_PAGES_CURPROC_ONLY" and
> see if the panic goes away.  If that works, the problem is
> pmap_pte_quick().
> 
> In looking at pmap_pte_quick, either it is wrong or line 2941 is wrong in
> always dereferencing pte.  pmap_pte_quick can return NULL (well 0).  It
> seems like pmap_pte_quick is wrong because vtopte() never returns NULL,
> just (PTmap + i386_btop(va)) i.e. a valid base plus some offset.

Obvious fix?

#ifndef PMAP_REMOVE_PAGES_CURPROC_ONLY
		pte = pmap_pte_quick(pv->pv_pmap, pv->pv_va);
		if (pte == NULL)
#endif
		pte = vtopte(pv->pv_va);

-- Terry

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