Date: Sun, 21 Jul 2013 10:18:42 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: Oliver Pinter <oliver.pntr@gmail.com> Cc: Gustau P?rez i Querol <gperez@entel.upc.edu>, freebsd-current@freebsd.org Subject: Re: Panic when starting X with Intel KMS Message-ID: <20130721071842.GZ5991@kib.kiev.ua> In-Reply-To: <CAPjTQNG7CBYNMQ4yitXv3Wy81YMk-osqcSH=BB1=HjsOqweszw@mail.gmail.com> References: <51E6EB0A.2060407@entel.upc.edu> <51EA5166.4020508@entel.upc.edu> <CAPjTQNG7CBYNMQ4yitXv3Wy81YMk-osqcSH=BB1=HjsOqweszw@mail.gmail.com>
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On Sat, Jul 20, 2013 at 01:20:56PM +0200, Oliver Pinter wrote:
> On 7/20/13, Gustau P?rez i Querol <gperez@entel.upc.edu> wrote:
> > Reading the backtrace I see this:
> >
> > panic: pmap_release: pmap resident count -398580 !=3D 0
> >
> > which comes from amd64/amd64/pmap.c:1936. I suspect that
> > pmap->pm_stats.resident_count being negative is a bug.
The issue happened somewhere before the process exit. Try the patch
below, the idea is that your overflow count is really big, so the
wrong-doer could cause underflow when acting.
diff --git a/sys/amd64/amd64/pmap.c b/sys/amd64/amd64/pmap.c
index 19be4e0..fcdc6af 100644
--- a/sys/amd64/amd64/pmap.c
+++ b/sys/amd64/amd64/pmap.c
@@ -465,6 +465,9 @@ pmap_resident_count_dec(pmap_t pmap, int count)
{
=20
PMAP_LOCK_ASSERT(pmap, MA_OWNED);
+ KASSERT(pmap->pm_stats.resident_count >=3D count,
+ ("pmap %p resident count underflow %ld %d", pmap,
+ pmap->pm_stats.resident_count, count));
pmap->pm_stats.resident_count -=3D count;
}
=20
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