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Date:      Sat, 05 Nov 2005 20:47:30 +0100
From:      Andre Oppermann <andre@freebsd.org>
To:        Gleb Smirnoff <glebius@FreeBSD.org>
Cc:        sam@FreeBSD.org, freebsd-current@FreeBSD.org, Giorgos Keramidas <keramida@linux.gr>, thierry@herbelot.com
Subject:   Re: panic: mb_dtor_pack: ref_cnt != 1
Message-ID:  <436D0C52.7A02137F@freebsd.org>
References:  <20051104092724.GA33945@xor.obsecurity.org> <436B885B.6010609@freebsd.org> <20051104163526.GC82727@flame.pc> <200511041833.30955.thierry@herbelot.com> <436BA8B5.9070104@freebsd.org> <20051105003420.GM91530@cell.sick.ru> <20051105034105.GA906@flame.pc> <20051105080116.GR91530@cell.sick.ru> <20051105084924.GT91530@cell.sick.ru>

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Gleb Smirnoff wrote:
> 
> On Sat, Nov 05, 2005 at 11:01:16AM +0300, Gleb Smirnoff wrote:
> T> On Sat, Nov 05, 2005 at 05:41:05AM +0200, Giorgos Keramidas wrote:
> T> G> On 2005-11-05 03:34, Gleb Smirnoff <glebius@freebsd.org> wrote:
> T> G> >   Andre, Thierry, Sam,
> T> G> >
> T> G> >   this patch should fix the problems
> T> G>
> T> G> But it panics in mb_dtor_pack() because ext_type != EXT_CLUSTER
> T> G> when my ath0 interface tries to associate with an AP.
> T> G>
> T> G> I had to change this too, to make things work:
> T>
> T> Updated patch.
> 
> One more update. Since I have removed this block:
> 
>                        if (*(m->m_ext.ref_cnt) == 0)
>                                *(m->m_ext.ref_cnt) = 1;
> 
> I have also altered KASSERT in mb_dtor_pack(). I don't like
> inventing an incorrect invariant check and then adding helpers
> to avoid it being triggered.

This block is still required for the packet zone as the refcount
is not re-initialized for mbuf+cluster out of the packet zone.
You may up with wrong refcounts if you remove this check.  It
is not directly related to the KASSERT in mb_dtor_pack() but to
the way atomic_fetchadd_int() works in concurrency situations.

I have committed a fix to the same effect as your proposed patch.
When UMA is fixed this may be reverted again.

-- 
Andre



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