Date: Tue, 29 Aug 2006 17:15:54 +0200 From: Andre Oppermann <andre@freebsd.org> To: Randall Stewart <rrs@cisco.com>, freebsd-net@freebsd.org, andre@FreeBSD.org Subject: Re: Problem with uipc_mbuf.c Message-ID: <44F45A2A.8030405@freebsd.org> In-Reply-To: <20060828224452.GK37035@funkthat.com> References: <44F35A65.3080605@cisco.com> <20060828224452.GK37035@funkthat.com>
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John-Mark Gurney wrote:
> Randall Stewart wrote this message on Mon, Aug 28, 2006 at 17:04 -0400:
>> atomic_fetchadd_int(m->m_ext.ref_cnt, -1) == 0) {
> ^
>
> This should be 1 not 0.. as apparently fetchadd_int returns the old value
> (at least that's what atomic(9) says), which means that if we ever race
> on this comparision, we won't free though we should of...
>
> if we look at refcount.h, it does:
> return (atomic_fetchadd_int(count, -1) == 1);
>
> which release a reference and apparently returns true if it needs to
> be free'd...
>
> Though the wierd part is that andre, "fixed" it to be 0 in 1.157:
> Fix a logic error introduced with mandatory mbuf cluster refcounting and
> freeing of mbufs+clusters back to the packet zone.
Honestly I'm a bit confused myself now and have to dig up things from
when I did the change. However I'm certain there was a problem and the
commit fixed it in some way (not necessarily the correct way). Before
the 'fix' there were some larger leaks going on.
--
Andre
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