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Date:      Fri, 01 Jun 2001 10:58:51 -0700
From:      Terry Lambert <tlambert2@mindspring.com>
To:        bmah@FreeBSD.ORG
Cc:        freebsd-current@FreeBSD.ORG
Subject:   Re: freelist corruption: more info
Message-ID:  <3B17D7DB.9469F2A2@mindspring.com>
References:  <200105301637.f4UGbor75863@bmah-freebsd-0.cisco.com>

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"Bruce A. Mah" wrote:
> 
> Trying to fix some make release problems, I've kept running into the
> same freelist corruption problems that kris and dougb experienced
> earlier this week.  Main difference is that I notice when the box
> (-CURRENT from 29 May, GENERIC kernel, UP) crashes.  :-p
> 
> Not being a -CURRENT guru, I haven't decided if I'm going to try Tor
> Egge's patch or just slug it out to try to finish fixing make release
> (which is my main goal at this point).
> 
> Just as an FYI, here's the tombstone and a stack trace in case it's
> useful to anyone.

FWIW, for me, these have _always_ (well, except for the
vnode reclaimer bug, but the vnode reclaimer is still a
stupid idea 5 years later) been reference count rollover
for things which free on 1->0 counts.

My recommendation is to look for a structure in the
kernel which is exactly 52 bytes long.

A somewhate more arcane way of doing this is to cause the
invariant that bitches about this in the allocator to
panic the system (I can't tell if the "Data modified"
message is a result of this having gone in or not -- I
suggested it a while back, after I found the credentials
reference count overflow).

Really, all reference counted objects need to be handled
by the same code -- macros, if we are to be able to do
an INVARIANTS instrumentation of all 0->1 and <max>->0
transitions.

This one looks like a "pagedep" reference overflow, rather
than free-without-reference, problem, which is what you'd
naievely think it was.

-- Terry

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