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From: "John S. Dyson" <toor@dyson.iquest.net>
Message-Id: <199610100354.WAA11855@dyson.iquest.net>
Subject: Re: 'dead' binary stays 'dead'?
To: msmith@atrad.adelaide.edu.au (Michael Smith)
Date: Wed, 9 Oct 1996 22:54:13 -0500 (EST)
Cc: dyson@FreeBSD.org, msmith@atrad.adelaide.edu.au, current@FreeBSD.org
In-Reply-To: <199610100257.MAA16615@genesis.atrad.adelaide.edu.au> from "Michael Smith" at Oct 10, 96 12:27:05 pm
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> John S. Dyson stands accused of saying:
> >
> > You are describing a problem that I know *can* happen, but I don't know
> > why.  In essence, once you have a copy of a programs .text, .data in
> > memory, it will continue to be cached until the memory is reclaimed.
> > If any part of that image gets modified, then it will stay modified.
> 
> ... but if these pages are the text and data, they're read-only, correct?
> ie. the only modification possible is via hardware error?
> 
Or software bug :-).  (Memory stomp could cause it, or an incorrect
mapping update in the VM code.)

> 
> The relevant part of the 'going away' incident looked like this :
> 
> $ ls
> <drat, another core>
> $ cp -r /usr/src/bin/ls .
> $ cd ls
> $ CFLAGS=-g; make
> $ gdb ls ../ls.core
> <traceback looks like total garbage>
> $ ./ls
> <works>
> $ ls
> <works>
> 
> So I guess it's possible that the memory was reclaimed while I was rebuilding
> a new 'ls'.
> 
Probably.

>
> > Are you using NFS?  Are you using the most recent -current (snap)?...
> > You know the typical questions :-).
> 
> Sorry 8)  NFS client only (but not on any of the filesystems being used),
> supped at about the same time as the latest SNAP.
> 
We all need to keep an eye on the problem...  This is the first time that
I have heard of it -- but doesn't mean that it isn't there :-)...

John