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Date:      Tue, 5 Jan 1999 03:59:48 +0000 (GMT)
From:      Terry Lambert <tlambert@primenet.com>
To:        lem@cantv.net (Luis =?iso-8859-1?Q?Mu=F1oz?=)
Cc:        spork@super-g.com, kaleb@ics.com, hackers@FreeBSD.ORG
Subject:   Re: inetd in realloc(): warning: junk pointer, too low to make
Message-ID:  <199901050359.UAA04503@usr05.primenet.com>
In-Reply-To: <3.0.6.32.19981221171019.008451f0@pop.cantv.net> from "Luis =?iso-8859-1?Q?Mu=F1oz?=" at Dec 21, 98 05:10:19 pm

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> >Well, here's what sendmail does here, it's pretty scary, with those
> >truncated messages about spwd.db:
> >
> >Dec 17 15:42:27 super-g Dec 17 15:42:27sendmail[: NOQUEUE
> >Dec 17 15:51:11 super-g Dec 17 15:51:11sendmail[: /etc/spwd.db
> >Dec 17 15:51:11 super-g sendmail[16594]: NOQUEUE: SYSERR(root): Out of
> >memory!!: Cannot allocate memory
> >Dec 17 16:30:01 super-g Dec 17 16:30:00sendmail[: /etc/spwd.db
> >Dec 17 16:30:16 super-g /kernel: pid 20618 (sendmail), uid 0: exited on
> >signal 11
> >Dec 17 16:30:57 super-g Dec 17 16:30:57sendmail[: /etc/spwd.db
> >Dec 17 16:30:57 super-g Dec 17 16:30:57sendmail[: NOQUEUE
> >Dec 17 16:30:57 super-g Dec 17 16:30:57sendmail[: /etc/spwd.db    
> >
> >Charles
> 
> Agreed. Are your files consistent/sane? I've never seen this
> before!

This is related to running out of memory.

The problem occurs because clean mmap'ed pages are reaped for reuse
in a swap low condition, but the "page present" bit is not correctly
unset in the places where it is referenced.

Effectively, this corrupts one page of the libc (which is mmap'ed)
that the sendmail is linked against, and basically damages its
ability to fork children.

You can work around the problem by statically link sendmail and/or
not running out of memory (e.g. run a newer version of Netscape,
use a DISPLAY variable that disables Netscape using the MIT SHM
extension, run Netscape from a remote machine using the local
machine as a display, which will also prevent it from using the
MIT SHM extension, or just disable the MIT SHM extension entirely).

You can also workaround the problem by not allowing the reaping of
pages in a mapping that references a vnode with a greater than one
reference count (not an ideal workaround, admittedly, but it works).


					Terry Lambert
					terry@lambert.org
---
Any opinions in this posting are my own and not those of my present
or previous employers.

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