Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!uunet!hsi!stevens
From: stevens@hsi.UUCP (Richard Stevens)
Newsgroups: comp.unix.questions
Subject: Re: Insufficient Resource Error on msgsnd Call
Summary: message queue problems - SVr2
Keywords: msgsnd, msgrcv, Ingres, UNIX, System V, message queues, Sun, SunOS4.0
Message-ID: <466@hsi86.hsi.UUCP>
Date: 25 May 89 09:25:49 GMT
References: <1023@dinl.mmc.UUCP> <20284@winchester.mips.COM>
Organization: Health Systems Intl., New Haven, CT
Lines: 22

In article <20284@winchester.mips.COM>, jay@mips.COM (Jay McCauley) writes:
> 
> We also felt, but could never prove, that there were flaws in the
> standard System V implementation of the message facilities.  Every so often
> we would see mysterious confusion in the ipcs reports that would only
> clear by rebooting.  This occured on several different vendor's systems,
> so we suspected that there was some sort of subtle synchronization
> glitch in the kernel msgop support.
> 

There is indeed a problem with the SVr2 implementation of message queues.
As I understand it, the problem occurs when data is copied between the
user space and the kernel *and* a page fault occurs.  Supposedly it was
fixed in SVr2.1 or SVr3.0, but I don't have the source for either of
these to check.  I heard they added a set of locks for each queue
so that common data structures aren't walked over if there is a page
fault during an iomove().

	Richard Stevens
	Health Systems International, New Haven, CT
	   stevens@hsi.com
           ... { uunet | yale } ! hsi ! stevens