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Date:      Tue, 24 Apr 2001 09:16:50 -0700
From:      Alfred Perlstein <bright@wintelcom.net>
To:        "Brian F. Feldman" <green@FreeBSD.ORG>
Cc:        hackers@FreeBSD.ORG
Subject:   Re: Anyone know of RFMEM vm/sysv_shm.c-related races?
Message-ID:  <20010424091650.L1790@fw.wintelcom.net>
In-Reply-To: <200104241207.f3OC7F159738@green.bikeshed.org>; from green@FreeBSD.ORG on Tue, Apr 24, 2001 at 08:07:14AM -0400
References:  <200104241207.f3OC7F159738@green.bikeshed.org>

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* Brian F. Feldman <green@FreeBSD.ORG> [010424 05:07] wrote:
> In some way, using Linux LinuxThreads programs that use shared memory, I've 
> ended up with dozens of shared memory segments that reportedly still have 1 
> attachment (which I'm really darn certain is impossible since I've killed
> _everything_ in sight).  I think something must have happened that for some 
> reason shmexit() was not called on process exit, vm_shm refcnt was increased 
> too many times, vm_shm refcnt was not decreased enough times... whatever the 
> case, there may be an old vmspace just floating around stranded, or just a 
> simple bug with vm_shm...
> 
> Does anyone have any clues about races or weird issues in this area?  It's 
> pretty exasperating to not be able to figure this one out.  I don't 
> immediately see any obvious races after half an hour of searching (since it 
> appears all calls that can modify vmspace directly require Giant being held).

sysv_shm registers atexit and atfork handlers, perhaps you can stick
some debugging code in there?

-- 
-Alfred Perlstein - [alfred@freebsd.org]
Instead of asking why a piece of software is using "1970s technology,"
start asking why software is ignoring 30 years of accumulated wisdom.

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