From owner-freebsd-alpha  Sat Nov  9 12:39:17 2002
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Date: Sat, 09 Nov 2002 14:38:28 -0600
From: "Alan L. Cox" <alc@imimic.com>
Organization: iMimic Networking, Inc.
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To: Jeff Roberson <jroberson@chesapeake.net>
Cc: Matthew Jacob <mjacob@feral.com>,
	Andrew Gallatin <gallatin@cs.duke.edu>, alpha@FreeBSD.ORG,
	alc@FreeBSD.ORG, John Baldwin <jhb@FreeBSD.ORG>
Subject: Re: alpha: top of tree kernel blooie
References: <20021109150359.B97372-100000@mail.chesapeake.net>
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Jeff Roberson wrote:
> 
> On Fri, 8 Nov 2002, Matthew Jacob wrote:
> 
> >
> > >
> > > Can you 'ps aux -o wchan' ?
> >
> > I tried a buildworld -j4 again- this time it was too far hung to let
> > anyone log in...
> >
> >
> 
> I ran into the vm_map_delete() duplicate free again.  This has been the
> same code path too many times for it to be a non logic bug.
> 
> Jeff

I'm still wondering if this isn't a false positive:

1. My reading of the UMA debug code is that two or more processors can
simultaneously read and modify us_freelist[].  The only lock held during
an access is the CPU private lock.

2. Don't we compile by default for the older Alphas that lack byte
manipulation instructions?  Thus, a byte store is implemented by a
read-modify-write sequence of instructions.  Thus, two simultaneous
uma_dbg_alloc()s on adjacent locations in us_freelist could cause
corruption.

Regards,
Alan

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