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Subject: Re: [Qemu-devel] kqemu freebsd host smp problems?
From: Antony T Curtis <antony.t.curtis@ntlworld.com>
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Date: Sun, 10 Jul 2005 12:10:28 +0100
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To: Norikatsu Shigemura <nork@FreeBSD.org>
Cc: Craig Boston <craig@xfoil.gank.org>, jhb@FreeBSD.org, alc@FreeBSD.org, jeff@FreeBSD.org, qemu-devel@nongnu.org, freebsd-current@FreeBSD.org, Bakul Shah <bakul@BitBlocks.com>, Juergen Lock <qemu-l@jelal.kn-bremen.de>

On Sun, 2005-07-10 at 13:39 +0900, Norikatsu Shigemura wrote:
> On Sun, 03 Jul 2005 17:37:42 -0700
> Bakul Shah <bakul@BitBlocks.com> wrote:
> > Lock writes:
> > >  Is kqemu and the freebsd wrapper smp aware?  I just saw this panic
> > > report again,
> > > 	http://lists.freebsd.org/pipermail/freebsd-current/2005-May/050161.html
> > > and noticed it apparently happened with an smp kernel.
> > My guess is
> > 	.d_flags = D_NEEDGIANT,
> > needs to be added to the initializer of kqemu_cdevsw for the
> > freebsd-current case.  AFAIK this flag ensures only one
> > thread can be in this driver at a time (but caveat emptor: I
> > don't play in the kernel these days).
> 
> 	I confirmed that qemu on latest FreeBSD 6-current got more
> 	stability!!, but more little slowly:-( and a panic:-( too.

IMO, That flag is not the cause of the panics and that it should(tm)
work without requiring GIANT...

I think it is possible that the kqemu code is freeing a page without
unlocking it so that when another process does file IO which requires
pages to be allocated, attempts to wire those pages results in failure
and so a panic occurrs.

Perhaps if a different method for allocating memory rather than
contigmalloc/contigfree should be used by the kernel module.

<snip>

Offtopic - but am I the only person who has modified the if_tap driver
to permit opening by non-superuser?

-- 
Antony T Curtis, BSc.                   UNIX, Linux, *BSD, Networking
antony.t.curtis@ntlworld.com            C++, J2EE, Perl, MySQL, Apache
                                        IT Consultancy.