linux-kernel - Re: 2.6.18-rc6-mm1: GPF loop on early boot

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Date:	Sun, 10 Sep 2006 15:55:51 +0200
From:	Andi Kleen <ak@...e.de>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Laurent Riffard <laurent.riffard@...e.fr>,
	Arjan van de Ven <arjan@...radead.org>,
	Andrew Morton <akpm@...l.org>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	Jeremy Fitzhardinge <jeremy@...source.com>
Subject: Re: 2.6.18-rc6-mm1: GPF loop on early boot

On Sunday 10 September 2006 15:26, Ingo Molnar wrote:
> * Andi Kleen <ak@...e.de> wrote:
> > > Basically, non-atomic setup of basic architecture state _is_ going to
> > > be a nightmare, lockdep or not, especially if it uses common
> > > infrastructure like 'current', spin_lock() or even something as simple
> > > as C functions. (for example the stack-footprint tracer was once hit by
> > > this weakness of the x86_64 code)
> >
> > I disagree with that.  The nightmare is putting stuff that needs so
> > much infrastructure into the most basic operations.
>
> ugh, "having a working current" is "so much infrastructure" ??

Together with stacktrace the infrastructure needed is quite
considerable.

>
> the i686 PDA patches introduce tons of early_current() uses. While i
> like the new PDA code, its bootstrap (like x86_64's PDA bootstrap) is
> too fragile in my opinion, and it will regularly hit instrumenting
> patches.

Or the instrumentation patches just always need to check
some global variable. Maybe system_state could be extended or something.

>
> Perhaps the early setup code (if we really want to do it all in C)

Sorry but moving it into assembler would be just crazy.

> should be moved into 32-bit early boot userspace code (like
> compressed/misc.c) and it will thus not depend on any kernel
> infrastructure.

Ok I guess it would make sense to add a i386_start_kernel to i386 and
initialize the boot PDA there. I would also move early_cpu_init
into there because that also avoids quite some mess later.

-Andi
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