linux-kernel - Re: 2.6.25-mm1: not looking good

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Date:	Fri, 18 Apr 2008 16:47:17 +0200
From:	"Vegard Nossum" <vegard.nossum@...il.com>
To:	"Jason Wessel" <jason.wessel@...driver.com>
Cc:	"Ingo Molnar" <mingo@...e.hu>,
	"Andrew Morton" <akpm@...ux-foundation.org>, tglx@...utronix.de,
	penberg@...helsinki.fi, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	jmorris@...ei.org, sds@...ho.nsa.gov
Subject: Re: 2.6.25-mm1: not looking good

On 4/18/08, Jason Wessel <jason.wessel@...driver.com> wrote:
> Vegard Nossum wrote:
> > On Fri, Apr 18, 2008 at 3:02 PM, Jason Wessel
> > <jason.wessel@...driver.com> wrote:
> >
> >> Vegard Nossum wrote:
> >>  > On Fri, Apr 18, 2008 at 2:34 PM, Ingo Molnar <mingo@...e.hu> wrote:
> >>  >
> >>  >>  * Vegard Nossum <vegard.nossum@...il.com> wrote:
> >>  >>
> >>  >>  > With the patch below, it seems 100% reproducible to me (7 out of 7
> >>  >>  > bootups hung).
> >>  >>  >
> >>  >>  > The number of loops it could do before hanging were, in order:
> 697,
> >>  >>  > 898, 237, 55, 45, 92, 59
> >>  >>
> >>  >>  cool! Jason: i think that particular self-test should be repeated
> 1000
> >>  >>  times before reporting success ;-)
> >>  >>
> >>  >
> >>  > BTW, I just tested a 32-bit config and it hung after 55 iterations as
> well.
> >>  >
> >>  > Vegard
> >>  >
> >>  >
> >>  >
> >>  I assume this was SMP?
> >>
> >
> > Yes. But now that I realize this, I tried running same kernel with
> > qemu, using -smp 16, and it seems to be stuck here:
> >
> >
>
> Unless you have a qemu with the NMI patches, kgdb does not work on SMP
> with qemu.  The very first test is going to fail because the IPI sent by
> the kernel is not handled in qemu's hardware emulation.

Oops, no, and that makes sense.

I now picked up qemu 0.9.1 and applied the three NMI/SMI patches by Jan Kiszka.

So in qemu it seems to run fine now, except that I need to prod it
sometimes (it gets stuck in cpu_clock() and I have to break/continue
from gdb to make it proceed). Oh, there it made it to 1056, and gdb
can't interrupt anymore. Hmm. This is probably not a very good
testing/debugging environment if the qemu support is that bad. Sorry
:-)

But booting with nosmp on real hardware gets easily above 100,000
iterations of the loop (before I reboot), so it seems to be related to
that, anyway.

Vegard

-- 
"The animistic metaphor of the bug that maliciously sneaked in while
the programmer was not looking is intellectually dishonest as it
disguises that the error is the programmer's own creation."
	-- E. W. Dijkstra, EWD1036
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