linux-kernel - Re: [xen] double fault: 0000 [#1] PREEMPT SMP DEBUG

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Message-ID: <20131008033518.GA9401@localhost>
Date:	Tue, 8 Oct 2013 11:35:18 +0800
From:	Fengguang Wu <fengguang.wu@...el.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	xen-devel@...ts.xenproject.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [xen] double fault: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC

On Mon, Oct 07, 2013 at 08:29:26PM -0700, Linus Torvalds wrote:
> On Mon, Oct 7, 2013 at 8:11 PM, Fengguang Wu <fengguang.wu@...el.com> wrote:
> >
> > Yeah, I see no timer usage in parport_pc driver, so it's still questionable.
> 
> The timer itself comes simply from the delayed_work that is used to
> delay the freeing of the kobject.
> 
> So that is not the surprising part.

OK.

> The surprising part is that I don't see parport_pc doing anything
> odd/bad with its kobject embedded in the 'struct dev'. It seems to
> just do a platform_device_register_simple() followed by a
> platform_device_unregister().
> 
> At least that's true for the normal parport_pc_probe_port() case that
> just passes in a NULL dev... But I only glanced at the driver, so I
> might have missed something.
> 
> > with some manual bisects, I find a good config (attached) that can
> > reliably boot the kernel up.
> >
> > Based on that config, I tried adding parport_pc and see that it still
> > boots fine.
> >
> > Adding drm, however will bring back the oops. Will try a kernel based
> > on the original kconfig with drm disabled only.

FYI I just confirmed that the original bad kconfig can be made
bootable by simply disabling CONFIG_DRM.

> Ok. The list corruption (which also pointed at parport_pc) might well
> be corrupted by removing the entries before or after the parport_pc,
> and moving the corruption to parport_pc that way (through the
> "prev->next = next" thing in list handling). So maybe it was something
> else all along. You could enable CONFIG_DEBUG_LIST to see if that
> triggers some dump earlier..

OK, I'll try enabling CONFIG_DEBUG_LIST.

Thanks,
Fengguang
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