linux-kernel - Re: [PATCH] x86, reboot: skip reboot

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Date:	Fri, 25 Jan 2013 10:13:03 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH] x86, reboot: skip reboot_fixups in early boot phase

Hello, Bjorn.

On Thu, Jan 24, 2013 at 10:45:13AM -0700, Bjorn Helgaas wrote:
> On Fri, Dec 28, 2012 at 6:50 AM, Joonsoo Kim <js1304@...il.com> wrote:
> > During early boot phase, PCI bus subsystem is not yet initialized.
> > If panic is occured in early boot phase and panic_timeout is set,
> > code flow go into emergency_restart() and hit mach_reboot_fixups(), then
> > encounter another panic. When second panic, we can't hold a panic_lock, so
> > code flow go into panic_smp_self_stop() which prevent system to restart.
> >
> > For avoid second panic, skip reboot_fixups in early boot phase.
> > It makes panic_timeout works in early boot phase.
> >
> > Cc: Thomas Gleixner <tglx@...utronix.de>
> > Cc: Ingo Molnar <mingo@...hat.com>
> > Cc: "H. Peter Anvin" <hpa@...or.com>
> > Signed-off-by: Joonsoo Kim <js1304@...il.com>
> >
> > diff --git a/arch/x86/kernel/reboot_fixups_32.c b/arch/x86/kernel/reboot_fixups_32.c
> > index c8e41e9..b9b8ec9 100644
> > --- a/arch/x86/kernel/reboot_fixups_32.c
> > +++ b/arch/x86/kernel/reboot_fixups_32.c
> > @@ -89,6 +89,10 @@ void mach_reboot_fixups(void)
> >         if (in_interrupt())
> >                 return;
> >
> > +       /* During early boot phase, PCI is not yet initialized */
> > +       if (system_state == SYSTEM_BOOTING)
> > +               return;
> > +
> >         for (i=0; i < ARRAY_SIZE(fixups_table); i++) {
> >                 cur = &(fixups_table[i]);
> >                 dev = pci_get_device(cur->vendor, cur->device, NULL);
> 
> I guess you're saying that if we call pci_get_device() too early, it
> panics?  Did you figure out why that happens?
> 
> If we call pci_get_device() before PCI has been initialized, it would
> be good if it just returned NULL, indicating that we didn't find any
> matching device.  I looked briefly, and I thought that's what would
> happen, but apparently I'm missing something.

In bus_find_device(), klist_iter_init_node() is called with 
@bus->p->klist_device. Before initialization, bus->p is NULL,
so panic is occured.

> Bjorn
> --
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