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

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Date:	Tue, 29 Jan 2013 15:03:57 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>,
	"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

On Thu, Jan 24, 2013 at 08:52:32PM -0800, Greg Kroah-Hartman wrote:
> On Thu, Jan 24, 2013 at 09:21:52PM -0700, Bjorn Helgaas wrote:
> > On Thu, Jan 24, 2013 at 9:14 PM, Greg Kroah-Hartman
> > <gregkh@...uxfoundation.org> wrote:
> > > On Thu, Jan 24, 2013 at 07:59:01PM -0700, Bjorn Helgaas wrote:
> > >> [+cc Greg for driver core]
> > >>
> > >> On Fri, Jan 25, 2013 at 10:13:03AM +0900, Joonsoo Kim wrote:
> > >> > 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.
> > >>
> > >> I see.  pci_bus_type.p is initialized by __bus_register() in this path:
> > >>
> > >>   pci_driver_init        # postcore_initcall
> > >>     bus_register(&pci_bus_type)
> > >>       __bus_register
> > >>         priv = kzalloc(sizeof(struct subsys_private))
> > >>       bus->p = priv
> > >>       klist_init(&priv->klist_devices, klist_devices_get, klist_devices_put)
> > >>
> > >> I was hoping we could statically initialize the klist, but that doesn't
> > >> seem likely.
> > >>
> > >> But I wonder if we could do something like the following.  If we could,
> > >> then callers wouldn't have to worry about whether or not the bus has been
> > >> initialized.
> > >
> > > <snip>
> > >
> > > I have no objection to that patch, but really, someone wants to call
> > > pci_find_device() before PCI is initialized?  Can't that be fixed
> > > instead, as that is the root problem, not the driver core.
> > >
> > > But, to paper over your subsystem's bugs, I guess I can take it :)
> > 
> > The caller is in the native_machine_emergency_restart() path.
> > Joonsoo's original patch does what I think you're suggesting:
> > 
> > >> > > > +       /* 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 think it's sort of ugly to check system_state before using
> > pci_get_device(), and there's not really an obvious connection between
> > system_state and PCI initialization.
> > 
> > But if you prefer that, Joonsoo's original patch is fine with me.
> 
> Both probably would be best, as there are probably other things that you
> don't want to touch when you are still booting and trying to restart the
> machine at the same time.

I agree that my patch is ugly :)
So I drop it and wait for your patch.

Thanks.

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