linux-kernel - Re: [PATCH] Driver core: treat unregistered bus

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Message-ID: <CAErSpo6B+TWKpP=P6hoNLzziq9Po-OwW2zGBHCc+qSJ2HtTYNQ@mail.gmail.com>
Date:	Tue, 29 Jan 2013 16:47:13 -0700
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Joonsoo Kim <js1304@...il.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] Driver core: treat unregistered bus_types as having no devices

On Tue, Jan 29, 2013 at 4:44 PM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:
> A bus_type has a list of devices (klist_devices), but the list and the
> subsys_private structure that contains it are not initialized until the
> bus_type is registered with bus_register().
>
> The panic/reboot path has fixups that look up devices in pci_bus_type.  If
> we panic before registering pci_bus_type, the bus_type exists but the list
> does not, so mach_reboot_fixups() trips over a null pointer and panics
> again:
>
>     mach_reboot_fixups
>       pci_get_device
>         ..
>           bus_find_device(&pci_bus_type, ...)
>             bus->p is NULL
>
> Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
> ---
>  drivers/base/bus.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/base/bus.c b/drivers/base/bus.c
> index 24eb078..6856303 100644
> --- a/drivers/base/bus.c
> +++ b/drivers/base/bus.c
> @@ -290,7 +290,7 @@ int bus_for_each_dev(struct bus_type *bus, struct device *start,
>         struct device *dev;
>         int error = 0;
>
> -       if (!bus)
> +       if (!bus || !bus->p)
>                 return -EINVAL;
>
>         klist_iter_init_node(&bus->p->klist_devices, &i,
> @@ -324,7 +324,7 @@ struct device *bus_find_device(struct bus_type *bus,
>         struct klist_iter i;
>         struct device *dev;
>
> -       if (!bus)
> +       if (!bus || !bus->p)
>                 return NULL;
>
>         klist_iter_init_node(&bus->p->klist_devices, &i,
>

Sorry, I meant to include this in the original post:

Joonsoo reported a problem when panicking before PCI was initialized.
I think this patch should be sufficient to replace the patch he posted
here: https://lkml.org/lkml/2012/12/28/75 ("[PATCH] x86, reboot: skip
reboot_fixups in early boot phase")
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