[ 3.5.y.z extended stable ] Patch "Driver core: treat unregistered bus_types as having no" has been added to staging queue

Luis Henriques luis.henriques at canonical.com
Tue Feb 26 16:13:09 UTC 2013

This is a note to let you know that I have just added a patch titled

    Driver core: treat unregistered bus_types as having no

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:


If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see



>From 2ed4f2b057593bca9ba19e506e0c8f84691b4b86 Mon Sep 17 00:00:00 2001
From: Bjorn Helgaas <bhelgaas at google.com>
Date: Tue, 29 Jan 2013 16:44:27 -0700
Subject: [PATCH] Driver core: treat unregistered bus_types as having no

commit 4fa3e78be7e985ca814ce2aa0c09cbee404efcf7 upstream.

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

          bus_find_device(&pci_bus_type, ...)
            bus->p is NULL

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")

Reported-by: Joonsoo Kim <js1304 at gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas at google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.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 2bcef65..287b7e2 100644
--- a/drivers/base/bus.c
+++ b/drivers/base/bus.c
@@ -293,7 +293,7 @@ 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,
@@ -327,7 +327,7 @@ 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,

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