[v2.6.34-stable 093/213] Driver core: treat unregistered bus_types as having no devices

From: Paul Gortmaker
Date: Wed Feb 05 2014 - 15:54:04 EST

From: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>

This is a commit scheduled for the next v2.6.34 longterm release.
If you see a problem with using this for longterm, please comment.

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@xxxxxxxxx>
Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
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 12eec3f633b1..1913e74ee582 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,

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/