Driver core: treat unregistered bus_types as having no devices

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
again:

    mach_reboot_fixups
      pci_get_device
        ..
          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@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/base/bus.c b/drivers/base/bus.c
index 000e7b2..8b8e8c0 100644 (file)
--- a/drivers/base/bus.c
+++ b/drivers/base/bus.c
@@ -289,7 +289,7 @@ 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,
@@ -323,7 +323,7 @@ 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,