[ 28/58] Driver core: treat unregistered bus_types as having no devices

[Greg Kroah-Hartman]

3.7-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>

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@xxxxxxxxx>
Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/base/bus.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/base/bus.c
+++ b/drivers/base/bus.c
@@ -293,7 +293,7 @@ int bus_for_each_dev(struct bus_type *bu
 	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 bu
 	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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