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Driver core: treat unregistered bus_types as having no devices
commit 4fa3e78 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 <firstname.lastname@example.org> Signed-off-by: Bjorn Helgaas <email@example.com> Signed-off-by: Greg Kroah-Hartman <firstname.lastname@example.org>
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