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    Subject[ 023/153] Driver core: treat unregistered bus_types as having no devices
    3.2-stable review patch.  If anyone has any objections, please let me know.

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

    From: Bjorn Helgaas <bhelgaas@google.com>

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

    --- a/drivers/base/bus.c
    +++ b/drivers/base/bus.c
    @@ -289,7 +289,7 @@ 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,
    @@ -323,7 +323,7 @@ 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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