Messages in this thread | | | From | Bjorn Helgaas <> | Date | Wed, 30 Jan 2013 10:21:07 -0700 | Subject | Re: [PATCH] Driver core: treat unregistered bus_types as having no devices |
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On Wed, Jan 30, 2013 at 1:09 AM, Greg Kroah-Hartman <gregkh@linuxfoundation.org> wrote: > On Tue, Jan 29, 2013 at 04:47:13PM -0700, Bjorn Helgaas wrote: >> On Tue, Jan 29, 2013 at 4:44 PM, Bjorn Helgaas <bhelgaas@google.com> wrote: >> > 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 >> > >> > Signed-off-by: Bjorn Helgaas <bhelgaas@google.com> >> > --- >> > 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 24eb078..6856303 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, >> > >> >> Sorry, I meant to include this in the original post: >> >> 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") > > Don't you think that should be applied as well? That makes things a bit > more explicit in the boot process as to exactly what is going on. The > driver core changes is good to have if other people mess things up like > this in the future, don't rely on it to protect you from foolish things.
mach_reboot_fixups() is not part of the boot process at all. That's why it seems ugly to me to clutter it with a system_state check. I don't really think of it as having messed up by calling pci_get_device() without checking system_state. Certainly we don't expect *every* caller to check system_state, and it's not trivial to determine at every call site whether pci_bus has been registered or not.
But if anybody wants to apply the https://lkml.org/lkml/2012/12/28/75 too, it's OK with me.
Tangential question ... I was curious as to why bus_for_each_dev() and bus_find_device() (and other driver core things) check for "!bus" in the first place. For all the callers I looked at, it's obvious at compile-time that bus can't be NULL. The question of whether "bus->p" is null can't be answered at compile-time because it depends on whether the bus has been registered.
Bjorn
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