Re: [PATCH v2] ACPI / hotplug / PCI: Don't scan for non-hotplug bridges if slot is not bridge

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I think this should also be applied to 4.18 and 4.19 as this fixes a boot hang.
-Peter

On Wed, 26 Sep 2018 at 00:01, Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote:
>
> On Mon, Sep 24, 2018 at 12:42:59PM +0300, Mika Westerberg wrote:
> > HP 6730b laptop has an ethernet NIC connected to one of the PCIe root
> > ports. The root ports itself are native PCIe hotplug capable. Now,
> > during boot after PCI devices are scanned the BIOS triggers ACPI bus
> > check directly to the NIC:
> >
> >   [    0.942239] ACPI: \_SB_.PCI0.RP06.NIC_: Bus check in hotplug_event()
> >
> > It is not clear why it is sending bus check but regardless the ACPI
> > hotplug notify handler calls enable_slot() directly (instead of going
> > through acpiphp_check_bridge() as there is no bridge) which ends up
> > handling special case for non-hotplug bridges with native PCIe hotplug.
> > This results a crash of some kind but the reporter only sees black
> > screen so it is hard to figure out the exact spot and what actually
> > happens. Based on few fix proposals it was tracked to crash somewhere
> > inside pci_assign_unassigned_bridge_resources().
> >
> > In any case we should not really be in that special branch at all
> > because the ACPI notify happened to a slot that is not a PCI bridge (it
> > is just a regular PCI device).
> >
> > Fix this so that we only go to that special branch if we are calling
> > enable_slot() for a bridge (e.g the ACPI notification was for the bridge).
> >
> > Link: https://bugzilla.kernel.org/show_bug.cgi?id=201127
> > Fixes: 84c8b58ed3ad ACPI / hotplug / PCI: Don't scan bridges managed by native hotplug
> > Reported-by: Peter Anemone <peter.anemone@xxxxxxxxx>
> > Signed-off-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>
>
> Applied with Rafael's reviewed-by to pci/hotplug for v4.20, thanks!
>
> > ---
> > Changes from v1:
> >
> >   * Pass bool instead of a bridge pointer
> >
> >  drivers/pci/hotplug/acpiphp_glue.c | 11 ++++++-----
> >  1 file changed, 6 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/pci/hotplug/acpiphp_glue.c b/drivers/pci/hotplug/acpiphp_glue.c
> > index ef0b1b6ba86f..12afa7fdf77e 100644
> > --- a/drivers/pci/hotplug/acpiphp_glue.c
> > +++ b/drivers/pci/hotplug/acpiphp_glue.c
> > @@ -457,17 +457,18 @@ static void acpiphp_native_scan_bridge(struct pci_dev *bridge)
> >  /**
> >   * enable_slot - enable, configure a slot
> >   * @slot: slot to be enabled
> > + * @bridge: true if enable is for the whole bridge (not a single slot)
> >   *
> >   * This function should be called per *physical slot*,
> >   * not per each slot object in ACPI namespace.
> >   */
> > -static void enable_slot(struct acpiphp_slot *slot)
> > +static void enable_slot(struct acpiphp_slot *slot, bool bridge)
> >  {
> >       struct pci_dev *dev;
> >       struct pci_bus *bus = slot->bus;
> >       struct acpiphp_func *func;
> >
> > -     if (bus->self && hotplug_is_native(bus->self)) {
> > +     if (bridge && bus->self && hotplug_is_native(bus->self)) {
> >               /*
> >                * If native hotplug is used, it will take care of hotplug
> >                * slot management and resource allocation for hotplug
> > @@ -701,7 +702,7 @@ static void acpiphp_check_bridge(struct acpiphp_bridge *bridge)
> >                                       trim_stale_devices(dev);
> >
> >                       /* configure all functions */
> > -                     enable_slot(slot);
> > +                     enable_slot(slot, true);
> >               } else {
> >                       disable_slot(slot);
> >               }
> > @@ -785,7 +786,7 @@ static void hotplug_event(u32 type, struct acpiphp_context *context)
> >               if (bridge)
> >                       acpiphp_check_bridge(bridge);
> >               else if (!(slot->flags & SLOT_IS_GOING_AWAY))
> > -                     enable_slot(slot);
> > +                     enable_slot(slot, false);
> >
> >               break;
> >
> > @@ -973,7 +974,7 @@ int acpiphp_enable_slot(struct acpiphp_slot *slot)
> >
> >       /* configure all functions */
> >       if (!(slot->flags & SLOT_ENABLED))
> > -             enable_slot(slot);
> > +             enable_slot(slot, false);
> >
> >       pci_unlock_rescan_remove();
> >       return 0;
> > --
> > 2.18.0
> >



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