On Wed, Jul 26, 2023 at 02:35:18PM +0200, Igor Mammedov wrote:
> Commit [1] switched acpiphp hotplug to use
> pci_assign_unassigned_bridge_resources()
> which depends on bridge being available, however in some cases
> when acpiphp is in use, enable_slot() can get a slot without
> bridge associated.
acpiphp is *always* in use if we get to enable_slot(), so that doesn't
really add information here.
> 1. legitimate case of hotplug on root bus
> (likely not exiting on real hw, but widely used in virt world)
> 2. broken firmware, that sends 'Bus check' events to non
> existing root ports (Dell Inspiron 7352/0W6WV0), which somehow
> endup at acpiphp:enable_slot(..., bridge = 0) and with bus
> without bridge assigned to it.
IIUC, the Inspiron problem happens when:
- acpiphp_context->bridge is NULL, so hotplug_event() calls
enable_slot() instead of acpiphp_check_bridge(), AND
- acpiphp_slot->bus->self is also NULL, because enable_slot() calls
pci_assign_unassigned_bridge_resources() with that NULL pointer,
which dereferences "bridge->subordinate"
But I can't figure out why acpiphp_context->bridge is NULL for RP07
and RP08 (which don't exist), but not for RP03 (which does).
I guess all the acpiphp_contexts (RP03, RP07, RP08) must be allocated in
acpiphp_add_context() by acpiphp_init_context().
Woody's lspci from [1] shows only one Root Port:
00:1c.0 Wildcat Point-LP PCI Express Root Port #3
The DSDT.DSL includes:
Device (RP01) _ADR 0x001C0000 # 1c.0
Device (RP02) _ADR 0x001C0001 # 1c.1
Device (RP03) _ADR 0x001C0002 # 1c.2
Device (RP04) _ADR 0x001C0003 # 1c.3
Device (RP05) _ADR 0x001C0004 # 1c.4
Device (RP06) _ADR 0x001C0005 # 1c.5
Device (RP07) _ADR 0x001C0006 # 1c.6
Device (RP08) _ADR 0x001C0007 # 1c.7
I can see why we might need a Bus Check after resume to see if
something got added while we were suspended. But I don't see why we
handle RP03 differently from RP07 and RP08.
Can you help me out? I'm lost in a maze of twisty passages, all
alike.
Bjorn
[1] https://lore.kernel.org/r/92150d8d-8a3a-d600-a996-f60a8e4c876c@xxxxxxxxx
