PCI: pci_slot: grab refcount on slot's bus

If a logical hot unplug (remove) is performed on a physical PCI slot's
parent bridge, and then pci_slot is unloaded, we will encounter an oops:

  [<ffffffff803a788a>] kobject_release+0x9a/0x290
  [<ffffffff803a77f0>] ? kobject_release+0x0/0x290
  [<ffffffff803a8ce7>] kref_put+0x37/0x80
  [<ffffffff803a76f7>] kobject_put+0x27/0x60
  [<ffffffff803bebcc>] ? pci_destroy_slot+0x3c/0xc0
  [<ffffffff803bebd5>] pci_destroy_slot+0x45/0xc0
  [<ffffffffa000f05c>] acpi_pci_slot_remove+0x5c/0x91 [pci_slot]
  [<ffffffff8040064b>] acpi_pci_unregister_driver+0x4b/0x62
  [<ffffffffa000f5c8>] acpi_pci_slot_exit+0x10/0x12 [pci_slot]
  [<ffffffff80276ce1>] sys_delete_module+0x161/0x250

We need to grab a reference to the parent PCI bus, which will pin
the bus and prevent it from being released until pci_slot is unloaded.

Cc: lenb@kernel.org
Reviewed-by: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Tested-by: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Reported-by: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Signed-off-by: Alex Chiang <achiang@hp.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

1 files changed, 5 insertions, 0 deletions

diff --git a/drivers/acpi/pci_slot.c b/drivers/acpi/pci_slot.c
index cd1f4467be7b..12158e0d009b 100644
--- a/drivers/acpi/pci_slot.c
+++ b/drivers/acpi/pci_slot.c
@@ -164,6 +164,8 @@ register_slot(acpi_handle handle, u32 lvl, void *context, void **rv)
         list_add(&slot->list, &slot_list);
         mutex_unlock(&slot_list_lock);
 
+        get_device(&pci_bus->dev);
+
         dbg("pci_slot: %p, pci_bus: %x, device: %d, name: %s\n",
                 pci_slot, pci_bus->number, device, name);
 
@@ -310,12 +312,15 @@ static void
 acpi_pci_slot_remove(acpi_handle handle)
 {
         struct acpi_pci_slot *slot, *tmp;
+        struct pci_bus *pbus;
 
         mutex_lock(&slot_list_lock);
         list_for_each_entry_safe(slot, tmp, &slot_list, list) {
                 if (slot->root_handle == handle) {
                         list_del(&slot->list);
+                        pbus = slot->pci_slot->bus;
                         pci_destroy_slot(slot->pci_slot);
+                        put_device(&pbus->dev);
                         kfree(slot);
                 }
         }