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    Subject[PATCH 3/3] PCI: pci_slot: grab refcount on slot's bus
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    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
    Reported-by: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
    Signed-off-by: Alex Chiang <achiang@hp.com>
    ---

    drivers/acpi/pci_slot.c | 5 +++++
    1 files changed, 5 insertions(+), 0 deletions(-)

    diff --git a/drivers/acpi/pci_slot.c b/drivers/acpi/pci_slot.c
    index cd1f446..c7ad9f2 100644
    --- a/drivers/acpi/pci_slot.c
    +++ b/drivers/acpi/pci_slot.c
    @@ -63,6 +63,7 @@ struct acpi_pci_slot {
    acpi_handle root_handle; /* handle of the root bridge */
    struct pci_slot *pci_slot; /* corresponding pci_slot */
    struct list_head list; /* node in the list of slots */
    + struct pci_bus *bus; /* bus the slot is on */
    };

    static int acpi_pci_slot_add(acpi_handle handle);
    @@ -159,11 +160,14 @@ register_slot(acpi_handle handle, u32 lvl, void *context, void **rv)

    slot->root_handle = parent_context->root_handle;
    slot->pci_slot = pci_slot;
    + slot->bus = pci_bus;
    INIT_LIST_HEAD(&slot->list);
    mutex_lock(&slot_list_lock);
    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);

    @@ -316,6 +320,7 @@ acpi_pci_slot_remove(acpi_handle handle)
    if (slot->root_handle == handle) {
    list_del(&slot->list);
    pci_destroy_slot(slot->pci_slot);
    + put_device(&slot->bus->dev);
    kfree(slot);
    }
    }


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