During early boot, the kernel performs ACPI enumeration in which host
bridges are discovered (subsys_initcall(acpi_pci_root_init)). Later
drivers, both built-in and modules such as the "ACPI PCI Slot Detection
Driver ("pci_slot")", are loaded (module_init(acpi_pci_slot_init)) thus we
end up with the following call chain:
acpi_pci_root_start
list_for_each_entry(..., acpi_pci_drivers, ...)
driver->add(root) # always no-op; list empty
pci_bus_add_devices
acpi_pci_slot_init # module_init
acpi_pci_register_driver(acpi_pci_slot_driver)
list_for_each_entry(..., &acpi_pci_roots, ...)
driver->add(root) # acpi_pci_slot_add()
Note that for host bridges present at boot time the 'acpi_pci_drivers'
list is always empty when acpi_pci_root_start() runs.
However, during a Host Bridge hot-add event, the "pci_slot" sub-driver is
already on the 'acpi_pci_drivers' list and we end up calling
acpi_pci_slot_add() before pci_bus_add_devices() and encounter the
following refcount WARNING:
calling acpi_pci_slot_add():
pci_bus 0000:03: dev 00, created physical slot 1
------------[ cut here ]------------
WARNING: at include/linux/kref.h:42 kobject_get+0x32/0x40()
Call Trace:
[<ffffffff812541d2>] kobject_get+0x32/0x40
[<ffffffff8133f0f9>] get_device+0x19/0x20
[<ffffffff812d9f11>] register_slot+0x216/0x26d
[<ffffffff812ce92f>] acpi_walk_namespace+0x8a/0xc4
[<ffffffff812d9cb9>] walk_p2p_bridge+0xf1/0x133
[<ffffffff812ce92f>] acpi_walk_namespace+0x8a/0xc4
[<ffffffff812d9b71>] acpi_pci_slot_add+0xe0/0x137
[<ffffffff812b8705>] acpi_pci_root_start+0x3e/0x59
This patch fixes this latent issue by moving up pci_bus_add_devices() so
that the refcount will be initialized before subsequent references, via
driver additions from the 'acpi_pci_drivers' list, occur.
Signed-off-by: Myron Stowe <myron.stowe@xxxxxxxxxx>
---
drivers/acpi/pci_root.c | 4 ++--
1 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
index d890322..f9be8fb 100644
--- a/drivers/acpi/pci_root.c
+++ b/drivers/acpi/pci_root.c
@@ -644,6 +644,8 @@ static int acpi_pci_root_start(struct acpi_device *device)
struct acpi_pci_root *root = acpi_driver_data(device);
struct acpi_pci_driver *driver;
+ pci_bus_add_devices(root->bus);
+
mutex_lock(&acpi_pci_root_lock);
list_for_each_entry(driver, &acpi_pci_drivers, node)
if (driver->add)
@@ -651,8 +653,6 @@ static int acpi_pci_root_start(struct acpi_device *device)
acpiphp_add_bridge(root);
mutex_unlock(&acpi_pci_root_lock);
- pci_bus_add_devices(root->bus);
-
return 0;
}
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