[PATCH] ACPI / PCI: Initialize PCI root drivers after PCI bus enumeration

From: Rafael J. Wysocki
Date: Tue Feb 12 2013 - 19:10:02 EST

From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>

After commit 1aeae82 (ACPI / PCI: avoid building pci_slot as module)
the pci_slot driver's .add() callback routine, acpi_pci_slot_add(),
is executed from within acpi_pci_root_add() before the PCI devices on
the bus are enumerated and that triggers the WARN_ON() in

WARNING: at /scratch/rafael/work/test/include/linux/kref.h:42 kobject_get+0x33/0x40()
Hardware name: PORTEGE R500
Modules linked in:
Pid: 1, comm: swapper/0 Not tainted 3.8.0-rc7+ #160
Call Trace:
[<ffffffff8103d38a>] warn_slowpath_common+0x7a/0xb0
[<ffffffff8103d3d5>] warn_slowpath_null+0x15/0x20
[<ffffffff812f99b3>] kobject_get+0x33/0x40
[<ffffffff81452b82>] get_device+0x12/0x30
[<ffffffff8138df7b>] register_slot+0x243/0x295
[<ffffffff810a7b6d>] ? trace_hardirqs_on+0xd/0x10
[<ffffffff8137b7b9>] acpi_ns_walk_namespace+0x10f/0x24a
[<ffffffff8138dd38>] ? walk_p2p_bridge+0x13b/0x13b
[<ffffffff8138dd38>] ? walk_p2p_bridge+0x13b/0x13b
[<ffffffff8137bdc3>] acpi_walk_namespace+0xe9/0x132
[<ffffffff8138dd38>] ? walk_p2p_bridge+0x13b/0x13b
[<ffffffff8138dcf5>] walk_p2p_bridge+0xf8/0x13b
[<ffffffff8134d606>] ? acpi_os_signal_semaphore+0x76/0x87
[<ffffffff8138dd38>] ? walk_p2p_bridge+0x13b/0x13b
[<ffffffff8137b7b9>] acpi_ns_walk_namespace+0x10f/0x24a
[<ffffffff8138dbfd>] ? do_sta_before_sun+0x2b/0x2b
[<ffffffff8138dbfd>] ? do_sta_before_sun+0x2b/0x2b
[<ffffffff8137bdc3>] acpi_walk_namespace+0xe9/0x132
[<ffffffff81356071>] ? acpi_pci_root_add+0x3e7/0x49a
[<ffffffff8138e07f>] acpi_pci_slot_add+0xb2/0x103
[<ffffffff8138dd38>] ? walk_p2p_bridge+0x13b/0x13b
[<ffffffff81356089>] acpi_pci_root_add+0x3ff/0x49a

which means that pci_bus->dev used in register_slot() has not been
registered yet at that point.

To fix this use the observation that before commit 1aeae82
acpi_pci_slot_add() was always run after pci_bus_add_devices()
and that happened to the acpiphp's .add() callback routine too.
Thus it is safe to reorder acpi_pci_root_add() to make the PCI root
drivers' .add() callbacks be run after pci_bus_add_devices(), so do

This approach was previously proposed by Myron Stowe.

References: https://patchwork.kernel.org/patch/1848781/
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>

The commit mentioned in the changelog above is in linux-pm.git/linux-next.


drivers/acpi/pci_root.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)

Index: test/drivers/acpi/pci_root.c
--- test.orig/drivers/acpi/pci_root.c
+++ test/drivers/acpi/pci_root.c
@@ -600,17 +600,20 @@ static int acpi_pci_root_add(struct acpi
if (system_state != SYSTEM_BOOTING)

+ /* need to after hot-added ioapic is registered */
+ if (system_state != SYSTEM_BOOTING)
+ pci_enable_bridges(root->bus);
+ pci_bus_add_devices(root->bus);
list_for_each_entry(driver, &acpi_pci_drivers, node)
if (driver->add)
- mutex_unlock(&acpi_pci_root_lock);

- /* need to after hot-added ioapic is registered */
- if (system_state != SYSTEM_BOOTING)
- pci_enable_bridges(root->bus);
+ mutex_unlock(&acpi_pci_root_lock);

- pci_bus_add_devices(root->bus);
return 1;


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