[PATCH 4.9 15/96] platform/x86: wmi: Call acpi_wmi_init() later

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

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

commit 98b8e4e5c17bf87c1b18ed929472051dab39878c upstream.

Calling acpi_wmi_init() at the subsys_initcall() level causes ordering
issues to appear on some systems and they are difficult to reproduce,
because there is no guaranteed ordering between subsys_initcall()
calls, so they may occur in different orders on different systems.

In particular, commit 86d9f48534e8 (mm/slab: fix kmemcg cache
creation delayed issue) exposed one of these issues where genl_init()
and acpi_wmi_init() are both called at the same initcall level, but
the former must run before the latter so as to avoid a NULL pointer
dereference.

For this reason, move the acpi_wmi_init() invocation to the
initcall_sync level which should still be early enough for things
to work correctly in the WMI land.

Link: https://marc.info/?t=151274596700002&r=1&w=2
Reported-by: Jonathan McDowell <noodles@xxxxxxxx>
Reported-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Tested-by: Jonathan McDowell <noodles@xxxxxxxx>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Signed-off-by: Darren Hart (VMware) <dvhart@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/platform/x86/wmi.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/platform/x86/wmi.c
+++ b/drivers/platform/x86/wmi.c
@@ -848,5 +848,5 @@ static void __exit acpi_wmi_exit(void)
 	pr_info("Mapper unloaded\n");
 }
 
-subsys_initcall(acpi_wmi_init);
+subsys_initcall_sync(acpi_wmi_init);
 module_exit(acpi_wmi_exit);