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

[Darren Hart <dvhart@infradead.org>]

commit 98b8e4e5c17bf87c1b18ed929472051dab39878c upstream
Please apply to 4.9.x and later stable kernel trees (this is as far back
as 86d9f48534e8 was applied).
This submission should have followed Option 1, but I failed to Cc:
stable in the original commit.

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@earth.li>
Reported-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Tested-by: Jonathan McDowell <noodles@earth.li>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>
---
 drivers/platform/x86/wmi.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/platform/x86/wmi.c b/drivers/platform/x86/wmi.c
index 791449a..daa68ac 100644
--- a/drivers/platform/x86/wmi.c
+++ b/drivers/platform/x86/wmi.c
@@ -1458,5 +1458,5 @@ static void __exit acpi_wmi_exit(void)
 	class_unregister(&wmi_bus_class);
 }
 
-subsys_initcall(acpi_wmi_init);
+subsys_initcall_sync(acpi_wmi_init);
 module_exit(acpi_wmi_exit);
-- 
2.9.4


-- 
Darren Hart
VMware Open Source Technology Center