[PATCH v2] gpu: Fix uninitialized buddy for built-in drivers

[Koen Koning <koen.koning@linux.intel.com>]

Use subsys_initcall instead of module_init for the GPU buddy allocator,
so its initialization code runs before any gpu drivers.
Otherwise, a built-in driver that tries to use the buddy allocator will
run into a kernel NULL pointer dereference because slab_blocks is
uninitialized.

Specifically, this fixes drm/xe (as built-in) running into a kernel
panic during boot, because it uses buddy during device probe.

Fixes: ba110db8e1bc ("gpu: Move DRM buddy allocator one level up (part two)")
Cc: Joel Fernandes <joelagnelf@nvidia.com>
Cc: Dave Airlie <airlied@redhat.com>
Cc: intel-xe@lists.freedesktop.org
Cc: Peter Senna Tschudin <peter.senna@linux.intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Koen Koning <koen.koning@linux.intel.com>
---
v2: use subsys_initcall instead of relying on (fragile) Makefile ordering
    (suggested by Joel Fernandes <joelagnelf@nvidia.com>)
---
 drivers/gpu/buddy.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/buddy.c b/drivers/gpu/buddy.c
index 603c59a2013a..81f57fdf913b 100644
--- a/drivers/gpu/buddy.c
+++ b/drivers/gpu/buddy.c
@@ -1315,7 +1315,7 @@ static int __init gpu_buddy_module_init(void)
 	return 0;
 }

-module_init(gpu_buddy_module_init);
+subsys_initcall(gpu_buddy_module_init);
 module_exit(gpu_buddy_module_exit);

 MODULE_DESCRIPTION("GPU Buddy Allocator");
--
2.48.1