[PATCH v2 0/1] Fix hmat_adist_nb for CXL

From: Alejandro Lucero <[email protected]>

 v2:
	- Add Fixes (Richarg Cheng)
	- Change commit as fix for Type2/Type3 (Richar Cheng)

RFC
===
While working on adding CXL Type2 support I found a problem with
register_mt_adistance_algorithm() which is used inside
cxl_region_probe(). It turns out my kernel config had not
CONFIG_MEMORY_HOTPLUG enabled leading to the hmat_adist_nb notifier
block deleted after kernel initialization without doing any notifer
block unregister, leaving the notifier chain unaware of this. A CXL
Type2 driver can be load after kernel initialization and with a kernel
not enabling memory hotplug, the notifier registration crashes if the
released memory from hmat_adist_nb is reused.

I'm not sure but I do not think this can happen for Type3 devices
because the related CXL driver is used only during kernel initialization
if memory hotplug not enabled. Type2, aka CXL accelerator drivers, is
coming and the problem will arise with certainty.

I have contemplated to modify how the identified __meminit and
__meminitdat are defined in linux/init.h, extending the case for being
empty definitions if CONFIG_CXL_MEM=y, but I think it makes sense to
only avoid the use of __meminit for hmat_adist_nb.

FWIW, a Type2 device should not require CONFIG_MEMORY_HOTPLUG and its
memory is currently initialized by the BIOS. Maybe not having memory
hotplug enabled is unusual and even more with CXL, so another option
could be to enable memory hotplug if CXL mem is enabled.

Alejandro Lucero (1):
  acpi/hmat: preserve hmat_adist_nb notifier block

 drivers/acpi/numa/hmat.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)


base-commit: 8cd9520d35a6c38db6567e97dd93b1f11f185dc6
-- 
2.34.1