Re: Patch "ACPI: APEI: GHES: Disable KASAN instrumentation when compile testing with clang < 18" has been added to the 6.12-stable tree

[Sasha Levin <sashal@kernel.org>]

On Mon, Mar 09, 2026 at 02:28:07PM -0700, Nathan Chancellor wrote:
>On Sun, Mar 08, 2026 at 12:41:28PM -0400, Sasha Levin wrote:
>> This is a note to let you know that I've just added the patch titled
>>
>>     ACPI: APEI: GHES: Disable KASAN instrumentation when compile testing with clang < 18
>>
>> to the 6.12-stable tree which can be found at:
>>     http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
>>
>> The filename of the patch is:
>>      acpi-apei-ghes-disable-kasan-instrumentation-when-co.patch
>> and it can be found in the queue-6.12 subdirectory.
>>
>> If you, or anyone else, feels it should not be added to the stable tree,
>> please let <stable@vger.kernel.org> know about it.
>>
>>
>>
>> commit ccd3cab8095d5c53eaf8a6598ff339ffaad6a696
>> Author: Nathan Chancellor <nathan@kernel.org>
>> Date:   Wed Jan 14 16:27:11 2026 -0700
>>
>>     ACPI: APEI: GHES: Disable KASAN instrumentation when compile testing with clang < 18
>>
>>     [ Upstream commit b584bfbd7ec417f257f651cc00a90c66e31dfbf1 ]
>>
>>     After a recent innocuous change to drivers/acpi/apei/ghes.c, building
>>     ARCH=arm64 allmodconfig with clang-17 or older (which has both
>>     CONFIG_KASAN=y and CONFIG_WERROR=y) fails with:
>>
>>       drivers/acpi/apei/ghes.c:902:13: error: stack frame size (2768) exceeds limit (2048) in 'ghes_do_proc' [-Werror,-Wframe-larger-than]
>>         902 | static void ghes_do_proc(struct ghes *ghes,
>>             |             ^
>>
>>     A KASAN pass that removes unneeded stack instrumentation, enabled by
>>     default in clang-18 [1], drastically improves stack usage in this case.
>>
>>     To avoid the warning in the common allmodconfig case when it can break
>>     the build, disable KASAN for ghes.o when compile testing with clang-17
>>     and older. Disabling KASAN outright may hide legitimate runtime issues,
>>     so live with the warning in that case; the user can either increase the
>>     frame warning limit or disable -Werror, which they should probably do
>>     when debugging with KASAN anyways.
>>
>>     Closes: https://github.com/ClangBuiltLinux/linux/issues/2148
>>     Link: https://github.com/llvm/llvm-project/commit/51fbab134560ece663517bf1e8c2a30300d08f1a [1]
>>     Signed-off-by: Nathan Chancellor <nathan@kernel.org>
>>     Cc: All applicable <stable@vger.kernel.org>
>>     Link: https://patch.msgid.link/20260114-ghes-avoid-wflt-clang-older-than-18-v1-1-9c8248bfe4f4@kernel.org
>>     Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>>     Signed-off-by: Sasha Levin <sashal@kernel.org>
>>
>> diff --git a/drivers/acpi/apei/Makefile b/drivers/acpi/apei/Makefile
>> index 5db61dfb46915..1a0b85923cd42 100644
>> --- a/drivers/acpi/apei/Makefile
>> +++ b/drivers/acpi/apei/Makefile
>> @@ -1,6 +1,10 @@
>>  # SPDX-License-Identifier: GPL-2.0
>>  obj-$(CONFIG_ACPI_APEI)		+= apei.o
>>  obj-$(CONFIG_ACPI_APEI_GHES)	+= ghes.o
>> +# clang versions prior to 18 may blow out the stack with KASAN
>> +ifeq ($(CONFIG_COMPILE_TEST)_$(CONFIG_CC_IS_CLANG)_$(call clang-min-version, 180000),y_y_)
>> +KASAN_SANITIZE_ghes.o := n
>> +endif
>>  obj-$(CONFIG_ACPI_APEI_PCIEAER)	+= ghes_helpers.o
>>  obj-$(CONFIG_ACPI_APEI_EINJ)	+= einj.o
>>  einj-y				:= einj-core.o
>
>The backports you have taken to make this apply cleanly to 6.12
>
>  20260308164114.18890-1-sashal@kernel.org
>  20260308164118.18945-1-sashal@kernel.org
>  20260308164121.19006-1-sashal@kernel.org
>  20260308164125.19064-1-sashal@kernel.org
>
>are excessive in my opinion. I think you should just address the
>conflict... There is absolutely no dependency on those changes so
>"Stable-dep-of" is a bit misleading.

ack

-- 
Thanks,
Sasha