Re: [PATCH 1/3] x86/x2apic: disable x2apic on resume if the kernel expects so

[Shashank Balaji]

On Tue, Feb 03, 2026 at 06:31:40AM +0800, kernel test robot wrote:
> Hi Shashank,
> 
> kernel test robot noticed the following build errors:
> 
> [auto build test ERROR on 18f7fcd5e69a04df57b563360b88be72471d6b62]
> 
> url:    https://github.com/intel-lab-lkp/linux/commits/Shashank-Balaji/x86-x2apic-disable-x2apic-on-resume-if-the-kernel-expects-so/20260202-181147
> base:   18f7fcd5e69a04df57b563360b88be72471d6b62
> patch link:    https://lore.kernel.org/r/20260202-x2apic-fix-v1-1-71c8f488a88b%40sony.com
> patch subject: [PATCH 1/3] x86/x2apic: disable x2apic on resume if the kernel expects so
> config: i386-randconfig-001-20260202 (https://download.01.org/0day-ci/archive/20260203/202602030600.jFhsJyEC-lkp@xxxxxxxxx/config)
> compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260203/202602030600.jFhsJyEC-lkp@xxxxxxxxx/reproduce)
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@xxxxxxxxx>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202602030600.jFhsJyEC-lkp@xxxxxxxxx/
> 
> All errors (new ones prefixed by >>):
> 
> >> arch/x86/kernel/apic/apic.c:2463:3: error: call to undeclared function '__x2apic_disable'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
>     2463 |                 __x2apic_disable();
>          |                 ^
>    arch/x86/kernel/apic/apic.c:2463:3: note: did you mean '__x2apic_enable'?
>    arch/x86/kernel/apic/apic.c:1896:20: note: '__x2apic_enable' declared here
>     1896 | static inline void __x2apic_enable(void) { }
>          |                    ^
>    1 error generated.

This happens when CONFIG_X86_X2APIC is disabled. This patch fixes it,
which I'll include in v2:

diff --git i/arch/x86/kernel/apic/apic.c w/arch/x86/kernel/apic/apic.c
index 8820b631f8a2..06cce23b89c1 100644
--- i/arch/x86/kernel/apic/apic.c
+++ w/arch/x86/kernel/apic/apic.c
@@ -1894,6 +1894,7 @@ void __init check_x2apic(void)

 static inline void try_to_enable_x2apic(int remap_mode) { }
 static inline void __x2apic_enable(void) { }
+static inline void __x2apic_disable(void) {}
 #endif /* !CONFIG_X86_X2APIC */

 void __init enable_IR_x2apic(void)