Re: [PATCH v2 12/12] mm/kasan: make kasan=on|off take effect for all three modes

[Baoquan He <bhe@redhat.com>]

On 08/13/25 at 06:23pm, kernel test robot wrote:
> Hi Baoquan,
> 
> kernel test robot noticed the following build errors:
> 
> [auto build test ERROR on powerpc/next]
> [also build test ERROR on powerpc/fixes jcmvbkbc-xtensa/xtensa-for-next linus/master v6.17-rc1]
> [cannot apply to akpm-mm/mm-everything next-20250813]
> [If your patch is applied to the wrong git tree, kindly drop us a note.
> And when submitting patch, we suggest to use '--base' as documented in
> https://git-scm.com/docs/git-format-patch#_base_tree_information]
> 
> url:    https://github.com/intel-lab-lkp/linux/commits/Baoquan-He/mm-kasan-add-conditional-checks-in-functions-to-return-directly-if-kasan-is-disabled/20250812-205253
> base:   https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git next
> patch link:    https://lore.kernel.org/r/20250812124941.69508-13-bhe%40redhat.com
> patch subject: [PATCH v2 12/12] mm/kasan: make kasan=on|off take effect for all three modes
> config: um-randconfig-001-20250813 (https://download.01.org/0day-ci/archive/20250813/202508131826.n8gKkeXB-lkp@intel.com/config)
> compiler: gcc-12 (Debian 12.2.0-14+deb12u1) 12.2.0
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250813/202508131826.n8gKkeXB-lkp@intel.com/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@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202508131826.n8gKkeXB-lkp@intel.com/
> 
> All errors (new ones prefixed by >>):
> 
>    In file included from include/linux/static_key.h:1,
>                     from include/linux/alloc_tag.h:15,
>                     from include/linux/percpu.h:5,
>                     from include/linux/percpu_counter.h:14,
>                     from include/linux/mm_types.h:21,
>                     from include/linux/mmzone.h:22,
>                     from include/linux/gfp.h:7,
>                     from include/linux/umh.h:4,
>                     from include/linux/kmod.h:9,
>                     from include/linux/module.h:17,
>                     from arch/um/kernel/mem.c:7:
>    arch/um/kernel/mem.c: In function 'arch_mm_preinit':
> >> arch/um/kernel/mem.c:65:31: error: 'kasan_flag_enabled' undeclared (first use in this function); did you mean 'kasan_hw_tags_enabled'?
>       65 |         static_branch_enable(&kasan_flag_enabled);
>          |                               ^~~~~~~~~~~~~~~~~~

Thanks for reporting this error. I reproduced it and fix it with below
change. While this change should be appended into patch 11.

It's because CONFIG_KASAN is unset, the static key kasan_flag_enabled
enabling is added in arch_mm_preinit() which is not in CONFIG_KASAN scope.  
So here wrap it up within CONFIG_KASAN ifdeffery scope.

And also move the kasan_arg_disabled chekcing before kasan_flag_enabled
enabling because kasan_init() is called before main(). So in
kasan_init(), kernel parameter kasan=on|off hasn't been parsed.

diff --git a/arch/um/kernel/mem.c b/arch/um/kernel/mem.c
index d62f494e0808..2395ca33112a 100644
--- a/arch/um/kernel/mem.c
+++ b/arch/um/kernel/mem.c
@@ -26,9 +26,6 @@
 int kasan_um_is_ready;
 void kasan_init(void)
 {
-
-	if (kasan_arg_disabled)
-		return;
 	/*
 	 * kasan_map_memory will map all of the required address space and
 	 * the host machine will allocate physical memory as necessary.
@@ -65,8 +62,12 @@ static unsigned long brk_end;
 
 void __init arch_mm_preinit(void)
 {
+
+#ifdef CONFIG_KASAN
 	/* Safe to call after jump_label_init(). Enables KASAN. */
-	static_branch_enable(&kasan_flag_enabled);
+	if (!kasan_arg_disabled)
+		static_branch_enable(&kasan_flag_enabled);
+#endif
 
 	/* clear the zero-page */
 	memset(empty_zero_page, 0, PAGE_SIZE);