[PATCH v3 1/2] kasan/hw-tags: introduce kasan.write_only option

[kernel test robot]

Hi Yeoreum,

kernel test robot noticed the following build warnings:

[auto build test WARNING on 8f5ae30d69d7543eee0d70083daf4de8fe15d585]

url:    https://github.com/intel-lab-lkp/linux/commits/Yeoreum-Yun/kasan-hw-tags-introduce-kasan-write_only-option/20250816-190300
base:   8f5ae30d69d7543eee0d70083daf4de8fe15d585
patch link:    https://lore.kernel.org/r/20250816110018.4055617-2-yeoreum.yun%40arm.com
patch subject: [PATCH v3 1/2] kasan/hw-tags: introduce kasan.write_only option
config: arm64-randconfig-r053-20250818 (https://download.01.org/0day-ci/archive/20250818/202508180747.PxkbPnyA-lkp@intel.com/config)
compiler: aarch64-linux-gcc (GCC) 10.5.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250818/202508180747.PxkbPnyA-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 at intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202508180747.PxkbPnyA-lkp@intel.com/

All warnings (new ones prefixed by >>):

   mm/kasan/hw_tags.c: In function 'kasan_enable_hw_tags':
>> mm/kasan/hw_tags.c:433:21: warning: comparison between 'enum kasan_arg_mode' and 'enum kasan_arg_write_only' [-Wenum-compare]
     433 |  if (kasan_arg_mode == KASAN_ARG_WRITE_ONLY_ON &&
         |                     ^~
   mm/kasan/hw_tags.c:435:18: warning: comparison between 'enum kasan_arg_mode' and 'enum kasan_arg_write_only' [-Wenum-compare]
     435 |   kasan_arg_mode == KASAN_ARG_WRITE_ONLY_OFF;
         |                  ^~
>> mm/kasan/hw_tags.c:435:18: warning: statement with no effect [-Wunused-value]
     435 |   kasan_arg_mode == KASAN_ARG_WRITE_ONLY_OFF;
         |   ~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~


vim +433 mm/kasan/hw_tags.c

   423	
   424	void kasan_enable_hw_tags(void)
   425	{
   426		if (kasan_arg_mode == KASAN_ARG_MODE_ASYNC)
   427			hw_enable_tag_checks_async();
   428		else if (kasan_arg_mode == KASAN_ARG_MODE_ASYMM)
   429			hw_enable_tag_checks_asymm();
   430		else
   431			hw_enable_tag_checks_sync();
   432	
 > 433		if (kasan_arg_mode == KASAN_ARG_WRITE_ONLY_ON &&
   434		    hw_enable_tag_checks_write_only()) {
 > 435			kasan_arg_mode == KASAN_ARG_WRITE_ONLY_OFF;
   436			kasan_flag_write_only = false;
   437			pr_warn_once("System doesn't support write-only option. Disable it\n");
   438		}
   439	}
   440	

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