[PATCH v5 3/3] xtensa: Emulate two-byte cmpxchg

[Bradley Morgan]

On 6 October 2026 16:44:13 BST, "Paul E. McKenney" <paulmck at kernel.org>
wrote:
>On Tue, Oct 06, 2026 at 05:54:53PM +0800, kernel test robot wrote:
>> Hi Bradley,
>> 
>> kernel test robot noticed the following build errors:
>> 
>> [auto build test ERROR on akpm-mm/mm-everything]
>> [also build test ERROR on vgupta-arc/for-curr
>jcmvbkbc-xtensa/xtensa-for-next linus/master v7.3-rc6 next-20261005]
>> [cannot apply to vgupta-arc/for-next]
>> [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/Bradley-Morgan/ARC-Emulate-two-byte-cmpxchg/20261005-120658
>> base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git
>mm-everything
>> patch link:   
>https://lore.kernel.org/r/20261005120700.383058-4-brads%40mainlining.org
>> patch subject: [PATCH v5 3/3] xtensa: Emulate two-byte cmpxchg
>> config: xtensa-allyesconfig
>(https://download.01.org/0day-ci/archive/20261006/202610061704.rvbolgPy-lkp@intel.com/config)
>> compiler: xtensa-linux-gcc (GCC) 16.1.0
>> reproduce (this is a W=1 build):
>(https://download.01.org/0day-ci/archive/20261006/202610061704.rvbolgPy-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/202610061704.rvbolgPy-lkp@intel.com/
>> 
>> All errors (new ones prefixed by >>):
>
>These patches need to be applied on top of my -rcu tree's "dev" branch,
>which supplies cmpxchg_emu_u16().
>
>Nevertheless, thank you for your testing efforts!

Do you reckon they are fine to you? The patches?

Arch maintainers may be busy unfortunately :(, I've done testing on all
the arches, 

>
>							Thanx, Paul
>
>>    In file included from arch/xtensa/include/asm/atomic.h:19,
>>                     from include/linux/atomic.h:7,
>>                     from include/asm-generic/bitops/atomic.h:5,
>>                     from arch/xtensa/include/asm/bitops.h:192,
>>                     from include/linux/bitops.h:67,
>>                     from include/linux/log2.h:12,
>>                     from kernel/bounds.c:14:
>>    arch/xtensa/include/asm/cmpxchg.h: In function '__cmpxchg':
>> >> arch/xtensa/include/asm/cmpxchg.h:79:25: error: implicit declaration
>of function 'cmpxchg_emu_u16'; did you mean 'cmpxchg_emu_u8'?
>[-Wimplicit-function-declaration]
>>       79 |         case 2:  return cmpxchg_emu_u16(ptr, old, new);
>>          |                         ^~~~~~~~~~~~~~~
>>          |                         cmpxchg_emu_u8
>>    make[3]: *** [scripts/Makefile.build:185: kernel/bounds.s] Error 1
>>    make[3]: Target 'prepare' not remade because of errors.
>>    make[2]: *** [Makefile:1405: prepare0] Error 2
>>    make[2]: Target 'prepare' not remade because of errors.
>>    make[1]: *** [Makefile:248: __sub-make] Error 2
>>    make[1]: Target 'prepare' not remade because of errors.
>>    make: *** [Makefile:248: __sub-make] Error 2
>>    make: Target 'prepare' not remade because of errors.
>> 
>> 
>> vim +79 arch/xtensa/include/asm/cmpxchg.h
>> 
>>     73	
>>     74	static __inline__ unsigned long
>>     75	__cmpxchg(volatile void *ptr, unsigned long old, unsigned long new, int size)
>>     76	{
>>     77		switch (size) {
>>     78		case 1:  return cmpxchg_emu_u8(ptr, old, new);
>>   > 79		case 2:  return cmpxchg_emu_u16(ptr, old, new);
>>     80		case 4:  return __cmpxchg_u32(ptr, old, new);
>>     81		default: __cmpxchg_called_with_bad_pointer();
>>     82			 return old;
>>     83		}
>>     84	}
>>     85	
>> 
>> --
>> 0-DAY CI Kernel Test Service
>> https://github.com/intel/lkp-tests/wiki

--- Thanks!
"I'm not a very positive person" - Linus torvalds