Re: [PATCH v5 1/3] ARC: Emulate two-byte cmpxchg

From: kernel test robot <lkp@intel.com>
To: Bradley Morgan <brads@mainlining.org>,
	akpm@linux-foundation.org, vgupta@kernel.org, guoren@kernel.org,
	chris@zankel.net, jcmvbkbc@gmail.com
Cc: oe-kbuild-all@lists.linux.dev, arnd@arndb.de, paulmck@kernel.org,
	david.laight.linux@gmail.com, glaubitz@physik.fu-berlin.de,
	ysato@users.sourceforge.jp, dalias@libc.org,
	linux-snps-arc@lists.infradead.org, linux-csky@vger.kernel.org,
	linux-kernel@vger.kernel.org, brads@mainlining.org
Subject: Re: [PATCH v5 1/3] ARC: Emulate two-byte cmpxchg
Date: Tue, 6 Oct 2026 17:55:38 +0800	[thread overview]
Message-ID: <202610061706.jjwf7ggl-lkp@intel.com> (raw)
In-Reply-To: <20261005120700.383058-2-brads@mainlining.org>

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/20261005120700.383058-2-brads%40mainlining.org
patch subject: [PATCH v5 1/3] ARC: Emulate two-byte cmpxchg
config: arc-allyesconfig (https://download.01.org/0day-ci/archive/20261006/202610061706.jjwf7ggl-lkp@intel.com/config)
compiler: arc-linux-gcc (GCC) 16.1.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20261006/202610061706.jjwf7ggl-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/202610061706.jjwf7ggl-lkp@intel.com/

All errors (new ones prefixed by >>):

   In file included from arch/arc/include/asm/atomic.h:13,
                    from include/linux/atomic.h:7,
                    from include/asm-generic/bitops/lock.h:5,
                    from arch/arc/include/asm/bitops.h:190,
                    from include/linux/bitops.h:67,
                    from include/linux/log2.h:12,
                    from kernel/bounds.c:14:
   include/linux/atomic/atomic-arch-fallback.h: In function 'raw_atomic_cmpxchg':
>> arch/arc/include/asm/cmpxchg.h:54:46: error: implicit declaration of function 'cmpxchg_emu_u16'; did you mean 'cmpxchg_emu_u8'? [-Wimplicit-function-declaration]
      54 |                 _prev_ = (__typeof__(*(ptr)))cmpxchg_emu_u16((volatile u16 *__force)_p_, (unsigned long)_o_, (unsigned long)_n_);       \
         |                                              ^~~~~~~~~~~~~~~
   include/linux/atomic.h:73:16: note: in expansion of macro 'arch_cmpxchg_relaxed'
      73 |         typeof(op##_relaxed(args)) __ret;                               \
         |                ^~
   include/linux/atomic/atomic-arch-fallback.h:58:9: note: in expansion of macro '__atomic_op_fence'
      58 |         __atomic_op_fence(arch_cmpxchg, __VA_ARGS__)
         |         ^~~~~~~~~~~~~~~~~
   include/linux/atomic/atomic-arch-fallback.h:2026:16: note: in expansion of macro 'raw_cmpxchg'
    2026 |         return raw_cmpxchg(&v->counter, old, new);
         |                ^~~~~~~~~~~
   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 +54 arch/arc/include/asm/cmpxchg.h

    41	
    42	#define arch_cmpxchg_relaxed(ptr, old, new)				\
    43	({									\
    44		__typeof__(ptr) _p_ = (ptr);					\
    45		__typeof__(*(ptr)) _o_ = (old);					\
    46		__typeof__(*(ptr)) _n_ = (new);					\
    47		__typeof__(*(ptr)) _prev_;					\
    48										\
    49		switch (sizeof(*(_p_))) {						\
    50		case 1:								\
    51			_prev_ = (__typeof__(*(ptr)))cmpxchg_emu_u8((volatile u8 *__force)_p_, (uintptr_t)_o_, (uintptr_t)_n_);	\
    52			break;							\
    53		case 2:								\
  > 54			_prev_ = (__typeof__(*(ptr)))cmpxchg_emu_u16((volatile u16 *__force)_p_, (unsigned long)_o_, (unsigned long)_n_);	\
    55			break;							\
    56		case 4:								\
    57			_prev_ = __cmpxchg(_p_, _o_, _n_);			\
    58			break;							\
    59		default:							\
    60			BUILD_BUG();						\
    61		}								\
    62		_prev_;								\
    63	})
    64	

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