Re: [PATCH bpf-next] locking/atomic: arc, hexagon, openrisc: Define arch_cmpxchg_local()

["Alexei Starovoitov" <alexei.starovoitov@gmail.com>]

On Sun Oct 18, 2026 at 1:29 PM UTC, Sasha Levin wrote:
> Commit ccb88db8dac8 ("bpf: Don't hand out a linked element as extra
> element") made alloc_htab_elem() take the per-cpu spare element with
> try_cmpxchg_local(), the first caller of cmpxchg_local() outside of
> architecture code. It doesn't build on arc, hexagon and openrisc:
>
>   include/linux/atomic/atomic-arch-fallback.h:384:27: error: implicit declaration of function 'arch_cmpxchg_local'; did you mean 'raw_cmpxchg_local'? [-Werror=implicit-function-declaration]
>
> raw_cmpxchg_local() maps to arch_cmpxchg_local() unconditionally, but
> these three architectures don't define it, and unlike nios2 and
> microblaze they don't get it from asm-generic/cmpxchg.h either.
>
> cmpxchg_local() only has to be atomic with respect to the local CPU, so
> an architecture's own arch_cmpxchg() can serve for the sizes it
> supports. arc uses its relaxed LLOCK/SCOND variant when ARC_HAS_LLSC is
> set and its atomic_ops_lock() variant otherwise, and openrisc uses its
> LL/SC arch_cmpxchg(), the way arm64, riscv and s390 alias theirs. The
> hexagon arch_cmpxchg() only handles 32-bit words, so hexagon uses the
> generic version that disables interrupts, like sh, sparc32 and xtensa
> do. Linux has no NMIs on hexagon, so that is sufficient there.
>
> Fixes: ccb88db8dac8 ("bpf: Don't hand out a linked element as extra element")
> Reported-by: kernelci.org bot <bot@kernelci.org>
> Closes: https://d.kernelci.org/i/maestro:78b65519ee4561df1fbf1e72f1dec9da7e5b153e
> Reported-by: kernel test robot <lkp@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202610181750.BoqAddaF-lkp@intel.com/
> Closes: https://lore.kernel.org/oe-kbuild-all/202610182048.aEaiBP8W-lkp@intel.com/
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
> The only user is in bpf-next, so it is probably easiest to take this
> through bpf-next with acks from the arc, hexagon and openrisc
> maintainers. A similar change was posted in 2023 for objpool and
> stalled once objpool stopped using try_cmpxchg_local():
> https://lore.kernel.org/all/20231121142347.241356-1-wuqiang.matt@bytedance.com/
>
> Build tested on arc with and without LLSC (including both KernelCI
> configs), hexagon (clang) and openrisc.

Thanks for the quick fix. Applied.