[PATCH v3 3/3] mm/armv6: work around armv6 cmpxchg support issue

[Matthew Wilcox]

On Tue, Sep 01, 2020 at 02:30:51PM +0800, Alex Shi wrote:
> seems there are couples archs can not do cmpxchg1
> So update the patch here. And it's easy to fix if more arch issue find here.

> +/*
> + * cmpxchg only support 32-bits operands on the following archs ARMv6, SPARC32
> + * sh2, XTENSA.
> + */
> +#if defined(CONFIG_CPU_V6) || defined(CONFIG_CPU_SH2) || \
> +	defined(CONFIG_SPARC32) || defined(CONFIG_XTENSA)

Looks like we need a HAVE_CMPXCHG_BYTE in Kconfig to parallel
HAVE_CMPXCHG_DOUBLE.