Hi Wuqiang,
On Tue, Nov 21, 2023 at 10:23:43PM +0800, wuqiang.matt wrote:
> arch_cmpxchg() should check data size rather than pointer size in case
> CONFIG_ARC_HAS_LLSC is defined. So rename __cmpxchg to __cmpxchg_32 to
> emphasize it's explicit support of 32bit data size with BUILD_BUG_ON()
> added to avoid any possible misuses with unsupported data types.
>
> In case CONFIG_ARC_HAS_LLSC is undefined, arch_cmpxchg() uses spinlock
> to accomplish SMP-safety, so the BUILD_BUG_ON checking is uncecessary.
>
> v2 -> v3:
> - Patches regrouped and has the improvement for xtensa included
> - Comments refined to address why these changes are needed
>
> v1 -> v2:
> - Try using native cmpxchg variants if avaialble, as Arnd advised
>
> Signed-off-by: wuqiang.matt <wuqiang.m...@bytedance.com>
> Reviewed-by: Masami Hiramatsu (Google) <mhira...@kernel.org>
> ---
> arch/arc/include/asm/cmpxchg.h | 12 ++++++------
> 1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/arch/arc/include/asm/cmpxchg.h b/arch/arc/include/asm/cmpxchg.h
> index e138fde067de..bf46514f6f12 100644
> --- a/arch/arc/include/asm/cmpxchg.h
> +++ b/arch/arc/include/asm/cmpxchg.h
> @@ -18,14 +18,16 @@
> * if (*ptr == @old)
> * *ptr = @new
> */
> -#define __cmpxchg(ptr, old, new) \
> +#define __cmpxchg_32(ptr, old, new) \
> ({ \
> __typeof__(*(ptr)) _prev; \
> \
> + BUILD_BUG_ON(sizeof(*(ptr)) != 4); \
> + \
> __asm__ __volatile__( \
> - "1: llock %0, [%1] \n" \
> + "1: llock %0, [%1] \n" \
> " brne %0, %2, 2f \n" \
> - " scond %3, [%1] \n" \
> + " scond %3, [%1] \n" \
> " bnz 1b \n" \
> "2: \n" \
> : "=&r"(_prev) /* Early clobber prevent reg reuse */ \
> @@ -47,7 +49,7 @@
> \
> switch(sizeof((_p_))) { \
> case 4: \
> - _prev_ = __cmpxchg(_p_, _o_, _n_); \
> + _prev_ = __cmpxchg_32(_p_, _o_, _n_); \
> break; \
> default: \
> BUILD_BUG(); \
> @@ -65,8 +67,6 @@
> __typeof__(*(ptr)) _prev_; \
> unsigned long __flags; \
> \
> - BUILD_BUG_ON(sizeof(_p_) != 4); \
> - \
I think I made some comments here that have not been addressed or
replied.
Thanks,
Andi
> /* \
> * spin lock/unlock provide the needed smp_mb() before/after \
> */ \
> --
> 2.40.1
