Re: [PATCH] LoongArch: Fixup cmpxchg sematic for memory barrier

[Guo Ren]

On Tue, Aug 1, 2023 at 12:37 PM WANG Rui <wangrui@xxxxxxxxxxx> wrote:
>
> On Tue, Aug 1, 2023 at 6:50 PM Guo Ren <guoren@xxxxxxxxxx> wrote:
> >
> > On Tue, Aug 1, 2023 at 5:32 PM WANG Rui <wangrui@xxxxxxxxxxx> wrote:
> > > No. LL and LL won't reorder because LL implies a memory barrier(though
> > > not acquire semantics).
> > That means we could remove __WEAK_LLSC_MB totally, right?
>
> More precisely, __WEAK_LLSC_MB is intended to prevent reordering
> between LL and normal LD used to fetch the expected value for cmpxchg.
Oh, that's unnecessary when cmpxchg fails.

Maybe you treat cmpxchg as a CoRR antidote in coincidence. Please
solve the CoRR problem by READ_ONCE.

See alpha architecture.

>
> Regards,
> --
> WANG Rui
>


-- 
Best Regards
 Guo Ren