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

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Message-ID: <CAHirt9gVqE=9vviJEY=kY=booVRmFPHrnFsKCXPXnXiWTB8bZQ@mail.gmail.com>
Date:   Tue, 1 Aug 2023 17:31:54 +0800
From:   WANG Rui <wangrui@...ngson.cn>
To:     Guo Ren <guoren@...nel.org>
Cc:     chenhuacai@...nel.or, kernel@...0n.name, arnd@...db.de,
        andi.shyti@...ux.intel.com, andrzej.hajda@...el.com,
        peterz@...radead.org, will@...nel.org, boqun.feng@...il.com,
        mark.rutland@....com, loongarch@...ts.linux.dev,
        linux-kernel@...r.kernel.org, Guo Ren <guoren@...ux.alibaba.com>
Subject: Re: [PATCH] LoongArch: Fixup cmpxchg sematic for memory barrier

Hello,

On Tue, Aug 1, 2023 at 5:05 PM Guo Ren <guoren@...nel.org> wrote:
>
> > The CoRR problem would cause wider problems than this.For this case,
> > do you mean your LL -> LL would be reordered?
> >
> > CPU 0
> >           CPU1
> > LL(2) (set ex-monitor)
> >
> >                 store (break the ex-monitor)
> > LL(1) (reordered instruction set ex-monitor
> > SC(3) (successes ?)
> Sorry for the mail client reformat, I mean:
>
> CPU0  LL(2) (set ex-monitor)
> CPU1  STORE (break the ex-monitor)
> CPU0  LL(1) (reordered instruction set ex-monitor
> CPU0  SC(3) (success?)

No. LL and LL won't reorder because LL implies a memory barrier(though
not acquire semantics).

Regards,
-- 
WANG Rui