linux-kernel - Re: [PATCH 2/6] locking/atomic/x86: Rewrite x86_32 arch_atomic64_{,fetch}

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Message-ID: <CAFULd4YM3ukFUst5ofMP8oz2gw8Spo_9A8UrAKHw_-dSyAwS7w@mail.gmail.com>
Date: Tue, 9 Apr 2024 18:53:30 +0200
From: Uros Bizjak <ubizjak@...il.com>
To: Mark Rutland <mark.rutland@....com>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, "H. Peter Anvin" <hpa@...or.com>, 
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 2/6] locking/atomic/x86: Rewrite x86_32
 arch_atomic64_{,fetch}_{and,or,xor}() functions

On Tue, Apr 9, 2024 at 6:34 PM Mark Rutland <mark.rutland@....com> wrote:

> > Something like this:
> >
> > --cut here--
> > /*
> >  * This function is intended to preload the value from atomic64_t
> >  * location in a non-atomic way. The read might be torn, but can
> >  * safely be consumed by the compare-and-swap loop.
> >  */
> > static __always_inline s64 arch_atomic64_read_tearable(atomic64_t *v)
> > {
> >     /*
> >      * See the comment in arch_atomic_read() on why we use
> >      * __READ_ONCE() instead of READ_ONCE_NOCHECK() here.
> >      */
> >     return __READ_ONCE(v->counter);
> > }
> > --cut here--
>
> Yeah, something of that shape.
>
> Having thought for a bit longer, it's probably better to use '_torn' rather
> than '_tearable' (i.e. name this arch_atomic64_read_torn()).

How about we simply name the function

arch_atomic64_read_nonatomic()

in the sense that it reads atomic64_t variables in a non-atomic way?

Uros.