linux-kernel - Re: [PATCH v2] atomics: fix atomic64_{read_acquire,set

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Date:   Sat, 5 Nov 2022 00:05:30 +0100 (CET)
From:   Thorsten Glaser <t.glaser@...ent.de>
To:     Mark Rutland <mark.rutland@....com>
cc:     linux-kernel@...r.kernel.org, ardb@...nel.org, arnd@...db.de,
        boqun.feng@...il.com, peterz@...radead.org, will@...nel.org
Subject: Re: [PATCH v2] atomics: fix atomic64_{read_acquire,set_release}
 fallbacks

On Thu, 3 Feb 2022, Mark Rutland wrote:

> -	smp_store_release(&(v)->counter, i);
> +	if (__native_word(atomic_t)) {
> +		smp_store_release(&(v)->counter, i);
> +	} else {
> +		__atomic_release_fence();
> +		arch_atomic_set(v, i);
> +	}

Shouldn’t this also update Documentation/atomic_t.txt which
currently states:

| The non-RMW ops are (typically) regular LOADs and STOREs and are canonically
| implemented using READ_ONCE(), WRITE_ONCE(), smp_load_acquire() and
| smp_store_release() respectively. Therefore, if you find yourself only using
| the Non-RMW operations of atomic_t, you do not in fact need atomic_t at all
| and are doing it wrong.

With this, direct use of atomic64_set_release() and atomic64_read_acquire()
is (IIUC) not “doing it wrong” any more?

bye,
//mirabilos
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