linux-kernel - Re: [PATCH RFC tip/core/rcu 12/15] lib/assoc_array: Remove smp_read_barrier

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Message-ID: <7484.1507738025@warthog.procyon.org.uk>
Date:   Wed, 11 Oct 2017 17:07:05 +0100
From:   David Howells <dhowells@...hat.com>
To:     paulmck@...ux.vnet.ibm.com
Cc:     dhowells@...hat.com, Will Deacon <will.deacon@....com>,
        linux-kernel@...r.kernel.org, mingo@...nel.org,
        torvalds@...ux-foundation.org, mark.rutland@....com,
        linux-arch@...r.kernel.org, peterz@...radead.org,
        Jonathan Corbet <corbet@....net>,
        Alexander Kuleshov <kuleshovmail@...il.com>, dvyukov@...gle.com
Subject: Re: [PATCH RFC tip/core/rcu 12/15] lib/assoc_array: Remove smp_read_barrier_depends()

Paul E. McKenney <paulmck@...ux.vnet.ibm.com> wrote:

> It does not.  In most cases, the barriered version would be
> smp_store_release().

Ummm... Is that good enough?  Is:

	WRITE_ONCE(x, 1);
	WRITE_ONCE(x, 2);

equivalent to:

	smp_store_release(x, 1);
	smp_store_release(x, 2);

if CONFIG_SMP=n?

(Consider what happens if an interrupt messes with x).

If it is good enough, should we be using smp_load_acquire() rather than
READ_ONCE()?

David