linux-kernel - Re: [PATCH tip/core/rcu 1/4] doc: Present the role of READ

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Message-ID: <20201109162006.GJ3249@paulmck-ThinkPad-P72>
Date:   Mon, 9 Nov 2020 08:20:06 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     rcu@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...com, mingo@...nel.org, jiangshanlai@...il.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, rostedt@...dmis.org,
        dhowells@...hat.com, edumazet@...gle.com, fweisbec@...il.com,
        oleg@...hat.com, joel@...lfernandes.org
Subject: Re: [PATCH tip/core/rcu 1/4] doc: Present the role of READ_ONCE()

On Mon, Nov 09, 2020 at 01:21:33PM +0100, Peter Zijlstra wrote:
> On Thu, Nov 05, 2020 at 03:05:07PM -0800, paulmck@...nel.org wrote:
> > From: "Paul E. McKenney" <paulmck@...nel.org>
> > 
> > This commit adds an explanation of the special cases where READ_ONCE()
> > may be used in place of a member of the rcu_dereference() family.
> 
> I am confused, there is no actual difference between rcu_dereference()
> and READ_ONCE() today. So we _may_ use READ_ONCE() at all times.
> 
> Now granted, we probably don't want that, but that does leave me
> somewhat confused vs the wording here.

There is a difference from the viewpoint of both lockdep and sparse.

Or am I missing your point?

							Thanx, Paul