linux-kernel - Re: [PATCH] list: Prevent compiler reloads inside 'safe' list iteration

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Message-Id: <20200311195810.959d4f40d6013ee59a238cf3@linux-foundation.org>
Date:   Wed, 11 Mar 2020 19:58:10 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     paulmck@...nel.org
Cc:     David Laight <David.Laight@...LAB.COM>,
        "'Marco Elver'" <elver@...gle.com>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH] list: Prevent compiler reloads inside 'safe' list
 iteration

On Tue, 10 Mar 2020 08:47:49 -0700 "Paul E. McKenney" <paulmck@...nel.org> wrote:

> On Tue, Mar 10, 2020 at 03:05:57PM +0000, David Laight wrote:
> > From: Marco Elver
> > > Sent: 10 March 2020 14:10
> > ...
> > > FWIW, for writes we're already being quite generous, in that plain
> > > aligned writes up to word-size are assumed to be "atomic" with the
> > > default (conservative) config, i.e. marking such writes is optional.
> > > Although, that's a generous assumption that is not always guaranteed
> > > to hold (https://lore.kernel.org/lkml/20190821103200.kpufwtviqhpbuv2n@willie-the-truck/).
> > 
> > Remind me to start writing everything in assembler.
> 
> Been there, done that.  :-/
> 
> > That and to mark all structure members 'volatile'.
> 
> Indeed.  READ_ONCE() and WRITE_ONCE() get this same effect, but without
> pessimizing non-concurrent accesses to those same members.  Plus KCSAN
> knows about READ_ONCE(), WRITE_ONCE(), and also volatile members.
> 

So I take it from all the above that we should do this.

Did anyone actually review the code? :)