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

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Message-Id: <20171011165004.GA14318@linux.vnet.ibm.com>
Date:   Wed, 11 Oct 2017 09:50:04 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     David Howells <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, 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()

On Wed, Oct 11, 2017 at 06:12:20PM +0200, Peter Zijlstra wrote:
> On Wed, Oct 11, 2017 at 08:59:48AM -0700, Paul E. McKenney wrote:
> > On Wed, Oct 11, 2017 at 04:17:25PM +0100, David Howells wrote:
> > > I will, however, quibble with the appropriateness of the name READ_ONCE()...
> > > I still think it's not sufficiently obvious that this is a barrier and the
> > > barrier is after.  Maybe READ_AND_BARRIER()?
> > 
> > Linus was unhappy with READ_ONCE_CTRL() to tag control dependencies, but
> > indicated that he might consider it if it helped code-analysis tools.
> > Adding Dmitry Vyukov for his thoughts on whether tagging READ_ONCE()
> > for dependencies would help.  Me, I would suggest READ_ONCE_DEP(), but
> > let's figure out if the bikeshed needs to be painted before arguing over
> > the color.  ;-)
> 
> Count me one vote for the READ_ONCE() name. This is about dependent
> reads, which are nothing special on anything except Alpha.

Agreed, unless specially marking them makes it easier for tools to
find bugs.  In which case, we should definitely specially mark them.

							Thanx, Paul