linux-kernel - Re: [PATCH] tools/memory-model: remove rb-dep, smp_read_barrier_depends, and lockless

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Message-ID: <20180221165143.gf5hhhrddediubdx@gmail.com>
Date:   Wed, 21 Feb 2018 17:51:43 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:     Alan Stern <stern@...land.harvard.edu>,
        Andrea Parri <parri.andrea@...il.com>,
        Akira Yokosawa <akiyks@...il.com>,
        Kernel development list <linux-kernel@...r.kernel.org>,
        Will Deacon <will.deacon@....com>, peterz@...radead.org,
        boqun.feng@...il.com, npiggin@...il.com, dhowells@...hat.com,
        Jade Alglave <j.alglave@....ac.uk>,
        Luc Maranget <luc.maranget@...ia.fr>,
        Patrick Bellasi <patrick.bellasi@....com>
Subject: Re: [PATCH] tools/memory-model: remove rb-dep,
 smp_read_barrier_depends, and lockless_dereference


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

> On Wed, Feb 21, 2018 at 10:00:20AM -0500, Alan Stern wrote:
> > On Fri, 16 Feb 2018, Paul E. McKenney wrote:
> > 
> > > On Fri, Feb 16, 2018 at 05:22:55PM -0500, Alan Stern wrote:
> > > > Since commit 76ebbe78f739 ("locking/barriers: Add implicit
> > > > smp_read_barrier_depends() to READ_ONCE()") was merged for the 4.15
> > > > kernel, it has not been necessary to use smp_read_barrier_depends().
> > > > Similarly, commit 59ecbbe7b31c ("locking/barriers: Kill
> > > > lockless_dereference()") removed lockless_dereference() from the
> > > > kernel.
> > > > 
> > > > Since these primitives are no longer part of the kernel, they do not
> > > > belong in the Linux Kernel Memory Consistency Model.  This patch
> > > > removes them, along with the internal rb-dep relation, and updates the
> > > > revelant documentation.
> > > > 
> > > > Signed-off-by: Alan Stern <stern@...land.harvard.edu>
> > > 
> > > I queued this, but would welcome an update that addressed Akira's
> > > feedback as appropriate.
> > 
> > Is it too late to send a v2 of this patch?  I didn't want to do it 
> > before now because the issue raised by Andrea wasn't settled.  (Some 
> > could claim that it still isn't fully settled...)
> 
> Would you be willing to send a delta patch?  I can then place it directly
> on top of your original patch, and once it settles out, I can ask Ingo
> if he is willing to update the patch in -tip.

It would be better to have followup fixes as separate patches. I applied the 
current set of fixes/improvements today to help move things along - it's all 
advancing very nicely!

Thanks,

	Ingo