linux-kernel - Re: [PATCH] Documentation: atomic_t.txt: Explain ordering provided by smp_mb__{before,after}

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Message-Id: <20190429144956.GQ3923@linux.ibm.com>
Date:   Mon, 29 Apr 2019 07:49:56 -0700
From:   "Paul E. McKenney" <paulmck@...ux.ibm.com>
To:     Johan Hovold <johan@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Nicholas Piggin <npiggin@...il.com>,
        LKMM Maintainers -- Akira Yokosawa <akiyks@...il.com>,
        Andrea Parri <andrea.parri@...rulasolutions.com>,
        Boqun Feng <boqun.feng@...il.com>,
        David Howells <dhowells@...hat.com>,
        Daniel Lustig <dlustig@...dia.com>,
        Jade Alglave <j.alglave@....ac.uk>,
        Kernel development list <linux-kernel@...r.kernel.org>,
        Luc Maranget <luc.maranget@...ia.fr>,
        Alan Stern <stern@...land.harvard.edu>,
        Will Deacon <will.deacon@....com>
Subject: Re: [PATCH] Documentation: atomic_t.txt: Explain ordering provided
 by smp_mb__{before,after}_atomic()

On Mon, Apr 29, 2019 at 11:24:30AM +0200, Johan Hovold wrote:
> On Tue, Apr 23, 2019 at 06:30:10AM -0700, Paul E. McKenney wrote:
> > On Tue, Apr 23, 2019 at 02:32:09PM +0200, Peter Zijlstra wrote:
> > > On Sat, Apr 20, 2019 at 01:54:40AM -0700, Paul E. McKenney wrote:
> 
> > > > 	And lock acquisition??? acm_read_bulk_callback().
> > > 
> > > I think it goes with the set_bit() earlier, but what do I know.
> > 
> > Quite possibly!  In that case it should be smp_mb__after_atomic(),
> > and it would be nice if it immediately followed the set_bit().
> 
> I noticed this one last week as well. The set_bit() had been incorrectly
> moved and without noticing the smp_mb__before_atomic(). I've submitted a
> patch to restore it and to fix a related issue to due missing barriers:
> 
> 	https://lkml.kernel.org/r/20190425160540.10036-5-johan@kernel.org

Good to know, thank you!

							Thanx, Paul