linux-kernel - Re: [PATCH doc] Emphasize that failed atomic operations give no ordering

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Message-ID: <5feeddda-f000-4b83-9981-e422c0d04881@paulmck-laptop>
Date: Tue, 30 Jan 2024 09:58:39 -0800
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Mark Rutland <mark.rutland@....com>
Cc: linux-kernel@...r.kernel.org,
	"E."@paulmck-thinkpad-p17-gen-1.smtp.subspace.kernel.org,
	Alan Stern <stern@...land.harvard.edu>,
	Andrea Parri <parri.andrea@...il.com>, Will Deacon <will@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Boqun Feng <boqun.feng@...il.com>,
	Nicholas Piggin <npiggin@...il.com>,
	David Howells <dhowells@...hat.com>,
	Jade Alglave <j.alglave@....ac.uk>,
	Luc Maranget <luc.maranget@...ia.fr>,
	Paul@...lmck-thinkpad-p17-gen-1.smtp.subspace.kernel.org,
	Akira Yokosawa <akiyks@...il.com>,
	Daniel Lustig <dlustig@...dia.com>,
	Joel Fernandes <joel@...lfernandes.org>,
	Jonathan Corbet <corbet@....net>, linux-arch@...r.kernel.org,
	linux-doc@...r.kernel.org,
	Anna-Maria Behnsen <anna-maria@...utronix.de>
Subject: Re: [PATCH doc] Emphasize that failed atomic operations give no
 ordering

On Tue, Jan 30, 2024 at 05:12:23PM +0000, Mark Rutland wrote:
> On Tue, Jan 30, 2024 at 06:53:38AM -0800, Paul E. McKenney wrote:
> > The ORDERING section of Documentation/atomic_t.txt can easily be read as
> > saying that conditional atomic RMW operations that fail are ordered when
> > those operations have the _acquire() or _release() prefixes.  This is
> > not the case, therefore update this section to make it clear that failed
> > conditional atomic RMW operations provide no ordering.
> > 
> > Reported-by: Anna-Maria Behnsen <anna-maria@...utronix.de>
> > Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
> > Cc: Alan Stern <stern@...land.harvard.edu>
> > Cc: Andrea Parri <parri.andrea@...il.com>
> > Cc: Will Deacon <will@...nel.org>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: Boqun Feng <boqun.feng@...il.com>
> > Cc: Nicholas Piggin <npiggin@...il.com>
> > Cc: David Howells <dhowells@...hat.com>
> > Cc: Jade Alglave <j.alglave@....ac.uk>
> > Cc: Luc Maranget <luc.maranget@...ia.fr>
> > Cc: "Paul E. McKenney" <paulmck@...nel.org>
> > Cc: Akira Yokosawa <akiyks@...il.com>
> > Cc: Daniel Lustig <dlustig@...dia.com>
> > Cc: Joel Fernandes <joel@...lfernandes.org>
> > Cc: Mark Rutland <mark.rutland@....com>
> > Cc: Jonathan Corbet <corbet@....net>
> > Cc: <linux-arch@...r.kernel.org>
> > Cc: <linux-doc@...r.kernel.org>
> > 
> > diff --git a/Documentation/atomic_t.txt b/Documentation/atomic_t.txt
> > index d7adc6d543db4..bee3b1bca9a7b 100644
> > --- a/Documentation/atomic_t.txt
> > +++ b/Documentation/atomic_t.txt
> > @@ -171,14 +171,14 @@ The rule of thumb:
> >   - RMW operations that are conditional are unordered on FAILURE,
> >     otherwise the above rules apply.
> >  
> > -Except of course when an operation has an explicit ordering like:
> > +Except of course when a successful operation has an explicit ordering like:
> >  
> >   {}_relaxed: unordered
> >   {}_acquire: the R of the RMW (or atomic_read) is an ACQUIRE
> >   {}_release: the W of the RMW (or atomic_set)  is a  RELEASE
> >  
> >  Where 'unordered' is against other memory locations. Address dependencies are
> > -not defeated.
> > +not defeated.  Conditional operations are still unordered on FAILURE.
> >  
> >  Fully ordered primitives are ordered against everything prior and everything
> >  subsequent. Therefore a fully ordered primitive is like having an smp_mb()
> > 
> 
> FWIW:
> 
> Acked-by: Mark Rutland <mark.rutland@....com>

Applied, thank you!

							Thanx, Paul