From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 55095C3567B for ; Thu, 27 Feb 2020 16:32:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3718E246A1 for ; Thu, 27 Feb 2020 16:32:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730187AbgB0QcM (ORCPT ); Thu, 27 Feb 2020 11:32:12 -0500 Received: from iolanthe.rowland.org ([192.131.102.54]:38776 "HELO iolanthe.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1730015AbgB0QcM (ORCPT ); Thu, 27 Feb 2020 11:32:12 -0500 Received: (qmail 3316 invoked by uid 2102); 27 Feb 2020 11:32:11 -0500 Received: from localhost (sendmail-bs@127.0.0.1) by localhost with SMTP; 27 Feb 2020 11:32:11 -0500 Date: Thu, 27 Feb 2020 11:32:11 -0500 (EST) From: Alan Stern X-X-Sender: stern@iolanthe.rowland.org To: Boqun Feng cc: linux-kernel@vger.kernel.org, Andrea Parri , Will Deacon , Peter Zijlstra , Nicholas Piggin , David Howells , Jade Alglave , Luc Maranget , "Paul E. McKenney" , Akira Yokosawa , Daniel Lustig , Jonathan Corbet , Mauro Carvalho Chehab , "David S. Miller" , Rob Herring , Greg Kroah-Hartman , Jonathan Cameron , , Subject: Re: [PATCH v3 1/5] tools/memory-model: Add an exception for limitations on _unless() family In-Reply-To: <20200227004049.6853-2-boqun.feng@gmail.com> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 27 Feb 2020, Boqun Feng wrote: > According to Luc, atomic_add_unless() is directly provided by herd7, > therefore it can be used in litmus tests. So change the limitation > section in README to unlimit the use of atomic_add_unless(). Is this really true? Why does herd treat atomic_add_unless() different from all the other atomic RMS ops? All the other ones we support do have entries in linux-kernel.def. Alan PS: It seems strange to support atomic_add_unless but not atomic_long_add_unless. The difference between the two is trivial. > > Cc: Luc Maranget > Signed-off-by: Boqun Feng > --- > tools/memory-model/README | 10 +++++++--- > 1 file changed, 7 insertions(+), 3 deletions(-) > > diff --git a/tools/memory-model/README b/tools/memory-model/README > index fc07b52f2028..409211b1c544 100644 > --- a/tools/memory-model/README > +++ b/tools/memory-model/README > @@ -207,11 +207,15 @@ The Linux-kernel memory model (LKMM) has the following limitations: > case as a store release. > > b. The "unless" RMW operations are not currently modeled: > - atomic_long_add_unless(), atomic_add_unless(), > - atomic_inc_unless_negative(), and > - atomic_dec_unless_positive(). These can be emulated > + atomic_long_add_unless(), atomic_inc_unless_negative(), > + and atomic_dec_unless_positive(). These can be emulated > in litmus tests, for example, by using atomic_cmpxchg(). > > + One exception of this limitation is atomic_add_unless(), > + which is provided directly by herd7 (so no corresponding > + definition in linux-kernel.def). atomic_add_unless() is > + modeled by herd7 therefore it can be used in litmus tests. > + > c. The call_rcu() function is not modeled. It can be > emulated in litmus tests by adding another process that > invokes synchronize_rcu() and the body of the callback >