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=-6.9 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,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 48370C2BA12 for ; Thu, 2 Apr 2020 03:58:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0C8A220705 for ; Thu, 2 Apr 2020 03:58:23 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=joelfernandes.org header.i=@joelfernandes.org header.b="Pc/GApux" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387440AbgDBD6V (ORCPT ); Wed, 1 Apr 2020 23:58:21 -0400 Received: from mail-qt1-f195.google.com ([209.85.160.195]:37153 "EHLO mail-qt1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387444AbgDBD6T (ORCPT ); Wed, 1 Apr 2020 23:58:19 -0400 Received: by mail-qt1-f195.google.com with SMTP id z24so2236016qtu.4 for ; Wed, 01 Apr 2020 20:58:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=joelfernandes.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=FIyZcbBeG4NXJvMIHPgjJKueNZcgIVXv/zRU7nobAb0=; b=Pc/GApuxKxKJ4bznwNkN+CkN4TiVYXmSvMHqy3rRcc2gAFWoLbpnys6Er6Ql+hrGx5 uWA5/opZRWMsm0gpqLB6ENnw2y+J3UKL1HFFWzEO3kqeNAUHHgdpqPP23VSHgYl4JylN Vh7w3QiNKuKjVsCz12A9nX5Tl3VEfmxtkYzg8= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=FIyZcbBeG4NXJvMIHPgjJKueNZcgIVXv/zRU7nobAb0=; b=XGqsPxqdrWCV5rYVU+ZLq8ZCSZAyeWg5/EbSR+Zaw/vxba09CigRcICPAvjCjDB471 YUx14wVKPjDjObg6ocxK+tSZbQRWdzAY1RUHJHSBhoZAyw1GjCoaZ/72aygF7XbLYTgt Z0cS3FOLWQqmb/fDhuLkZdUyODwpQyFS4qzTtOOb0bad3Udtw0OAj+hPWzi+ET1s9hon jcb2+Hr2WUACEJmchb29zK791a44GM5tW25GL1Dm2YNh44cy/atQeF8v07K3bc+S+8aK IEiTJ+bni9mRrn4oK3ZiDTCdNb3fESOuMnQBY8iJjVNcw1qyUhOepkIEOW+tXEHhiYR4 4KJA== X-Gm-Message-State: AGi0Pub9Bc9yFCGi2jFWwAdG1Rq9Q3VDC4g4SiQvPqmpdj5R/2uhMSBH e4cHREpoWHkI3a9cP+rpuxGPpQ== X-Google-Smtp-Source: APiQypLI/ljsVswFPJHBN8JmhzhORetkqVNWwTsAxc6mCYlKhNGyM+vomCJUSXIada/n7ObMO2EvJw== X-Received: by 2002:ac8:33cd:: with SMTP id d13mr990302qtb.265.1585799897328; Wed, 01 Apr 2020 20:58:17 -0700 (PDT) Received: from localhost ([2620:15c:6:12:9c46:e0da:efbf:69cc]) by smtp.gmail.com with ESMTPSA id x74sm2833685qkb.40.2020.04.01.20.58.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 01 Apr 2020 20:58:16 -0700 (PDT) Date: Wed, 1 Apr 2020 23:58:16 -0400 From: Joel Fernandes To: Boqun Feng Cc: linux-kernel@vger.kernel.org, Alan Stern , 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 , linux-arch@vger.kernel.org, linux-doc@vger.kernel.org Subject: Re: [PATCH v4 0/4] Documentation/litmus-tests: Add litmus tests for atomic APIs Message-ID: <20200402035816.GA46686@google.com> References: <20200326024022.7566-1-boqun.feng@gmail.com> <20200327221843.GA226939@google.com> <20200331014037.GB59159@debian-boqun.qqnc3lrjykvubdpftowmye0fmh.lx.internal.cloudapp.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200331014037.GB59159@debian-boqun.qqnc3lrjykvubdpftowmye0fmh.lx.internal.cloudapp.net> Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Tue, Mar 31, 2020 at 09:40:37AM +0800, Boqun Feng wrote: > On Fri, Mar 27, 2020 at 06:18:43PM -0400, Joel Fernandes wrote: > > On Thu, Mar 26, 2020 at 10:40:18AM +0800, Boqun Feng wrote: > > > A recent discussion raises up the requirement for having test cases for > > > atomic APIs: > > > > > > https://lore.kernel.org/lkml/20200213085849.GL14897@hirez.programming.kicks-ass.net/ > > > > > > , and since we already have a way to generate a test module from a > > > litmus test with klitmus[1]. It makes sense that we add more litmus > > > tests for atomic APIs. And based on the previous discussion, I create a > > > new directory Documentation/atomic-tests and put these litmus tests > > > here. > > > > > > This patchset starts the work by adding the litmus tests which are > > > already used in atomic_t.txt, and also improve the atomic_t.txt to make > > > it consistent with the litmus tests. > > > > > > Previous version: > > > v1: https://lore.kernel.org/linux-doc/20200214040132.91934-1-boqun.feng@gmail.com/ > > > v2: https://lore.kernel.org/lkml/20200219062627.104736-1-boqun.feng@gmail.com/ > > > v3: https://lore.kernel.org/linux-doc/20200227004049.6853-1-boqun.feng@gmail.com/ > > > > For full series: > > > > Reviewed-by: Joel Fernandes (Google) > > > > One question I had was in the existing atomic_set() documentation, it talks > > about atomic_add_unless() implementation based on locking could have issues. > > It says the way to fix such cases is: > > > > Quote: > > the typical solution is to then implement atomic_set{}() with > > atomic_xchg(). > > > > I didn't get how using atomic_xchg() fixes it. Is the assumption there that > > atomic_xchg() would be implemented using locking to avoid atomic_set() having > > Right, I think that's the intent of the sentence. > > > issues? If so, we could clarify that in the document. > > > > Patches are welcome ;-) ---8<----------------------- Like this? I'll add it to my tree and send it to Paul during my next series, unless you disagree ;-) Subject: [PATCH] doc: atomic_t: Document better about the locking within atomic_xchg() It is not fully clear how the atomic_set() would not cause an issue with preservation of the atomicity of RMW in this example. Make it clear that locking within atomic_xchg() would save the day. Suggested-by: Boqun Feng Signed-off-by: Joel Fernandes (Google) --- Documentation/atomic_t.txt | 2 ++ 1 file changed, 2 insertions(+) diff --git a/Documentation/atomic_t.txt b/Documentation/atomic_t.txt index 0f1fdedf36bbb..1d9c307c73a7c 100644 --- a/Documentation/atomic_t.txt +++ b/Documentation/atomic_t.txt @@ -129,6 +129,8 @@ with a lock: unlock(); the typical solution is to then implement atomic_set{}() with atomic_xchg(). +The locking within the atomic_xchg() in CPU1 would ensure that the value read +in CPU0 would not be overwritten. RMW ops: -- 2.26.0.292.g33ef6b2f38-goog