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=-2.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT autolearn=ham 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 BDFD8C6778A for ; Sat, 7 Jul 2018 19:54:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 69060208DB for ; Sat, 7 Jul 2018 19:54:52 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=amarulasolutions.com header.i=@amarulasolutions.com header.b="RcK0VYQ5" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 69060208DB Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=amarulasolutions.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754338AbeGGTys (ORCPT ); Sat, 7 Jul 2018 15:54:48 -0400 Received: from mail-wm0-f65.google.com ([74.125.82.65]:50887 "EHLO mail-wm0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754249AbeGGTyq (ORCPT ); Sat, 7 Jul 2018 15:54:46 -0400 Received: by mail-wm0-f65.google.com with SMTP id v25-v6so17647137wmc.0 for ; Sat, 07 Jul 2018 12:54:45 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amarulasolutions.com; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=gpBJCYDJFzqtJX3TLOV7ArANrDsOHqJFby7SpF5ExUE=; b=RcK0VYQ5KsvUhVna0w1W/G+uMu21VtuOFy4v+o51PzrkaARHgABkBGBXP1tPknsGLN PKe9sP7TEMHwIu58IL2ZV1JX6Ssv5w4728slmMrKc/0Eo7qqbKzN3i3Ei62Ol7r3GtuP 5HGj4cpR00/Xf3uRiWXypk3FXI9D9ibZ6lwxQ= 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:user-agent; bh=gpBJCYDJFzqtJX3TLOV7ArANrDsOHqJFby7SpF5ExUE=; b=Cjq7Ema7HyKw0XlmjvmlcPFGPNzp100mhdQLut+DGUe5s7VbEfn2Fe4yyrsZ3EcZr5 yZN4L7pJ3pRpz7BYfYADeQiO7Ld79G+ugKNT0woQfgMSVZqjZBfL2xJX34TnQNAPUSKA 67i8Txc9+QCGbgS5ainan1lHTUSmNeXMaITyuSEDoKL83NKTqIUjnMlTwZ/sb1GlW6N+ cFSushtIeAf/kr9cdyrVIPBeVootN8P8Hv+PLrWj8YZ7NGtGK26YrHL1cFrPv8EjLWuF HTCcqiOGWVQlVQbEIMTEh4xz+IJPHKcv5XV/+popwzu1SfxudAApJwPZZb00eCLpuKNL P6RQ== X-Gm-Message-State: APt69E2gyR0QPRcN6FTy0gu8zIZ7U63AQ37G5A2O/+UCM5wxgP+YChQz i7joausiesvkl4jVa6lm1q93OA== X-Google-Smtp-Source: AAOMgpeWgXBGwXGzwRMXAGLW/VDUp8loDdwNY3P2KahrHlymeK1h86k1ipiAAG7QOS+Jkcmk9H56zw== X-Received: by 2002:a1c:8e54:: with SMTP id q81-v6mr8545176wmd.135.1530993284907; Sat, 07 Jul 2018 12:54:44 -0700 (PDT) Received: from andrea ([94.230.152.15]) by smtp.gmail.com with ESMTPSA id f15-v6sm6206585wrr.10.2018.07.07.12.54.43 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sat, 07 Jul 2018 12:54:44 -0700 (PDT) Date: Sat, 7 Jul 2018 21:54:37 +0200 From: Andrea Parri To: Guo Ren Cc: Peter Zijlstra , linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, tglx@linutronix.de, daniel.lezcano@linaro.org, jason@lakedaemon.net, arnd@arndb.de, c-sky_gcc_upstream@c-sky.com, gnu-csky@mentor.com, thomas.petazzoni@bootlin.com, wbx@uclibc-ng.org, green.hu@gmail.com, Will Deacon Subject: Re: [PATCH V2 11/19] csky: Atomic operations Message-ID: <20180707195437.GA3225@andrea> References: <860b8db036b33d7b3648cb1f4ec827a53dc1a01b.1530465326.git.ren_guo@c-sky.com> <20180705175059.GE2530@hirez.programming.kicks-ass.net> <20180706110129.GC8707@guoren> <20180706115614.GV2476@hirez.programming.kicks-ass.net> <20180707074209.GA32147@guoren> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180707074209.GA32147@guoren> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Guo, On Sat, Jul 07, 2018 at 03:42:10PM +0800, Guo Ren wrote: > On Fri, Jul 06, 2018 at 01:56:14PM +0200, Peter Zijlstra wrote: > > CPU0 CPU1 > > > > r1 = READ_ONCE(x); WRITE_ONCE(y, 1); > > r2 = xchg(&y, 2); smp_store_release(&x, 1); > > > > must not allow: r1==1 && r2==0 > CPU1 smp_store_release could be finished before WRITE_ONCE, so r1=1 && > r2=0? The emphasis is on the "must": your implementation __must__ prevent this from happening (say, by inserting memory barriers in smp_store_release()); if your implementation allows the state (r1==1 && r2==0), then the imple- mentation is incorrect. I'd suggest you have a look at the Linux-kernel memory consistency model documentation and the associated tools, starting with: Documentation/memory-barriers.txt tools/memory-model/ (and please do not hesitate to ask questions about them, if something is unclear). Andrea