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=-2.1 required=3.0 tests=DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,T_DKIM_INVALID, URIBL_BLOCKED,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 58D92C43144 for ; Tue, 26 Jun 2018 19:21:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 003D226F27 for ; Tue, 26 Jun 2018 19:21:42 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="vjhjN/2b" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 003D226F27 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org 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 S1752409AbeFZTVk (ORCPT ); Tue, 26 Jun 2018 15:21:40 -0400 Received: from merlin.infradead.org ([205.233.59.134]:54858 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751409AbeFZTVj (ORCPT ); Tue, 26 Jun 2018 15:21:39 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=VUKUFhyaojLz/2g1FkYPnStlyJi5/TRWc1jk89XzZZM=; b=vjhjN/2brGJuVaLDeqh9UGhvJ 4NX+xuZrThHCak32reMvnVNqdt40i490TJ/OV25lfkbLECCOqi9eUf2ullRQTgh09/dULZo0/j62B zfwUjPIyL47QtRMtW73Y3SNGKpYUnrcKT1vfCGgRhFbMTh0VaAEe9/1hIcct+sNiMe/ZdOYfq8Px/ BCcuWLhofrZFElbhpj2zK8IcfZMSZyWwEf4rVZkbV/SJUzA5+MUmAKMf8inyAohWO3E0zcDTR9H1y yzULAHHFM8PiKaXOXtgBIfdBjnpCx2m2oIolAT4PT/pgEFGh8K5LUWCC91xVpwf+291nm2jBT6pBf sqVtWHf3Q==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1fXtWe-0005Ma-N5; Tue, 26 Jun 2018 19:21:17 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id DBDE62029FA0A; Tue, 26 Jun 2018 21:21:13 +0200 (CEST) Date: Tue, 26 Jun 2018 21:21:13 +0200 From: Peter Zijlstra To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org Subject: Re: [PATCH tip/core/rcu 16/27] rcu: Add comment documenting how rcu_seq_snap works Message-ID: <20180626192113.GM2494@hirez.programming.kicks-ass.net> References: <20180626003448.GA26209@linux.vnet.ibm.com> <20180626003513.27812-16-paulmck@linux.vnet.ibm.com> <20180626171454.GI2494@hirez.programming.kicks-ass.net> <20180626180855.GE3593@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180626180855.GE3593@linux.vnet.ibm.com> User-Agent: Mutt/1.10.0 (2018-05-17) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 26, 2018 at 11:08:55AM -0700, Paul E. McKenney wrote: > On Tue, Jun 26, 2018 at 07:14:54PM +0200, Peter Zijlstra wrote: > > On Mon, Jun 25, 2018 at 05:35:02PM -0700, Paul E. McKenney wrote: > > > From: "Joel Fernandes (Google)" > > > > > > rcu_seq_snap may be tricky to decipher. Lets document how it works with > > > an example to make it easier. > > > > Since you had me looking at them functions; why isn't rcu_seq_snap() > > using smp_load_acquire() and rcu_seq_end() using smp_store_release() ? > > Their respective comments seem to suggest that would be sufficent. > > I do not believe that this would suffice. Would it make sense to refer > to Documentation/RCU/Design/Memory-Ordering in the comment header? No, because I can't read that thing in an editor. > Except that this would invite sprinkling this pathname far and wide... > > The key point is that these functions are part of the any-to-any > memory-ordering guarantee that RCU grace periods provide. Then the existing comment is misleading and really needs change.