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=-8.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 02DBCC10F14 for ; Thu, 3 Oct 2019 16:52:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CD6242070B for ; Thu, 3 Oct 2019 16:52:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1570121546; bh=OUugZjslnsj6bkH8Kgibo54v4RZVPhAyJAsWjicMKWc=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=w+jTupuYHfkeLmzJ+eLx+H2BC7kD+JrzGcEk9AnWLagx7QDFqtE+GCcbGEaXqlqSK eOd0hc4+Nm6mnGA1C9gGk1U4wvB1xlrJRLrEiEnaLHXTKFlvQo6hrS03rvWz35mf9Q v7/rBCPfO7K6Cr9N+OUd15nKG+O7MeYrNWhMJft4= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2406182AbfJCQwZ (ORCPT ); Thu, 3 Oct 2019 12:52:25 -0400 Received: from mail.kernel.org ([198.145.29.99]:39992 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2406168AbfJCQwX (ORCPT ); Thu, 3 Oct 2019 12:52:23 -0400 Received: from paulmck-ThinkPad-P72 (50-39-105-78.bvtn.or.frontiernet.net [50.39.105.78]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 126022086A; Thu, 3 Oct 2019 16:52:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1570121542; bh=OUugZjslnsj6bkH8Kgibo54v4RZVPhAyJAsWjicMKWc=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=gXknnOx7unn5OX2+O0PII4w/o0Y6zfk6Sw2Pzd0mn64eTX/j6hX4Zf/O4Ws08jyOm KJ1JEmDOw4MY3Gwacm5ajON64GSO2MR5RRwK7Rx5BiznSUOQSrKlBjrlMVIVXsJ0/p Bi1KN9Ig1sCDE4iutxF7M9qBA7HiWRge3F5FLJTM= Date: Thu, 3 Oct 2019 09:52:20 -0700 From: "Paul E. McKenney" To: Mathieu Desnoyers Cc: rcu , linux-kernel , Ingo Molnar , Lai Jiangshan , dipankar , Andrew Morton , Josh Triplett , Thomas Gleixner , Peter Zijlstra , rostedt , David Howells , Eric Dumazet , fweisbec , Oleg Nesterov , "Joel Fernandes, Google" , Bart Van Assche , Christoph Hellwig , Hannes Reinecke , Johannes Thumshirn , Shane M Seymour , Martin Subject: Re: [PATCH tip/core/rcu 1/9] rcu: Upgrade rcu_swap_protected() to rcu_replace() Message-ID: <20191003165220.GZ2689@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20191003014153.GA13156@paulmck-ThinkPad-P72> <20191003014310.13262-1-paulmck@kernel.org> <644598334.955.1570120530976.JavaMail.zimbra@efficios.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <644598334.955.1570120530976.JavaMail.zimbra@efficios.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 03, 2019 at 12:35:30PM -0400, Mathieu Desnoyers wrote: > ----- On Oct 2, 2019, at 9:43 PM, paulmck paulmck@kernel.org wrote: > > > From: "Paul E. McKenney" > > > > Although the rcu_swap_protected() macro follows the example of swap(), > > the interactions with RCU make its update of its argument somewhat > > counter-intuitive. This commit therefore introduces an rcu_replace() > > that returns the old value of the RCU pointer instead of doing the > > argument update. Once all the uses of rcu_swap_protected() are updated > > to instead use rcu_replace(), rcu_swap_protected() will be removed. > > We expose the rcu_xchg_pointer() API in liburcu (Userspace RCU) project. > Any reason for not going that way and keep the kernel and user-space RCU > APIs alike ? > > It's of course fine if they diverge, but we might want to at least consider > if using the same API name would be OK. Different semantics. An rcu_xchg_pointer() allows concurrent updates, and rcu_replace() does not. But yes, if someone needs the concurrent updates, rcu_xchg_pointer() would certainly be my choice for the name. Thanx, Paul > Thanks, > > Mathieu > > > > > > Link: > > https://lore.kernel.org/lkml/CAHk-=wiAsJLw1egFEE=Z7-GGtM6wcvtyytXZA1+BHqta4gg6Hw@mail.gmail.com/ > > Reported-by: Linus Torvalds > > Signed-off-by: Paul E. McKenney > > Cc: Bart Van Assche > > Cc: Christoph Hellwig > > Cc: Hannes Reinecke > > Cc: Johannes Thumshirn > > Cc: Shane M Seymour > > Cc: Martin K. Petersen > > --- > > include/linux/rcupdate.h | 18 ++++++++++++++++++ > > 1 file changed, 18 insertions(+) > > > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h > > index 75a2ede..3b73287 100644 > > --- a/include/linux/rcupdate.h > > +++ b/include/linux/rcupdate.h > > @@ -383,6 +383,24 @@ do { \ > > } while (0) > > > > /** > > + * rcu_replace() - replace an RCU pointer, returning its old value > > + * @rcu_ptr: RCU pointer, whose old value is returned > > + * @ptr: regular pointer > > + * @c: the lockdep conditions under which the dereference will take place > > + * > > + * Perform a replacement, where @rcu_ptr is an RCU-annotated > > + * pointer and @c is the lockdep argument that is passed to the > > + * rcu_dereference_protected() call used to read that pointer. The old > > + * value of @rcu_ptr is returned, and @rcu_ptr is set to @ptr. > > + */ > > +#define rcu_replace(rcu_ptr, ptr, c) \ > > +({ \ > > + typeof(ptr) __tmp = rcu_dereference_protected((rcu_ptr), (c)); \ > > + rcu_assign_pointer((rcu_ptr), (ptr)); \ > > + __tmp; \ > > +}) > > + > > +/** > > * rcu_swap_protected() - swap an RCU and a regular pointer > > * @rcu_ptr: RCU pointer > > * @ptr: regular pointer > > -- > > 2.9.5 > > -- > Mathieu Desnoyers > EfficiOS Inc. > http://www.efficios.com