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[209.132.180.67]) by mx.google.com with ESMTP id l22si1854203edq.174.2019.10.03.10.42.44; Thu, 03 Oct 2019 10:43:09 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; dkim=pass header.i=@efficios.com header.s=default header.b=KiZHIewA; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=efficios.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390515AbfJCRVT (ORCPT + 99 others); Thu, 3 Oct 2019 13:21:19 -0400 Received: from mail.efficios.com ([167.114.142.138]:55856 "EHLO mail.efficios.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390269AbfJCRVR (ORCPT ); Thu, 3 Oct 2019 13:21:17 -0400 Received: from localhost (ip6-localhost [IPv6:::1]) by mail.efficios.com (Postfix) with ESMTP id 8A9DC33BACB; Thu, 3 Oct 2019 13:21:15 -0400 (EDT) Received: from mail.efficios.com ([IPv6:::1]) by localhost (mail02.efficios.com [IPv6:::1]) (amavisd-new, port 10032) with ESMTP id 15gIMQsNbnqv; Thu, 3 Oct 2019 13:21:15 -0400 (EDT) Received: from localhost (ip6-localhost [IPv6:::1]) by mail.efficios.com (Postfix) with ESMTP id 08C9D33BAC8; Thu, 3 Oct 2019 13:21:15 -0400 (EDT) DKIM-Filter: OpenDKIM Filter v2.10.3 mail.efficios.com 08C9D33BAC8 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=efficios.com; s=default; t=1570123275; bh=RLuzIee1S32NDi4Tv+0aI32L8zZ0nDhk1T9b8GhkcBU=; h=Date:From:To:Message-ID:MIME-Version; b=KiZHIewAlL06CJ7JpCxXFqL5RrUWK5SehDIJNvcvgZ8zwCv+okTZDaGMpSUVjva7H U0dk/rMmJQOoRtgn6rjBvlaTMK8eounJyjfSXQ8vAcRfOwy1ypI0IHGEOP1jkwxRGH xl2Cw+h6wkN0eFSjKc1aIHgtLBGtTziAT/OzhQMKeQFkq1i4+6BK7D0+54rd2Xymxk NB+C0uGM3L4/RBPQ23vn7E4g7VB//sLr4ChG49+f+gPwxJDuf+e5QIobaX0GDPlU2I JQBEHN/kw7+Nartp12oLzTODROjnM8xs3iHrRF9K+iJYf4zJFwTW0Tbwv2y7HSTRV4 UzL72JTBRfieA== X-Virus-Scanned: amavisd-new at efficios.com Received: from mail.efficios.com ([IPv6:::1]) by localhost (mail02.efficios.com [IPv6:::1]) (amavisd-new, port 10026) with ESMTP id P-qZ7VLaWfcd; Thu, 3 Oct 2019 13:21:14 -0400 (EDT) Received: from mail02.efficios.com (mail02.efficios.com [167.114.142.138]) by mail.efficios.com (Postfix) with ESMTP id DC88133BABF; Thu, 3 Oct 2019 13:21:14 -0400 (EDT) Date: Thu, 3 Oct 2019 13:21:14 -0400 (EDT) From: Mathieu Desnoyers To: paulmck 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 Message-ID: <618064891.1049.1570123274780.JavaMail.zimbra@efficios.com> In-Reply-To: <20191003165220.GZ2689@paulmck-ThinkPad-P72> References: <20191003014153.GA13156@paulmck-ThinkPad-P72> <20191003014310.13262-1-paulmck@kernel.org> <644598334.955.1570120530976.JavaMail.zimbra@efficios.com> <20191003165220.GZ2689@paulmck-ThinkPad-P72> Subject: Re: [PATCH tip/core/rcu 1/9] rcu: Upgrade rcu_swap_protected() to rcu_replace() MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Originating-IP: [167.114.142.138] X-Mailer: Zimbra 8.8.15_GA_3847 (ZimbraWebClient - FF69 (Linux)/8.8.15_GA_3847) Thread-Topic: Upgrade rcu_swap_protected() to rcu_replace() Thread-Index: 0tPV4uUWfCTmCxvYNNuRP6QBGE0Q/A== Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ----- On Oct 3, 2019, at 12:52 PM, paulmck paulmck@kernel.org wrote: > 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. Then considering that its assignment counterpart is "rcu_assign_pointer()" (and not "rcu_assign()"), would "rcu_replace_pointer()" be less ambiguous about its intended use ? Thanks, Mathieu > > 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 -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com