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=-3.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no 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 D8E7AC433E6 for ; Fri, 28 Aug 2020 08:30:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B07D620C56 for ; Fri, 28 Aug 2020 08:30:36 +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="Y+/niy0d" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728666AbgH1Iaf (ORCPT ); Fri, 28 Aug 2020 04:30:35 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56462 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728269AbgH1Iab (ORCPT ); Fri, 28 Aug 2020 04:30:31 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9E202C061264 for ; Fri, 28 Aug 2020 01:30:31 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.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; bh=U2ldR6xzPBv+6k+oJRaius2b5lZqMbGSNQquGmhHMdo=; b=Y+/niy0dQsqt6fTP2Sx45/kBCt 3KkQ61Loc0XLxreekumo+EctLcAD0TBEy4NDBhZXy+euo71i9lNlGHnci9scSvHI2R9TrWJdZ41Lo 2h0GgozNqHwl2Lwkn34LxCjwPEsr/w+C0o/yiRtkxuzsaDAQ+vflEWzDMyyxUZwD5QGCkV9Z+oklT hpNDukZiWBn+WFdOzzbaEqe6w2wXPbJDd0yaKk4oN/crMGhScvDtfvqyJvxxQ5wCEPfbbZRTAujNt HlXdGtcaKw47dosnDXTvlOiD6PzXChpyCOubdTkpb0SjADv0HrQ4trl8rwszd2QKYsrMdyFrWsXPX FtbeCQ3Q==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1kBZmB-00046c-0e; Fri, 28 Aug 2020 08:30:25 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 5C65A300238; Fri, 28 Aug 2020 10:30:22 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 42CFB2C5F134B; Fri, 28 Aug 2020 10:30:22 +0200 (CEST) Date: Fri, 28 Aug 2020 10:30:22 +0200 From: peterz@infradead.org To: "Ahmed S. Darwish" Cc: Ingo Molnar , Will Deacon , Thomas Gleixner , "Sebastian A. Siewior" , "Paul E. McKenney" , Steven Rostedt , LKML Subject: Re: [PATCH v1 3/5] seqlock: seqcount_t: Implement all read APIs as statement expressions Message-ID: <20200828083022.GO1362448@hirez.programming.kicks-ass.net> References: <20200519214547.352050-1-a.darwish@linutronix.de> <20200828010710.5407-1-a.darwish@linutronix.de> <20200828010710.5407-4-a.darwish@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200828010710.5407-4-a.darwish@linutronix.de> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 28, 2020 at 03:07:08AM +0200, Ahmed S. Darwish wrote: > #define __read_seqcount_begin(s) \ > +({ \ > + unsigned seq; \ > + \ > + do { \ > + seq = __seqcount_sequence(s); \ > + if (likely(! (seq & 1))) \ > + break; \ > + cpu_relax(); \ > + } while (true); \ > + \ > + kcsan_atomic_next(KCSAN_SEQLOCK_REGION_MAX); \ > + seq; \ > +}) Since we're there anyway, does it make sense to (re)write this like: while ((seq = __seqcount_sequence(s)) & 1) cpu_relax(); ?