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=-8.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 0A977C35254 for ; Mon, 17 Feb 2020 12:42:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D74FA20725 for ; Mon, 17 Feb 2020 12:42:50 +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="UlXbNpkn" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728436AbgBQMmt (ORCPT ); Mon, 17 Feb 2020 07:42:49 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:58714 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726401AbgBQMmt (ORCPT ); Mon, 17 Feb 2020 07:42:49 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.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=5zdmD/tRh0T6nvqIold9dp9SYMkW5fAoU/COsGQS5uY=; b=UlXbNpkn9WO4qTjaK0Bcl29DzL hkkUlQTzEUT5vD3E58v89R1iZFGtv5YftLLBoZKtSGGjzWV7d1jRbbf1kstbNXeTFgPgehp3VMfGR XPhVfx5TCVqC3zLV8PssFnYzKDkxD/aL+jywaq1ZJGDd5wn+dXkp6ywi2gPkx/lXw1D8QzbvH/vkK 5t9YDpl6Kp9q6LgOSK50n3qOgvfTxMeYEp8I3e6degkk6IpCFWCneSs/olW3vAGGg0UgjShq2RxLe q84bx6DjdvFvr9mINTuTi7IQRBfo4QMHJyEJ/H/0OZrTqH4HJD93hkujF5CAVPrF+StCocNFBgipF u1fmwfUw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1j3fjN-00069E-SD; Mon, 17 Feb 2020 12:42:34 +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 53B13300606; Mon, 17 Feb 2020 13:40:40 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id BAA902B782E23; Mon, 17 Feb 2020 13:42:31 +0100 (CET) Date: Mon, 17 Feb 2020 13:42:31 +0100 From: Peter Zijlstra To: paulmck@kernel.org Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com, 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 1/4] srcu: Fix __call_srcu()/process_srcu() datarace Message-ID: <20200217124231.GS14914@hirez.programming.kicks-ass.net> References: <20200215002907.GA15895@paulmck-ThinkPad-P72> <20200215002932.15976-1-paulmck@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200215002932.15976-1-paulmck@kernel.org> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Feb 14, 2020 at 04:29:29PM -0800, paulmck@kernel.org wrote: > From: "Paul E. McKenney" > > The srcu_node structure's ->srcu_gp_seq_needed_exp field is accessed > locklessly, so updates must use WRITE_ONCE(). This commit therefore > adds the needed WRITE_ONCE() invocations. > > This data race was reported by KCSAN. Not appropriate for backporting > due to failure being unlikely. This does indeed look like there can be a failure; but this Changelog fails to describe an actual problem. > Signed-off-by: Paul E. McKenney > --- > kernel/rcu/srcutree.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c > index 657e6a7..b1edac9 100644 > --- a/kernel/rcu/srcutree.c > +++ b/kernel/rcu/srcutree.c > @@ -550,7 +550,7 @@ static void srcu_gp_end(struct srcu_struct *ssp) > snp->srcu_have_cbs[idx] = gpseq; > rcu_seq_set_state(&snp->srcu_have_cbs[idx], 1); > if (ULONG_CMP_LT(snp->srcu_gp_seq_needed_exp, gpseq)) > - snp->srcu_gp_seq_needed_exp = gpseq; > + WRITE_ONCE(snp->srcu_gp_seq_needed_exp, gpseq); > mask = snp->srcu_data_have_cbs[idx]; > snp->srcu_data_have_cbs[idx] = 0; > spin_unlock_irq_rcu_node(snp); > @@ -660,7 +660,7 @@ static void srcu_funnel_gp_start(struct srcu_struct *ssp, struct srcu_data *sdp, > if (snp == sdp->mynode) > snp->srcu_data_have_cbs[idx] |= sdp->grpmask; > if (!do_norm && ULONG_CMP_LT(snp->srcu_gp_seq_needed_exp, s)) > - snp->srcu_gp_seq_needed_exp = s; > + WRITE_ONCE(snp->srcu_gp_seq_needed_exp, s); > spin_unlock_irqrestore_rcu_node(snp, flags); > } > > -- > 2.9.5 >