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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 748AEC4332F for ; Sat, 31 Dec 2022 18:25:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235775AbiLaSZa (ORCPT ); Sat, 31 Dec 2022 13:25:30 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44782 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235696AbiLaSZO (ORCPT ); Sat, 31 Dec 2022 13:25:14 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 23AF1E9E; Sat, 31 Dec 2022 10:25:14 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id D9100B801BE; Sat, 31 Dec 2022 18:25:12 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 20EE7C433EF; Sat, 31 Dec 2022 18:25:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1672511111; bh=untildj83gdrgB5eLYPyziJwlrL6AaeJlm/kfFmc2ic=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=KIudxlN2FVqrOCypw/GjiUwwY3a8EWMrt/HQYJ67m4zPJtWA5+gDXiggXYHPZR1Ci d0azq3JnJmVaAl9wev3f1beNoOrsSW8obW5+P+q+/htvxNaXZtcYVY41/YcdEKIA5k xI1TMTR88OpEX1kndD06ycmuy4Slg2kUOeVeo50qhNGn91oh2cUGOyJ+UTk4T9N+84 mLPF6rOb7HUcfUU4orqMfzpw8urPXdoDtdWRPtEfQLHw5AD/SHa6dLc5MEQ2BuM6tI rnfNPnw1eSMOGOa+3oKNK1WLVgyXf29UDUluJG2O8XoEsNSv4dMjdngJR2+xpT+u6W OqsoWp+X72lig== Date: Sat, 31 Dec 2022 19:25:08 +0100 From: Frederic Weisbecker To: "Paul E. McKenney" Cc: Zqiang , quic_neeraju@quicinc.com, joel@joelfernandes.org, rcu@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] rcu: Fix race in set and clear TICK_DEP_BIT_RCU_EXP bitmask Message-ID: <20221231182508.GB205110@lothringen> References: <20221220112520.3596920-1-qiang1.zhang@intel.com> <20221221200849.GG4001@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221221200849.GG4001@paulmck-ThinkPad-P17-Gen-1> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Dec 21, 2022 at 12:08:49PM -0800, Paul E. McKenney wrote: > diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h > index 249c2967d9e6c..7cc4856da0817 100644 > --- a/kernel/rcu/tree_exp.h > +++ b/kernel/rcu/tree_exp.h > @@ -594,6 +594,7 @@ static void synchronize_rcu_expedited_wait(void) > struct rcu_data *rdp; > struct rcu_node *rnp; > struct rcu_node *rnp_root = rcu_get_root(); > + unsigned long flags; > > trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("startwait")); > jiffies_stall = rcu_exp_jiffies_till_stall_check(); > @@ -602,17 +603,17 @@ static void synchronize_rcu_expedited_wait(void) > if (synchronize_rcu_expedited_wait_once(1)) > return; > rcu_for_each_leaf_node(rnp) { > + raw_spin_lock_irqsave_rcu_node(rnp, flags); > mask = READ_ONCE(rnp->expmask); > for_each_leaf_node_cpu_mask(rnp, cpu, mask) { > rdp = per_cpu_ptr(&rcu_data, cpu); > if (rdp->rcu_forced_tick_exp) > continue; > rdp->rcu_forced_tick_exp = true; > - preempt_disable(); > if (cpu_online(cpu)) > tick_dep_set_cpu(cpu, TICK_DEP_BIT_RCU_EXP); > - preempt_enable(); > } > + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); > } > j = READ_ONCE(jiffies_till_first_fqs); > if (synchronize_rcu_expedited_wait_once(j + HZ)) Reviewed-by: Frederic Weisbecker BTW why are we forcing the tick on the whole node? And shouldn't we set the tick dependency from rcu_exp_handler() instead? Thanks.