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 42304C43334 for ; Tue, 19 Jul 2022 09:29:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237273AbiGSJ2e (ORCPT ); Tue, 19 Jul 2022 05:28:34 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58072 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237228AbiGSJ2M (ORCPT ); Tue, 19 Jul 2022 05:28:12 -0400 Received: from alexa-out-sd-02.qualcomm.com (alexa-out-sd-02.qualcomm.com [199.106.114.39]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 569F91FCE4; Tue, 19 Jul 2022 02:28:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=quicinc.com; i=@quicinc.com; q=dns/txt; s=qcdkim; t=1658222891; x=1689758891; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=leGrc9xXUuRzZfE+huco6T6eawpHA5+J1INEV2knv98=; b=P7RiMy/vpnP3YZyaU7zk8WfOA7rKxaNFjcxlbEOxsjdxQ2EcgCOcL3N4 ZeXxD++zP1+kSiJK9YSA5PJDrfD5JrFv9jczhLlgznMbX/iCHNfa6Mpcf WYICc1+J1GSzhvvLME8J2ndlz20wsaum1B5JFxUUzHiBHU49DGiJWmncK o=; Received: from unknown (HELO ironmsg03-sd.qualcomm.com) ([10.53.140.143]) by alexa-out-sd-02.qualcomm.com with ESMTP; 19 Jul 2022 02:28:11 -0700 X-QCInternal: smtphost Received: from nasanex01b.na.qualcomm.com ([10.46.141.250]) by ironmsg03-sd.qualcomm.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 19 Jul 2022 02:28:11 -0700 Received: from [10.50.41.193] (10.80.80.8) by nasanex01b.na.qualcomm.com (10.46.141.250) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.986.22; Tue, 19 Jul 2022 02:28:07 -0700 Message-ID: <5fff0b52-ae83-52ea-b606-1aa73def05aa@quicinc.com> Date: Tue, 19 Jul 2022 14:58:04 +0530 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.9.1 Subject: Re: [PATCH rcu 2/7] rcu/nocb: Invert rcu_state.barrier_mutex VS hotplug lock locking order Content-Language: en-US To: "Paul E. McKenney" , CC: , , , Zqiang , Boqun Feng , Uladzislau Rezki , Joel Fernandes , Frederic Weisbecker References: <20220620224455.GA3840881@paulmck-ThinkPad-P17-Gen-1> <20220620224503.3841196-2-paulmck@kernel.org> From: Neeraj Upadhyay In-Reply-To: <20220620224503.3841196-2-paulmck@kernel.org> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.80.80.8] X-ClientProxiedBy: nasanex01a.na.qualcomm.com (10.52.223.231) To nasanex01b.na.qualcomm.com (10.46.141.250) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 6/21/2022 4:14 AM, Paul E. McKenney wrote: > From: Zqiang > > In case of failure to spawn either rcuog or rcuo[p] kthreads for a given > rdp, rcu_nocb_rdp_deoffload() needs to be called with the hotplug > lock and the barrier_mutex held. However cpus write lock is already held > while calling rcutree_prepare_cpu(). It's not possible to call > rcu_nocb_rdp_deoffload() from there with just locking the barrier_mutex > or this would result in a locking inversion against > rcu_nocb_cpu_deoffload() which holds both locks in the reverse order. > > Simply solve this with inverting the locking order inside > rcu_nocb_cpu_[de]offload(). This will be a pre-requisite to toggle NOCB > states toward cpusets anyway. > > Signed-off-by: Zqiang > Cc: Neeraj Upadhyay > Cc: Boqun Feng > Cc: Uladzislau Rezki > Cc: Joel Fernandes > Signed-off-by: Frederic Weisbecker > Signed-off-by: Paul E. McKenney > --- Reviewed-by: Neeraj Upadhyay Thanks Neeraj > kernel/rcu/tree_nocb.h | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h > index dac74952e1d1b..f2f2cab6285a1 100644 > --- a/kernel/rcu/tree_nocb.h > +++ b/kernel/rcu/tree_nocb.h > @@ -1055,8 +1055,8 @@ int rcu_nocb_cpu_deoffload(int cpu) > struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); > int ret = 0; > > - mutex_lock(&rcu_state.barrier_mutex); > cpus_read_lock(); > + mutex_lock(&rcu_state.barrier_mutex); > if (rcu_rdp_is_offloaded(rdp)) { > if (cpu_online(cpu)) { > ret = work_on_cpu(cpu, rcu_nocb_rdp_deoffload, rdp); > @@ -1067,8 +1067,8 @@ int rcu_nocb_cpu_deoffload(int cpu) > ret = -EINVAL; > } > } > - cpus_read_unlock(); > mutex_unlock(&rcu_state.barrier_mutex); > + cpus_read_unlock(); > > return ret; > } > @@ -1134,8 +1134,8 @@ int rcu_nocb_cpu_offload(int cpu) > struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); > int ret = 0; > > - mutex_lock(&rcu_state.barrier_mutex); > cpus_read_lock(); > + mutex_lock(&rcu_state.barrier_mutex); > if (!rcu_rdp_is_offloaded(rdp)) { > if (cpu_online(cpu)) { > ret = work_on_cpu(cpu, rcu_nocb_rdp_offload, rdp); > @@ -1146,8 +1146,8 @@ int rcu_nocb_cpu_offload(int cpu) > ret = -EINVAL; > } > } > - cpus_read_unlock(); > mutex_unlock(&rcu_state.barrier_mutex); > + cpus_read_unlock(); > > return ret; > }