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 5A4BBC4332F for ; Thu, 3 Feb 2022 15:23:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235931AbiBCPXc (ORCPT ); Thu, 3 Feb 2022 10:23:32 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:43583 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1351856AbiBCPXb (ORCPT ); Thu, 3 Feb 2022 10:23:31 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1643901810; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=hSeQIZ/CtCE+d0vB+jizfse1LNxVSYoWhLdejmi7nC0=; b=RrP7Oz/LWFR9TSQrEfVSKMwBJWTgkrMqccWJRXCBVmkGCxiOF7P8V2SiualnRvbCvyrdqm IlVWY9xWOPqvY3AvGyoEVpfbc5drckvKtw3MMaAJ4pcgyo9/LCRb+8PPrN7pt4fC50J0Ls m37j2OlDVtubtWzXZv1V0KIxm3HqQ5I= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-158-7Tkyf_ElOHip_BSdOCUVyA-1; Thu, 03 Feb 2022 10:23:27 -0500 X-MC-Unique: 7Tkyf_ElOHip_BSdOCUVyA-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id A065583DB83; Thu, 3 Feb 2022 15:23:25 +0000 (UTC) Received: from lorien.usersys.redhat.com (unknown [10.22.32.210]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 8373384A3C; Thu, 3 Feb 2022 15:23:24 +0000 (UTC) Date: Thu, 3 Feb 2022 10:23:22 -0500 From: Phil Auld To: Waiman Long Cc: Tejun Heo , Zefan Li , Johannes Weiner , cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] cgroup/cpuset: Fix "suspicious RCU usage" lockdep warning Message-ID: References: <20220203033103.773030-1-longman@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220203033103.773030-1-longman@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 02, 2022 at 10:31:03PM -0500 Waiman Long wrote: > It was found that a "suspicious RCU usage" lockdep warning was issued > with the rcu_read_lock() call in update_sibling_cpumasks(). It is > because the update_cpumasks_hier() function may sleep. So we have > to release the RCU lock, call update_cpumasks_hier() and reacquire > it afterward. > > Also add a percpu_rwsem_assert_held() in update_sibling_cpumasks() > instead of stating that in the comment. > > Fixes: 4716909cc5c5 ("cpuset: Track cpusets that use parent's effective_cpus") > Signed-off-by: Waiman Long > --- > kernel/cgroup/cpuset.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c > index dc653ab26e50..b147acece984 100644 > --- a/kernel/cgroup/cpuset.c > +++ b/kernel/cgroup/cpuset.c > @@ -1522,10 +1522,15 @@ static void update_sibling_cpumasks(struct cpuset *parent, struct cpuset *cs, > struct cpuset *sibling; > struct cgroup_subsys_state *pos_css; > > + percpu_rwsem_assert_held(&cpuset_rwsem); > + > /* > * Check all its siblings and call update_cpumasks_hier() > * if their use_parent_ecpus flag is set in order for them > * to use the right effective_cpus value. > + * > + * The update_cpumasks_hier() function may sleep. So we have to > + * release the RCU read lock before calling it. > */ > rcu_read_lock(); > cpuset_for_each_child(sibling, pos_css, parent) { > @@ -1533,8 +1538,13 @@ static void update_sibling_cpumasks(struct cpuset *parent, struct cpuset *cs, > continue; > if (!sibling->use_parent_ecpus) > continue; > + if (!css_tryget_online(&sibling->css)) > + continue; > > + rcu_read_unlock(); > update_cpumasks_hier(sibling, tmp); > + rcu_read_lock(); > + css_put(&sibling->css); > } > rcu_read_unlock(); > } > -- > 2.27.0 > This looks good. Thanks Waiman. Tested-by: Phil Auld Reviewed-by: Phil Auld Cheers, Phil --