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 D7F37C35272 for ; Mon, 7 Feb 2022 11:44:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1385376AbiBGLbk (ORCPT ); Mon, 7 Feb 2022 06:31:40 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60186 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1382631AbiBGLU0 (ORCPT ); Mon, 7 Feb 2022 06:20:26 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 87A62C03E94C; Mon, 7 Feb 2022 03:20:12 -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 dfw.source.kernel.org (Postfix) with ESMTPS id 25CF46126D; Mon, 7 Feb 2022 11:20:12 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id F36D3C004E1; Mon, 7 Feb 2022 11:20:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1644232811; bh=tB5ykpycoZ7rTEDHLWjtzHvL5qtmrfWQCoQ0Z7I1mNo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=wbaHFfLZXDwfg0EiY1gFWVzOJsJYbm3KcG0ne5nXFccgM0wx6uqu915I0FXoajjmX Jft6wDg4G9pNiGFkLMsPKz0JNjUeqcFn/WJxy+jPnwmNFTBvqPwUfQqXS9FlaoIhSO GUcQfcNXjG6x91d7eraTWGAaItkHQm7MHNVkOt0w= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Waiman Long , Phil Auld , Tejun Heo Subject: [PATCH 5.4 44/44] cgroup/cpuset: Fix "suspicious RCU usage" lockdep warning Date: Mon, 7 Feb 2022 12:07:00 +0100 Message-Id: <20220207103754.590640611@linuxfoundation.org> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20220207103753.155627314@linuxfoundation.org> References: <20220207103753.155627314@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Waiman Long commit 2bdfd2825c9662463371e6691b1a794e97fa36b4 upstream. 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 Tested-by: Phil Auld Reviewed-by: Phil Auld Signed-off-by: Tejun Heo Signed-off-by: Greg Kroah-Hartman --- kernel/cgroup/cpuset.c | 10 ++++++++++ 1 file changed, 10 insertions(+) --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -1473,10 +1473,15 @@ static void update_sibling_cpumasks(stru 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) { @@ -1484,8 +1489,13 @@ static void update_sibling_cpumasks(stru 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(); }