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=-9.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham 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 D9EDBC2D0A3 for ; Tue, 3 Nov 2020 20:48:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 88CBD22447 for ; Tue, 3 Nov 2020 20:48:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604436518; bh=XpVGLq94+KKOiYrxhWttVWeedqtom3bFNP9WqutPqzg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=eYHdq6B4aP20M8nyxw6J8Y406id4Nyuf0Oo0th7vwT2xCnQ/1l+LJsN5oKr0Y8Pdv qH5zhbboOhicYSQ4Fbj1hDsQ2AqOhcuOGyIdb2vEAFzCOmlc1jGxlgciKB67bObUmi Rh3OqGCIl5Kn0sXGlueL3nS9OfmbUD/5ZmEsBfSk= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731551AbgKCUsg (ORCPT ); Tue, 3 Nov 2020 15:48:36 -0500 Received: from mail.kernel.org ([198.145.29.99]:40204 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731521AbgKCUsd (ORCPT ); Tue, 3 Nov 2020 15:48:33 -0500 Received: from localhost (83-86-74-64.cable.dynamic.v4.ziggo.nl [83.86.74.64]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id C2E7D22404; Tue, 3 Nov 2020 20:48:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604436512; bh=XpVGLq94+KKOiYrxhWttVWeedqtom3bFNP9WqutPqzg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=tbgb9COxxFf44OtXKjUetUeVpioJqWMkOex9+ecgqVEiQwEik5L9ITKPmQg8ePNxY 5ylGW2o2Vu3ph52KksEYK6oHl+80m2nXucFoucffxcEUI2nWkPct8DjCVmf8kgWleP haAOzuFC0e8MoflvVSYQk7Sa63wXSSnCuAsQZKT4= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Alexei Starovoitov , Daniel Borkmann , Jiri Olsa , bpf@vger.kernel.org, "Paul E. McKenney" Subject: [PATCH 5.9 282/391] rcu-tasks: Enclose task-list scan in rcu_read_lock() Date: Tue, 3 Nov 2020 21:35:33 +0100 Message-Id: <20201103203406.066176422@linuxfoundation.org> X-Mailer: git-send-email 2.29.2 In-Reply-To: <20201103203348.153465465@linuxfoundation.org> References: <20201103203348.153465465@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: Paul E. McKenney commit f747c7e15d7bc71a967a94ceda686cf2460b69e8 upstream. The rcu_tasks_trace_postgp() function uses for_each_process_thread() to scan the task list without the benefit of RCU read-side protection, which can result in use-after-free errors on task_struct structures. This error was missed because the TRACE01 rcutorture scenario enables lockdep, but also builds with CONFIG_PREEMPT_NONE=y. In this situation, preemption is disabled everywhere, so lockdep thinks everywhere can be a legitimate RCU reader. This commit therefore adds the needed rcu_read_lock() and rcu_read_unlock(). Note that this bug can occur only after an RCU Tasks Trace CPU stall warning, which by default only happens after a grace period has extended for ten minutes (yes, not a typo, minutes). Fixes: 4593e772b502 ("rcu-tasks: Add stall warnings for RCU Tasks Trace") Cc: Alexei Starovoitov Cc: Daniel Borkmann Cc: Jiri Olsa Cc: Cc: # 5.7.x Signed-off-by: Paul E. McKenney Signed-off-by: Greg Kroah-Hartman --- kernel/rcu/tasks.h | 2 ++ 1 file changed, 2 insertions(+) --- a/kernel/rcu/tasks.h +++ b/kernel/rcu/tasks.h @@ -1078,9 +1078,11 @@ static void rcu_tasks_trace_postgp(struc if (ret) break; // Count reached zero. // Stall warning time, so make a list of the offenders. + rcu_read_lock(); for_each_process_thread(g, t) if (READ_ONCE(t->trc_reader_special.b.need_qs)) trc_add_holdout(t, &holdouts); + rcu_read_unlock(); firstreport = true; list_for_each_entry_safe(t, g, &holdouts, trc_holdout_list) { if (READ_ONCE(t->trc_reader_special.b.need_qs))