From patchwork Wed May 18 22:53:52 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Eric W. Biederman" X-Patchwork-Id: 574089 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 D788AC43217 for ; Wed, 18 May 2022 22:57:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230245AbiERW5y (ORCPT ); Wed, 18 May 2022 18:57:54 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39980 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230523AbiERWzf (ORCPT ); Wed, 18 May 2022 18:55:35 -0400 Received: from out02.mta.xmission.com (out02.mta.xmission.com [166.70.13.232]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D9C2922DA2A; Wed, 18 May 2022 15:55:14 -0700 (PDT) Received: from in01.mta.xmission.com ([166.70.13.51]:55520) by out02.mta.xmission.com with esmtps (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1nrSZV-003bfZ-Um; Wed, 18 May 2022 16:55:13 -0600 Received: from ip68-227-174-4.om.om.cox.net ([68.227.174.4]:38724 helo=localhost.localdomain) by in01.mta.xmission.com with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1nrSZU-002Z0O-Ps; Wed, 18 May 2022 16:55:13 -0600 From: "Eric W. Biederman" To: linux-kernel@vger.kernel.org Cc: rjw@rjwysocki.net, Oleg Nesterov , mingo@kernel.org, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, mgorman@suse.de, bigeasy@linutronix.de, Will Deacon , tj@kernel.org, linux-pm@vger.kernel.org, Peter Zijlstra , Richard Weinberger , Anton Ivanov , Johannes Berg , linux-um@lists.infradead.org, Chris Zankel , Max Filippov , linux-xtensa@linux-xtensa.org, Kees Cook , Jann Horn , linux-ia64@vger.kernel.org, Robert OCallahan , Kyle Huey , Richard Henderson , Ivan Kokshaysky , Matt Turner , Jason Wessel , Daniel Thompson , Douglas Anderson , Douglas Miller , Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , "Eric W. Biederman" Date: Wed, 18 May 2022 17:53:52 -0500 Message-Id: <20220518225355.784371-13-ebiederm@xmission.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <871qwq5ucx.fsf_-_@email.froward.int.ebiederm.org> References: <871qwq5ucx.fsf_-_@email.froward.int.ebiederm.org> MIME-Version: 1.0 X-XM-SPF: eid=1nrSZU-002Z0O-Ps; ; ; mid=<20220518225355.784371-13-ebiederm@xmission.com>; ; ; hst=in01.mta.xmission.com; ; ; ip=68.227.174.4; ; ; frm=ebiederm@xmission.com; ; ; spf=softfail X-XM-AID: U2FsdGVkX18zEH9NpD628NHFl0dZMZNqY3TpzcDYfhc= X-SA-Exim-Connect-IP: 68.227.174.4 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: [PATCH 13/16] ptrace: Document why ptrace_setoptions does not need a lock X-SA-Exim-Version: 4.2.1 (built Sat, 08 Feb 2020 21:53:50 +0000) X-SA-Exim-Scanned: Yes (on in01.mta.xmission.com) Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org The functions that change ->ptrace are: ptrace_attach, ptrace_traceme, ptrace_init_task, __ptrace_unlink, ptrace_setoptions. Except for ptrace_setoptions all of the places where ->ptrace is modified hold tasklist_lock for write, and either the tracee or the tracer is modifies ->ptrace. When ptrace_setoptions is called the tracee has been frozen with ptrace_freeze_traced, and most be explicitly unfrozen by the tracer before it can do anything. As ptrace_setoption is run in the tracer there can be no contention by the simple fact that the tracee can't run. Signed-off-by: "Eric W. Biederman" --- kernel/ptrace.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/kernel/ptrace.c b/kernel/ptrace.c index d0527b6e2b29..fbadd2f21f09 100644 --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -689,7 +689,10 @@ static int ptrace_setoptions(struct task_struct *child, unsigned long data) if (ret) return ret; - /* Avoid intermediate state when all opts are cleared */ + /* + * With a frozen tracee, only the tracer modifies ->ptrace. + * Avoid intermediate state when all opts are cleared. + */ flags = child->ptrace; flags &= ~(PTRACE_O_MASK << PT_OPT_FLAG_SHIFT); flags |= (data << PT_OPT_FLAG_SHIFT);