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 10245C433EF for ; Thu, 28 Apr 2022 18:24:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1349622AbiD1S1e (ORCPT ); Thu, 28 Apr 2022 14:27:34 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45794 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1349020AbiD1S1d (ORCPT ); Thu, 28 Apr 2022 14:27:33 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 2BF0EB7C78 for ; Thu, 28 Apr 2022 11:24:18 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1651170257; 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=wg1zSD0Uo/cTh9pTTNBJKpd3vPv/btm0DQ5/ukfcHhE=; b=g/OK0+7yz9GPE6zjxT/AbFu6W+XWwqgmmVNyd0cTHh5U662FufUFsex689mhuf03Y3UUEr Bxhk10sFV4woQ4juh6SAjKAFurf/EQHcB4Gls+eXcAh+zXx6g/frNZbR9LsXgkQUbWIgW6 6/OfaEA3dBYbVmuSxcHW8TGR4pMeLoM= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-64-X_Q1Ros3MBKMs6aBD5Bn7Q-1; Thu, 28 Apr 2022 14:23:05 -0400 X-MC-Unique: X_Q1Ros3MBKMs6aBD5Bn7Q-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 019A6802819; Thu, 28 Apr 2022 18:23:04 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.40.192.151]) by smtp.corp.redhat.com (Postfix) with SMTP id 1264453CF; Thu, 28 Apr 2022 18:22:58 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Thu, 28 Apr 2022 20:23:03 +0200 (CEST) Date: Thu, 28 Apr 2022 20:22:58 +0200 From: Oleg Nesterov To: Peter Zijlstra Cc: "Eric W. Biederman" , linux-kernel@vger.kernel.org, rjw@rjwysocki.net, 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, Richard Weinberger , Anton Ivanov , Johannes Berg , linux-um@lists.infradead.org, Chris Zankel , Max Filippov , inux-xtensa@linux-xtensa.org, Kees Cook , Jann Horn Subject: Re: [PATCH 6/9] signal: Always call do_notify_parent_cldstop with siglock held Message-ID: <20220428182257.GE15485@redhat.com> References: <878rrrh32q.fsf_-_@email.froward.int.ebiederm.org> <20220426225211.308418-6-ebiederm@xmission.com> <20220427141018.GA17421@redhat.com> <874k2ea9q4.fsf@email.froward.int.ebiederm.org> <87zgk67fdd.fsf@email.froward.int.ebiederm.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.11.54.5 Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org On 04/28, Peter Zijlstra wrote: > > I've not had time to fully appreciate the nested locking here, but if it > is possible to rework things to always take both locks at the same time, > then it would be possible to impose an arbitrary lock order on things > and break the cycle that way. This is clear, but this is not that simple. For example (with this series at least), ptrace_stop() already holds current->sighand->siglock which (in particular) we need to protect current->parent, but then we need current->parent->sighand->siglock in do_notify_parent_cldstop(). Oleg.