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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 2DE1BC18E5B for ; Mon, 9 Mar 2020 18:13:18 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id E618320578 for ; Mon, 9 Mar 2020 18:13:17 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E618320578 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=xmission.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 892E06B000A; Mon, 9 Mar 2020 14:13:17 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 842CB6B000C; Mon, 9 Mar 2020 14:13:17 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6E2E76B000D; Mon, 9 Mar 2020 14:13:17 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0139.hostedemail.com [216.40.44.139]) by kanga.kvack.org (Postfix) with ESMTP id 52DCE6B000A for ; Mon, 9 Mar 2020 14:13:17 -0400 (EDT) Received: from smtpin20.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 21887181AEF0B for ; Mon, 9 Mar 2020 18:13:17 +0000 (UTC) X-FDA: 76576620834.20.cats20_56d6a33204a51 X-HE-Tag: cats20_56d6a33204a51 X-Filterd-Recvd-Size: 8079 Received: from out01.mta.xmission.com (out01.mta.xmission.com [166.70.13.231]) by imf02.hostedemail.com (Postfix) with ESMTP for ; Mon, 9 Mar 2020 18:13:16 +0000 (UTC) Received: from in01.mta.xmission.com ([166.70.13.51]) by out01.mta.xmission.com with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1jBMtm-0006L5-Mh; Mon, 09 Mar 2020 12:13:06 -0600 Received: from ip68-227-160-95.om.om.cox.net ([68.227.160.95] helo=x220.xmission.com) by in01.mta.xmission.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.87) (envelope-from ) id 1jBMtl-0002m4-KU; Mon, 09 Mar 2020 12:13:06 -0600 From: ebiederm@xmission.com (Eric W. Biederman) To: Bernd Edlinger Cc: Christian Brauner , Kees Cook , Jann Horn , Jonathan Corbet , Alexander Viro , Andrew Morton , Alexey Dobriyan , Thomas Gleixner , Oleg Nesterov , Frederic Weisbecker , Andrei Vagin , Ingo Molnar , "Peter Zijlstra \(Intel\)" , Yuyang Du , David Hildenbrand , Sebastian Andrzej Siewior , Anshuman Khandual , David Howells , James Morris , Greg Kroah-Hartman , Shakeel Butt , Jason Gunthorpe , Christian Kellner , Andrea Arcangeli , Aleksa Sarai , "Dmitry V. Levin" , "linux-doc\@vger.kernel.org" , "linux-kernel\@vger.kernel.org" , "linux-fsdevel\@vger.kernel.org" , "linux-mm\@kvack.org" , "stable\@vger.kernel.org" , "linux-api\@vger.kernel.org" References: <202003021531.C77EF10@keescook> <20200303085802.eqn6jbhwxtmz4j2x@wittgenstein> <87v9nlii0b.fsf@x220.int.ebiederm.org> <87a74xi4kz.fsf@x220.int.ebiederm.org> <87r1y8dqqz.fsf@x220.int.ebiederm.org> <87tv32cxmf.fsf_-_@x220.int.ebiederm.org> <87v9ne5y4y.fsf_-_@x220.int.ebiederm.org> <87zhcq4jdj.fsf_-_@x220.int.ebiederm.org> <878sk94eay.fsf@x220.int.ebiederm.org> Date: Mon, 09 Mar 2020 13:10:48 -0500 In-Reply-To: (Bernd Edlinger's message of "Mon, 9 Mar 2020 18:01:35 +0000") Message-ID: <87r1y12yc7.fsf@x220.int.ebiederm.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-SPF: eid=1jBMtl-0002m4-KU;;;mid=<87r1y12yc7.fsf@x220.int.ebiederm.org>;;;hst=in01.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX18QzwMdGCf8P173K+LAq8xnIr+Kw2IIWJI= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: [PATCH v2 5/5] exec: Add a exec_update_mutex to replace cred_guard_mutex X-SA-Exim-Version: 4.2.1 (built Thu, 05 May 2016 13:38:54 -0600) X-SA-Exim-Scanned: Yes (on in01.mta.xmission.com) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Bernd Edlinger writes: > On 3/9/20 6:40 PM, Eric W. Biederman wrote: >> Bernd Edlinger writes: >> >>> On 3/8/20 10:38 PM, Eric W. Biederman wrote: >>>> >>>> The cred_guard_mutex is problematic. The cred_guard_mutex is held >>>> over the userspace accesses as the arguments from userspace are read. >>>> The cred_guard_mutex is held of PTRACE_EVENT_EXIT as the the other >> ^ over >>> >>> ... is held while waiting for the trace parent to handle PTRACE_EVENT_EXIT >>> or something? >> >> Yes. Let me see if I can phrase that better. >> >>> I wonder if we also should mention that >>> it is held while waiting for the trace parent to >>> receive the exit code with "wait"? >> >> I don't think we have to spell out the details of how it all works, >> unless that makes things clearer. Kernel developers can be expected >> to figure out how the kernel works. The critical thing is that it is >> an indefinite wait for userspace to take action. >> >> But I will look. >> >>>> threads are killed. The cred_guard_mutex is held over >>>> "put_user(0, tsk->clear_child_tid)" in exit_mm(). >>>> >>>> Any of those can result in deadlock, as the cred_guard_mutex is held >>>> over a possible indefinite userspace waits for userspace. >>>> >>>> Add exec_update_mutex that is only held over exec updating process >>> >>> Add ? >> >> Yes. That is what the change does: add exec_update_mutex. >> > > I just kind of missed the "subject" in this sentence, > like "This patch adds an exec_update_mutex that is ..." > but english is a foreign language for me, so may be okay as is. English has a lot of options. I think this is a stylistic difference. Instead of being an observer and describing what the change does: "This patch adds exec_update_mutex ..." I was being there in the moment and saying/commading what is happening: "Add exec_update_mutex ..." Using the more immdediate form ends up with more concise and clearer sentences. Every one of my writing teachers in school emphasized that point and I see the who it works when I write things. But writing is hard and I still tend toward long rambling sentences with many qualifiers that confuse and detract from the point rather than make it clear what is happening. Eric