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 1321AC3F2C6 for ; Mon, 9 Mar 2020 18:26:55 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id BF69124649 for ; Mon, 9 Mar 2020 18:26:54 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BF69124649 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 442CB6B000A; Mon, 9 Mar 2020 14:26:54 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 4198F6B000C; Mon, 9 Mar 2020 14:26:54 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 308E06B000D; Mon, 9 Mar 2020 14:26:54 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0099.hostedemail.com [216.40.44.99]) by kanga.kvack.org (Postfix) with ESMTP id 16CAA6B000A for ; Mon, 9 Mar 2020 14:26:54 -0400 (EDT) Received: from smtpin29.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id D9573812F for ; Mon, 9 Mar 2020 18:26:53 +0000 (UTC) X-FDA: 76576655106.29.humor58_3c278c05b4957 X-HE-Tag: humor58_3c278c05b4957 X-Filterd-Recvd-Size: 8343 Received: from out03.mta.xmission.com (out03.mta.xmission.com [166.70.13.233]) by imf38.hostedemail.com (Postfix) with ESMTP for ; Mon, 9 Mar 2020 18:26:53 +0000 (UTC) Received: from in01.mta.xmission.com ([166.70.13.51]) by out03.mta.xmission.com with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1jBN72-0001Yq-SW; Mon, 09 Mar 2020 12:26:48 -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 1jBN71-00066p-Tz; Mon, 09 Mar 2020 12:26:48 -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> <87r1y12yc7.fsf@x220.int.ebiederm.org> Date: Mon, 09 Mar 2020 13:24:30 -0500 In-Reply-To: <87r1y12yc7.fsf@x220.int.ebiederm.org> (Eric W. Biederman's message of "Mon, 09 Mar 2020 13:10:48 -0500") Message-ID: <87k13t2xpd.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=1jBN71-00066p-Tz;;;mid=<87k13t2xpd.fsf@x220.int.ebiederm.org>;;;hst=in01.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX1/WnV4wYiwwbgU9GE0A9FUPBqxzJcDuRb4= 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: ebiederm@xmission.com (Eric W. Biederman) writes: > 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. And reading through it all now I can see your confusion. That description of my changes was not well done. Reworking it now. Eric