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=-3.8 required=3.0 tests=BAYES_00, 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 C483EC4320E for ; Fri, 27 Aug 2021 15:59:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9F59660F5B for ; Fri, 27 Aug 2021 15:59:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S245377AbhH0QAF (ORCPT ); Fri, 27 Aug 2021 12:00:05 -0400 Received: from out03.mta.xmission.com ([166.70.13.233]:52212 "EHLO out03.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235955AbhH0QAF (ORCPT ); Fri, 27 Aug 2021 12:00:05 -0400 Received: from in01.mta.xmission.com ([166.70.13.51]:43614) by out03.mta.xmission.com with esmtps (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1mJeG4-009BWI-Gt; Fri, 27 Aug 2021 09:59:08 -0600 Received: from ip68-227-160-95.om.om.cox.net ([68.227.160.95]:57244 helo=email.xmission.com) by in01.mta.xmission.com with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1mJeFz-001ekB-NI; Fri, 27 Aug 2021 09:59:06 -0600 From: ebiederm@xmission.com (Eric W. Biederman) To: David Laight Cc: David Hildenbrand , Andy Lutomirski , Linus Torvalds , Linux Kernel Mailing List , Andrew Morton , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , Al Viro , Alexey Dobriyan , "Steven Rostedt" , "Peter Zijlstra \(Intel\)" , Arnaldo Carvalho de Melo , "Mark Rutland" , Alexander Shishkin , Jiri Olsa , "Namhyung Kim" , Petr Mladek , "Sergey Senozhatsky" , Andy Shevchenko , Rasmus Villemoes , Kees Cook , Greg Ungerer , Geert Uytterhoeven , "Mike Rapoport" , Vlastimil Babka , "Vincenzo Frascino" , Chinwen Chang , Michel Lespinasse , "Catalin Marinas" , "Matthew Wilcox \(Oracle\)" , Huang Ying , Jann Horn , Feng Tang , Kevin Brodsky , Michael Ellerman , "Shawn Anastasio" , Steven Price , "Nicholas Piggin" , Christian Brauner , Jens Axboe , "Gabriel Krisman Bertazi" , Peter Xu , "Suren Baghdasaryan" , Shakeel Butt , "Marco Elver" , Daniel Jordan , Nicolas Viennot , Thomas Cedeno , Collin Fijalkovich , Michal Hocko , Miklos Szeredi , Chengguang Xu , Christian =?utf-8?Q?K=C3=B6nig?= , "linux-unionfs\@vger.kernel.org" , Linux API , "the arch\/x86 maintainers" , "linux-fsdevel\@vger.kernel.org" , Linux-MM , "Florian Weimer" , Michael Kerrisk References: <20210812084348.6521-1-david@redhat.com> <87o8a2d0wf.fsf@disp2133> <60db2e61-6b00-44fa-b718-e4361fcc238c@www.fastmail.com> <87lf56bllc.fsf@disp2133> <87eeay8pqx.fsf@disp2133> <5b0d7c1e73ca43ef9ce6665fec6c4d7e@AcuMS.aculab.com> <87h7ft2j68.fsf@disp2133> <0ed69079-9e13-a0f4-776c-1f24faa9daec@redhat.com> <87mtp3g8gv.fsf@disp2133> <04e61e79ebad4a5d872d0a2b5be4c23d@AcuMS.aculab.com> Date: Fri, 27 Aug 2021 10:58:32 -0500 In-Reply-To: <04e61e79ebad4a5d872d0a2b5be4c23d@AcuMS.aculab.com> (David Laight's message of "Fri, 27 Aug 2021 08:22:07 +0000") Message-ID: <87fsuug9qv.fsf@disp2133> 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=1mJeFz-001ekB-NI;;;mid=<87fsuug9qv.fsf@disp2133>;;;hst=in01.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX18o5haSFLbKAaOyrbFGNCpTZ+ZVgKismqA= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: [PATCH v1 0/7] Remove in-tree usage of MAP_DENYWRITE 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-unionfs@vger.kernel.org David Laight writes: > From: Eric W. Biederman >> Sent: 26 August 2021 23:14 > ... >> I also ran into this issue not too long ago when I refactored the >> usermode_driver code. My challenge was not being in userspace >> the delayed fput was not happening in my kernel thread. Which meant >> that writing the file, then closing the file, then execing the file >> consistently reported -ETXTBSY. >> >> The kernel code wound up doing: >> /* Flush delayed fput so exec can open the file read-only */ >> flush_delayed_fput(); >> task_work_run(); >> >> As I read the code the delay for userspace file descriptors is >> always done with task_work_add, so userspace should not hit >> that kind of silliness, and should be able to actually close >> the file descriptor before the exec. > > If task_work_add ends up adding it to a task that is already > running on a different cpu, and that cpu takes a hardware > interrupt that takes some time and/or schedules the softint > code to run immediately the hardware interrupt completes > then it may well be possible for userspace to have 'issues'. It it task_work_add(current). Which punts the work to the return to userspace. > Any flags associated with O_DENY_WRITE would need to be cleared > synchronously in the close() rather then in any delayed fput(). Eric