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 167E1C433FE for ; Wed, 5 Jan 2022 19:39:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243634AbiAETjP (ORCPT ); Wed, 5 Jan 2022 14:39:15 -0500 Received: from cloud48395.mywhc.ca ([173.209.37.211]:49804 "EHLO cloud48395.mywhc.ca" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243596AbiAETjN (ORCPT ); Wed, 5 Jan 2022 14:39:13 -0500 Received: from modemcable064.203-130-66.mc.videotron.ca ([66.130.203.64]:43070 helo=[192.168.1.179]) by cloud48395.mywhc.ca with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1n5C7r-0007nD-6h; Wed, 05 Jan 2022 14:39:11 -0500 Message-ID: <8b6f2ce48c4097a23f5d03d631ed9363ecd45ddf.camel@trillion01.com> Subject: Re: [RFC] coredump: Do not interrupt dump for TIF_NOTIFY_SIGNAL From: Olivier Langlois To: Pavel Begunkov , "Eric W. Biederman" , linux-kernel@vger.kernel.org Cc: linux-fsdevel@vger.kernel.org, io-uring@vger.kernel.org, Alexander Viro , Jens Axboe , Oleg Nesterov , Linus Torvalds Date: Wed, 05 Jan 2022 14:39:09 -0500 In-Reply-To: <13250a8d-1a59-4b7b-92e4-1231d73cbdda@gmail.com> References: <192c9697e379bf084636a8213108be6c3b948d0b.camel@trillion01.com> <9692dbb420eef43a9775f425cb8f6f33c9ba2db9.camel@trillion01.com> <87h7i694ij.fsf_-_@disp2133> <1b519092-2ebf-3800-306d-c354c24a9ad1@gmail.com> <13250a8d-1a59-4b7b-92e4-1231d73cbdda@gmail.com> Organization: Trillion01 Inc Content-Type: text/plain; charset="ISO-8859-1" User-Agent: Evolution 3.42.2 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - cloud48395.mywhc.ca X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - trillion01.com X-Get-Message-Sender-Via: cloud48395.mywhc.ca: authenticated_id: olivier@trillion01.com X-Authenticated-Sender: cloud48395.mywhc.ca: olivier@trillion01.com X-Source: X-Source-Args: X-Source-Dir: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2021-12-24 at 10:37 +0000, Pavel Begunkov wrote: > On 12/24/21 01:34, Olivier Langlois wrote: > > On Fri, 2021-10-22 at 15:13 +0100, Pavel Begunkov wrote: > > > On 6/9/21 21:17, Eric W. Biederman wrote: > > > In short, a task creates an io_uring worker thread, then the > > > worker > > > submits a task_work item to the creator task and won't die until > > > the item is executed/cancelled. And I found that the creator task > > > is > > > sleeping in do_coredump() -> wait_for_completion() > > > > [...] > > > A hack executing tws there helps (see diff below). > > > Any chance anyone knows what this is and how to fix it? > > > > [...] > > Pavel, > > > > I cannot comment on the merit of the proposed hack but my proposed > > patch to fix the coredump truncation issue when a process using > > io_uring core dumps that I submitted back in August is still > > unreviewed! > > That's unfortunate. Not like I can help in any case, but I assumed > it was dealt with by > > commit 06af8679449d4ed282df13191fc52d5ba28ec536 > Author: Eric W. Biederman > Date:   Thu Jun 10 15:11:11 2021 -0500 > >      coredump: Limit what can interrupt coredumps >      >      Olivier Langlois has been struggling with coredumps being > incompletely written in >      processes using io_uring. >      ... > It was a partial fix only. Oleg Nesterov pointed out that the fix was not good if if the core dump was written into a pipe. https://lore.kernel.org/io-uring/20210614141032.GA13677@redhat.com/ > > https://lore.kernel.org/lkml/1625bc89782bf83d9d8c7c63e8ffcb651ccb15 > > fa.1629655338.git.olivier@trillion01.com/ > > > > I have been using it since then I must have generated many dozens > > of > > perfect core dump files with it and I have not seen a single > > truncated > > core dump files like I used to have prior to the patch. > > > > I am bringing back my patch to your attention because one nice side > > effect of it is that it would have avoided totally the problem that > > you > > have encountered in coredump_wait() since it does cancel io_uring > > resources before calling coredump_wait()! > > FWIW, I worked it around in io_uring back then by breaking the > dependency. > Yes I have seen your work to fix the problem. It just seems to me that there is no good reason to keep io_uring process requests once you are generating a core dump and simply cancelling io_uring before generating the core dump would have avoided the problem that you have encountered plus any other similar issues yet to come... Greetings,