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 60969C32789 for ; Tue, 23 Aug 2022 03:35:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240060AbiHWDft convert rfc822-to-8bit (ORCPT ); Mon, 22 Aug 2022 23:35:49 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60938 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240120AbiHWDfm (ORCPT ); Mon, 22 Aug 2022 23:35:42 -0400 Received: from cloud48395.mywhc.ca (cloud48395.mywhc.ca [173.209.37.211]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 064E25AC57; Mon, 22 Aug 2022 20:35:40 -0700 (PDT) Received: from [45.44.224.220] (port=49018 helo=[192.168.1.179]) by cloud48395.mywhc.ca with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.95) (envelope-from ) id 1oQKhX-0005Vz-6L; Mon, 22 Aug 2022 23:35:39 -0400 Message-ID: Subject: Re: [PATCH 2/2] coredump: Allow coredumps to pipes to work with io_uring From: Olivier Langlois To: "Eric W. Biederman" , Jens Axboe Cc: Pavel Begunkov , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, io-uring@vger.kernel.org, Alexander Viro , Oleg Nesterov , Linus Torvalds Date: Mon, 22 Aug 2022 23:35:37 -0400 In-Reply-To: <61abfb5a517e0ee253b0dc7ba9cd32ebd558bcb0.camel@trillion01.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> <878rw9u6fb.fsf@email.froward.int.ebiederm.org> <303f7772-eb31-5beb-2bd0-4278566591b0@gmail.com> <87ilsg13yz.fsf@email.froward.int.ebiederm.org> <8218f1a245d054c940e25142fd00a5f17238d078.camel@trillion01.com> <87y1wnrap0.fsf_-_@email.froward.int.ebiederm.org> <87mtd3rals.fsf_-_@email.froward.int.ebiederm.org> <61abfb5a517e0ee253b0dc7ba9cd32ebd558bcb0.camel@trillion01.com> Organization: Trillion01 Inc Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 8BIT User-Agent: Evolution 3.44.3 MIME-Version: 1.0 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-fsdevel@vger.kernel.org On Mon, 2022-08-22 at 17:16 -0400, Olivier Langlois wrote: > > What is stopping the task calling do_coredump() to be interrupted and > call task_work_add() from the interrupt context? > > This is precisely what I was experiencing last summer when I did work > on this issue. > > My understanding of how async I/O works with io_uring is that the > task > is added to a wait queue without being put to sleep and when the > io_uring callback is called from the interrupt context, > task_work_add() > is called so that the next time io_uring syscall is invoked, pending > work is processed to complete the I/O. > > So if: > > 1. io_uring request is initiated AND the task is in a wait queue > 2. do_coredump() is called before the I/O is completed > > IMHO, this is how you end up having task_work_add() called while the > coredump is generated. > I forgot to add that I have experienced the issue with TCP/IP I/O. I suspect that with a TCP socket, the race condition window is much larger than if it was disk I/O and this might make it easier to reproduce the issue this way...