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, URIBL_BLOCKED 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 8737BC48BE0 for ; Thu, 10 Jun 2021 14:27:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6E387610A5 for ; Thu, 10 Jun 2021 14:27:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231383AbhFJO3M (ORCPT ); Thu, 10 Jun 2021 10:29:12 -0400 Received: from out02.mta.xmission.com ([166.70.13.232]:60282 "EHLO out02.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231401AbhFJO3K (ORCPT ); Thu, 10 Jun 2021 10:29:10 -0400 Received: from in02.mta.xmission.com ([166.70.13.52]) by out02.mta.xmission.com with esmtps (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1lrLeK-005eYA-SA; Thu, 10 Jun 2021 08:27:12 -0600 Received: from ip68-227-160-95.om.om.cox.net ([68.227.160.95] helo=email.xmission.com) by in02.mta.xmission.com with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1lrLeJ-002BZf-W0; Thu, 10 Jun 2021 08:27:12 -0600 From: ebiederm@xmission.com (Eric W. Biederman) To: Olivier Langlois Cc: Linus Torvalds , Linux Kernel Mailing List , linux-fsdevel , io-uring , Alexander Viro , Jens Axboe , "Pavel Begunkov\>" , Oleg Nesterov References: <192c9697e379bf084636a8213108be6c3b948d0b.camel@trillion01.com> <9692dbb420eef43a9775f425cb8f6f33c9ba2db9.camel@trillion01.com> <87h7i694ij.fsf_-_@disp2133> <198e912402486f66214146d4eabad8cb3f010a8e.camel@trillion01.com> <87eeda7nqe.fsf@disp2133> Date: Thu, 10 Jun 2021 09:26:47 -0500 In-Reply-To: (Olivier Langlois's message of "Wed, 09 Jun 2021 17:26:30 -0400") Message-ID: <87pmwt6biw.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=1lrLeJ-002BZf-W0;;;mid=<87pmwt6biw.fsf@disp2133>;;;hst=in02.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX199QinEjQu0zfzLvNcJi/BI0qDO2ZVou6s= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: [RFC] coredump: Do not interrupt dump for TIF_NOTIFY_SIGNAL X-SA-Exim-Version: 4.2.1 (built Sat, 08 Feb 2020 21:53:50 +0000) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Olivier Langlois writes: > On Wed, 2021-06-09 at 16:05 -0500, Eric W. Biederman wrote: >> > >> > So the TIF_NOTIFY_SIGNAL does get set WHILE the core dump is >> > written. >> >> Did you mean? >> >> So the TIF_NOTIFY_SIGNAL does _not_ get set WHILE the core dump is >> written. >> >> > Absolutely not. I did really mean what I have said. Bear with me that, > I am not qualifying myself as an expert kernel dev yet so feel free to > correct me if I say some heresy... No. I was just asking to make certain I understood what you said. I thought you said you were getting a consistent 0 byte coredump, and that implied that TIF_NOTIFY_SIGNAL was coming in before the coredump even started. > io_uring is placing my task in my TCP socket wait queue because it > wants to read data from it. > > The task returns to user space and core dump with a SEGV. > > now my understanding is that the code that is waking up tasks, it is > the NIC driver interrupt handler which can occur while the core dump is > written. > > does that make sense? > > my testing is telling me that this is exactly what happens... If you are getting partial coredumps that completely makes sense. I was hoping that by this time Jens or Oleg would have been able to chime in and at least confirm I am not missing something subtle. I was afraid for a little bit that the file system code in called in dump_emit would be checking signal_pending. After looking into that I see that the filesystem code very reasonably limits itself to testing fatal_signal_pending (because by definition disk I/O on unix is not interruptible). So I will spin up a good version of my patch (based on your patch) so we can unbreak coredumps. Eric