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=-8.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=unavailable 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 CA20CC48BDF for ; Tue, 15 Jun 2021 22:09:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A9AB0610EA for ; Tue, 15 Jun 2021 22:09:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230012AbhFOWLV (ORCPT ); Tue, 15 Jun 2021 18:11:21 -0400 Received: from out01.mta.xmission.com ([166.70.13.231]:50622 "EHLO out01.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229601AbhFOWLT (ORCPT ); Tue, 15 Jun 2021 18:11:19 -0400 Received: from in02.mta.xmission.com ([166.70.13.52]) by out01.mta.xmission.com with esmtps (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1ltHFB-00GqjY-1s; Tue, 15 Jun 2021 16:09:13 -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 1ltHFA-00FYjE-0t; Tue, 15 Jun 2021 16:09:12 -0600 From: ebiederm@xmission.com (Eric W. Biederman) To: Oleg Nesterov Cc: Linus Torvalds , Olivier Langlois , Linux Kernel Mailing List , linux-fsdevel , io-uring , Alexander Viro , Jens Axboe , "Pavel Begunkov\>" References: <198e912402486f66214146d4eabad8cb3f010a8e.camel@trillion01.com> <87eeda7nqe.fsf@disp2133> <87pmwt6biw.fsf@disp2133> <87czst5yxh.fsf_-_@disp2133> <87y2bh4jg5.fsf@disp2133> <87sg1p4h0g.fsf_-_@disp2133> <20210614141032.GA13677@redhat.com> Date: Tue, 15 Jun 2021 17:08:23 -0500 In-Reply-To: <20210614141032.GA13677@redhat.com> (Oleg Nesterov's message of "Mon, 14 Jun 2021 16:10:33 +0200") Message-ID: <87pmwmn5m0.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=1ltHFA-00FYjE-0t;;;mid=<87pmwmn5m0.fsf@disp2133>;;;hst=in02.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX18kVU+BRNg3PW0YZn2DSgz4GvEBbVLZxeI= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: [PATCH] coredump: Limit what can interrupt coredumps 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-fsdevel@vger.kernel.org Oleg Nesterov writes: >> --- a/fs/coredump.c >> +++ b/fs/coredump.c >> @@ -519,7 +519,7 @@ static bool dump_interrupted(void) >> * but then we need to teach dump_write() to restart and clear >> * TIF_SIGPENDING. >> */ >> - return signal_pending(current); >> + return fatal_signal_pending(current) || freezing(current); >> } > > > Well yes, this is what the comment says. > > But note that there is another reason why dump_interrupted() returns true > if signal_pending(), it assumes thagt __dump_emit()->__kernel_write() may > fail anyway if signal_pending() is true. Say, pipe_write(), or iirc nfs, > perhaps something else... > > That is why zap_threads() clears TIF_SIGPENDING. Perhaps it should clear > TIF_NOTIFY_SIGNAL as well and we should change io-uring to not abuse the > dumping threads? > > Or perhaps we should change __dump_emit() to clear signal_pending() and > restart __kernel_write() if it fails or returns a short write. > > Otherwise the change above doesn't look like a full fix to me. Agreed. The coredump to a pipe will still be short. That needs something additional. The problem Olivier Langlois reported was core dumps coming up short because TIF_NOTIFY_SIGNAL was being set during a core dump. We can see this with pipe_write returning -ERESTARTSYS on a full pipe if signal_pending which includes TIF_NOTIFY_SIGNAL is true. Looking further if the thread that is core dumping initiated any io_uring work then io_ring_exit_work will use task_work_add to request that thread clean up it's io_uring state. Perhaps we can put a big comment in dump_emit and if we get back -ERESTARTSYS run tracework_notify_signal. I am not seeing any locks held at that point in the coredump, so it should be safe. The coredump is run inside of file_start_write which is the only potential complication. The code flow is complicated but it looks like the entire point of the exercise is to call io_uring_del_task_file on the originating thread. I suppose that keeps the locking of the xarray in io_uring_task simple. Hmm. All of this comes from io_uring_release. How do we get to io_uring_release? The coredump should be catching everything in exit_mm before exit_files? Confused and hopeful someone can explain to me what is going on, and perhaps simplify it. Eric