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 1BADAC433F5 for ; Fri, 24 Dec 2021 02:33:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1350354AbhLXCdY (ORCPT ); Thu, 23 Dec 2021 21:33:24 -0500 Received: from cloud48395.mywhc.ca ([173.209.37.211]:42350 "EHLO cloud48395.mywhc.ca" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233638AbhLXCdX (ORCPT ); Thu, 23 Dec 2021 21:33:23 -0500 X-Greylist: delayed 3505 seconds by postgrey-1.27 at vger.kernel.org; Thu, 23 Dec 2021 21:33:22 EST Received: from modemcable064.203-130-66.mc.videotron.ca ([66.130.203.64]:42768 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 1n0ZU0-0002N8-9d; Thu, 23 Dec 2021 20:34:56 -0500 Message-ID: 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: Thu, 23 Dec 2021 20:34:54 -0500 In-Reply-To: <1b519092-2ebf-3800-306d-c354c24a9ad1@gmail.com> References: <192c9697e379bf084636a8213108be6c3b948d0b.camel@trillion01.com> <9692dbb420eef43a9775f425cb8f6f33c9ba2db9.camel@trillion01.com> <87h7i694ij.fsf_-_@disp2133> <1b519092-2ebf-3800-306d-c354c24a9ad1@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, 2021-10-22 at 15:13 +0100, Pavel Begunkov wrote: > On 6/9/21 21:17, Eric W. Biederman wrote: > > > > Folks, > > > > Olivier Langlois has been struggling with coredumps getting > > truncated in > > tasks using io_uring.  He has also apparently been struggling with > > the some of his email messages not making it to the lists. > > Looks syzbot hit something relevant, see > https://lore.kernel.org/io- > uring/0000000000000012fb05cee99477@google.com/ > > 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() > > 0xffffffff81343ccb is in do_coredump (fs/coredump.c:469). > 464 > 465             if (core_waiters > 0) { > 466                     struct core_thread *ptr; > 467 > 468                     freezer_do_not_count(); > 469                     wait_for_completion(&core_state->startup); > 470                     freezer_count(); > > > A hack executing tws there helps (see diff below). > Any chance anyone knows what this is and how to fix it? > > > diff --git a/fs/coredump.c b/fs/coredump.c > index 3224dee44d30..f6f9dfb02296 100644 > --- a/fs/coredump.c > +++ b/fs/coredump.c > @@ -466,7 +466,8 @@ static int coredump_wait(int exit_code, struct > core_state *core_state) >           struct core_thread *ptr; >   >           freezer_do_not_count(); > -        wait_for_completion(&core_state->startup); > +        while (wait_for_completion_interruptible(&core_state- > >startup)) > +            tracehook_notify_signal(); >           freezer_count(); >           /* >            * Wait for all the threads to become inactive, so that > > > > 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! https://lore.kernel.org/lkml/1625bc89782bf83d9d8c7c63e8ffcb651ccb15fa.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()! Greetings, Olivier