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 69E0BC7EE23 for ; Wed, 24 May 2023 14:45:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236064AbjEXOpX (ORCPT ); Wed, 24 May 2023 10:45:23 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35396 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236032AbjEXOpP (ORCPT ); Wed, 24 May 2023 10:45:15 -0400 Received: from out02.mta.xmission.com (out02.mta.xmission.com [166.70.13.232]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3CE501A4 for ; Wed, 24 May 2023 07:45:07 -0700 (PDT) Received: from in01.mta.xmission.com ([166.70.13.51]:32916) by out02.mta.xmission.com with esmtps (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1q1pjc-007WwM-J3; Wed, 24 May 2023 08:45:04 -0600 Received: from ip68-110-29-46.om.om.cox.net ([68.110.29.46]:53910 helo=email.froward.int.ebiederm.org.xmission.com) by in01.mta.xmission.com with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1q1pjb-00BGTu-L9; Wed, 24 May 2023 08:45:04 -0600 From: "Eric W. Biederman" To: Oleg Nesterov Cc: Mike Christie , linux@leemhuis.info, nicolas.dichtel@6wind.com, axboe@kernel.dk, torvalds@linux-foundation.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, mst@redhat.com, sgarzare@redhat.com, jasowang@redhat.com, stefanha@redhat.com, brauner@kernel.org References: <20230522025124.5863-1-michael.christie@oracle.com> <20230522025124.5863-4-michael.christie@oracle.com> <20230522123029.GA22159@redhat.com> <20230522174757.GC22159@redhat.com> <20230523121506.GA6562@redhat.com> <87bkib6nxr.fsf@email.froward.int.ebiederm.org> <20230524141022.GA19091@redhat.com> Date: Wed, 24 May 2023 09:44:29 -0500 In-Reply-To: <20230524141022.GA19091@redhat.com> (Oleg Nesterov's message of "Wed, 24 May 2023 16:10:23 +0200") Message-ID: <87ttw1zt4i.fsf@email.froward.int.ebiederm.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-SPF: eid=1q1pjb-00BGTu-L9;;;mid=<87ttw1zt4i.fsf@email.froward.int.ebiederm.org>;;;hst=in01.mta.xmission.com;;;ip=68.110.29.46;;;frm=ebiederm@xmission.com;;;spf=pass X-XM-AID: U2FsdGVkX1/h3a+xGe9HgY6D1YHRegHcTvlq0mGfsXU= X-SA-Exim-Connect-IP: 68.110.29.46 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: [PATCH 3/3] fork, vhost: Use CLONE_THREAD to fix freezer/ps regression X-SA-Exim-Version: 4.2.1 (built Sat, 08 Feb 2020 21:53:50 +0000) X-SA-Exim-Scanned: Yes (on in01.mta.xmission.com) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Oleg Nesterov writes: > On 05/23, Eric W. Biederman wrote: >> >> I want to point out that we need to consider not just SIGKILL, but >> SIGABRT that causes a coredump, as well as the process peforming >> an ordinary exit(2). All of which will cause get_signal to return >> SIGKILL in this context. > > Yes, but probably SIGABRT/exit doesn't really differ from SIGKILL wrt > vhost_worker(). Actually I think it reveals that exiting with SIGABRT will cause a deadlock. coredump_wait will wait for all of the threads to reach coredump_task_exit. Meanwhile vhost_worker is waiting for all of the other threads to reach exit_files to close their file descriptors. So it looks like the final pieces of work will actually need to be moved into to vhost_xxx_flush or vhost_xxx_release to avoid the exiting threads from waiting on each other, instead of depending upon the vhost_worker to do the work. Which gets back to most of your other questions. >> It is probably not the worst thing in the world, but what this means >> is now if you pass a copy of the vhost file descriptor to another >> process the vhost_worker will persist, and thus the process will persist >> until that copy of the file descriptor is closed. > > Hadn't thought about it. > > I am fighting with internal bugzillas today, will try to write another > email tomorrow. > > But before that, I would like to have an answer to my "main" question in > my previois email. Otherwise I am still not sure I understand what exactly > we need to fix. Let me repeat your "main" question just for clarity here. If a signal comes in after the signal_pending check but before the "work->fn(work)" call is "work->fn(work)" expected to run correctly with signal_pending() or fatal_signal_pending returning true? Eric