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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 7175FC433ED for ; Wed, 14 Apr 2021 11:27:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3C2FC613C3 for ; Wed, 14 Apr 2021 11:27:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241695AbhDNL2G (ORCPT ); Wed, 14 Apr 2021 07:28:06 -0400 Received: from mx2.suse.de ([195.135.220.15]:52102 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232069AbhDNL2G (ORCPT ); Wed, 14 Apr 2021 07:28:06 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 2713EAFE1; Wed, 14 Apr 2021 11:27:44 +0000 (UTC) Date: Wed, 14 Apr 2021 13:27:43 +0200 (CEST) From: Miroslav Benes To: xiaojun.zhao141@gmail.com cc: josef@toxicpanda.com, linux-kernel@vger.kernel.org, live-patching@vger.kernel.org Subject: Re: the qemu-nbd process automatically exit with the commit 43347d56c 'livepatch: send a fake signal to all blocking tasks' In-Reply-To: <20210414115548.0cdb529b@slime> Message-ID: References: <20210414115548.0cdb529b@slime> User-Agent: Alpine 2.21 (LSU 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org Hi, On Wed, 14 Apr 2021, xiaojun.zhao141@gmail.com wrote: > I found the qemu-nbd process(started with qemu-nbd -t -c /dev/nbd0 > nbd.qcow2) will automatically exit when I patched for functions of > the nbd with livepatch. > > The nbd relative source: > static int nbd_start_device_ioctl(struct nbd_device *nbd, struct block_device *bdev) > { > struct nbd_config *config = nbd->config; > int ret; > > ret = nbd_start_device(nbd); > if (ret) > return ret; > > if (max_part) > bdev->bd_invalidated = 1; > mutex_unlock(&nbd->config_lock); > ret = wait_event_interruptible(config->recv_wq, > atomic_read(&config->recv_threads) == 0); > if (ret) > sock_shutdown(nbd); > flush_workqueue(nbd->recv_workq); > > mutex_lock(&nbd->config_lock); > nbd_bdev_reset(bdev); > /* user requested, ignore socket errors */ > if (test_bit(NBD_RT_DISCONNECT_REQUESTED, &config->runtime_flags)) > ret = 0; > if (test_bit(NBD_RT_TIMEDOUT, &config->runtime_flags)) > ret = -ETIMEDOUT; > return ret; > } So my understanding is that ndb spawns a number (config->recv_threads) of workqueue jobs and then waits for them to finish. It waits interruptedly. Now, any signal would make wait_event_interruptible() to return -ERESTARTSYS. Livepatch fake signal is no exception there. The error is then propagated back to the userspace. Unless a user requested a disconnection or there is timeout set. How does the userspace then reacts to it? Is _interruptible there because the userspace sends a signal in case of NBD_RT_DISCONNECT_REQUESTED set? How does the userspace handles ordinary signals? This all sounds a bit strange, but I may be missing something easily. > When the nbd waits for atomic_read(&config->recv_threads) == 0, the klp > will send a fake signal to it then the qemu-nbd process exits. And the > signal of sysfs to control this action was removed in the commit > 10b3d52790e 'livepatch: Remove signal sysfs attribute'. Are there other > ways to control this action? How? No, there is no way currently. We send a fake signal automatically. Regards Miroslav