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 D5115C4332F for ; Thu, 20 Oct 2022 10:31:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230354AbiJTKb2 (ORCPT ); Thu, 20 Oct 2022 06:31:28 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42276 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230147AbiJTKbQ (ORCPT ); Thu, 20 Oct 2022 06:31:16 -0400 Received: from smtp-out2.suse.de (smtp-out2.suse.de [IPv6:2001:67c:2178:6::1d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 23E3F169CC5 for ; Thu, 20 Oct 2022 03:31:06 -0700 (PDT) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id 945881FA0B; Thu, 20 Oct 2022 10:30:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1666261846; h=from:from:reply-to:reply-to:date:date:message-id:message-id:to:to: cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=j2npfToEZqSD943t+AIhJGEaS4hfBHUeIL0TiPXg5g0=; b=H24lMvQmLxNYTkW9KUMcjVidNm9xUR1sC5nQRV5c8waRvRPTyNLke6yISbKhUok5vU9baK OVfrjcl4+NpMBgCNnh3HbfGtgjEcVtUaaVHK9HRjX7NeAVBBKBwgMczGQUnrMqwKK57P2o Qd/Kyih4PiRSvNIilNbqB6MSi5lEP4o= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1666261846; h=from:from:reply-to:reply-to:date:date:message-id:message-id:to:to: cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=j2npfToEZqSD943t+AIhJGEaS4hfBHUeIL0TiPXg5g0=; b=PGy7AW7naxq+AkSqlZRPim5P6dPZhTnmpXrDcnMnMKkl8EIrsUzQsHvYqjtjR2NzsOswMr Kq0Mb/1gcZPmtkDA== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 298BC13AF5; Thu, 20 Oct 2022 10:30:44 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id gWnqKFQjUWPxXwAAMHmgww (envelope-from ); Thu, 20 Oct 2022 10:30:44 +0000 Date: Thu, 20 Oct 2022 12:30:39 +0200 From: Petr Vorel To: Torsten Hilbrich Cc: linux-kernel@vger.kernel.org, Andrew Morton , Kroah-Hartman Subject: Re: v6.1-rc1: Regression in notification of sethostname changes Message-ID: Reply-To: Petr Vorel References: <0c2b92a6-0f25-9538-178f-eee3b06da23f@secunet.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On 19.10.22 14:31, Petr Vorel wrote: > >> Hi Torsten, > >>> Hello Petr, > >>> your commit > >>> commit bfca3dd3d0680fc2fc7f659a152234afbac26e4d > >>> Author: Petr Vorel > >>> Date: Thu Sep 1 21:44:03 2022 +0200 > >>> kernel/utsname_sysctl.c: print kernel arch > >>> Print the machine hardware name (UTS_MACHINE) in /proc/sys/kernel/arch. > >>> This helps people who debug kernel with initramfs with minimal environment > >>> (i.e. without coreutils or even busybox) or allow to open sysfs file > >>> instead of run 'uname -m' in high level languages. > >>> broke the notification mechanism between the sethostname syscall and the pollers of /proc/sys/kernel/hostname. > >>> The table uts_kern_table is addressed within uts_proc_notify by the enum value, however no new enum value was added in "enum uts_proc". > >>> I noticed the problem when journald-systemd failed to detect hostname changes made with the sethostname syscall (as used by the hostname tool). > >>> When setting the hostname through /proc/sys/kernel/hostname the poll notification was working. > >> Thanks a lot for your report, working on a fix! > >> Andrew, Greg, sorry for a regression. > > Hi Torsten, > > could you please post exact steps to reproduce the problem. > > Although the required fix to add new enum into enum uts_proc is trivial, > > I was not able to reproduce the problem with 6.1.0-rc1 (actually > > 6.1.0-rc1-4.g1d716d8-default which contains few extra patches). > > # hostname; hostnamectl hostname; cat /proc/sys/kernel/hostname > > opensuse-tumbleweed.20221001 > > opensuse-tumbleweed.20221001 > > opensuse-tumbleweed.20221001 > > # hostnamectl set-hostname foo; echo $? > > 0 > > # hostname; hostnamectl hostname; cat /proc/sys/kernel/hostname > > foo > > foo > > foo > > # hostname bar; echo $? > > 0 > > # hostname; hostnamectl hostname; cat /proc/sys/kernel/hostname > > bar > > bar > > bar > > # echo "baz" > /proc/sys/kernel/hostname > > # hostname; hostnamectl hostname; cat /proc/sys/kernel/hostname > > baz > > baz > > baz > > # hostnamectl set-hostname foo; reboot > > After reboot it's 'foo'. > > What am I missing? > > BTW I originally tested the feature only on dracut initramfs (with rapido [1]), > > which obviously bypass systemd. For a fix I'm creating rpm package (binrpm-pkg). > The problem is happening in the systemd-journald poll notification. I was checking for the problem by attaching gdb to the running systemd-journald and setting a breakpoint to the server_cache_hostname function. This function is triggered via dispatch_hostname_change whenever the hostname changes. This is done via sd_event API in systemd. > Here is an example program for this functionality without any further dependency: > #include > #include > #include > #include > #include > int main() > { > struct pollfd info; > info.fd = open("/proc/sys/kernel/hostname", O_RDONLY); > info.events = 0; > info.revents = 0; > while (true) { > int res = poll(&info, 1, -1); > if (res > 0) { > if (info.revents != 0) { > char buffer[64]; > gethostname(buffer, sizeof(buffer)); > printf("Hostname has changed to: %s\n", buffer); > } > } > } > } Rigth, poll() is broken. Thanks a lot for a simple reproducer! I'll send a fix shortly. Kind regards, Petr > I have also attached this program. > If you call this program and issue calls of the hostname utility to change the hostname some message should be printed. > Torsten > #include > #include > #include > #include > #include > int main() > { > struct pollfd info; > info.fd = open("/proc/sys/kernel/hostname", O_RDONLY); > info.events = 0; > info.revents = 0; > while (true) { > int res = poll(&info, 1, -1); > if (res > 0) { > if (info.revents != 0) { > char buffer[64]; > gethostname(buffer, sizeof(buffer)); > printf("Hostname has changed to: %s\n", buffer); > } > } > } > }