linux-kernel - v6.1-rc1: Regression in notification of sethostname changes

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Date:   Wed, 19 Oct 2022 10:29:13 +0200
From:   Torsten Hilbrich <torsten.hilbrich@...unet.com>
To:     Petr Vorel <pvorel@...e.cz>
CC:     <linux-kernel@...r.kernel.org>
Subject: v6.1-rc1: Regression in notification of sethostname changes

Hello Petr,

your commit

commit bfca3dd3d0680fc2fc7f659a152234afbac26e4d
Author: Petr Vorel <pvorel@...e.cz>
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.

	Torsten