[Bug 1876018] Re: 40-vm-hotadd.rules attempts to set non-existent sysfs parameters

[Dan Streetman]

focal:

with the reproducer hack from the description (comment out the 'goto'
line in the udev rule), and the system rebooted:

ubuntu at lp1876018-f:~$ dpkg -l systemd|grep systemd
ii  systemd        245.4-4ubuntu3.1 amd64        system and service manager
ubuntu at lp1876018-f:~$ journalctl -g vm-hotadd
-- Logs begin at Wed 2020-07-22 18:11:53 UTC, end at Wed 2020-07-22 18:46:23 UTC. --
Jul 22 18:45:15 lp1876018-f sudo[12380]:   ubuntu : TTY=ttyS0 ; PWD=/home/ubuntu ; USER=root ; COMMAND=/usr/bin/vi /lib/udev/rules.d/40-vm-hotadd.rules
-- Reboot --
Jul 22 18:45:48 lp1876018-f systemd-udevd[457]: memory0: /usr/lib/udev/rules.d/40-vm-hotadd.rules:9 Failed to write ATTR{/sys/devices/system/memory/memory0/state}, ignoring: Invalid argument
Jul 22 18:45:48 lp1876018-f systemd-udevd[457]: memory1: /usr/lib/udev/rules.d/40-vm-hotadd.rules:9 Failed to write ATTR{/sys/devices/system/memory/memory1/state}, ignoring: Invalid argument
Jul 22 18:45:48 lp1876018-f systemd-udevd[457]: memory10: /usr/lib/udev/rules.d/40-vm-hotadd.rules:9 Failed to write ATTR{/sys/devices/system/memory/memory10/state}, ignoring: Invalid argument
...(many more)...


and with the udev rule again edited after the systemd upgrade (since it
replaces the edited file), and the system rebooted:

ubuntu at lp1876018-f:~$ dpkg -l systemd|grep systemd
ii  systemd        245.4-4ubuntu3.2 amd64        system and service manager
ubuntu at lp1876018-f:~$ journalctl -b -g vm-hotadd
-- Logs begin at Wed 2020-07-22 18:11:53 UTC, end at Wed 2020-07-22 18:50:00 UT>
-- No entries --


** Tags removed: verification-needed verification-needed-focal
** Tags added: verification-done verification-done-focal

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https://bugs.launchpad.net/bugs/1876018

Title:
  40-vm-hotadd.rules attempts to set non-existent sysfs parameters

Status in systemd package in Ubuntu:
  Fix Released
Status in systemd source package in Xenial:
  In Progress
Status in systemd source package in Bionic:
  In Progress
Status in systemd source package in Focal:
  Fix Committed

Bug description:
  [impact]

  40-vm-hotadd.rules unconditionally tries onlining memory, which
  results in logged error messages if the memory is already online

  [test case]

  since this rules file restricts operation to only hyper-v or xen
  guests, boot a hyper-v or xen vm guest, and check for logged error
  msgs like:

  Apr 29 22:36:46 focal01 systemd-udevd[266]: memory7:
  /usr/lib/udev/rules.d/40-vm-hotadd.rules:9 Failed to write
  ATTR{/sys/devices/system/memory/memory7/state}, ignoring: Invalid
  argument

  alternately, to test on a vm guest other than hyper-v or xen,
  comment/remove the 'GOTO="vm_hotadd_end"' line from the rules file and
  reboot.

  [regression potential]

  as this adds a check before attempting to online memory for hyper-v
  and xen vm guests, any regression would likely involve failure to
  correctly online all memory on those guest platforms.

  [scope]

  this rule has been around for a long time, so is needed for x/b/f/g.

  [original description]

  In focal, udev's 40-vm-hotadd.rules (from debian/extra/rules-ubuntu)
  tries to write to invalid (as of 5.4.0-1010-azure) sysfs nodes
  resulting in warnings such as:

  Apr 29 22:36:46 focal01 systemd-udevd[266]: memory7:
  /usr/lib/udev/rules.d/40-vm-hotadd.rules:9 Failed to write
  ATTR{/sys/devices/system/memory/memory7/state}, ignoring: Invalid
  argument

  Perhaps 40-vm-hotadd.rules needs to be updated for 5.4 semantics,
  removed, or something else. This behavior is present on systems
  upgraded from 18.04 (via d-r-u) as well as new focal systems, upon
  first reboot of the VM.

  udev: 245.4-4ubuntu3

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