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

[Dan Streetman]

bionic verified, with udev rule changed per description testcase:

ii  systemd        237-3ubuntu10.42 amd64        system and service manager
ubuntu at lp1876018-b:~$ journalctl -b |grep vm-hot
Jul 30 16:25:23 lp1876018-b systemd-udevd[509]: Reading rules file: /lib/udev/rules.d/40-vm-hotadd.rules


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

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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:
  Fix Committed
Status in systemd source package in Focal:
  Fix Released

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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