[Bug 2037569] Re: udev issues with mantic beta

[Dan Bungert]

Spent some time analyzing this.

Frank loaned me a test system.  The test system in the "idle" state is
enough to see the issue, with a persistent load of 3+ when nothing is
happening except event loop spin.  The test system is using a dasd as
the disk that it is running from.

With some udev tracing, one can see an apparent loop, with udisks2
opening /dev/dasda, which triggers an inotify, which triggers udev
rules, which trigger udisks2 again, or something similar to this flow.

Workarounds include:
* adding a nowatch rule 'ACTION=="add|change", KERNEL=="dasd*", OPTIONS:="nowatch"'
* systemctl stop udisks2

I've begun exploring udev changes for udisks2 to ignore dasd.

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Title:
  udev issues with mantic beta

Status in Ubuntu on IBM z Systems:
  New
Status in systemd package in Ubuntu:
  Confirmed
Status in udisks2 package in Ubuntu:
  Confirmed

Bug description:
  While installing mantic beta (on s390x, LPAR and z/VM - but this might not be architecture specific) I faced issues with udev.
  In my installation I've updated the installer to "edge/lp-2009141" (subiquity  22.02.2+git1762.1b1ee6f4  5164).

  During my installations I first noticed bad response times in case of
  dealing with devices (like enabling new devices with chzdev). chzdev
  is used during the installation, hence the installation procedure is
  also affected by this. (I mainly notice this issue in case of DASD
  ECKD disk enablements.)

  But even after after a successful (but due to this issue less snappier) installation, means after the post-install reboot, in the installed system I can find several udev related processes, like:
    69448 root      20   0   31280  11944   2560 S  39.2   0.0   2:51.67 (udev-worker)    
      509 root      20   0   31276  13812   4600 S  20.6   0.0   2:07.76 systemd-udevd    
      893 root      20   0  469016  13544  10496 R  17.3   0.0   1:43.53 udisksd          
        1 root      20   0  168664  12748   8396 S  16.3   0.0   1:40.47 systemd  
  which is not only unusual, but (as one can see) they consume quite some resources.
  Even the remote ssh into that system is impacted by this high load.

  So far I only see this in mantic.
  I tried 20.04.3 as well as lunar, but both do not seem to be affected by this udev problem.
  I neither face the bad response on device enablement, nor can see any udev related processes still running after post-install-reboot in the installed system.

  (Sometimes I could also see a growing log file 'syslog').

  I cannot say yet what is causing this, but since I see 'systemd-udevd'
  as prominent process in top, I'll first of all mark this as affecting
  systemd-udevd (or systemd).

  I've attached the outcome of some more investigations I did ...

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