[Bug 1798883] Re: Ubuntu 18.04 LTS: pam_systemd: Failure to create session under heavy I/O load

[Dan Streetman]

please reopen if this is still an issue

** Changed in: systemd (Ubuntu)
       Status: New => Invalid

** Changed in: dbus (Ubuntu)
       Status: New => Invalid

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Title:
  Ubuntu 18.04 LTS: pam_systemd: Failure to create session under heavy
  I/O load

Status in dbus package in Ubuntu:
  Invalid
Status in systemd package in Ubuntu:
  Invalid

Bug description:
  I have a file server running Ubuntu 18.04 LTS which has strange
  behavior with systemd and dbus during heavy I/O load. The file server
  is set up with RAID60 with mdadm serving via NFS. When I/O load
  becomes high, it appears that dbus and systemd-logind are slowing down
  for SSH connections and I lose SSH connectivity due to login failure
  with pam_systemd:

  Oct 19 11:14:56 nfsserver sshd[20635]: pam_systemd(sshd:session): Failed to create session: Connection timed out
  Oct 19 11:15:06 nfsserver sshd[20821]: pam_systemd(sshd:session): Failed to create session: Connection timed out
  Oct 19 11:15:06 nfsserver sshd[20837]: pam_systemd(sshd:session): Failed to create session: Connection timed out
  Oct 19 12:05:58 nfsserver sshd[25143]: pam_systemd(sshd:session): Failed to create session: Connection timed out
  Oct 19 13:03:07 nfsserver sshd[47296]: pam_systemd(sshd:session): Failed to release session: Connection timed out
  Oct 19 13:05:39 nfsserver sshd[48532]: pam_systemd(sshd:session): Failed to create session: Message recipient disconnected from message bus without replying
  Oct 19 13:05:39 nfsserver sshd[48570]: pam_systemd(sshd:session): Failed to create session: Message recipient disconnected from message bus without rep

  CPU load gets near 50 or 60%, but not 100%. Looking through bug
  reports and issues that others have experienced with previous
  versions, it seems that when systemd-logind doesn't process the IPC
  queue from dbus fast enough, dbus will kick systemd-logind resulting
  in this failure. This appears to be so in socket statistics whereby
  the dbus IPC Send-Q fills and does not move during heavy load:

  Netid State Recv-Q Send-Q Local Address:Port Peer Address:Port
  u_str ESTAB 0 153088 /var/run/dbus/system_bus_socket -2002184190 * -2002209306

  The Recv-Q on the other end does not keep up:

  Netid State Recv-Q Send-Q Local Address:Port Peer Address:Port
  u_str ESTAB 37892 0 * -2002209306 * -2002184190

  I have tried to renice dbus, systemd, systemd-logind without success.
  The only way to resolve this issue is to reduce I/O load. Any
  thoughts?

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