[Bug 1540407] Re: multipathd drops paths of a temporarily lost device

[Dimitri John Ledkov]

The upload with this bugfix has been prepared, however it breaks the
Feature Freeze. A feature freeze exception has been requested and is
currently awaiting Release Team review. Once/If the release team reviews
the feature freeze exception, the package will be uploaded into xenial-
proposed. You can track the progress of the Feature Freeze Exception
here https://bugs.launchpad.net/ubuntu/+source/multipath-
tools/+bug/1551952 hence setting the status of this bug report to in
progress.

** Changed in: multipath-tools (Ubuntu)
       Status: Triaged => In Progress

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Title:
  multipathd drops paths of a temporarily lost device

Status in multipath-tools package in Ubuntu:
  In Progress

Bug description:
  == Comment: #0 - Thorsten Diehl <thorsten.diehl at de.ibm.com> - 2016-02-01 08:57:28 ==
  # uname -a
  Linux s83lp31 4.4.0-1-generic #15-Ubuntu SMP Thu Jan 21 22:19:04 UTC 2016 s390x s390x s390x GNU/Linux

  # dpkg -s multipath-tools|grep ^Version:
  Version: 0.5.0-7ubuntu9

  # cat /etc/multipath.conf
  defaults {
      default_features "1 queue_if_no_path"
      user_friendly_names yes
      path_grouping_policy multibus
      dev_loss_tmo 2147483647
      fast_io_fail_tmo 5
  }

  blacklist {
      devnode '*'
  }

  blacklist_exceptions {
      devnode "^sd[a-z]+"
  }

  ---------------------------------------
  On a z Systems LPAR with a single LUN, 2 zfcp devices, 2 storage ports, and the following multipath topology:

  mpatha (36005076304ffc3e80000000000003050) dm-0 IBM,2107900
  size=1.0G features='1 queue_if_no_path' hwhandler='0' wp=rw
  `-+- policy='round-robin 0' prio=1 status=active
    |- 0:0:0:1079001136 sda 8:0  active ready running
    |- 0:0:1:1079001136 sdb 8:16 active ready running
    |- 1:0:0:1079001136 sdc 8:32 active ready running
    `- 1:0:1:1079001136 sdd 8:48 active ready running

  I observed the following:
  When I deconfigure one of the two zfcp devices (e.g. via chchp -c 0, or directly on the HMC), the multipathd removes the two paths via these devices from the pathgroup after 10 seconds. When the zfcp devices comes back, it runs through zfcp error recovery and is being set up properly, and also the mid layer objects are looking fine. However, the multipathd does not add them to the path group again.

  Expected behaviour: multipathd does not remove the paths from topology
  list, but holds them as "failed faulty offline" until dev_loss_tmo
  timout is reached (which is infinite here).

  I discussed this already with zfcp development, and it looks most
  likely as a problem with multipathd, rather than zfcp or mid-layer.

  Easy to reproduce: you need two zfcp devices, one LUN, and preferably
  two ports on the storage server (WWPNs). Configure LUN via 2 zfcp
  devices * 2 WWPNs = 4 paths.

  This can be also reproduced on a z/VM guest. Instead of configuing the
  CHPID off, just detach one zfcp device and re-attach it after 30....60
  seconds. Same problem.

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