[Bug 690387] Re: udev block naming breaks failover and sd kref release cycle

[Serge Hallyn]

** Description changed:

  Binary package hint: multipath-tools
+ 
+ ================================================================
+ SRU Justification:
+ 1. Impact: multipath fail-over events are not handled by multipathd. The system therefore does not cleanly survive FOFB.
+ 2. How addressed: a bug from upstream is cherry-picked which fixes multipathd to look for the correct device pathnames in uevents it sees.
+ 3. Patch: see debdiff attached
+ 4. To reproduce: Start multipathd with -v4 argument. Reset an SCM to initiate FOFB. Watch /var/log/daemon.log for uevents relating to drives. Without the patch they don't show up. Additionally, upon failback, new block device names will be used (i.e. /dev/sdo instead of /dev/sda).
+ 5. Regression potential: the patch is to multipathd, so non-multipath users will not be affected. Multipathd users with an older kernel which uses the old pathanames could get the same behavior which uptodate users now have without this patch.
+ 
+ ================================================================
  
  This was exposed on the Intel IMS SAN which is an ODM'd Promise Vtrak
  variant on 10.04 server. The SAN has Active/Standby capabilities and
  is configured for failover. It probably affects other SANs too.
  
  Setup:
  multipath'd SAN consisting of SD block devices.
  
  Symptoms:
  On failover, multipath isn't gettng the right signals to tear down
  the defunct path. This was traced down to the fact that the path UDEV
  was presenting to multipath was different from what it was expecting.
  It simply dropped the request to gracefully remove the device, and
  instead responded to the SCSI mid-layer SD IO state change,
  SDEV_CANCEL/DEL which puts the device offline.
  
  Problem is device mapper still has an handle on the SD device, as
  can be seen from /sys/block/dm-x/slaves, and as a result,
  scsi_target_destroy is never called. The outward symptom of this
  is the SD suffix is not recycled because of course the previous
  reference never dropped.
  
  Solution:
  A fix was developed independently of upstream by Serge Hallyn,
  later it was found that it was fixed upstream, in 2008.
  The patch is:
  
  commit 7fa7affc3d23dd9dc906804d22a61144bca9f9b9
  Author: Benjamin Marzinski <bmarzins at redhat.com>
  Date: Thu Dec 11 16:03:28 2008 -0600
  
      Fix for uevent devpath handling
  
      This is necessary to make uevents work on fedora, since devpath appears as
      something like:
      '/devices/pci0000:00/0000:00:0a.0/0000:06:00.0/host11/rport-11:0-1/target11:0:1/11:0:1:0/block/s
  
      It simply strips off the everything up to the /block.
  
      Signed-off-by: Benjamin Marzinski <bmarzins at redhat.com>
  
  It integrates simply and can be found in PPAs here:
  ppa:peter-petrakis/storage

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https://bugs.launchpad.net/bugs/690387

Title:
  udev block naming breaks failover and sd kref release cycle

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