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

[Peter Petrakis]

Public bug reported:

Binary package hint: multipath-tools

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

** Affects: multipath-tools (Ubuntu)
     Importance: High
     Assignee: Serge Hallyn (serge-hallyn)
         Status: Confirmed

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

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