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[Tim Gardner <tim.gardner@xxxxxxxxxxxxx>]

Vivid 3.19.0-49.55
Wily 4.2.0-27.32

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https://bugs.launchpad.net/bugs/1517142

Title:
  ubuntu guest with 10G n/w and Texan iSCSI crashes during FIO

Status in linux package in Ubuntu:
  Fix Committed
Status in linux source package in Vivid:
  Fix Committed
Status in linux source package in Wily:
  Fix Committed
Status in linux source package in Xenial:
  Fix Committed

Bug description:
  Issues were found in iSCSI tests with hardware remote targets.
  Specifically, kernel crash happens due to dereferencing a null pointer
  (sc->device->lun at libiscsi.c:369, with sc==NULL). During the crash,
  lots of messages regarding lists invalid accesses are showed in kernel
  log.

  The commit 659743b02c41 ("[SCSI] libiscsi: Reduce locking contention
  in fast path") appears to be the cause.

  Reverting the commit solve the issue, at least until we can discuss and
  find the exact problem (and its solution) in the commit
  659743b02c41 ("[SCSI] libiscsi: Reduce locking contention in fast path").

  A test kernel was patched to revert the offend commit - Prashantha is
  running tests to check if the problem is solved.

  With the patched kernel, I am unable to recreate the crash. The patch appears
  to be working.

  A discussion is ongoing in linux-scsi mailing list, to revert the
  patch upstream (look the following link).

  http://marc.info/?l=linux-scsi&m=144730474819919

  Another quick discussion, started by me, it's on open-iscsi mailing
  list, on Google Groups:

  https://groups.google.com/forum/#!topic/open-iscsi/0S5fEM_Aafk

  The iscsi maintainer wants to revert, but patch co-author wants more
  study before reverting. Prashantha is performing some performance
  analysis to check the impact of the patch on iscsi performance.

  Mirroring to Launchpad for Canonical's awareness. Once the discussion
  settles on the final solution, a patch or link to the upstream commit
  will be provided for Canonical to review for acceptance in the 14.04
  LTS kernel and SRU.

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