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[Launchpad Bug Tracker <1517142@xxxxxxxxxxxxxxxxxx>]

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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.

** Affects: linux (Ubuntu)
     Importance: Undecided
     Assignee: Taco Screen team (taco-screen-team)
         Status: New


** Tags: architecture-ppc64le bugnameltc-133001 severity-critical targetmilestone-inin14043
-- 
ubuntu guest with 10G n/w and Texan iSCSI crashes during FIO
https://bugs.launchpad.net/bugs/1517142
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