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[Launchpad Bug Tracker <1517142@xxxxxxxxxxxxxxxxxx>]

This bug was fixed in the package linux - 3.19.0-49.55

---------------
linux (3.19.0-49.55) vivid; urgency=low

  [ Brad Figg ]

  * Release Tracking Bug
    - LP: #1536775

  [ Colin Ian King ]

  * SAUCE: (no-up) ACPI / tables: Add acpi_force_32bit_fadt_addr option to
    force 32 bit FADT addresses
    - LP: #1529381

  [ Tim Gardner ]

  * [Config] Add DRM ast driver to udeb installer image
    - LP: #1514711
  * SAUCE: (no-up) Revert "[SCSI] libiscsi: Reduce locking contention in
    fast path"
    - LP: #1517142

  [ Upstream Kernel Changes ]

  * powerpc/eeh: Fix recursive fenced PHB on Broadcom shiner adapter
    - LP: #1532942
  * Drivers: hv: vmbus: prevent cpu offlining on newer hypervisors
    - LP: #1440103
  * Drivers: hv: vmbus: teardown hv_vmbus_con workqueue and
    vmbus_connection pages on shutdown
    - LP: #1440103
  * drivers: hv: vmbus: Teardown synthetic interrupt controllers on module
    unload
    - LP: #1440103
  * clockevents: export clockevents_unbind_device instead of
    clockevents_unbind
    - LP: #1440103
  * Drivers: hv: vmbus: Teardown clockevent devices on module unload
    - LP: #1440103
  * Drivers: hv: vmbus: Add support for VMBus panic notifier handler
    - LP: #1440103
  * hv: run non-blocking message handlers in the dispatch tasklet
    - LP: #1440103
  * Drivers: hv: vmbus: unregister panic notifier on module unload
    - LP: #1440103
  * Drivers: hv: vmbus: Implement the protocol for tearing down vmbus state
    - LP: #1440103
  * kexec: define kexec_in_progress in !CONFIG_KEXEC case
    - LP: #1440103
  * Drivers: hv: vmbus: add special kexec handler
    - LP: #1440103
  * Drivers: hv: don't do hypercalls when hypercall_page is NULL
    - LP: #1440103
  * Drivers: hv: vmbus: add special crash handler
    - LP: #1440103
  * Drivers: hv: vmbus: prefer 'die' notification chain to 'panic'
    - LP: #1440103
  * hyperv: Implement netvsc_get_channels() ethool op
    - LP: #1494423
  * hv_netvsc: Properly size the vrss queues
    - LP: #1494423
  * hv_netvsc: Allocate the sendbuf in a NUMA aware way
    - LP: #1494423
  * hv_netvsc: Allocate the receive buffer from the correct NUMA node
    - LP: #1494423
  * Drivers: hv: vmbus: Implement NUMA aware CPU affinity for channels
    - LP: #1494423
  * Drivers: hv: vmbus: Allocate ring buffer memory in NUMA aware fashion
    - LP: #1494423
  * Drivers: hv: vmbus: Improve the CPU affiliation for channels
    - LP: #1494423
  * Drivers: hv: vmbus: Further improve CPU affiliation logic
    - LP: #1494423

linux (3.19.0-48.54) vivid; urgency=low

  [ Luis Henriques ]

  * Release Tracking Bug
    - LP: #1536124
  * Merged back Ubuntu-3.19.0-46.52

 -- Brad Figg <brad.figg@xxxxxxxxxxxxx>  Thu, 21 Jan 2016 12:29:48 -0800

** Changed in: linux (Ubuntu Vivid)
       Status: Fix Committed => Fix Released

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

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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