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[Andy Schmitz <1559563@xxxxxxxxxxxxxxxxxx>]

** Attachment added: "oops.log"
   https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1559563/+attachment/4604778/+files/oops.log

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https://bugs.launchpad.net/bugs/1559563

Title:
  Kernel Oops - unable to handle kernel paging request at
  fffffffffffffff8; EIP is at gss_wrap_req_priv.isra.10+0x183/0x2d0

Status in linux package in Ubuntu:
  New

Bug description:
  This is a kernel oops that appears to occur under heavy load.
  Unfortunately, it is not easy to reproduce, and I haven't been able to
  isolate whether it's associated with NFS load, CPU load, both, or
  neither. (NFS appears to be relevant, I'm using NFS4 with Kerberos in
  krb5p, and the oops is in GSS code. I am not using Kerberos for login
  or other features.)

  The oops output is attached. Nothing occurs in the console output for
  hours before it, and I suspect the second oops is related to the first
  one in some way. Shortly afterward, soft lockups on all other cores
  (including those on a physically separate processor) make the computer
  unresponsive.

  The issue appears to be in net/sunrpc/auth_gss/auth_gss.c's gss_wrap_req_priv, in the following line:
      tmp = page_address(rqstp->rq_enc_pages[rqstp->rq_enc_pages_num - 1]);

  It appears that rqstp is set, but both rqstp->rq_enc_Pages and
  rqstp->rq_enc_pages_num are zero, leading the kernel to attempt
  dereferencing an invalid address. Because this surfaces only under
  load, and is on a multiple-processor system, I'm inclined to guess
  there is a race condition between accesses to rqstp on different
  cores, but I haven't been able to determine where at this point.

  Unfortunately, /proc/version_signature isn't currently available as
  the computer got updated to a 3.13.0-77-generic upon restart, but this
  was running on a stock "3.13.0-76-generic #120-Ubuntu" kernel on
  14.04/trusty.

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