BugLink: http://bugs.launchpad.net/bugs/1471892

Commit b9496d0c in the 3.13.y-ckt tree is an
incomplete backport of upstream commit 33692f27.
The commit notes that the changes to mm/gup.c were omitted - presumably because
that file didn't exist in 3.13. However, the relevant code does exist in
3.13.y - it just hadn't been split out from mm/memory.c yet.

This introduced a regression in the Ubuntu kernel that resulted in panics
on arm64 when running the coreutils test suite:

  [...]
  PASS: tests/misc/chcon-fail.sh
  PASS: tests/misc/cut.pl
  [  141.509350] Kernel panic - not syncing: BUG!
  [  141.510301] CPU: 0 PID: 22674 Comm: bash Not tainted 3.13.11-ckt22 #20
  [  141.511641] Call trace:
  [  141.512115] [<ffffffc00008839c>] dump_backtrace+0x0/0x164
  [  141.513133] [<ffffffc000088510>] show_stack+0x10/0x1c
  [  141.514079] [<ffffffc000615460>] dump_stack+0x78/0x94
  [  141.515022] [<ffffffc000613fd8>] panic+0xe0/0x20c
  [  141.515903] [<ffffffc00017a7e4>] __get_user_pages+0x454/0x4c8
  [  141.516971] [<ffffffc00017a898>] get_user_pages+0x40/0x4c
  [  141.517973] [<ffffffc0001b1580>] get_arg_page+0x40/0xb4
  [  141.518956] [<ffffffc0001b1fb0>] copy_strings.isra.21+0x158/0x248
  [  141.520095] [<ffffffc0001b2d50>] do_execve_common.isra.26+0x3f4/0x5a0
  [  141.521280] [<ffffffc0001b2f14>] do_execve+0x18/0x24
  [  141.522203] [<ffffffc0001b3174>] SyS_execve+0x34/0x70

This commit completes the backport by retrofiting the missing changes to
mm/memory.c. This does not appear to impact upstream stable kernels. I checked
3.12.y, and it has already included these changes in the initial backport.
Signed-off-by: dann frazier <dannf@ubuntu.com>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>