ARC: Incorrect mm reference used in vmalloc fault handler
ARC: Incorrect mm reference used in vmalloc fault handler

A vmalloc fault needs to sync up PGD/PTE entry from init_mm to current
task's "active_mm".  ARC vmalloc fault handler however was using mm.

A vmalloc fault for non user task context (actually pre-userland, from
init thread's open for /dev/console) caused the handler to deref NULL mm
(for mm->pgd)

The reasons it worked so far is amazing:

1. By default (!SMP), vmalloc fault handler uses a cached value of PGD.
   In SMP that MMU register is repurposed hence need for mm pointer deref.

2. In pre-3.12 SMP kernel, the problem triggering vmalloc didn't exist in
   pre-userland code path - it was introduced with commit 20bafb3d23d108bc
   "n_tty: Move buffers into n_tty_data"

Signed-off-by: Vineet Gupta <af669d95a4c0de051445d4cafdbb2c5c4a2838be@synopsys.com>
Cc: Gilad Ben-Yossef <27506c49d0aa0134c702962114d52970047df659@benyossef.com>
Cc: Noam Camus <5aa4b9705348d1692ae3b503c5c840c9fdcd7054@ezchip.com>
Cc: 4fbacc2fa0ffdbb11bf1ad6925b886ebd08dd15f@vger.kernel.org    #3.10 and 3.11
Cc: Peter Hurley <4b8373d016f277527198385ba72fda0feb5da015@hurleysoftware.com>
Signed-off-by: Linus Torvalds <69652caca27c8b940640ad396ab71f93cacec34f@linux-foundation.org>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs