Moving from get_user_pages() to get_user_pages_unlocked() simplifies the
code and takes advantage of VM_FAULT_RETRY functionality when faulting
in pages.

Link: http://lkml.kernel.org/r/20170103205024.6704-1-lstoakes@gmail.comSigned-off-by: NLorenzo Stoakes <lstoakes@gmail.com>
Acked-by: NAlexandre Bounine <alexandre.bounine@idt.com>
Cc: Matt Porter <mporter@kernel.crashing.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>