mremap: don't do mm_populate(new_addr) on failure

move_vma() sets *locked even if move_page_tables() or ->mremap() fails,
change sys_mremap() to check "ret & ~PAGE_MASK".

I think we should simply remove the VM_LOCKED code in move_vma(), that is
why this patch doesn't change move_vma().  But this needs more cleanups.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: David Rientjes <rientjes@google.com>
Cc: Benjamin LaHaise <bcrl@kvack.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jeff Moyer <jmoyer@redhat.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Laurent Dufour <ldufour@linux.vnet.ibm.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>