mm/memory.c: don't forget to set softdirty on file mapped fault

Otherwise we may not notice that pte was softdirty because
pte_mksoft_dirty helper _returns_ new pte but doesn't modify the
argument.

In case if page fault happend on dirty filemapping the newly created pte
may loose softdirty bit thus if a userspace program is tracking memory
changes with help of a memory tracker (CONFIG_MEM_SOFT_DIRTY) it might
miss modification of a memory page (which in worts case may lead to data
inconsistency).

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Acked-by: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memory.c

@@ -2744,7 +2744,7 @@ void do_set_pte(struct vm_area_struct *vma, unsigned long address,
 	if (write)
 		entry = maybe_mkwrite(pte_mkdirty(entry), vma);
 	else if (pte_file(*pte) && pte_file_soft_dirty(*pte))
-		pte_mksoft_dirty(entry);
+		entry = pte_mksoft_dirty(entry);
 	if (anon) {
 		inc_mm_counter_fast(vma->vm_mm, MM_ANONPAGES);
 		page_add_new_anon_rmap(page, vma, address);