mm: softdirty: keep bit when zapping file pte

This fixes the same bug as b43790eedd31 ("mm: softdirty: don't forget to
save file map softdiry bit on unmap") and 9aed8614af5a ("mm/memory.c:
don't forget to set softdirty on file mapped fault") where the return
value of pte_*mksoft_dirty was being ignored.

To be sure that no other pte/pmd "mk" function return values were being
ignored, I annotated the functions in arch/x86/include/asm/pgtable.h
with __must_check and rebuilt.

The userspace effect of this bug is that the softdirty mark might be
lost if a file mapped pte get zapped.

Signed-off-by: Peter Feiner <pfeiner@google.com>
Acked-by: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Jamie Liu <jamieliu@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: <stable@vger.kernel.org>	[3.12+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/memory.c b/mm/memory.c
index d17f1bcd2a91c3090cae29639fa0a4d2642f294b..e229970e4223ff02cb24b43b9e47e5ee211555d6 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1127,7 +1127,7 @@ again:
                                                addr) != page->index) {
                                pte_t ptfile = pgoff_to_pte(page->index);
                                if (pte_soft_dirty(ptent))
-                                       pte_file_mksoft_dirty(ptfile);
+                                       ptfile = pte_file_mksoft_dirty(ptfile);
                                set_pte_at(mm, addr, pte, ptfile);
                        }
                        if (PageAnon(page))