[PATCH] shmem: fix pageflags after swapping DMA32 object

[Hugh Dickins]

If shmem_alloc_page() does not set PageLocked and PageSwapBacked, then
shmem_replace_page() needs to do so for itself.  Without this, it puts
newpage on the wrong lru, re-unlocks the unlocked newpage, and system
descends into "Bad page" reports and freeze; or if CONFIG_DEBUG_VM=y,
it hits an earlier VM_BUG_ON_PAGE(!PageLocked), depending on config.

But shmem_replace_page() is not a common path: it's only called when
swapin (or swapoff) finds the page was already read into an unsuitable
zone: usually all zones are suitable, but gem objects for a few drm
devices (gma500, omapdrm, crestline, broadwater) require zone DMA32
if there's more than 4GB of ram.

Fixes: 800d8c63b2e9 ("shmem: add huge pages support")
Cc: stable@xxxxxxxxxxxxxxx # v4.8
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
---

 mm/shmem.c |    2 ++
 1 file changed, 2 insertions(+)

--- 4.9-rc4/mm/shmem.c	2016-10-15 12:52:13.157533478 -0700
+++ linux/mm/shmem.c	2016-11-06 12:45:49.626193769 -0800
@@ -1483,6 +1483,8 @@ static int shmem_replace_page(struct pag
 	copy_highpage(newpage, oldpage);
 	flush_dcache_page(newpage);
 
+	__SetPageLocked(newpage);
+	__SetPageSwapBacked(newpage);
 	SetPageUptodate(newpage);
 	set_page_private(newpage, swap_index);
 	SetPageSwapCache(newpage);