[PATCH 4.14 143/146] mm: use swp_offset as key in shmem_replace_page()

From: Greg Kroah-Hartman
Date: Tue Dec 04 2018 - 06:07:29 EST


4.14-stable review patch. If anyone has any objections, please let me know.

------------------

From: Yu Zhao <yuzhao@xxxxxxxxxx>

commit c1cb20d43728aa9b5393bd8d489bc85c142949b2 upstream.

We changed the key of swap cache tree from swp_entry_t.val to
swp_offset. We need to do so in shmem_replace_page() as well.

Hugh said:
"shmem_replace_page() has been wrong since the day I wrote it: good
enough to work on swap "type" 0, which is all most people ever use
(especially those few who need shmem_replace_page() at all), but
broken once there are any non-0 swp_type bits set in the higher order
bits"

Link: http://lkml.kernel.org/r/20181121215442.138545-1-yuzhao@xxxxxxxxxx
Fixes: f6ab1f7f6b2d ("mm, swap: use offset of swap entry as key of swap cache")
Signed-off-by: Yu Zhao <yuzhao@xxxxxxxxxx>
Reviewed-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Acked-by: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [4.9+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
mm/shmem.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1532,11 +1532,13 @@ static int shmem_replace_page(struct pag
{
struct page *oldpage, *newpage;
struct address_space *swap_mapping;
+ swp_entry_t entry;
pgoff_t swap_index;
int error;

oldpage = *pagep;
- swap_index = page_private(oldpage);
+ entry.val = page_private(oldpage);
+ swap_index = swp_offset(entry);
swap_mapping = page_mapping(oldpage);

/*
@@ -1555,7 +1557,7 @@ static int shmem_replace_page(struct pag
__SetPageLocked(newpage);
__SetPageSwapBacked(newpage);
SetPageUptodate(newpage);
- set_page_private(newpage, swap_index);
+ set_page_private(newpage, entry.val);
SetPageSwapCache(newpage);

/*