[PATCH 4.4 30/91] mm: do not access page->mapping directly on page_endio

From: Greg Kroah-Hartman
Date: Fri Mar 10 2017 - 04:15:06 EST

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


From: Minchan Kim <minchan@xxxxxxxxxx>

commit dd8416c47715cf324c9a16f13273f9fda87acfed upstream.

With rw_page, page_endio is used for completing IO on a page and it
propagates write error to the address space if the IO fails. The
problem is it accesses page->mapping directly which might be okay for
file-backed pages but it shouldn't for anonymous page. Otherwise, it
can corrupt one of field from anon_vma under us and system goes panic


I encountered the BUG during developing new zram feature and it was
really hard to figure it out because it made random crash, somtime
mmap_sem lockdep, sometime other places where places never related to
zram/zsmalloc, and not reproducible with some configuration.

When I consider how that bug is subtle and people do fast-swap test with
brd, it's worth to add stable mark, I think.

Fixes: dd6bd0d9c7db ("swap: use bdev_read_page() / bdev_write_page()")
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

mm/filemap.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -865,9 +865,12 @@ void page_endio(struct page *page, int r
} else { /* rw == WRITE */
if (err) {
+ struct address_space *mapping;
- if (page->mapping)
- mapping_set_error(page->mapping, err);
+ mapping = page_mapping(page);
+ if (mapping)
+ mapping_set_error(mapping, err);