Patch "mm: do not access page->mapping directly on page_endio" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

    mm: do not access page->mapping directly on page_endio

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
mm-do-not-access-page-mapping-directly-on-page_endio.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Minchan Kim <[email protected]>
Date: Fri, 24 Feb 2017 14:59:59 -0800
Subject: mm: do not access page->mapping directly on page_endio

From: Minchan Kim <[email protected]>

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 randomly.

swap_writepage
bdev_writepage

    ops->rw_page

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.

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

@@ -865,9 +865,12 @@ void page_endio(struct page *page, int r
 		unlock_page(page);
 	} else { /* rw == WRITE */
 		if (err) {
+			struct address_space *mapping;
+
 			SetPageError(page);
-			if (page->mapping)
-				mapping_set_error(page->mapping, err);
+			mapping = page_mapping(page);
+			if (mapping)
+				mapping_set_error(mapping, err);
 		}
 		end_page_writeback(page);
 	}

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/mm-vmpressure-fix-sending-wrong-events-on-underflow.patch queue-4.4/mm-do-not-access-page-mapping-directly-on-page_endio.patch