Patch "mm: filemap: fix mapping->nrpages double accounting in fuse" has been added to the 4.8-stable tree

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

    mm: filemap: fix mapping->nrpages double accounting in fuse

to the 4.8-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-filemap-fix-mapping-nrpages-double-accounting-in-fuse.patch
and it can be found in the queue-4.8 subdirectory.

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

From: Johannes Weiner <[email protected]>
Date: Tue, 4 Oct 2016 16:58:06 +0200
Subject: mm: filemap: fix mapping->nrpages double accounting in fuse

From: Johannes Weiner <[email protected]>

commit 3ddf40e8c31964b744ff10abb48c8e36a83ec6e7 upstream.

Commit 22f2ac51b6d6 ("mm: workingset: fix crash in shadow node shrinker caused by replace_page_cache_page()") switched replace_page_cache() from raw radix tree operations to page_cache_tree_insert() but didn't take into account that the latter function, unlike the raw radix tree op, handles mapping->nrpages. As a result, that counter is bumped for each page replacement rather than balanced out even.

The mapping->nrpages counter is used to skip needless radix tree walks when invalidating, truncating, syncing inodes without pages, as well as statistics for userspace. Since the error is positive, we'll do more page cache tree walks than necessary; we won't miss a necessary one. And we'll report more buffer pages to userspace than there are. The error is limited to fuse inodes.

---
 mm/filemap.c |    1 -
 1 file changed, 1 deletion(-)

@@ -619,7 +619,6 @@ int replace_page_cache_page(struct page
 		__delete_from_page_cache(old, NULL);
 		error = page_cache_tree_insert(mapping, new, NULL);
 		BUG_ON(error);
-		mapping->nrpages++;
 
 		/*
 		 * hugetlb pages do not participate in page cache accounting.

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

queue-4.8/mm-filemap-fix-mapping-nrpages-double-accounting-in-fuse.patch queue-4.8/mm-filemap-don-t-plant-shadow-entries-without-radix-tree-node.patch