Commit 3ddf40e8 authored Oct 04, 2016 by Johannes Weiner Committed by Linus Torvalds Oct 05, 2016

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

Commit 22f2ac51 ("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.

Fixes: 22f2ac51 ("mm: workingset: fix crash in shadow node shrinker caused by replace_page_cache_page()")
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent d3798ae8

mm/filemap.c

+0 −1

Original line number	Diff line number	Diff line
		@@ -633,7 +633,6 @@ int replace_page_cache_page(struct page old, struct page new, gfp_t gfp_mask)
		__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.

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