[PATCH 4/4] anonvma: when setting up page->mapping, we need to pickthe _oldest_ anonvma

[Linus Torvalds]

From: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Date: Mon, 12 Apr 2010 12:44:29 -0700
Subject: [PATCH 4/4] anonvma: when setting up page->mapping, we need to pick the _oldest_ anonvma

Otherwise we might be mapping in a page in a new mapping, but that page
(through the swapcache) would later be mapped into an old mapping too.
The page->mapping must be the case that works for everybody, not just
the mapping that happened to page it in first.

This can be improved in certain cases: if we know the page is private to
just this particular mapping (for example, it's a new page, or it is the
only swapcache entry), we could pick the top (most specific) anon_vma.

But that's a future optimization. Make it _work_ reliably first.

Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
---
 mm/rmap.c |   15 +++++++++++++--
 1 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/mm/rmap.c b/mm/rmap.c
index ee97d38..4bad326 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -734,9 +734,20 @@ void page_move_anon_rmap(struct page *page,
 static void __page_set_anon_rmap(struct page *page,
 	struct vm_area_struct *vma, unsigned long address)
 {
-	struct anon_vma *anon_vma = vma->anon_vma;
+	struct anon_vma_chain *avc;
+	struct anon_vma *anon_vma;
+
+	BUG_ON(!vma->anon_vma);
+
+	/*
+	 * We must use the _oldest_ possible anon_vma for the page mapping!
+	 *
+	 * So take the last AVC chain entry in the vma, which is the deepest
+	 * ancestor, and use the anon_vma from that.
+	 */
+	avc = list_entry(vma->anon_vma_chain.prev, struct anon_vma_chain, same_vma);
+	anon_vma = avc->anon_vma;
 
-	BUG_ON(!anon_vma);
 	anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
 	page->mapping = (struct address_space *) anon_vma;
 	page->index = linear_page_index(vma, address);
-- 
1.7.1.rc1.dirty

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/