linux-kernel - [PATCH 4/4] anonvma: when setting up page->mapping, we need to pick the _oldest

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Date:	Mon, 12 Apr 2010 13:23:50 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Borislav Petkov <bp@...en8.de>
cc:	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Minchan Kim <minchan.kim@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Nick Piggin <npiggin@...e.de>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	sgunderson@...foot.com
Subject: [PATCH 4/4] anonvma: when setting up page->mapping, we need to pick
 the _oldest_ anonvma


From: Linus Torvalds <torvalds@...ux-foundation.org>
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@...ux-foundation.org>
---
 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

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