linux-kernel - [PATCH -mm] rmap: remove obsolete check from __page_check_anon

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Message-ID: <20100128014312.47c5045d@annuminas.surriel.com>
Date:	Thu, 28 Jan 2010 01:43:12 -0500
From:	Rik van Riel <riel@...hat.com>
To:	linux-mm@...ck.org
Cc:	linux-kernel@...r.kernel.org,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	lwoodman@...hat.com, akpm@...ux-foundation.org,
	Lee Schermerhorn <Lee.Schermerhorn@...com>, aarcange@...hat.com
Subject: [PATCH -mm] rmap: remove obsolete check from __page_check_anon_rmap

When an anonymous page is inherited from a parent process, the
vma->anon_vma can differ from the page anon_vma.  This can trip
up __page_check_anon_rmap, which is indirectly called from
do_swap_page().

Remove that obsolete check to prevent an oops.

Signed-off-by: Rik van Riel <riel@...hat.com>
---
The previous patch survived a short AIM7 run and only got upset when I
invoked pkill.  Presumably pkill paged in a page that was created in the
parent process of the process is was scanning.  With this patch it all
seems to be stable.

diff --git a/mm/rmap.c b/mm/rmap.c
index de7fde0..9e63424 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -755,9 +755,6 @@ static void __page_check_anon_rmap(struct page *page,
 	 * are initially only visible via the pagetables, and the pte is locked
 	 * over the call to page_add_new_anon_rmap.
 	 */
-	struct anon_vma *anon_vma = vma->anon_vma;
-	anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
-	BUG_ON(page->mapping != (struct address_space *)anon_vma);
 	BUG_ON(page->index != linear_page_index(vma, address));
 #endif
 }
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