[PATCH -mm] rmap: remove obsolete check from __page_check_anon_rmap

[Rik van Riel]

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@xxxxxxxxxx>
---
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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