Messages in this thread Patch in this message | | | Date | Mon, 12 Apr 2010 13:23:50 -0700 (PDT) | From | Linus Torvalds <> | Subject | [PATCH 4/4] anonvma: when setting up page->mapping, we need to pick the _oldest_ anonvma |
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From: Linus Torvalds <torvalds@linux-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@linux-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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