From: Rik van Riel on
On 04/22/2010 01:42 AM, Naoya Horiguchi wrote:
> I found a bug on page_address_in_vma() related to anon_vma_chain.
> I wrote a patch, but according to a comment in include/linux/rmap.h,
> I suspect this doesn't meet lock requirement of anon_vma_chain
> (mmap_sem and page_table_lock, see below).
> mmap_sem page_table_lock
> mm/ksm.c:
> write_protect_page() hold not hold
> replace_page() hold not hold
> mm/memory-failure.c:
> add_to_kill() not hold hold
> mm/mempolicy.c:
> new_vma_page() hold not hold
> mm/swapfile.c:
> unuse_vma() hold not hold
> Any comments?

Good catch.

However, for anonymous pages, page_address_in_vma only
ever determined whether the page _could_ be part of the
VMA, never whether it actually was.

The function page_address_in_vma has always given
false positives, which means all of the callers already
check that the page is actually part of the process.

This means we may be able to get away with not verifying
the anon_vma at all. After all, verifying that the VMA
has the anon_vma mapped does not mean the VMA has this

Doing away with that check gets rid of your locking
conundrum :)

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