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SubjectRe: [PATCH -v2] rmap: make anon_vma_prepare link in all the anon_vmas of a mergeable VMA
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>  struct anon_vma *page_lock_anon_vma(struct page *page)
> {
> @@ -294,14 +309,24 @@ struct anon_vma *page_lock_anon_vma(struct page *page)
> unsigned long anon_mapping;
>
> rcu_read_lock();
> - anon_mapping = (unsigned long) ACCESS_ONCE(page->mapping);
> + anon_mapping = (unsigned long)rcu_dereference(page->mapping);
> if ((anon_mapping & PAGE_MAPPING_FLAGS) != PAGE_MAPPING_ANON)
> goto out;
> - if (!page_mapped(page))
> - goto out;
>
> anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);
> spin_lock(&anon_vma->lock);

Does anon->lock dereference is guranteed if page->_mapcount==-1?
It can be freed miliseconds ago, rcu_read_lock() doesn't provide such
gurantee.

perhaps, I'm missing your point.




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