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SubjectRe: [PATCH] mm: fix hang on anon_vma->root->lock
On Fri, 27 Aug 2010, Hugh Dickins wrote:

> Eh? My solution was a second page_mapped(page) test i.e. testing an atomic.

Argh. Right. Looked like a global to me. Did not see the earlier local

If you still use a pointer then what does insure that the root
pointer was not changed after the ACCESS_ONCE? The free semantics
of an anon_vma?

Since there is no lock taken before the mapped check none of the
earlier reads from the anon vma structure nor the page mapped check
necessarily reflect a single state of the anon_vma.

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