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    SubjectRe: REGRESSION: Performance regressions from switching anon_vma->lock to mutex
    On Thu, Jun 16, 2011 at 2:06 PM, Linus Torvalds
    <torvalds@linux-foundation.org> wrote:
    > On Thu, Jun 16, 2011 at 2:05 PM, Linus Torvalds
    > <torvalds@linux-foundation.org> wrote:
    >>
    >> This patch is UNTESTED!
    >
    > It was also UNATTACHED!

    Hmm. And it doesn't work. We deadlock when we free the anon_vma
    because the *freeing* path wants to take the anon_vma lock. See that
    horrid code in anon_vma_free().

    So now we now hold the root over the whole series of frees, and get an
    instant deadlock.

    We also can happen to free the root anon_vma before we release the
    lock in it, which is another slight problem ;)

    So the unlink_anon_vmas() case is actually much more complicated than
    the clone case.

    In other words, just forget that second patch. I'll have to think about it.

    Linus


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