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    SubjectRe: [PATCH 00/21] mm: Preemptibility -v6
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    On Fri, 2011-01-21 at 16:33 +0100, Peter Zijlstra wrote:

    > Index: linux-2.6/mm/rmap.c
    > ===================================================================
    > --- linux-2.6.orig/mm/rmap.c
    > +++ linux-2.6/mm/rmap.c
    > @@ -1559,9 +1559,20 @@ void __put_anon_vma(struct anon_vma *ano
    > * Synchronize against page_lock_anon_vma() such that
    > * we can safely hold the lock without the anon_vma getting
    > * freed.
    > + *
    > + * Relies on the full mb implied by the atomic_dec_and_test() from
    > + * put_anon_vma() against the full mb implied by mutex_trylock() from
    > + * page_lock_anon_vma(). This orders:
    > + *
    > + * page_lock_anon_vma() VS put_anon_vma()
    > + * mutex_trylock() atomic_dec_and_test()
    > + * smp_mb() smp_mb()
    > + * atomic_read() mutex_is_locked()

    Bah!, I thought all mutex_trylock() implementations used an atomic op
    with return value (which implies a mb), but it looks like (at least*)
    PPC doesn't and only provides a LOCK barrier.


    * possibly ARM and SH don't either, but I can't read either ASMs well
    enough to tell.



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