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    SubjectRe: [Lse-tech] Subject: [RFC][PATCH] Fix for unsafe notifier chain mechanism
    On Sat, 12 Nov 2005, Paul E. McKenney wrote:

    > > > > > The above can simply be "n->next = *nl;". The reason is that this change
    > > > > > of state is not visible to RCU readers until after the following statement,
    > > > > > and it therefore need not be an RCU-reader-safe assignment. You only need
    > > > > > to use rcu_assign_pointer() when the results of the assignment are
    > > > > > immediately visible to RCU readers.
    > > > >
    > > > > Correct, the rcu call isn't really needed. It doesn't hurt perceptibly,
    > > > > though, and part of the RCU documentation states:
    > > > >
    > > > > * ... More importantly, this
    > > > > * call documents which pointers will be dereferenced by RCU read-side
    > > > > * code.
    > > > >
    > > > > For that reason, I felt it was worth putting it in.
    > > >
    > > > But the following statement does a much better job of documenting the
    > > > pointer that is to be RCU-dereferenced. Duplicate documentation can
    > > > be just as confusing as no documentation.
    > >
    > > It's not really duplicate documentation since _both_ pointers are to be
    > > RCU-dereferenced. But maybe you mean that only the second pointer can be
    > > RCU-dereferenced at the time the write occurs? I don't think that's what
    > > the documentation comment intended.
    >
    > I am the guy who wrote that documentation ocmment. ;-)

    In that case I bow to your advice. :-)

    Alan Stern

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