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    SubjectRe: [PATCH tip/core/rcu 12/15] rcu: Remove redundant memory barrier from __call_rcu()
    On Fri, Aug 31, 2012 at 11:30:35AM -0700, Josh Triplett wrote:
    > On Thu, Aug 30, 2012 at 11:56:25AM -0700, Paul E. McKenney wrote:
    > > From: "Paul E. McKenney" <paul.mckenney@linaro.org>
    > >
    > > The first memory barrier in __call_rcu() is supposed to order any
    > > updates done beforehand by the caller against the actual queuing
    > > of the callback. However, the second memory barrier (which is intended
    > > to order incrementing the queue lengths before queuing the callback)
    > > is also between the caller's updates and the queuing of the callback.
    > > The second memory barrier can therefore serve both purposes.
    > >
    > > This commit therefore removes the first memory barrier.
    >
    > I don't see any such second memory barrier in __call_rcu(), at least not
    > in current master. Right after this smp_mb(), __call_rcu() enqueues the
    > callback and increments the queue length.
    >
    > Did you add a second memory barrier in some other patch that hasn't made
    > it upstream yet? If so, could you note that patch dependency explicitly
    > in the commit message?

    Argh, nevermind. Looked at the wrong branch, not master. Looking at
    master, I do indeed see the second smp_mb().

    Reviewed-by: Josh Triplett <josh@joshtriplett.org>


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