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    SubjectRe: [PATCH tip/urgent] rcu: add rcu_access_pointer and rcu_dereference_protected
    On Wed, Apr 07, 2010 at 06:00:27PM +0100, David Howells wrote:
    > Paul E. McKenney <> wrote:
    > > The new rcu_access_pointer() primitive is for the case where the pointer
    > > is be fetch and not dereferenced. This primitive may be used without
    > > protection, RCU or otherwise, due to the fact that it uses ACCESS_ONCE().
    > > ...
    > > +#define rcu_access_pointer(p, c) \
    > NAK. This shouldn't have the conditional parameter 'c'. Given that 'c' (by
    > analogy to rcu_dereference_check()) is there to describe the conditions under
    > which it's permitted to dereference the pointer, why is that relevant here?
    > What is it you're proving?

    In some cases, the value of 'c' will indeed be '1', and in those cases,
    there needs to be a comment stating why it is OK, similar to those
    required for smp_mb() and friends.

    In other cases, there will be a reference counter or a "not yet fully
    initialized" flag that can (and should) be tested.

    Thanx, Paul

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