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    SubjectRe: [PATCH 07/10] module: __rcu annotations
    On Thursday 25 February 2010, Paul E. McKenney wrote:
    > >
    > > The nice thing about this is that we don't end up with the API explosion
    > > for the RCU list primitives. However, it does require that a given
    > > rcu_list_head have a single synchronization-design rule for all uses.
    > > Of course, if there were multiple rules, one could construct a check
    > > that was simply the union of all the rules, but that would miss some
    > > types of errors.

    What would it miss? E.g. having the module code check for
    (mutex_is_locked(&module_lock) || rcu_read_lock_held) should
    cover all cases as far as I can tell.

    > > Of course, if this became a problem, there could be an argument to the
    > > ->check function that the normal list_for_each_entry_rcu() defaults to
    > > "no effect".

    I've also been thinking about adding a list_for_each_entry_norcu()
    macro that takes an rcu_list_head but then just performs a simple

    > > Or is there a better way to handle this?
    > One approach would be to use your original sparse-based approach, but
    > use an rcu_deference_const(ptr,lockdep_condition) for cases when the
    > value cannot change, for example, when the update-side lock is held.
    > This should eliminate most of the false positives, in particular,
    > eliminate the need for otherwise-useless rcu_read_lock()s -- and also
    > for the compiler constraints in the normal rcu_dereference().


    > Your pointer-to-function idea could be a really cool way to handle the
    > tree algorithms that can be protected either by RCU or by locking.
    > The tree nodes could have the pointer to check function, and the
    > current rcu_dereference_raw() calls could be replaced by an invocation
    > of rcu_dereference_check() that calls the check function. A check
    > function for an RCU-protected tree would use "rcu_read_lock_held() ||
    > lockdep_is_held(&update_side_lock)", while a lock-protected tree would
    > just use "lockdep_is_held(&update_side_lock)".

    I've postponed that problem for now, and updated my series to split
    the rculist annotations from the basic __rcu pointer annotations,
    as well as to apply on top of your patches in tip/core/rcu,

    Should we merge the simple annotations in this merge window and
    then think about rculist and trees separately?


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