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    SubjectRe: [PATCH RFC tip/core/rcu 18/18] rcu: add primitives to check for RCU read-side critical sections
    On Wed, Dec 16, 2009 at 11:31:34AM +0100, Peter Zijlstra wrote:
    > On Tue, 2009-12-15 at 15:02 -0800, Paul E. McKenney wrote:
    > >
    > > Also create rcu_dereference_check(), which takes a second boolean argument
    > > into which one puts rcu_read_lock_held() or similar. For example:
    > >
    > > rcu_dereference_check(gp, rcu_read_lock_held() ||
    > > lockdep_is_held(my_lock));
    >
    > Ah, so you're going to tackle this the other way around, interesting :-)

    Still feeling my way around this one, but for the moment, yes. ;-)

    One potential issue is that for lockdep, avoiding false positives means
    erring on the side of the lock -not- being held, while for this approach
    to rcu_dereference() checking, avoiding false positives means erring on
    the side of the lock being held.

    I might need to create a CONFIG_PROVE_LOCKING_RCU to allow shutting off
    the more-detailed RCU checking when people want to do partial deadlock
    checking, but will see how it goes.

    Thanx, Paul


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