Re: Real-Time Preemption and RCU

[Ingo Molnar]

there's a problem in #5's rcu_read_lock():

        void
        rcu_read_lock(void)
        {
                preempt_disable();
                if (current->rcu_read_lock_nesting++ == 0) {
                        current->rcu_read_lock_ptr =
                                &__get_cpu_var(rcu_data).lock;
                        read_lock(current->rcu_read_lock_ptr);
                }
                preempt_enable();
        }

not only are read_lock()-ed sections preemptible, read_lock() itself may
block, so it cannot be called from within preempt_disable(). How about
something like:

        void
        rcu_read_lock(void)
        {
                preempt_disable();
                if (current->rcu_read_lock_nesting++ == 0) {
                        current->rcu_read_lock_ptr =
                                &__get_cpu_var(rcu_data).lock;
                        preempt_enable();
                        read_lock(current->rcu_read_lock_ptr);
                } else
                        preempt_enable();
        }

this would still make it 'statistically scalable' - but is it correct?

	Ingo
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