On Mon, Dec 07, 2015 at 08:45:04AM +0800, Boqun Feng wrote:

quoted

quoted

Or maybe, we introduce another address space of sparse like:

	# define __private	__attribute__((noderef, address_space(6)))

and macro to dereference private

	# define private_dereference(p) ((typeof(*p) *) p)

and define struct rcu_node like:

	struct rcu_node {
		raw_spinlock_t __private lock;	/* Root rcu_node's lock protects some */
		...
	};

and finally raw_spin_{un}lock_rcu_node() like:

	static inline void raw_spin_lock_rcu_node(struct rcu_node *rnp)
	{
		raw_spin_lock(private_dereference(&rnp->lock));
		smp_mb__after_unlock_lock();
	}

	static inline void raw_spin_unlock_rcu_node(struct rcu_node *rnp)
	{
		raw_spin_unlock(private_dereference(&rnp->lock));
	}

This __private mechanism also works for others who wants to private
their fields of struct, which is not supported by C.

I will send two patches(one introduces __private and one uses it for
rcu_node->lock) if you think this is not a bad idea ;-)

If rcu_node->lock is the only user then this is probably a bad idea, but
if others also want to have a way to privatize some fields of the
structure, this may be not that bad?

Thomas might also want this for things like
irq_common_data::state_use_accessors for instance.

And I'm fairly sure there's more out there.