> So the address_space attribute says what the pointer points to rather > than where the pointer resides, correct? Yeah. It's currently used for __user and __iomem. Using it for rcu wouldn't be quite the way it was intended, I think, but hey :) > It might be. There are a number of places where it is legal to access > RCU-protected pointers directly, and all of these would need to be > changed. For example, in the example above, one could do: > > foo = NULL; Yeah, all of those would lead to sparse warnings. Are we willing to change all that code? > I recently tried to modify rcu_assign_pointer() to issue the memory > memory barrier only when the pointer was non-NULL, but this ended badly. > Probably because I am not the greatest gcc expert around... We ended > up having to define an rcu_assign_index() to handle the possibility of > assigning a zero-value array index, but my attempts to do type-checking > backfired, and I eventually gave it up. Again, someone a bit more clued > in to gcc than I am could probably pull it off. I don't think I would be that person :) > In addition, it is legal to omit rcu_dereference() and rcu_assign_pointer() > when holding the update-side lock. Right. Those too would lead to problems, unless we change that code to use those (or other) macros. > So I very much like this approach in general, but it will require some > care to implement. I would be very happy to review and comment!!! I'll play with it a bit if I get around, was just reviewing some RCU usage and had the feeling that it should be possible to automate. johannes
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