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SubjectRe: [patch 0/6] rcu head debugobjects
On Mon, Mar 29, 2010 at 09:39:33AM -0400, Mathieu Desnoyers wrote:
> Hi Paul,
> Thinking about the rcu head init topic, we might be able to drop the
> init_rcu_head() initializer. The idea is the following:
> - We need init_rcu_head_on_stack()/destroy_rcu_head_on_stack().
> - call_rcu() populates the rcu_head and normally does not care about it being
> pre-initialized.
> - The activation fixup can detect if a non-initialized rcu head is being
> activated and just perform the fixup without complaining.
> - If we have two call_rcu() in a row in the same GP on the same rcu_head, the
> activation check will detect it.
> So either we remove all the init_rcu_head(), as was originally proposed, or we
> use one that is a no-op on !DEBUG configs and initialize the object with DEBUG
> configs.
> That removes the dependency on object_is_static().

If I understand correctly, this does sound good. Here is what I think
you are proposing:

o call_rcu() and friends only complain if handed an rcu_head
structure that is still queued awaiting a grace period.
They don't care otherwise.

o rcu_do_batch() complains unless the rcu_head structure has
most recently been enqueued by call_rcu() or one if its friends.

Did I get it right?

Thanx, Paul

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