On Fri, Jul 31, 2015 at 07:08:04PM +0200, Sebastian Andrzej Siewior wrote:
> Hi Peter,
>
> this series was made before I noticed that you introduced a RB tree for
> lookup but the old way still remains under !CONFIG_MODULES_TREE_LOOKUP.
> In the old way the caller had preempt_disable() while invoking
> list_for_each_safe_rcu() which is (according to the RCU checklist) not a
> substitute for rcu_readlock().
This is true. preempt_disable() != rcu_read_lock().
> With your CONFIG_MODULES_TREE_LOOKUP I fail to understand what blocks
> free_module() until all mod_find() callers have dropped their refrence to
> the obtained struct mod. We had synchronize_sched() in RCU case.
We still have synchronize_sched(), but that is not RCU, that is
RCU-sched, and rcu_read_lock_sched() == preempt_disable() (+- some
debugging bits).
The code used to be broken in this regard, see 0be964be0d45 ("module:
Sanitize RCU usage and locking"), that fixed things to be consistent.
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