linux-kernel - [RFC 0/4] use rcu_read_lock() during module list walk

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Date:	Fri, 31 Jul 2015 19:08:04 +0200
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
	tglx@...utronix.de
Subject: [RFC 0/4] use rcu_read_lock() during module list walk

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().
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.

Sebastian

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