pkt_sched: Perform bulk of qdisc destruction in RCU. (8a34c5dc) · Commits · 戴 / test

This allows less strict control of access to the qdisc attached to a netdev_queue. It is even allowed to enqueue into a qdisc which is in the process of being destroyed. The RCU handler will toss out those packets. We will need this to handle sharing of a qdisc amongst multiple TX queues. In such a setup the lock has to be shared, so will be inside of the qdisc itself. At which point the netdev_queue lock cannot be used to hard synchronize access to the ->qdisc pointer. One operation we have to keep inside of qdisc_destroy() is the list deletion. It is the only piece of state visible after the RCU quiesce period, so we have to undo it early and under the appropriate locking. The operations in the RCU handler do not need any looking because the qdisc tree is no longer visible to anything at that point. Signed-off-by:

David S. Miller <davem@davemloft.net>

net/sched/sch_generic.c

+11 −9

Original line number	Diff line number	Diff line
		@@ -545,6 +545,17 @@ EXPORT_SYMBOL(qdisc_reset);
		static void __qdisc_destroy(struct rcu_head *head)
		{
		struct Qdisc *qdisc = container_of(head, struct Qdisc, q_rcu);
		const struct Qdisc_ops *ops = qdisc->ops;

		gen_kill_estimator(&qdisc->bstats, &qdisc->rate_est);
		if (ops->reset)
		ops->reset(qdisc);
		if (ops->destroy)
		ops->destroy(qdisc);

		module_put(ops->owner);
		dev_put(qdisc_dev(qdisc));

		kfree((char *) qdisc - qdisc->padded);
		}

		@@ -552,21 +563,12 @@ static void __qdisc_destroy(struct rcu_head *head)

		void qdisc_destroy(struct Qdisc *qdisc)
		{
		const struct Qdisc_ops *ops = qdisc->ops;

		if (qdisc->flags & TCQ_F_BUILTIN \|\|
		!atomic_dec_and_test(&qdisc->refcnt))
		return;

		list_del(&qdisc->list);
		gen_kill_estimator(&qdisc->bstats, &qdisc->rate_est);
		if (ops->reset)
		ops->reset(qdisc);
		if (ops->destroy)
		ops->destroy(qdisc);

		module_put(ops->owner);
		dev_put(qdisc_dev(qdisc));
		call_rcu(&qdisc->q_rcu, __qdisc_destroy);
		}
		EXPORT_SYMBOL(qdisc_destroy);

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