sch_generic.c

/*
 * net/sched/sch_generic.c	Generic packet scheduler routines.
 *
 *		This program is free software; you can redistribute it and/or
 *		modify it under the terms of the GNU General Public License
 *		as published by the Free Software Foundation; either version
 *		2 of the License, or (at your option) any later version.
 *
 * Authors:	Alexey Kuznetsov, <kuznet@ms2.inr.ac.ru>
 *              Jamal Hadi Salim, <hadi@cyberus.ca> 990601
 *              - Ingress support
 */

#include <linux/bitops.h>
#include <linux/module.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/string.h>
#include <linux/errno.h>
#include <linux/netdevice.h>
#include <linux/skbuff.h>
#include <linux/rtnetlink.h>
#include <linux/init.h>
#include <linux/rcupdate.h>
#include <linux/list.h>
#include <net/pkt_sched.h>

/* Main transmission queue. */

/* Modifications to data participating in scheduling must be protected with
 * qdisc_root_lock(qdisc) spinlock.
 *
 * The idea is the following:
 * - enqueue, dequeue are serialized via qdisc root lock
 * - ingress filtering is also serialized via qdisc root lock
 * - updates to tree and tree walking are only done under the rtnl mutex.
 */

static inline int qdisc_qlen(struct Qdisc *q)
{
	return q->q.qlen;
}

static inline int dev_requeue_skb(struct sk_buff *skb, struct Qdisc *q)
{
	if (unlikely(skb->next))
		q->gso_skb = skb;
	else
		q->ops->requeue(skb, q);

	__netif_schedule(q);
	return 0;
}

static inline struct sk_buff *dequeue_skb(struct Qdisc *q)
{
	struct sk_buff *skb;

	if ((skb = q->gso_skb))
		q->gso_skb = NULL;
	else
		skb = q->dequeue(q);

	return skb;
}

static inline int handle_dev_cpu_collision(struct sk_buff *skb,
					   struct netdev_queue *dev_queue,
					   struct Qdisc *q)
{
	int ret;

	if (unlikely(dev_queue->xmit_lock_owner == smp_processor_id())) {
		/*
		 * Same CPU holding the lock. It may be a transient
		 * configuration error, when hard_start_xmit() recurses. We
		 * detect it by checking xmit owner and drop the packet when
		 * deadloop is detected. Return OK to try the next skb.
		 */
		kfree_skb(skb);
		if (net_ratelimit())
			printk(KERN_WARNING "Dead loop on netdevice %s, "
			       "fix it urgently!\n", dev_queue->dev->name);
		ret = qdisc_qlen(q);
	} else {
		/*
		 * Another cpu is holding lock, requeue & delay xmits for
		 * some time.
		 */
		__get_cpu_var(netdev_rx_stat).cpu_collision++;
		ret = dev_requeue_skb(skb, q);
	}

	return ret;
}

/*
 * NOTE: Called under qdisc_lock(q) with locally disabled BH.
 *
 * __QDISC_STATE_RUNNING guarantees only one CPU can process
 * this qdisc at a time. qdisc_lock(q) serializes queue accesses for
 * this queue.
 *
 *  netif_tx_lock serializes accesses to device driver.
 *
 *  qdisc_lock(q) and netif_tx_lock are mutually exclusive,
 *  if one is grabbed, another must be free.
 *
 * Note, that this procedure can be called by a watchdog timer
 *
 * Returns to the caller:
 *				0  - queue is empty or throttled.
 *				>0 - queue is not empty.
 *
 */
static inline int qdisc_restart(struct Qdisc *q)
{
	struct netdev_queue *txq;
	int ret = NETDEV_TX_BUSY;
	struct net_device *dev;
	spinlock_t *root_lock;
	struct sk_buff *skb;

	/* Dequeue packet */
	if (unlikely((skb = dequeue_skb(q)) == NULL))
		return 0;

	root_lock = qdisc_root_lock(q);

	/* And release qdisc */
	spin_unlock(root_lock);

	dev = qdisc_dev(q);
	txq = netdev_get_tx_queue(dev, skb_get_queue_mapping(skb));

	HARD_TX_LOCK(dev, txq, smp_processor_id());
	if (!netif_subqueue_stopped(dev, skb))
		ret = dev_hard_start_xmit(skb, dev, txq);
	HARD_TX_UNLOCK(dev, txq);

	spin_lock(root_lock);

	switch (ret) {
	case NETDEV_TX_OK:
		/* Driver sent out skb successfully */
		ret = qdisc_qlen(q);
		break;

	case NETDEV_TX_LOCKED:
		/* Driver try lock failed */
		ret = handle_dev_cpu_collision(skb, txq, q);
		break;

	default:
		/* Driver returned NETDEV_TX_BUSY - requeue skb */
		if (unlikely (ret != NETDEV_TX_BUSY && net_ratelimit()))
			printk(KERN_WARNING "BUG %s code %d qlen %d\n",
			       dev->name, ret, q->q.qlen);

		ret = dev_requeue_skb(skb, q);
		break;
	}

	if (ret && netif_tx_queue_stopped(txq))
		ret = 0;

	return ret;
}

void __qdisc_run(struct Qdisc *q)
{
	unsigned long start_time = jiffies;

	while (qdisc_restart(q)) {
		/*
		 * Postpone processing if
		 * 1. another process needs the CPU;
		 * 2. we've been doing it for too long.
		 */
		if (need_resched() || jiffies != start_time) {
			__netif_schedule(q);
			break;
		}
	}

	clear_bit(__QDISC_STATE_RUNNING, &q->state);
}

static void dev_watchdog(unsigned long arg)
{
	struct net_device *dev = (struct net_device *)arg;

	netif_tx_lock(dev);
	if (!qdisc_tx_is_noop(dev)) {
		if (netif_device_present(dev) &&
		    netif_running(dev) &&
		    netif_carrier_ok(dev)) {
			int some_queue_stopped = 0;
			unsigned int i;

			for (i = 0; i < dev->num_tx_queues; i++) {
				struct netdev_queue *txq;

				txq = netdev_get_tx_queue(dev, i);
				if (netif_tx_queue_stopped(txq)) {
					some_queue_stopped = 1;
					break;
				}
			}

			if (some_queue_stopped &&
			    time_after(jiffies, (dev->trans_start +
						 dev->watchdog_timeo))) {
				printk(KERN_INFO "NETDEV WATCHDOG: %s: "
				       "transmit timed out\n",
				       dev->name);
				dev->tx_timeout(dev);
				WARN_ON_ONCE(1);
			}
			if (!mod_timer(&dev->watchdog_timer,
				       round_jiffies(jiffies +
						     dev->watchdog_timeo)))
				dev_hold(dev);
		}
	}
	netif_tx_unlock(dev);

	dev_put(dev);
}

void __netdev_watchdog_up(struct net_device *dev)
{
	if (dev->tx_timeout) {
		if (dev->watchdog_timeo <= 0)
			dev->watchdog_timeo = 5*HZ;
		if (!mod_timer(&dev->watchdog_timer,
			       round_jiffies(jiffies + dev->watchdog_timeo)))
			dev_hold(dev);
	}
}

static void dev_watchdog_up(struct net_device *dev)
{
	__netdev_watchdog_up(dev);
}

static void dev_watchdog_down(struct net_device *dev)
{
	netif_tx_lock_bh(dev);
	if (del_timer(&dev->watchdog_timer))
		dev_put(dev);
	netif_tx_unlock_bh(dev);
}

/**
 *	netif_carrier_on - set carrier
 *	@dev: network device
 *
 * Device has detected that carrier.
 */
void netif_carrier_on(struct net_device *dev)
{
	if (test_and_clear_bit(__LINK_STATE_NOCARRIER, &dev->state)) {
		linkwatch_fire_event(dev);
		if (netif_running(dev))
			__netdev_watchdog_up(dev);
	}
}
EXPORT_SYMBOL(netif_carrier_on);

/**
 *	netif_carrier_off - clear carrier
 *	@dev: network device
 *
 * Device has detected loss of carrier.
 */
void netif_carrier_off(struct net_device *dev)
{
	if (!test_and_set_bit(__LINK_STATE_NOCARRIER, &dev->state))
		linkwatch_fire_event(dev);
}
EXPORT_SYMBOL(netif_carrier_off);

/* "NOOP" scheduler: the best scheduler, recommended for all interfaces
   under all circumstances. It is difficult to invent anything faster or
   cheaper.
 */

static int noop_enqueue(struct sk_buff *skb, struct Qdisc * qdisc)
{
	kfree_skb(skb);
	return NET_XMIT_CN;
}

static struct sk_buff *noop_dequeue(struct Qdisc * qdisc)
{
	return NULL;
}

static int noop_requeue(struct sk_buff *skb, struct Qdisc* qdisc)
{
	if (net_ratelimit())
		printk(KERN_DEBUG "%s deferred output. It is buggy.\n",
		       skb->dev->name);
	kfree_skb(skb);
	return NET_XMIT_CN;
}

struct Qdisc_ops noop_qdisc_ops __read_mostly = {
	.id		=	"noop",
	.priv_size	=	0,
	.enqueue	=	noop_enqueue,
	.dequeue	=	noop_dequeue,
	.requeue	=	noop_requeue,
	.owner		=	THIS_MODULE,
};

static struct netdev_queue noop_netdev_queue = {
	.qdisc		=	&noop_qdisc,
};

struct Qdisc noop_qdisc = {
	.enqueue	=	noop_enqueue,
	.dequeue	=	noop_dequeue,
	.flags		=	TCQ_F_BUILTIN,
	.ops		=	&noop_qdisc_ops,
	.list		=	LIST_HEAD_INIT(noop_qdisc.list),
	.q.lock		=	__SPIN_LOCK_UNLOCKED(noop_qdisc.q.lock),
	.dev_queue	=	&noop_netdev_queue,
};
EXPORT_SYMBOL(noop_qdisc);

static struct Qdisc_ops noqueue_qdisc_ops __read_mostly = {
	.id		=	"noqueue",
	.priv_size	=	0,
	.enqueue	=	noop_enqueue,
	.dequeue	=	noop_dequeue,
	.requeue	=	noop_requeue,
	.owner		=	THIS_MODULE,
};

static struct Qdisc noqueue_qdisc = {
	.enqueue	=	NULL,
	.dequeue	=	noop_dequeue,
	.flags		=	TCQ_F_BUILTIN,
	.ops		=	&noqueue_qdisc_ops,
	.list		=	LIST_HEAD_INIT(noqueue_qdisc.list),
};


static int fifo_fast_enqueue(struct sk_buff *skb, struct Qdisc* qdisc)
{
	struct sk_buff_head *list = &qdisc->q;

	if (skb_queue_len(list) < qdisc_dev(qdisc)->tx_queue_len)
		return __qdisc_enqueue_tail(skb, qdisc, list);

	return qdisc_drop(skb, qdisc);
}

static struct sk_buff *fifo_fast_dequeue(struct Qdisc* qdisc)
{
	struct sk_buff_head *list = &qdisc->q;

	if (!skb_queue_empty(list))
		return __qdisc_dequeue_head(qdisc, list);

	return NULL;
}

static int fifo_fast_requeue(struct sk_buff *skb, struct Qdisc* qdisc)
{
	return __qdisc_requeue(skb, qdisc, &qdisc->q);
}

static void fifo_fast_reset(struct Qdisc* qdisc)
{
	__qdisc_reset_queue(qdisc, &qdisc->q);
	qdisc->qstats.backlog = 0;
}

static struct Qdisc_ops fifo_fast_ops __read_mostly = {
	.id		=	"fifo_fast",
	.priv_size	=	0,
	.enqueue	=	fifo_fast_enqueue,
	.dequeue	=	fifo_fast_dequeue,
	.requeue	=	fifo_fast_requeue,
	.reset		=	fifo_fast_reset,
	.owner		=	THIS_MODULE,
};

struct Qdisc *qdisc_alloc(struct netdev_queue *dev_queue,
			  struct Qdisc_ops *ops)
{
	void *p;
	struct Qdisc *sch;
	unsigned int size;
	int err = -ENOBUFS;

	/* ensure that the Qdisc and the private data are 32-byte aligned */
	size = QDISC_ALIGN(sizeof(*sch));
	size += ops->priv_size + (QDISC_ALIGNTO - 1);

	p = kzalloc(size, GFP_KERNEL);
	if (!p)
		goto errout;
	sch = (struct Qdisc *) QDISC_ALIGN((unsigned long) p);
	sch->padded = (char *) sch - (char *) p;

	INIT_LIST_HEAD(&sch->list);
	skb_queue_head_init(&sch->q);
	sch->ops = ops;
	sch->enqueue = ops->enqueue;
	sch->dequeue = ops->dequeue;
	sch->dev_queue = dev_queue;
	dev_hold(qdisc_dev(sch));
	atomic_set(&sch->refcnt, 1);

	return sch;
errout:
	return ERR_PTR(err);
}

struct Qdisc * qdisc_create_dflt(struct net_device *dev,
				 struct netdev_queue *dev_queue,
				 struct Qdisc_ops *ops,
				 unsigned int parentid)
{
	struct Qdisc *sch;

	sch = qdisc_alloc(dev_queue, ops);
	if (IS_ERR(sch))
		goto errout;
	sch->parent = parentid;

	if (!ops->init || ops->init(sch, NULL) == 0)
		return sch;

	qdisc_destroy(sch);
errout:
	return NULL;
}
EXPORT_SYMBOL(qdisc_create_dflt);

/* Under qdisc_root_lock(qdisc) and BH! */

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

	if (ops->reset)
		ops->reset(qdisc);
}
EXPORT_SYMBOL(qdisc_reset);

/* this is the rcu callback function to clean up a qdisc when there
 * are no further references to it */

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_skb(qdisc->gso_skb);

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

/* Under qdisc_root_lock(qdisc) and BH! */

void qdisc_destroy(struct Qdisc *qdisc)
{
	struct net_device *dev = qdisc_dev(qdisc);

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

	spin_lock_bh(&dev->qdisc_list_lock);
	list_del(&qdisc->list);
	spin_unlock_bh(&dev->qdisc_list_lock);

	call_rcu(&qdisc->q_rcu, __qdisc_destroy);
}
EXPORT_SYMBOL(qdisc_destroy);

static bool dev_all_qdisc_sleeping_noop(struct net_device *dev)
{
	unsigned int i;

	for (i = 0; i < dev->num_tx_queues; i++) {
		struct netdev_queue *txq = netdev_get_tx_queue(dev, i);

		if (txq->qdisc_sleeping != &noop_qdisc)
			return false;
	}
	return true;
}

static void attach_one_default_qdisc(struct net_device *dev,
				     struct netdev_queue *dev_queue,
				     void *_unused)
{
	struct Qdisc *qdisc;

	if (dev->tx_queue_len) {
		qdisc = qdisc_create_dflt(dev, dev_queue,
					  &fifo_fast_ops, TC_H_ROOT);
		if (!qdisc) {
			printk(KERN_INFO "%s: activation failed\n", dev->name);
			return;
		}
		spin_lock_bh(&dev->qdisc_list_lock);
		list_add_tail(&qdisc->list, &dev->qdisc_list);
		spin_unlock_bh(&dev->qdisc_list_lock);
	} else {
		qdisc =  &noqueue_qdisc;
	}
	dev_queue->qdisc_sleeping = qdisc;
}

static void transition_one_qdisc(struct net_device *dev,
				 struct netdev_queue *dev_queue,
				 void *_need_watchdog)
{
	struct Qdisc *new_qdisc = dev_queue->qdisc_sleeping;
	int *need_watchdog_p = _need_watchdog;

	rcu_assign_pointer(dev_queue->qdisc, new_qdisc);
	if (new_qdisc != &noqueue_qdisc)
		*need_watchdog_p = 1;
}

void dev_activate(struct net_device *dev)
{
	int need_watchdog;

	/* No queueing discipline is attached to device;
	 * create default one i.e. fifo_fast for devices,
	 * which need queueing and noqueue_qdisc for
	 * virtual interfaces.
	 */

	if (dev_all_qdisc_sleeping_noop(dev))
		netdev_for_each_tx_queue(dev, attach_one_default_qdisc, NULL);

	if (!netif_carrier_ok(dev))
		/* Delay activation until next carrier-on event */
		return;

	need_watchdog = 0;
	netdev_for_each_tx_queue(dev, transition_one_qdisc, &need_watchdog);

	if (need_watchdog) {
		dev->trans_start = jiffies;
		dev_watchdog_up(dev);
	}
}

static void dev_deactivate_queue(struct net_device *dev,
				 struct netdev_queue *dev_queue,
				 void *_qdisc_default)
{
	struct Qdisc *qdisc_default = _qdisc_default;
	struct sk_buff *skb = NULL;
	struct Qdisc *qdisc;

	qdisc = dev_queue->qdisc;
	if (qdisc) {
		spin_lock_bh(qdisc_lock(qdisc));

		dev_queue->qdisc = qdisc_default;
		qdisc_reset(qdisc);

		spin_unlock_bh(qdisc_lock(qdisc));
	}

	kfree_skb(skb);
}

static bool some_qdisc_is_running(struct net_device *dev, int lock)
{
	unsigned int i;

	for (i = 0; i < dev->num_tx_queues; i++) {
		struct netdev_queue *dev_queue;
		spinlock_t *root_lock;
		struct Qdisc *q;
		int val;

		dev_queue = netdev_get_tx_queue(dev, i);
		q = dev_queue->qdisc;
		root_lock = qdisc_root_lock(q);

		if (lock)
			spin_lock_bh(root_lock);

		val = test_bit(__QDISC_STATE_RUNNING, &q->state);

		if (lock)
			spin_unlock_bh(root_lock);

		if (val)
			return true;
	}
	return false;
}

void dev_deactivate(struct net_device *dev)
{
	bool running;

	netdev_for_each_tx_queue(dev, dev_deactivate_queue, &noop_qdisc);

	dev_watchdog_down(dev);

	/* Wait for outstanding qdisc-less dev_queue_xmit calls. */
	synchronize_rcu();

	/* Wait for outstanding qdisc_run calls. */
	do {
		while (some_qdisc_is_running(dev, 0))
			yield();

		/*
		 * Double-check inside queue lock to ensure that all effects
		 * of the queue run are visible when we return.
		 */
		running = some_qdisc_is_running(dev, 1);

		/*
		 * The running flag should never be set at this point because
		 * we've already set dev->qdisc to noop_qdisc *inside* the same
		 * pair of spin locks.  That is, if any qdisc_run starts after
		 * our initial test it should see the noop_qdisc and then
		 * clear the RUNNING bit before dropping the queue lock.  So
		 * if it is set here then we've found a bug.
		 */
	} while (WARN_ON_ONCE(running));
}

static void dev_init_scheduler_queue(struct net_device *dev,
				     struct netdev_queue *dev_queue,
				     void *_qdisc)
{
	struct Qdisc *qdisc = _qdisc;

	dev_queue->qdisc = qdisc;
	dev_queue->qdisc_sleeping = qdisc;
}

void dev_init_scheduler(struct net_device *dev)
{
	netdev_for_each_tx_queue(dev, dev_init_scheduler_queue, &noop_qdisc);
	dev_init_scheduler_queue(dev, &dev->rx_queue, NULL);

	setup_timer(&dev->watchdog_timer, dev_watchdog, (unsigned long)dev);
}

static void shutdown_scheduler_queue(struct net_device *dev,
				     struct netdev_queue *dev_queue,
				     void *_qdisc_default)
{
	struct Qdisc *qdisc = dev_queue->qdisc_sleeping;
	struct Qdisc *qdisc_default = _qdisc_default;

	if (qdisc) {
		spinlock_t *root_lock = qdisc_root_lock(qdisc);

		dev_queue->qdisc = qdisc_default;
		dev_queue->qdisc_sleeping = qdisc_default;

		spin_lock(root_lock);
		qdisc_destroy(qdisc);
		spin_unlock(root_lock);
	}
}

void dev_shutdown(struct net_device *dev)
{
	netdev_for_each_tx_queue(dev, shutdown_scheduler_queue, &noop_qdisc);
	shutdown_scheduler_queue(dev, &dev->rx_queue, NULL);
	BUG_TRAP(!timer_pending(&dev->watchdog_timer));
}