[deliverable/linux.git] / net / core / dst.c

/*
 * net/core/dst.c	Protocol independent destination cache.
 *
 * Authors:		Alexey Kuznetsov, <kuznet@ms2.inr.ac.ru>
 *
 */

#include <linux/bitops.h>
#include <linux/errno.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/workqueue.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/netdevice.h>
#include <linux/skbuff.h>
#include <linux/string.h>
#include <linux/types.h>
#include <net/net_namespace.h>
#include <linux/sched.h>
#include <linux/prefetch.h>
#include <net/lwtunnel.h>

#include <net/dst.h>
#include <net/dst_metadata.h>

/*
 * Theory of operations:
 * 1) We use a list, protected by a spinlock, to add
 *    new entries from both BH and non-BH context.
 * 2) In order to keep spinlock held for a small delay,
 *    we use a second list where are stored long lived
 *    entries, that are handled by the garbage collect thread
 *    fired by a workqueue.
 * 3) This list is guarded by a mutex,
 *    so that the gc_task and dst_dev_event() can be synchronized.
 */

/*
 * We want to keep lock & list close together
 * to dirty as few cache lines as possible in __dst_free().
 * As this is not a very strong hint, we dont force an alignment on SMP.
 */
static struct {
	spinlock_t		lock;
	struct dst_entry	*list;
	unsigned long		timer_inc;
	unsigned long		timer_expires;
} dst_garbage = {
	.lock = __SPIN_LOCK_UNLOCKED(dst_garbage.lock),
	.timer_inc = DST_GC_MAX,
};
static void dst_gc_task(struct work_struct *work);
static void ___dst_free(struct dst_entry *dst);

static DECLARE_DELAYED_WORK(dst_gc_work, dst_gc_task);

static DEFINE_MUTEX(dst_gc_mutex);
/*
 * long lived entries are maintained in this list, guarded by dst_gc_mutex
 */
static struct dst_entry         *dst_busy_list;

static void dst_gc_task(struct work_struct *work)
{
	int    delayed = 0;
	int    work_performed = 0;
	unsigned long expires = ~0L;
	struct dst_entry *dst, *next, head;
	struct dst_entry *last = &head;

	mutex_lock(&dst_gc_mutex);
	next = dst_busy_list;

loop:
	while ((dst = next) != NULL) {
		next = dst->next;
		prefetch(&next->next);
		cond_resched();
		if (likely(atomic_read(&dst->__refcnt))) {
			last->next = dst;
			last = dst;
			delayed++;
			continue;
		}
		work_performed++;

		dst = dst_destroy(dst);
		if (dst) {
			/* NOHASH and still referenced. Unless it is already
			 * on gc list, invalidate it and add to gc list.
			 *
			 * Note: this is temporary. Actually, NOHASH dst's
			 * must be obsoleted when parent is obsoleted.
			 * But we do not have state "obsoleted, but
			 * referenced by parent", so it is right.
			 */
			if (dst->obsolete > 0)
				continue;

			___dst_free(dst);
			dst->next = next;
			next = dst;
		}
	}

	spin_lock_bh(&dst_garbage.lock);
	next = dst_garbage.list;
	if (next) {
		dst_garbage.list = NULL;
		spin_unlock_bh(&dst_garbage.lock);
		goto loop;
	}
	last->next = NULL;
	dst_busy_list = head.next;
	if (!dst_busy_list)
		dst_garbage.timer_inc = DST_GC_MAX;
	else {
		/*
		 * if we freed less than 1/10 of delayed entries,
		 * we can sleep longer.
		 */
		if (work_performed <= delayed/10) {
			dst_garbage.timer_expires += dst_garbage.timer_inc;
			if (dst_garbage.timer_expires > DST_GC_MAX)
				dst_garbage.timer_expires = DST_GC_MAX;
			dst_garbage.timer_inc += DST_GC_INC;
		} else {
			dst_garbage.timer_inc = DST_GC_INC;
			dst_garbage.timer_expires = DST_GC_MIN;
		}
		expires = dst_garbage.timer_expires;
		/*
		 * if the next desired timer is more than 4 seconds in the
		 * future then round the timer to whole seconds
		 */
		if (expires > 4*HZ)
			expires = round_jiffies_relative(expires);
		schedule_delayed_work(&dst_gc_work, expires);
	}

	spin_unlock_bh(&dst_garbage.lock);
	mutex_unlock(&dst_gc_mutex);
}

int dst_discard_out(struct net *net, struct sock *sk, struct sk_buff *skb)
{
	kfree_skb(skb);
	return 0;
}
EXPORT_SYMBOL(dst_discard_out);

const u32 dst_default_metrics[RTAX_MAX + 1] = {
	/* This initializer is needed to force linker to place this variable
	 * into const section. Otherwise it might end into bss section.
	 * We really want to avoid false sharing on this variable, and catch
	 * any writes on it.
	 */
	[RTAX_MAX] = 0xdeadbeef,
};

void dst_init(struct dst_entry *dst, struct dst_ops *ops,
	      struct net_device *dev, int initial_ref, int initial_obsolete,
	      unsigned short flags)
{
	dst->child = NULL;
	dst->dev = dev;
	if (dev)
		dev_hold(dev);
	dst->ops = ops;
	dst_init_metrics(dst, dst_default_metrics, true);
	dst->expires = 0UL;
	dst->path = dst;
	dst->from = NULL;
#ifdef CONFIG_XFRM
	dst->xfrm = NULL;
#endif
	dst->input = dst_discard;
	dst->output = dst_discard_out;
	dst->error = 0;
	dst->obsolete = initial_obsolete;
	dst->header_len = 0;
	dst->trailer_len = 0;
#ifdef CONFIG_IP_ROUTE_CLASSID
	dst->tclassid = 0;
#endif
	dst->lwtstate = NULL;
	atomic_set(&dst->__refcnt, initial_ref);
	dst->__use = 0;
	dst->lastuse = jiffies;
	dst->flags = flags;
	dst->pending_confirm = 0;
	dst->next = NULL;
	if (!(flags & DST_NOCOUNT))
		dst_entries_add(ops, 1);
}
EXPORT_SYMBOL(dst_init);

void *dst_alloc(struct dst_ops *ops, struct net_device *dev,
		int initial_ref, int initial_obsolete, unsigned short flags)
{
	struct dst_entry *dst;

	if (ops->gc && dst_entries_get_fast(ops) > ops->gc_thresh) {
		if (ops->gc(ops))
			return NULL;
	}

	dst = kmem_cache_alloc(ops->kmem_cachep, GFP_ATOMIC);
	if (!dst)
		return NULL;

	dst_init(dst, ops, dev, initial_ref, initial_obsolete, flags);

	return dst;
}
EXPORT_SYMBOL(dst_alloc);

static void ___dst_free(struct dst_entry *dst)
{
	/* The first case (dev==NULL) is required, when
	   protocol module is unloaded.
	 */
	if (dst->dev == NULL || !(dst->dev->flags&IFF_UP)) {
		dst->input = dst_discard;
		dst->output = dst_discard_out;
	}
	dst->obsolete = DST_OBSOLETE_DEAD;
}

void __dst_free(struct dst_entry *dst)
{
	spin_lock_bh(&dst_garbage.lock);
	___dst_free(dst);
	dst->next = dst_garbage.list;
	dst_garbage.list = dst;
	if (dst_garbage.timer_inc > DST_GC_INC) {
		dst_garbage.timer_inc = DST_GC_INC;
		dst_garbage.timer_expires = DST_GC_MIN;
		mod_delayed_work(system_wq, &dst_gc_work,
				 dst_garbage.timer_expires);
	}
	spin_unlock_bh(&dst_garbage.lock);
}
EXPORT_SYMBOL(__dst_free);

struct dst_entry *dst_destroy(struct dst_entry * dst)
{
	struct dst_entry *child;

	smp_rmb();

again:
	child = dst->child;

	if (!(dst->flags & DST_NOCOUNT))
		dst_entries_add(dst->ops, -1);

	if (dst->ops->destroy)
		dst->ops->destroy(dst);
	if (dst->dev)
		dev_put(dst->dev);

	lwtstate_put(dst->lwtstate);

	if (dst->flags & DST_METADATA)
		metadata_dst_free((struct metadata_dst *)dst);
	else
		kmem_cache_free(dst->ops->kmem_cachep, dst);

	dst = child;
	if (dst) {
		int nohash = dst->flags & DST_NOHASH;

		if (atomic_dec_and_test(&dst->__refcnt)) {
			/* We were real parent of this dst, so kill child. */
			if (nohash)
				goto again;
		} else {
			/* Child is still referenced, return it for freeing. */
			if (nohash)
				return dst;
			/* Child is still in his hash table */
		}
	}
	return NULL;
}
EXPORT_SYMBOL(dst_destroy);

static void dst_destroy_rcu(struct rcu_head *head)
{
	struct dst_entry *dst = container_of(head, struct dst_entry, rcu_head);

	dst = dst_destroy(dst);
	if (dst)
		__dst_free(dst);
}

void dst_release(struct dst_entry *dst)
{
	if (dst) {
		int newrefcnt;
		unsigned short nocache = dst->flags & DST_NOCACHE;

		newrefcnt = atomic_dec_return(&dst->__refcnt);
		if (unlikely(newrefcnt < 0))
			net_warn_ratelimited("%s: dst:%p refcnt:%d\n",
					     __func__, dst, newrefcnt);
		if (!newrefcnt && unlikely(nocache))
			call_rcu(&dst->rcu_head, dst_destroy_rcu);
	}
}
EXPORT_SYMBOL(dst_release);

u32 *dst_cow_metrics_generic(struct dst_entry *dst, unsigned long old)
{
	u32 *p = kmalloc(sizeof(u32) * RTAX_MAX, GFP_ATOMIC);

	if (p) {
		u32 *old_p = __DST_METRICS_PTR(old);
		unsigned long prev, new;

		memcpy(p, old_p, sizeof(u32) * RTAX_MAX);

		new = (unsigned long) p;
		prev = cmpxchg(&dst->_metrics, old, new);

		if (prev != old) {
			kfree(p);
			p = __DST_METRICS_PTR(prev);
			if (prev & DST_METRICS_READ_ONLY)
				p = NULL;
		}
	}
	return p;
}
EXPORT_SYMBOL(dst_cow_metrics_generic);

/* Caller asserts that dst_metrics_read_only(dst) is false.  */
void __dst_destroy_metrics_generic(struct dst_entry *dst, unsigned long old)
{
	unsigned long prev, new;

	new = ((unsigned long) dst_default_metrics) | DST_METRICS_READ_ONLY;
	prev = cmpxchg(&dst->_metrics, old, new);
	if (prev == old)
		kfree(__DST_METRICS_PTR(old));
}
EXPORT_SYMBOL(__dst_destroy_metrics_generic);

static struct dst_ops md_dst_ops = {
	.family =		AF_UNSPEC,
};

static int dst_md_discard_out(struct net *net, struct sock *sk, struct sk_buff *skb)
{
	WARN_ONCE(1, "Attempting to call output on metadata dst\n");
	kfree_skb(skb);
	return 0;
}

static int dst_md_discard(struct sk_buff *skb)
{
	WARN_ONCE(1, "Attempting to call input on metadata dst\n");
	kfree_skb(skb);
	return 0;
}

static void __metadata_dst_init(struct metadata_dst *md_dst, u8 optslen)
{
	struct dst_entry *dst;

	dst = &md_dst->dst;
	dst_init(dst, &md_dst_ops, NULL, 1, DST_OBSOLETE_NONE,
		 DST_METADATA | DST_NOCACHE | DST_NOCOUNT);

	dst->input = dst_md_discard;
	dst->output = dst_md_discard_out;

	memset(dst + 1, 0, sizeof(*md_dst) + optslen - sizeof(*dst));
}

struct metadata_dst *metadata_dst_alloc(u8 optslen, gfp_t flags)
{
	struct metadata_dst *md_dst;

	md_dst = kmalloc(sizeof(*md_dst) + optslen, flags);
	if (!md_dst)
		return NULL;

	__metadata_dst_init(md_dst, optslen);

	return md_dst;
}
EXPORT_SYMBOL_GPL(metadata_dst_alloc);

void metadata_dst_free(struct metadata_dst *md_dst)
{
#ifdef CONFIG_DST_CACHE
	dst_cache_destroy(&md_dst->u.tun_info.dst_cache);
#endif
	kfree(md_dst);
}

struct metadata_dst __percpu *metadata_dst_alloc_percpu(u8 optslen, gfp_t flags)
{
	int cpu;
	struct metadata_dst __percpu *md_dst;

	md_dst = __alloc_percpu_gfp(sizeof(struct metadata_dst) + optslen,
				    __alignof__(struct metadata_dst), flags);
	if (!md_dst)
		return NULL;

	for_each_possible_cpu(cpu)
		__metadata_dst_init(per_cpu_ptr(md_dst, cpu), optslen);

	return md_dst;
}
EXPORT_SYMBOL_GPL(metadata_dst_alloc_percpu);

/* Dirty hack. We did it in 2.2 (in __dst_free),
 * we have _very_ good reasons not to repeat
 * this mistake in 2.3, but we have no choice
 * now. _It_ _is_ _explicit_ _deliberate_
 * _race_ _condition_.
 *
 * Commented and originally written by Alexey.
 */
static void dst_ifdown(struct dst_entry *dst, struct net_device *dev,
		       int unregister)
{
	if (dst->ops->ifdown)
		dst->ops->ifdown(dst, dev, unregister);

	if (dev != dst->dev)
		return;

	if (!unregister) {
		dst->input = dst_discard;
		dst->output = dst_discard_out;
	} else {
		dst->dev = dev_net(dst->dev)->loopback_dev;
		dev_hold(dst->dev);
		dev_put(dev);
	}
}

static int dst_dev_event(struct notifier_block *this, unsigned long event,
			 void *ptr)
{
	struct net_device *dev = netdev_notifier_info_to_dev(ptr);
	struct dst_entry *dst, *last = NULL;

	switch (event) {
	case NETDEV_UNREGISTER_FINAL:
	case NETDEV_DOWN:
		mutex_lock(&dst_gc_mutex);
		for (dst = dst_busy_list; dst; dst = dst->next) {
			last = dst;
			dst_ifdown(dst, dev, event != NETDEV_DOWN);
		}

		spin_lock_bh(&dst_garbage.lock);
		dst = dst_garbage.list;
		dst_garbage.list = NULL;
		spin_unlock_bh(&dst_garbage.lock);

		if (last)
			last->next = dst;
		else
			dst_busy_list = dst;
		for (; dst; dst = dst->next)
			dst_ifdown(dst, dev, event != NETDEV_DOWN);
		mutex_unlock(&dst_gc_mutex);
		break;
	}
	return NOTIFY_DONE;
}

static struct notifier_block dst_dev_notifier = {
	.notifier_call	= dst_dev_event,
	.priority = -10, /* must be called after other network notifiers */
};

void __init dst_subsys_init(void)
{
	register_netdevice_notifier(&dst_dev_notifier);
}
Commit	Line	Data
	1	/*
	2	* net/core/dst.c Protocol independent destination cache.
	3	*
	4	* Authors: Alexey Kuznetsov, <kuznet@ms2.inr.ac.ru>
	5	*
	6	*/
	7
	8	#include <linux/bitops.h>
	9	#include <linux/errno.h>
	10	#include <linux/init.h>
	11	#include <linux/kernel.h>
	12	#include <linux/workqueue.h>
	13	#include <linux/mm.h>
	14	#include <linux/module.h>
	15	#include <linux/slab.h>
	16	#include <linux/netdevice.h>
	17	#include <linux/skbuff.h>
	18	#include <linux/string.h>
	19	#include <linux/types.h>
	20	#include <net/net_namespace.h>
	21	#include <linux/sched.h>
	22	#include <linux/prefetch.h>
	23	#include <net/lwtunnel.h>
	24
	25	#include <net/dst.h>
	26	#include <net/dst_metadata.h>
	27
	28	/*
	29	* Theory of operations:
	30	* 1) We use a list, protected by a spinlock, to add
	31	* new entries from both BH and non-BH context.
	32	* 2) In order to keep spinlock held for a small delay,
	33	* we use a second list where are stored long lived
	34	* entries, that are handled by the garbage collect thread
	35	* fired by a workqueue.
	36	* 3) This list is guarded by a mutex,
	37	* so that the gc_task and dst_dev_event() can be synchronized.
	38	*/
	39
	40	/*
	41	* We want to keep lock & list close together
	42	* to dirty as few cache lines as possible in __dst_free().
	43	* As this is not a very strong hint, we dont force an alignment on SMP.
	44	*/
	45	static struct {
	46	spinlock_t lock;
	47	struct dst_entry *list;
	48	unsigned long timer_inc;
	49	unsigned long timer_expires;
	50	} dst_garbage = {
	51	.lock = __SPIN_LOCK_UNLOCKED(dst_garbage.lock),
	52	.timer_inc = DST_GC_MAX,
	53	};
	54	static void dst_gc_task(struct work_struct *work);
	55	static void ___dst_free(struct dst_entry *dst);
	56
	57	static DECLARE_DELAYED_WORK(dst_gc_work, dst_gc_task);
	58
	59	static DEFINE_MUTEX(dst_gc_mutex);
	60	/*
	61	* long lived entries are maintained in this list, guarded by dst_gc_mutex
	62	*/
	63	static struct dst_entry *dst_busy_list;
	64
	65	static void dst_gc_task(struct work_struct *work)
	66	{
	67	int delayed = 0;
	68	int work_performed = 0;
	69	unsigned long expires = ~0L;
	70	struct dst_entry dst, next, head;
	71	struct dst_entry *last = &head;
	72
	73	mutex_lock(&dst_gc_mutex);
	74	next = dst_busy_list;
	75
	76	loop:
	77	while ((dst = next) != NULL) {
	78	next = dst->next;
	79	prefetch(&next->next);
	80	cond_resched();
	81	if (likely(atomic_read(&dst->__refcnt))) {
	82	last->next = dst;
	83	last = dst;
	84	delayed++;
	85	continue;
	86	}
	87	work_performed++;
	88
	89	dst = dst_destroy(dst);
	90	if (dst) {
	91	/* NOHASH and still referenced. Unless it is already
	92	* on gc list, invalidate it and add to gc list.
	93	*
	94	* Note: this is temporary. Actually, NOHASH dst's
	95	* must be obsoleted when parent is obsoleted.
	96	* But we do not have state "obsoleted, but
	97	* referenced by parent", so it is right.
	98	*/
	99	if (dst->obsolete > 0)
	100	continue;
	101
	102	___dst_free(dst);
	103	dst->next = next;
	104	next = dst;
	105	}
	106	}
	107
	108	spin_lock_bh(&dst_garbage.lock);
	109	next = dst_garbage.list;
	110	if (next) {
	111	dst_garbage.list = NULL;
	112	spin_unlock_bh(&dst_garbage.lock);
	113	goto loop;
	114	}
	115	last->next = NULL;
	116	dst_busy_list = head.next;
	117	if (!dst_busy_list)
	118	dst_garbage.timer_inc = DST_GC_MAX;
	119	else {
	120	/*
	121	* if we freed less than 1/10 of delayed entries,
	122	* we can sleep longer.
	123	*/
	124	if (work_performed <= delayed/10) {
	125	dst_garbage.timer_expires += dst_garbage.timer_inc;
	126	if (dst_garbage.timer_expires > DST_GC_MAX)
	127	dst_garbage.timer_expires = DST_GC_MAX;
	128	dst_garbage.timer_inc += DST_GC_INC;
	129	} else {
	130	dst_garbage.timer_inc = DST_GC_INC;
	131	dst_garbage.timer_expires = DST_GC_MIN;
	132	}
	133	expires = dst_garbage.timer_expires;
	134	/*
	135	* if the next desired timer is more than 4 seconds in the
	136	* future then round the timer to whole seconds
	137	*/
	138	if (expires > 4*HZ)
	139	expires = round_jiffies_relative(expires);
	140	schedule_delayed_work(&dst_gc_work, expires);
	141	}
	142
	143	spin_unlock_bh(&dst_garbage.lock);
	144	mutex_unlock(&dst_gc_mutex);
	145	}
	146
	147	int dst_discard_out(struct net net, struct sock sk, struct sk_buff *skb)
	148	{
	149	kfree_skb(skb);
	150	return 0;
	151	}
	152	EXPORT_SYMBOL(dst_discard_out);
	153
	154	const u32 dst_default_metrics[RTAX_MAX + 1] = {
	155	/* This initializer is needed to force linker to place this variable
	156	* into const section. Otherwise it might end into bss section.
	157	* We really want to avoid false sharing on this variable, and catch
	158	* any writes on it.
	159	*/
	160	[RTAX_MAX] = 0xdeadbeef,
	161	};
	162
	163	void dst_init(struct dst_entry dst, struct dst_ops ops,
	164	struct net_device *dev, int initial_ref, int initial_obsolete,
	165	unsigned short flags)
	166	{
	167	dst->child = NULL;
	168	dst->dev = dev;
	169	if (dev)
	170	dev_hold(dev);
	171	dst->ops = ops;
	172	dst_init_metrics(dst, dst_default_metrics, true);
	173	dst->expires = 0UL;
	174	dst->path = dst;
	175	dst->from = NULL;
	176	#ifdef CONFIG_XFRM
	177	dst->xfrm = NULL;
	178	#endif
	179	dst->input = dst_discard;
	180	dst->output = dst_discard_out;
	181	dst->error = 0;
	182	dst->obsolete = initial_obsolete;
	183	dst->header_len = 0;
	184	dst->trailer_len = 0;
	185	#ifdef CONFIG_IP_ROUTE_CLASSID
	186	dst->tclassid = 0;
	187	#endif
	188	dst->lwtstate = NULL;
	189	atomic_set(&dst->__refcnt, initial_ref);
	190	dst->__use = 0;
	191	dst->lastuse = jiffies;
	192	dst->flags = flags;
	193	dst->pending_confirm = 0;
	194	dst->next = NULL;
	195	if (!(flags & DST_NOCOUNT))
	196	dst_entries_add(ops, 1);
	197	}
	198	EXPORT_SYMBOL(dst_init);
	199
	200	void dst_alloc(struct dst_ops ops, struct net_device *dev,
	201	int initial_ref, int initial_obsolete, unsigned short flags)
	202	{
	203	struct dst_entry *dst;
	204
	205	if (ops->gc && dst_entries_get_fast(ops) > ops->gc_thresh) {
	206	if (ops->gc(ops))
	207	return NULL;
	208	}
	209
	210	dst = kmem_cache_alloc(ops->kmem_cachep, GFP_ATOMIC);
	211	if (!dst)
	212	return NULL;
	213
	214	dst_init(dst, ops, dev, initial_ref, initial_obsolete, flags);
	215
	216	return dst;
	217	}
	218	EXPORT_SYMBOL(dst_alloc);
	219
	220	static void ___dst_free(struct dst_entry *dst)
	221	{
	222	/* The first case (dev==NULL) is required, when
	223	protocol module is unloaded.
	224	*/
	225	if (dst->dev == NULL \|\| !(dst->dev->flags&IFF_UP)) {
	226	dst->input = dst_discard;
	227	dst->output = dst_discard_out;
	228	}
	229	dst->obsolete = DST_OBSOLETE_DEAD;
	230	}
	231
	232	void __dst_free(struct dst_entry *dst)
	233	{
	234	spin_lock_bh(&dst_garbage.lock);
	235	___dst_free(dst);
	236	dst->next = dst_garbage.list;
	237	dst_garbage.list = dst;
	238	if (dst_garbage.timer_inc > DST_GC_INC) {
	239	dst_garbage.timer_inc = DST_GC_INC;
	240	dst_garbage.timer_expires = DST_GC_MIN;
	241	mod_delayed_work(system_wq, &dst_gc_work,
	242	dst_garbage.timer_expires);
	243	}
	244	spin_unlock_bh(&dst_garbage.lock);
	245	}
	246	EXPORT_SYMBOL(__dst_free);
	247
	248	struct dst_entry dst_destroy(struct dst_entry dst)
	249	{
	250	struct dst_entry *child;
	251
	252	smp_rmb();
	253
	254	again:
	255	child = dst->child;
	256
	257	if (!(dst->flags & DST_NOCOUNT))
	258	dst_entries_add(dst->ops, -1);
	259
	260	if (dst->ops->destroy)
	261	dst->ops->destroy(dst);
	262	if (dst->dev)
	263	dev_put(dst->dev);
	264
	265	lwtstate_put(dst->lwtstate);
	266
	267	if (dst->flags & DST_METADATA)
	268	metadata_dst_free((struct metadata_dst *)dst);
	269	else
	270	kmem_cache_free(dst->ops->kmem_cachep, dst);
	271
	272	dst = child;
	273	if (dst) {
	274	int nohash = dst->flags & DST_NOHASH;
	275
	276	if (atomic_dec_and_test(&dst->__refcnt)) {
	277	/* We were real parent of this dst, so kill child. */
	278	if (nohash)
	279	goto again;
	280	} else {
	281	/* Child is still referenced, return it for freeing. */
	282	if (nohash)
	283	return dst;
	284	/* Child is still in his hash table */
	285	}
	286	}
	287	return NULL;
	288	}
	289	EXPORT_SYMBOL(dst_destroy);
	290
	291	static void dst_destroy_rcu(struct rcu_head *head)
	292	{
	293	struct dst_entry *dst = container_of(head, struct dst_entry, rcu_head);
	294
	295	dst = dst_destroy(dst);
	296	if (dst)
	297	__dst_free(dst);
	298	}
	299
	300	void dst_release(struct dst_entry *dst)
	301	{
	302	if (dst) {
	303	int newrefcnt;
	304	unsigned short nocache = dst->flags & DST_NOCACHE;
	305
	306	newrefcnt = atomic_dec_return(&dst->__refcnt);
	307	if (unlikely(newrefcnt < 0))
	308	net_warn_ratelimited("%s: dst:%p refcnt:%d\n",
	309	__func__, dst, newrefcnt);
	310	if (!newrefcnt && unlikely(nocache))
	311	call_rcu(&dst->rcu_head, dst_destroy_rcu);
	312	}
	313	}
	314	EXPORT_SYMBOL(dst_release);
	315
	316	u32 dst_cow_metrics_generic(struct dst_entry dst, unsigned long old)
	317	{
	318	u32 p = kmalloc(sizeof(u32) RTAX_MAX, GFP_ATOMIC);
	319
	320	if (p) {
	321	u32 *old_p = __DST_METRICS_PTR(old);
	322	unsigned long prev, new;
	323
	324	memcpy(p, old_p, sizeof(u32) * RTAX_MAX);
	325
	326	new = (unsigned long) p;
	327	prev = cmpxchg(&dst->_metrics, old, new);
	328
	329	if (prev != old) {
	330	kfree(p);
	331	p = __DST_METRICS_PTR(prev);
	332	if (prev & DST_METRICS_READ_ONLY)
	333	p = NULL;
	334	}
	335	}
	336	return p;
	337	}
	338	EXPORT_SYMBOL(dst_cow_metrics_generic);
	339
	340	/* Caller asserts that dst_metrics_read_only(dst) is false. */
	341	void __dst_destroy_metrics_generic(struct dst_entry *dst, unsigned long old)
	342	{
	343	unsigned long prev, new;
	344
	345	new = ((unsigned long) dst_default_metrics) \| DST_METRICS_READ_ONLY;
	346	prev = cmpxchg(&dst->_metrics, old, new);
	347	if (prev == old)
	348	kfree(__DST_METRICS_PTR(old));
	349	}
	350	EXPORT_SYMBOL(__dst_destroy_metrics_generic);
	351
	352	static struct dst_ops md_dst_ops = {
	353	.family = AF_UNSPEC,
	354	};
	355
	356	static int dst_md_discard_out(struct net net, struct sock sk, struct sk_buff *skb)
	357	{
	358	WARN_ONCE(1, "Attempting to call output on metadata dst\n");
	359	kfree_skb(skb);
	360	return 0;
	361	}
	362
	363	static int dst_md_discard(struct sk_buff *skb)
	364	{
	365	WARN_ONCE(1, "Attempting to call input on metadata dst\n");
	366	kfree_skb(skb);
	367	return 0;
	368	}
	369
	370	static void __metadata_dst_init(struct metadata_dst *md_dst, u8 optslen)
	371	{
	372	struct dst_entry *dst;
	373
	374	dst = &md_dst->dst;
	375	dst_init(dst, &md_dst_ops, NULL, 1, DST_OBSOLETE_NONE,
	376	DST_METADATA \| DST_NOCACHE \| DST_NOCOUNT);
	377
	378	dst->input = dst_md_discard;
	379	dst->output = dst_md_discard_out;
	380
	381	memset(dst + 1, 0, sizeof(md_dst) + optslen - sizeof(dst));
	382	}
	383
	384	struct metadata_dst *metadata_dst_alloc(u8 optslen, gfp_t flags)
	385	{
	386	struct metadata_dst *md_dst;
	387
	388	md_dst = kmalloc(sizeof(*md_dst) + optslen, flags);
	389	if (!md_dst)
	390	return NULL;
	391
	392	__metadata_dst_init(md_dst, optslen);
	393
	394	return md_dst;
	395	}
	396	EXPORT_SYMBOL_GPL(metadata_dst_alloc);
	397
	398	void metadata_dst_free(struct metadata_dst *md_dst)
	399	{
	400	#ifdef CONFIG_DST_CACHE
	401	dst_cache_destroy(&md_dst->u.tun_info.dst_cache);
	402	#endif
	403	kfree(md_dst);
	404	}
	405
	406	struct metadata_dst __percpu *metadata_dst_alloc_percpu(u8 optslen, gfp_t flags)
	407	{
	408	int cpu;
	409	struct metadata_dst __percpu *md_dst;
	410
	411	md_dst = __alloc_percpu_gfp(sizeof(struct metadata_dst) + optslen,
	412	__alignof__(struct metadata_dst), flags);
	413	if (!md_dst)
	414	return NULL;
	415
	416	for_each_possible_cpu(cpu)
	417	__metadata_dst_init(per_cpu_ptr(md_dst, cpu), optslen);
	418
	419	return md_dst;
	420	}
	421	EXPORT_SYMBOL_GPL(metadata_dst_alloc_percpu);
	422
	423	/* Dirty hack. We did it in 2.2 (in __dst_free),
	424	* we have _very_ good reasons not to repeat
	425	* this mistake in 2.3, but we have no choice
	426	* now. _It_ _is_ _explicit_ _deliberate_
	427	* _race_ _condition_.
	428	*
	429	* Commented and originally written by Alexey.
	430	*/
	431	static void dst_ifdown(struct dst_entry dst, struct net_device dev,
	432	int unregister)
	433	{
	434	if (dst->ops->ifdown)
	435	dst->ops->ifdown(dst, dev, unregister);
	436
	437	if (dev != dst->dev)
	438	return;
	439
	440	if (!unregister) {
	441	dst->input = dst_discard;
	442	dst->output = dst_discard_out;
	443	} else {
	444	dst->dev = dev_net(dst->dev)->loopback_dev;
	445	dev_hold(dst->dev);
	446	dev_put(dev);
	447	}
	448	}
	449
	450	static int dst_dev_event(struct notifier_block *this, unsigned long event,
	451	void *ptr)
	452	{
	453	struct net_device *dev = netdev_notifier_info_to_dev(ptr);
	454	struct dst_entry dst, last = NULL;
	455
	456	switch (event) {
	457	case NETDEV_UNREGISTER_FINAL:
	458	case NETDEV_DOWN:
	459	mutex_lock(&dst_gc_mutex);
	460	for (dst = dst_busy_list; dst; dst = dst->next) {
	461	last = dst;
	462	dst_ifdown(dst, dev, event != NETDEV_DOWN);
	463	}
	464
	465	spin_lock_bh(&dst_garbage.lock);
	466	dst = dst_garbage.list;
	467	dst_garbage.list = NULL;
	468	spin_unlock_bh(&dst_garbage.lock);
	469
	470	if (last)
	471	last->next = dst;
	472	else
	473	dst_busy_list = dst;
	474	for (; dst; dst = dst->next)
	475	dst_ifdown(dst, dev, event != NETDEV_DOWN);
	476	mutex_unlock(&dst_gc_mutex);
	477	break;
	478	}
	479	return NOTIFY_DONE;
	480	}
	481
	482	static struct notifier_block dst_dev_notifier = {
	483	.notifier_call = dst_dev_event,
	484	.priority = -10, /* must be called after other network notifiers */
	485	};
	486
	487	void __init dst_subsys_init(void)
	488	{
	489	register_netdevice_notifier(&dst_dev_notifier);
	490	}