dst.c revision 4ec93edb14fe5fdee9fae6335f2cbba204627eac 
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/mm.h>
13#include <linux/module.h>
14#include <linux/netdevice.h>
15#include <linux/sched.h>
16#include <linux/skbuff.h>
17#include <linux/string.h>
18#include <linux/types.h>
19
20#include <net/dst.h>
21
22/* Locking strategy:
23 * 1) Garbage collection state of dead destination cache
24 *    entries is protected by dst_lock.
25 * 2) GC is run only from BH context, and is the only remover
26 *    of entries.
27 * 3) Entries are added to the garbage list from both BH
28 *    and non-BH context, so local BH disabling is needed.
29 * 4) All operations modify state, so a spinlock is used.
30 */
31static struct dst_entry 	*dst_garbage_list;
32#if RT_CACHE_DEBUG >= 2
33static atomic_t			 dst_total = ATOMIC_INIT(0);
34#endif
35static DEFINE_SPINLOCK(dst_lock);
36
37static unsigned long dst_gc_timer_expires;
38static unsigned long dst_gc_timer_inc = DST_GC_MAX;
39static void dst_run_gc(unsigned long);
40static void ___dst_free(struct dst_entry * dst);
41
42static DEFINE_TIMER(dst_gc_timer, dst_run_gc, DST_GC_MIN, 0);
43
44static void dst_run_gc(unsigned long dummy)
45{
46	int    delayed = 0;
47	int    work_performed;
48	struct dst_entry * dst, **dstp;
49
50	if (!spin_trylock(&dst_lock)) {
51		mod_timer(&dst_gc_timer, jiffies + HZ/10);
52		return;
53	}
54
55	del_timer(&dst_gc_timer);
56	dstp = &dst_garbage_list;
57	work_performed = 0;
58	while ((dst = *dstp) != NULL) {
59		if (atomic_read(&dst->__refcnt)) {
60			dstp = &dst->next;
61			delayed++;
62			continue;
63		}
64		*dstp = dst->next;
65		work_performed = 1;
66
67		dst = dst_destroy(dst);
68		if (dst) {
69			/* NOHASH and still referenced. Unless it is already
70			 * on gc list, invalidate it and add to gc list.
71			 *
72			 * Note: this is temporary. Actually, NOHASH dst's
73			 * must be obsoleted when parent is obsoleted.
74			 * But we do not have state "obsoleted, but
75			 * referenced by parent", so it is right.
76			 */
77			if (dst->obsolete > 1)
78				continue;
79
80			___dst_free(dst);
81			dst->next = *dstp;
82			*dstp = dst;
83			dstp = &dst->next;
84		}
85	}
86	if (!dst_garbage_list) {
87		dst_gc_timer_inc = DST_GC_MAX;
88		goto out;
89	}
90	if (!work_performed) {
91		if ((dst_gc_timer_expires += dst_gc_timer_inc) > DST_GC_MAX)
92			dst_gc_timer_expires = DST_GC_MAX;
93		dst_gc_timer_inc += DST_GC_INC;
94	} else {
95		dst_gc_timer_inc = DST_GC_INC;
96		dst_gc_timer_expires = DST_GC_MIN;
97	}
98#if RT_CACHE_DEBUG >= 2
99	printk("dst_total: %d/%d %ld\n",
100	       atomic_read(&dst_total), delayed,  dst_gc_timer_expires);
101#endif
102	/* if the next desired timer is more than 4 seconds in the future
103	 * then round the timer to whole seconds
104	 */
105	if (dst_gc_timer_expires > 4*HZ)
106		mod_timer(&dst_gc_timer,
107			round_jiffies(jiffies + dst_gc_timer_expires));
108	else
109		mod_timer(&dst_gc_timer, jiffies + dst_gc_timer_expires);
110
111out:
112	spin_unlock(&dst_lock);
113}
114
115static int dst_discard_in(struct sk_buff *skb)
116{
117	kfree_skb(skb);
118	return 0;
119}
120
121static int dst_discard_out(struct sk_buff *skb)
122{
123	kfree_skb(skb);
124	return 0;
125}
126
127void * dst_alloc(struct dst_ops * ops)
128{
129	struct dst_entry * dst;
130
131	if (ops->gc && atomic_read(&ops->entries) > ops->gc_thresh) {
132		if (ops->gc())
133			return NULL;
134	}
135	dst = kmem_cache_alloc(ops->kmem_cachep, GFP_ATOMIC);
136	if (!dst)
137		return NULL;
138	memset(dst, 0, ops->entry_size);
139	atomic_set(&dst->__refcnt, 0);
140	dst->ops = ops;
141	dst->lastuse = jiffies;
142	dst->path = dst;
143	dst->input = dst_discard_in;
144	dst->output = dst_discard_out;
145#if RT_CACHE_DEBUG >= 2
146	atomic_inc(&dst_total);
147#endif
148	atomic_inc(&ops->entries);
149	return dst;
150}
151
152static void ___dst_free(struct dst_entry * dst)
153{
154	/* The first case (dev==NULL) is required, when
155	   protocol module is unloaded.
156	 */
157	if (dst->dev == NULL || !(dst->dev->flags&IFF_UP)) {
158		dst->input = dst_discard_in;
159		dst->output = dst_discard_out;
160	}
161	dst->obsolete = 2;
162}
163
164void __dst_free(struct dst_entry * dst)
165{
166	spin_lock_bh(&dst_lock);
167	___dst_free(dst);
168	dst->next = dst_garbage_list;
169	dst_garbage_list = dst;
170	if (dst_gc_timer_inc > DST_GC_INC) {
171		dst_gc_timer_inc = DST_GC_INC;
172		dst_gc_timer_expires = DST_GC_MIN;
173		mod_timer(&dst_gc_timer, jiffies + dst_gc_timer_expires);
174	}
175	spin_unlock_bh(&dst_lock);
176}
177
178struct dst_entry *dst_destroy(struct dst_entry * dst)
179{
180	struct dst_entry *child;
181	struct neighbour *neigh;
182	struct hh_cache *hh;
183
184	smp_rmb();
185
186again:
187	neigh = dst->neighbour;
188	hh = dst->hh;
189	child = dst->child;
190
191	dst->hh = NULL;
192	if (hh && atomic_dec_and_test(&hh->hh_refcnt))
193		kfree(hh);
194
195	if (neigh) {
196		dst->neighbour = NULL;
197		neigh_release(neigh);
198	}
199
200	atomic_dec(&dst->ops->entries);
201
202	if (dst->ops->destroy)
203		dst->ops->destroy(dst);
204	if (dst->dev)
205		dev_put(dst->dev);
206#if RT_CACHE_DEBUG >= 2
207	atomic_dec(&dst_total);
208#endif
209	kmem_cache_free(dst->ops->kmem_cachep, dst);
210
211	dst = child;
212	if (dst) {
213		int nohash = dst->flags & DST_NOHASH;
214
215		if (atomic_dec_and_test(&dst->__refcnt)) {
216			/* We were real parent of this dst, so kill child. */
217			if (nohash)
218				goto again;
219		} else {
220			/* Child is still referenced, return it for freeing. */
221			if (nohash)
222				return dst;
223			/* Child is still in his hash table */
224		}
225	}
226	return NULL;
227}
228
229/* Dirty hack. We did it in 2.2 (in __dst_free),
230 * we have _very_ good reasons not to repeat
231 * this mistake in 2.3, but we have no choice
232 * now. _It_ _is_ _explicit_ _deliberate_
233 * _race_ _condition_.
234 *
235 * Commented and originally written by Alexey.
236 */
237static inline void dst_ifdown(struct dst_entry *dst, struct net_device *dev,
238			      int unregister)
239{
240	if (dst->ops->ifdown)
241		dst->ops->ifdown(dst, dev, unregister);
242
243	if (dev != dst->dev)
244		return;
245
246	if (!unregister) {
247		dst->input = dst_discard_in;
248		dst->output = dst_discard_out;
249	} else {
250		dst->dev = &loopback_dev;
251		dev_hold(&loopback_dev);
252		dev_put(dev);
253		if (dst->neighbour && dst->neighbour->dev == dev) {
254			dst->neighbour->dev = &loopback_dev;
255			dev_put(dev);
256			dev_hold(&loopback_dev);
257		}
258	}
259}
260
261static int dst_dev_event(struct notifier_block *this, unsigned long event, void *ptr)
262{
263	struct net_device *dev = ptr;
264	struct dst_entry *dst;
265
266	switch (event) {
267	case NETDEV_UNREGISTER:
268	case NETDEV_DOWN:
269		spin_lock_bh(&dst_lock);
270		for (dst = dst_garbage_list; dst; dst = dst->next) {
271			dst_ifdown(dst, dev, event != NETDEV_DOWN);
272		}
273		spin_unlock_bh(&dst_lock);
274		break;
275	}
276	return NOTIFY_DONE;
277}
278
279static struct notifier_block dst_dev_notifier = {
280	.notifier_call	= dst_dev_event,
281};
282
283void __init dst_init(void)
284{
285	register_netdevice_notifier(&dst_dev_notifier);
286}
287
288EXPORT_SYMBOL(__dst_free);
289EXPORT_SYMBOL(dst_alloc);
290EXPORT_SYMBOL(dst_destroy);
291