xref: /openbmc/linux/net/core/dst.c (revision d5cb9783536a41df9f9cba5b0a1d78047ed787f7)
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  */
31 static struct dst_entry 	*dst_garbage_list;
32 #if RT_CACHE_DEBUG >= 2
33 static atomic_t			 dst_total = ATOMIC_INIT(0);
34 #endif
35 static DEFINE_SPINLOCK(dst_lock);
36 
37 static unsigned long dst_gc_timer_expires;
38 static unsigned long dst_gc_timer_inc = DST_GC_MAX;
39 static void dst_run_gc(unsigned long);
40 static void ___dst_free(struct dst_entry * dst);
41 
42 static DEFINE_TIMER(dst_gc_timer, dst_run_gc, DST_GC_MIN, 0);
43 
44 static 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 	dst_gc_timer.expires = jiffies + dst_gc_timer_expires;
99 #if RT_CACHE_DEBUG >= 2
100 	printk("dst_total: %d/%d %ld\n",
101 	       atomic_read(&dst_total), delayed,  dst_gc_timer_expires);
102 #endif
103 	add_timer(&dst_gc_timer);
104 
105 out:
106 	spin_unlock(&dst_lock);
107 }
108 
109 static int dst_discard_in(struct sk_buff *skb)
110 {
111 	kfree_skb(skb);
112 	return 0;
113 }
114 
115 static int dst_discard_out(struct sk_buff *skb)
116 {
117 	kfree_skb(skb);
118 	return 0;
119 }
120 
121 void * dst_alloc(struct dst_ops * ops)
122 {
123 	struct dst_entry * dst;
124 
125 	if (ops->gc && atomic_read(&ops->entries) > ops->gc_thresh) {
126 		if (ops->gc())
127 			return NULL;
128 	}
129 	dst = kmem_cache_alloc(ops->kmem_cachep, SLAB_ATOMIC);
130 	if (!dst)
131 		return NULL;
132 	memset(dst, 0, ops->entry_size);
133 	atomic_set(&dst->__refcnt, 0);
134 	dst->ops = ops;
135 	dst->lastuse = jiffies;
136 	dst->path = dst;
137 	dst->input = dst_discard_in;
138 	dst->output = dst_discard_out;
139 #if RT_CACHE_DEBUG >= 2
140 	atomic_inc(&dst_total);
141 #endif
142 	atomic_inc(&ops->entries);
143 	return dst;
144 }
145 
146 static void ___dst_free(struct dst_entry * dst)
147 {
148 	/* The first case (dev==NULL) is required, when
149 	   protocol module is unloaded.
150 	 */
151 	if (dst->dev == NULL || !(dst->dev->flags&IFF_UP)) {
152 		dst->input = dst_discard_in;
153 		dst->output = dst_discard_out;
154 	}
155 	dst->obsolete = 2;
156 }
157 
158 void __dst_free(struct dst_entry * dst)
159 {
160 	spin_lock_bh(&dst_lock);
161 	___dst_free(dst);
162 	dst->next = dst_garbage_list;
163 	dst_garbage_list = dst;
164 	if (dst_gc_timer_inc > DST_GC_INC) {
165 		dst_gc_timer_inc = DST_GC_INC;
166 		dst_gc_timer_expires = DST_GC_MIN;
167 		mod_timer(&dst_gc_timer, jiffies + dst_gc_timer_expires);
168 	}
169 	spin_unlock_bh(&dst_lock);
170 }
171 
172 struct dst_entry *dst_destroy(struct dst_entry * dst)
173 {
174 	struct dst_entry *child;
175 	struct neighbour *neigh;
176 	struct hh_cache *hh;
177 
178 	smp_rmb();
179 
180 again:
181 	neigh = dst->neighbour;
182 	hh = dst->hh;
183 	child = dst->child;
184 
185 	dst->hh = NULL;
186 	if (hh && atomic_dec_and_test(&hh->hh_refcnt))
187 		kfree(hh);
188 
189 	if (neigh) {
190 		dst->neighbour = NULL;
191 		neigh_release(neigh);
192 	}
193 
194 	atomic_dec(&dst->ops->entries);
195 
196 	if (dst->ops->destroy)
197 		dst->ops->destroy(dst);
198 	if (dst->dev)
199 		dev_put(dst->dev);
200 #if RT_CACHE_DEBUG >= 2
201 	atomic_dec(&dst_total);
202 #endif
203 	kmem_cache_free(dst->ops->kmem_cachep, dst);
204 
205 	dst = child;
206 	if (dst) {
207 		int nohash = dst->flags & DST_NOHASH;
208 
209 		if (atomic_dec_and_test(&dst->__refcnt)) {
210 			/* We were real parent of this dst, so kill child. */
211 			if (nohash)
212 				goto again;
213 		} else {
214 			/* Child is still referenced, return it for freeing. */
215 			if (nohash)
216 				return dst;
217 			/* Child is still in his hash table */
218 		}
219 	}
220 	return NULL;
221 }
222 
223 /* Dirty hack. We did it in 2.2 (in __dst_free),
224  * we have _very_ good reasons not to repeat
225  * this mistake in 2.3, but we have no choice
226  * now. _It_ _is_ _explicit_ _deliberate_
227  * _race_ _condition_.
228  *
229  * Commented and originally written by Alexey.
230  */
231 static inline void dst_ifdown(struct dst_entry *dst, struct net_device *dev,
232 			      int unregister)
233 {
234 	if (dst->ops->ifdown)
235 		dst->ops->ifdown(dst, dev, unregister);
236 
237 	if (dev != dst->dev)
238 		return;
239 
240 	if (!unregister) {
241 		dst->input = dst_discard_in;
242 		dst->output = dst_discard_out;
243 	} else {
244 		dst->dev = &loopback_dev;
245 		dev_hold(&loopback_dev);
246 		dev_put(dev);
247 		if (dst->neighbour && dst->neighbour->dev == dev) {
248 			dst->neighbour->dev = &loopback_dev;
249 			dev_put(dev);
250 			dev_hold(&loopback_dev);
251 		}
252 	}
253 }
254 
255 static int dst_dev_event(struct notifier_block *this, unsigned long event, void *ptr)
256 {
257 	struct net_device *dev = ptr;
258 	struct dst_entry *dst;
259 
260 	switch (event) {
261 	case NETDEV_UNREGISTER:
262 	case NETDEV_DOWN:
263 		spin_lock_bh(&dst_lock);
264 		for (dst = dst_garbage_list; dst; dst = dst->next) {
265 			dst_ifdown(dst, dev, event != NETDEV_DOWN);
266 		}
267 		spin_unlock_bh(&dst_lock);
268 		break;
269 	}
270 	return NOTIFY_DONE;
271 }
272 
273 static struct notifier_block dst_dev_notifier = {
274 	.notifier_call	= dst_dev_event,
275 };
276 
277 void __init dst_init(void)
278 {
279 	register_netdevice_notifier(&dst_dev_notifier);
280 }
281 
282 EXPORT_SYMBOL(__dst_free);
283 EXPORT_SYMBOL(dst_alloc);
284 EXPORT_SYMBOL(dst_destroy);
285