xref: /linux/net/core/dst.c (revision a33f32244d8550da8b4a26e277ce07d5c6d158b5) 
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 
23 #include <net/dst.h>
24 
25 /*
26  * Theory of operations:
27  * 1) We use a list, protected by a spinlock, to add
28  *    new entries from both BH and non-BH context.
29  * 2) In order to keep spinlock held for a small delay,
30  *    we use a second list where are stored long lived
31  *    entries, that are handled by the garbage collect thread
32  *    fired by a workqueue.
33  * 3) This list is guarded by a mutex,
34  *    so that the gc_task and dst_dev_event() can be synchronized.
35  */
36 #if RT_CACHE_DEBUG >= 2
37 static atomic_t			 dst_total = ATOMIC_INIT(0);
38 #endif
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 #if RT_CACHE_DEBUG >= 2
73 	ktime_t time_start = ktime_get();
74 	struct timespec elapsed;
75 #endif
76 
77 	mutex_lock(&dst_gc_mutex);
78 	next = dst_busy_list;
79 
80 loop:
81 	while ((dst = next) != NULL) {
82 		next = dst->next;
83 		prefetch(&next->next);
84 		cond_resched();
85 		if (likely(atomic_read(&dst->__refcnt))) {
86 			last->next = dst;
87 			last = dst;
88 			delayed++;
89 			continue;
90 		}
91 		work_performed++;
92 
93 		dst = dst_destroy(dst);
94 		if (dst) {
95 			/* NOHASH and still referenced. Unless it is already
96 			 * on gc list, invalidate it and add to gc list.
97 			 *
98 			 * Note: this is temporary. Actually, NOHASH dst's
99 			 * must be obsoleted when parent is obsoleted.
100 			 * But we do not have state "obsoleted, but
101 			 * referenced by parent", so it is right.
102 			 */
103 			if (dst->obsolete > 1)
104 				continue;
105 
106 			___dst_free(dst);
107 			dst->next = next;
108 			next = dst;
109 		}
110 	}
111 
112 	spin_lock_bh(&dst_garbage.lock);
113 	next = dst_garbage.list;
114 	if (next) {
115 		dst_garbage.list = NULL;
116 		spin_unlock_bh(&dst_garbage.lock);
117 		goto loop;
118 	}
119 	last->next = NULL;
120 	dst_busy_list = head.next;
121 	if (!dst_busy_list)
122 		dst_garbage.timer_inc = DST_GC_MAX;
123 	else {
124 		/*
125 		 * if we freed less than 1/10 of delayed entries,
126 		 * we can sleep longer.
127 		 */
128 		if (work_performed <= delayed/10) {
129 			dst_garbage.timer_expires += dst_garbage.timer_inc;
130 			if (dst_garbage.timer_expires > DST_GC_MAX)
131 				dst_garbage.timer_expires = DST_GC_MAX;
132 			dst_garbage.timer_inc += DST_GC_INC;
133 		} else {
134 			dst_garbage.timer_inc = DST_GC_INC;
135 			dst_garbage.timer_expires = DST_GC_MIN;
136 		}
137 		expires = dst_garbage.timer_expires;
138 		/*
139 		 * if the next desired timer is more than 4 seconds in the future
140 		 * then round the timer to whole seconds
141 		 */
142 		if (expires > 4*HZ)
143 			expires = round_jiffies_relative(expires);
144 		schedule_delayed_work(&dst_gc_work, expires);
145 	}
146 
147 	spin_unlock_bh(&dst_garbage.lock);
148 	mutex_unlock(&dst_gc_mutex);
149 #if RT_CACHE_DEBUG >= 2
150 	elapsed = ktime_to_timespec(ktime_sub(ktime_get(), time_start));
151 	printk(KERN_DEBUG "dst_total: %d delayed: %d work_perf: %d"
152 		" expires: %lu elapsed: %lu us\n",
153 		atomic_read(&dst_total), delayed, work_performed,
154 		expires,
155 		elapsed.tv_sec * USEC_PER_SEC + elapsed.tv_nsec / NSEC_PER_USEC);
156 #endif
157 }
158 
159 int dst_discard(struct sk_buff *skb)
160 {
161 	kfree_skb(skb);
162 	return 0;
163 }
164 EXPORT_SYMBOL(dst_discard);
165 
166 void * dst_alloc(struct dst_ops * ops)
167 {
168 	struct dst_entry * dst;
169 
170 	if (ops->gc && atomic_read(&ops->entries) > ops->gc_thresh) {
171 		if (ops->gc(ops))
172 			return NULL;
173 	}
174 	dst = kmem_cache_zalloc(ops->kmem_cachep, GFP_ATOMIC);
175 	if (!dst)
176 		return NULL;
177 	atomic_set(&dst->__refcnt, 0);
178 	dst->ops = ops;
179 	dst->lastuse = jiffies;
180 	dst->path = dst;
181 	dst->input = dst->output = dst_discard;
182 #if RT_CACHE_DEBUG >= 2
183 	atomic_inc(&dst_total);
184 #endif
185 	atomic_inc(&ops->entries);
186 	return dst;
187 }
188 
189 static void ___dst_free(struct dst_entry * dst)
190 {
191 	/* The first case (dev==NULL) is required, when
192 	   protocol module is unloaded.
193 	 */
194 	if (dst->dev == NULL || !(dst->dev->flags&IFF_UP)) {
195 		dst->input = dst->output = dst_discard;
196 	}
197 	dst->obsolete = 2;
198 }
199 
200 void __dst_free(struct dst_entry * dst)
201 {
202 	spin_lock_bh(&dst_garbage.lock);
203 	___dst_free(dst);
204 	dst->next = dst_garbage.list;
205 	dst_garbage.list = dst;
206 	if (dst_garbage.timer_inc > DST_GC_INC) {
207 		dst_garbage.timer_inc = DST_GC_INC;
208 		dst_garbage.timer_expires = DST_GC_MIN;
209 		cancel_delayed_work(&dst_gc_work);
210 		schedule_delayed_work(&dst_gc_work, dst_garbage.timer_expires);
211 	}
212 	spin_unlock_bh(&dst_garbage.lock);
213 }
214 
215 struct dst_entry *dst_destroy(struct dst_entry * dst)
216 {
217 	struct dst_entry *child;
218 	struct neighbour *neigh;
219 	struct hh_cache *hh;
220 
221 	smp_rmb();
222 
223 again:
224 	neigh = dst->neighbour;
225 	hh = dst->hh;
226 	child = dst->child;
227 
228 	dst->hh = NULL;
229 	if (hh && atomic_dec_and_test(&hh->hh_refcnt))
230 		kfree(hh);
231 
232 	if (neigh) {
233 		dst->neighbour = NULL;
234 		neigh_release(neigh);
235 	}
236 
237 	atomic_dec(&dst->ops->entries);
238 
239 	if (dst->ops->destroy)
240 		dst->ops->destroy(dst);
241 	if (dst->dev)
242 		dev_put(dst->dev);
243 #if RT_CACHE_DEBUG >= 2
244 	atomic_dec(&dst_total);
245 #endif
246 	kmem_cache_free(dst->ops->kmem_cachep, dst);
247 
248 	dst = child;
249 	if (dst) {
250 		int nohash = dst->flags & DST_NOHASH;
251 
252 		if (atomic_dec_and_test(&dst->__refcnt)) {
253 			/* We were real parent of this dst, so kill child. */
254 			if (nohash)
255 				goto again;
256 		} else {
257 			/* Child is still referenced, return it for freeing. */
258 			if (nohash)
259 				return dst;
260 			/* Child is still in his hash table */
261 		}
262 	}
263 	return NULL;
264 }
265 
266 void dst_release(struct dst_entry *dst)
267 {
268 	if (dst) {
269                int newrefcnt;
270 
271 		smp_mb__before_atomic_dec();
272                newrefcnt = atomic_dec_return(&dst->__refcnt);
273                WARN_ON(newrefcnt < 0);
274 	}
275 }
276 EXPORT_SYMBOL(dst_release);
277 
278 /* Dirty hack. We did it in 2.2 (in __dst_free),
279  * we have _very_ good reasons not to repeat
280  * this mistake in 2.3, but we have no choice
281  * now. _It_ _is_ _explicit_ _deliberate_
282  * _race_ _condition_.
283  *
284  * Commented and originally written by Alexey.
285  */
286 static inline void dst_ifdown(struct dst_entry *dst, struct net_device *dev,
287 			      int unregister)
288 {
289 	if (dst->ops->ifdown)
290 		dst->ops->ifdown(dst, dev, unregister);
291 
292 	if (dev != dst->dev)
293 		return;
294 
295 	if (!unregister) {
296 		dst->input = dst->output = dst_discard;
297 	} else {
298 		dst->dev = dev_net(dst->dev)->loopback_dev;
299 		dev_hold(dst->dev);
300 		dev_put(dev);
301 		if (dst->neighbour && dst->neighbour->dev == dev) {
302 			dst->neighbour->dev = dst->dev;
303 			dev_hold(dst->dev);
304 			dev_put(dev);
305 		}
306 	}
307 }
308 
309 static int dst_dev_event(struct notifier_block *this, unsigned long event, void *ptr)
310 {
311 	struct net_device *dev = ptr;
312 	struct dst_entry *dst, *last = NULL;
313 
314 	switch (event) {
315 	case NETDEV_UNREGISTER:
316 	case NETDEV_DOWN:
317 		mutex_lock(&dst_gc_mutex);
318 		for (dst = dst_busy_list; dst; dst = dst->next) {
319 			last = dst;
320 			dst_ifdown(dst, dev, event != NETDEV_DOWN);
321 		}
322 
323 		spin_lock_bh(&dst_garbage.lock);
324 		dst = dst_garbage.list;
325 		dst_garbage.list = NULL;
326 		spin_unlock_bh(&dst_garbage.lock);
327 
328 		if (last)
329 			last->next = dst;
330 		else
331 			dst_busy_list = dst;
332 		for (; dst; dst = dst->next) {
333 			dst_ifdown(dst, dev, event != NETDEV_DOWN);
334 		}
335 		mutex_unlock(&dst_gc_mutex);
336 		break;
337 	}
338 	return NOTIFY_DONE;
339 }
340 
341 static struct notifier_block dst_dev_notifier = {
342 	.notifier_call	= dst_dev_event,
343 };
344 
345 void __init dst_init(void)
346 {
347 	register_netdevice_notifier(&dst_dev_notifier);
348 }
349 
350 EXPORT_SYMBOL(__dst_free);
351 EXPORT_SYMBOL(dst_alloc);
352 EXPORT_SYMBOL(dst_destroy);
353