xref: /openbmc/linux/net/core/dst.c (revision b6dcefde) 
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/netdevice.h>
16 #include <linux/skbuff.h>
17 #include <linux/string.h>
18 #include <linux/types.h>
19 #include <net/net_namespace.h>
20 #include <linux/sched.h>
21 
22 #include <net/dst.h>
23 
24 /*
25  * Theory of operations:
26  * 1) We use a list, protected by a spinlock, to add
27  *    new entries from both BH and non-BH context.
28  * 2) In order to keep spinlock held for a small delay,
29  *    we use a second list where are stored long lived
30  *    entries, that are handled by the garbage collect thread
31  *    fired by a workqueue.
32  * 3) This list is guarded by a mutex,
33  *    so that the gc_task and dst_dev_event() can be synchronized.
34  */
35 #if RT_CACHE_DEBUG >= 2
36 static atomic_t			 dst_total = ATOMIC_INIT(0);
37 #endif
38 
39 /*
40  * We want to keep lock & list close together
41  * to dirty as few cache lines as possible in __dst_free().
42  * As this is not a very strong hint, we dont force an alignment on SMP.
43  */
44 static struct {
45 	spinlock_t		lock;
46 	struct dst_entry 	*list;
47 	unsigned long		timer_inc;
48 	unsigned long		timer_expires;
49 } dst_garbage = {
50 	.lock = __SPIN_LOCK_UNLOCKED(dst_garbage.lock),
51 	.timer_inc = DST_GC_MAX,
52 };
53 static void dst_gc_task(struct work_struct *work);
54 static void ___dst_free(struct dst_entry * dst);
55 
56 static DECLARE_DELAYED_WORK(dst_gc_work, dst_gc_task);
57 
58 static DEFINE_MUTEX(dst_gc_mutex);
59 /*
60  * long lived entries are maintained in this list, guarded by dst_gc_mutex
61  */
62 static struct dst_entry         *dst_busy_list;
63 
64 static void dst_gc_task(struct work_struct *work)
65 {
66 	int    delayed = 0;
67 	int    work_performed = 0;
68 	unsigned long expires = ~0L;
69 	struct dst_entry *dst, *next, head;
70 	struct dst_entry *last = &head;
71 #if RT_CACHE_DEBUG >= 2
72 	ktime_t time_start = ktime_get();
73 	struct timespec elapsed;
74 #endif
75 
76 	mutex_lock(&dst_gc_mutex);
77 	next = dst_busy_list;
78 
79 loop:
80 	while ((dst = next) != NULL) {
81 		next = dst->next;
82 		prefetch(&next->next);
83 		cond_resched();
84 		if (likely(atomic_read(&dst->__refcnt))) {
85 			last->next = dst;
86 			last = dst;
87 			delayed++;
88 			continue;
89 		}
90 		work_performed++;
91 
92 		dst = dst_destroy(dst);
93 		if (dst) {
94 			/* NOHASH and still referenced. Unless it is already
95 			 * on gc list, invalidate it and add to gc list.
96 			 *
97 			 * Note: this is temporary. Actually, NOHASH dst's
98 			 * must be obsoleted when parent is obsoleted.
99 			 * But we do not have state "obsoleted, but
100 			 * referenced by parent", so it is right.
101 			 */
102 			if (dst->obsolete > 1)
103 				continue;
104 
105 			___dst_free(dst);
106 			dst->next = next;
107 			next = dst;
108 		}
109 	}
110 
111 	spin_lock_bh(&dst_garbage.lock);
112 	next = dst_garbage.list;
113 	if (next) {
114 		dst_garbage.list = NULL;
115 		spin_unlock_bh(&dst_garbage.lock);
116 		goto loop;
117 	}
118 	last->next = NULL;
119 	dst_busy_list = head.next;
120 	if (!dst_busy_list)
121 		dst_garbage.timer_inc = DST_GC_MAX;
122 	else {
123 		/*
124 		 * if we freed less than 1/10 of delayed entries,
125 		 * we can sleep longer.
126 		 */
127 		if (work_performed <= delayed/10) {
128 			dst_garbage.timer_expires += dst_garbage.timer_inc;
129 			if (dst_garbage.timer_expires > DST_GC_MAX)
130 				dst_garbage.timer_expires = DST_GC_MAX;
131 			dst_garbage.timer_inc += DST_GC_INC;
132 		} else {
133 			dst_garbage.timer_inc = DST_GC_INC;
134 			dst_garbage.timer_expires = DST_GC_MIN;
135 		}
136 		expires = dst_garbage.timer_expires;
137 		/*
138 		 * if the next desired timer is more than 4 seconds in the future
139 		 * then round the timer to whole seconds
140 		 */
141 		if (expires > 4*HZ)
142 			expires = round_jiffies_relative(expires);
143 		schedule_delayed_work(&dst_gc_work, expires);
144 	}
145 
146 	spin_unlock_bh(&dst_garbage.lock);
147 	mutex_unlock(&dst_gc_mutex);
148 #if RT_CACHE_DEBUG >= 2
149 	elapsed = ktime_to_timespec(ktime_sub(ktime_get(), time_start));
150 	printk(KERN_DEBUG "dst_total: %d delayed: %d work_perf: %d"
151 		" expires: %lu elapsed: %lu us\n",
152 		atomic_read(&dst_total), delayed, work_performed,
153 		expires,
154 		elapsed.tv_sec * USEC_PER_SEC + elapsed.tv_nsec / NSEC_PER_USEC);
155 #endif
156 }
157 
158 int dst_discard(struct sk_buff *skb)
159 {
160 	kfree_skb(skb);
161 	return 0;
162 }
163 EXPORT_SYMBOL(dst_discard);
164 
165 void * dst_alloc(struct dst_ops * ops)
166 {
167 	struct dst_entry * dst;
168 
169 	if (ops->gc && atomic_read(&ops->entries) > ops->gc_thresh) {
170 		if (ops->gc(ops))
171 			return NULL;
172 	}
173 	dst = kmem_cache_zalloc(ops->kmem_cachep, GFP_ATOMIC);
174 	if (!dst)
175 		return NULL;
176 	atomic_set(&dst->__refcnt, 0);
177 	dst->ops = ops;
178 	dst->lastuse = jiffies;
179 	dst->path = dst;
180 	dst->input = dst->output = dst_discard;
181 #if RT_CACHE_DEBUG >= 2
182 	atomic_inc(&dst_total);
183 #endif
184 	atomic_inc(&ops->entries);
185 	return dst;
186 }
187 
188 static void ___dst_free(struct dst_entry * dst)
189 {
190 	/* The first case (dev==NULL) is required, when
191 	   protocol module is unloaded.
192 	 */
193 	if (dst->dev == NULL || !(dst->dev->flags&IFF_UP)) {
194 		dst->input = dst->output = dst_discard;
195 	}
196 	dst->obsolete = 2;
197 }
198 
199 void __dst_free(struct dst_entry * dst)
200 {
201 	spin_lock_bh(&dst_garbage.lock);
202 	___dst_free(dst);
203 	dst->next = dst_garbage.list;
204 	dst_garbage.list = dst;
205 	if (dst_garbage.timer_inc > DST_GC_INC) {
206 		dst_garbage.timer_inc = DST_GC_INC;
207 		dst_garbage.timer_expires = DST_GC_MIN;
208 		cancel_delayed_work(&dst_gc_work);
209 		schedule_delayed_work(&dst_gc_work, dst_garbage.timer_expires);
210 	}
211 	spin_unlock_bh(&dst_garbage.lock);
212 }
213 
214 struct dst_entry *dst_destroy(struct dst_entry * dst)
215 {
216 	struct dst_entry *child;
217 	struct neighbour *neigh;
218 	struct hh_cache *hh;
219 
220 	smp_rmb();
221 
222 again:
223 	neigh = dst->neighbour;
224 	hh = dst->hh;
225 	child = dst->child;
226 
227 	dst->hh = NULL;
228 	if (hh && atomic_dec_and_test(&hh->hh_refcnt))
229 		kfree(hh);
230 
231 	if (neigh) {
232 		dst->neighbour = NULL;
233 		neigh_release(neigh);
234 	}
235 
236 	atomic_dec(&dst->ops->entries);
237 
238 	if (dst->ops->destroy)
239 		dst->ops->destroy(dst);
240 	if (dst->dev)
241 		dev_put(dst->dev);
242 #if RT_CACHE_DEBUG >= 2
243 	atomic_dec(&dst_total);
244 #endif
245 	kmem_cache_free(dst->ops->kmem_cachep, dst);
246 
247 	dst = child;
248 	if (dst) {
249 		int nohash = dst->flags & DST_NOHASH;
250 
251 		if (atomic_dec_and_test(&dst->__refcnt)) {
252 			/* We were real parent of this dst, so kill child. */
253 			if (nohash)
254 				goto again;
255 		} else {
256 			/* Child is still referenced, return it for freeing. */
257 			if (nohash)
258 				return dst;
259 			/* Child is still in his hash table */
260 		}
261 	}
262 	return NULL;
263 }
264 
265 void dst_release(struct dst_entry *dst)
266 {
267 	if (dst) {
268                int newrefcnt;
269 
270 		smp_mb__before_atomic_dec();
271                newrefcnt = atomic_dec_return(&dst->__refcnt);
272                WARN_ON(newrefcnt < 0);
273 	}
274 }
275 EXPORT_SYMBOL(dst_release);
276 
277 /* Dirty hack. We did it in 2.2 (in __dst_free),
278  * we have _very_ good reasons not to repeat
279  * this mistake in 2.3, but we have no choice
280  * now. _It_ _is_ _explicit_ _deliberate_
281  * _race_ _condition_.
282  *
283  * Commented and originally written by Alexey.
284  */
285 static inline void dst_ifdown(struct dst_entry *dst, struct net_device *dev,
286 			      int unregister)
287 {
288 	if (dst->ops->ifdown)
289 		dst->ops->ifdown(dst, dev, unregister);
290 
291 	if (dev != dst->dev)
292 		return;
293 
294 	if (!unregister) {
295 		dst->input = dst->output = dst_discard;
296 	} else {
297 		dst->dev = dev_net(dst->dev)->loopback_dev;
298 		dev_hold(dst->dev);
299 		dev_put(dev);
300 		if (dst->neighbour && dst->neighbour->dev == dev) {
301 			dst->neighbour->dev = dst->dev;
302 			dev_hold(dst->dev);
303 			dev_put(dev);
304 		}
305 	}
306 }
307 
308 static int dst_dev_event(struct notifier_block *this, unsigned long event, void *ptr)
309 {
310 	struct net_device *dev = ptr;
311 	struct dst_entry *dst, *last = NULL;
312 
313 	switch (event) {
314 	case NETDEV_UNREGISTER:
315 	case NETDEV_DOWN:
316 		mutex_lock(&dst_gc_mutex);
317 		for (dst = dst_busy_list; dst; dst = dst->next) {
318 			last = dst;
319 			dst_ifdown(dst, dev, event != NETDEV_DOWN);
320 		}
321 
322 		spin_lock_bh(&dst_garbage.lock);
323 		dst = dst_garbage.list;
324 		dst_garbage.list = NULL;
325 		spin_unlock_bh(&dst_garbage.lock);
326 
327 		if (last)
328 			last->next = dst;
329 		else
330 			dst_busy_list = dst;
331 		for (; dst; dst = dst->next) {
332 			dst_ifdown(dst, dev, event != NETDEV_DOWN);
333 		}
334 		mutex_unlock(&dst_gc_mutex);
335 		break;
336 	}
337 	return NOTIFY_DONE;
338 }
339 
340 static struct notifier_block dst_dev_notifier = {
341 	.notifier_call	= dst_dev_event,
342 };
343 
344 void __init dst_init(void)
345 {
346 	register_netdevice_notifier(&dst_dev_notifier);
347 }
348 
349 EXPORT_SYMBOL(__dst_free);
350 EXPORT_SYMBOL(dst_alloc);
351 EXPORT_SYMBOL(dst_destroy);
352