xref: /openbmc/linux/net/core/dst.c (revision 84764a41) 
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 
24 #include <net/dst.h>
25 
26 /*
27  * Theory of operations:
28  * 1) We use a list, protected by a spinlock, to add
29  *    new entries from both BH and non-BH context.
30  * 2) In order to keep spinlock held for a small delay,
31  *    we use a second list where are stored long lived
32  *    entries, that are handled by the garbage collect thread
33  *    fired by a workqueue.
34  * 3) This list is guarded by a mutex,
35  *    so that the gc_task and dst_dev_event() can be synchronized.
36  */
37 
38 /*
39  * We want to keep lock & list close together
40  * to dirty as few cache lines as possible in __dst_free().
41  * As this is not a very strong hint, we dont force an alignment on SMP.
42  */
43 static struct {
44 	spinlock_t		lock;
45 	struct dst_entry	*list;
46 	unsigned long		timer_inc;
47 	unsigned long		timer_expires;
48 } dst_garbage = {
49 	.lock = __SPIN_LOCK_UNLOCKED(dst_garbage.lock),
50 	.timer_inc = DST_GC_MAX,
51 };
52 static void dst_gc_task(struct work_struct *work);
53 static void ___dst_free(struct dst_entry *dst);
54 
55 static DECLARE_DELAYED_WORK(dst_gc_work, dst_gc_task);
56 
57 static DEFINE_MUTEX(dst_gc_mutex);
58 /*
59  * long lived entries are maintained in this list, guarded by dst_gc_mutex
60  */
61 static struct dst_entry         *dst_busy_list;
62 
63 static void dst_gc_task(struct work_struct *work)
64 {
65 	int    delayed = 0;
66 	int    work_performed = 0;
67 	unsigned long expires = ~0L;
68 	struct dst_entry *dst, *next, head;
69 	struct dst_entry *last = &head;
70 
71 	mutex_lock(&dst_gc_mutex);
72 	next = dst_busy_list;
73 
74 loop:
75 	while ((dst = next) != NULL) {
76 		next = dst->next;
77 		prefetch(&next->next);
78 		cond_resched();
79 		if (likely(atomic_read(&dst->__refcnt))) {
80 			last->next = dst;
81 			last = dst;
82 			delayed++;
83 			continue;
84 		}
85 		work_performed++;
86 
87 		dst = dst_destroy(dst);
88 		if (dst) {
89 			/* NOHASH and still referenced. Unless it is already
90 			 * on gc list, invalidate it and add to gc list.
91 			 *
92 			 * Note: this is temporary. Actually, NOHASH dst's
93 			 * must be obsoleted when parent is obsoleted.
94 			 * But we do not have state "obsoleted, but
95 			 * referenced by parent", so it is right.
96 			 */
97 			if (dst->obsolete > 0)
98 				continue;
99 
100 			___dst_free(dst);
101 			dst->next = next;
102 			next = dst;
103 		}
104 	}
105 
106 	spin_lock_bh(&dst_garbage.lock);
107 	next = dst_garbage.list;
108 	if (next) {
109 		dst_garbage.list = NULL;
110 		spin_unlock_bh(&dst_garbage.lock);
111 		goto loop;
112 	}
113 	last->next = NULL;
114 	dst_busy_list = head.next;
115 	if (!dst_busy_list)
116 		dst_garbage.timer_inc = DST_GC_MAX;
117 	else {
118 		/*
119 		 * if we freed less than 1/10 of delayed entries,
120 		 * we can sleep longer.
121 		 */
122 		if (work_performed <= delayed/10) {
123 			dst_garbage.timer_expires += dst_garbage.timer_inc;
124 			if (dst_garbage.timer_expires > DST_GC_MAX)
125 				dst_garbage.timer_expires = DST_GC_MAX;
126 			dst_garbage.timer_inc += DST_GC_INC;
127 		} else {
128 			dst_garbage.timer_inc = DST_GC_INC;
129 			dst_garbage.timer_expires = DST_GC_MIN;
130 		}
131 		expires = dst_garbage.timer_expires;
132 		/*
133 		 * if the next desired timer is more than 4 seconds in the
134 		 * future then round the timer to whole seconds
135 		 */
136 		if (expires > 4*HZ)
137 			expires = round_jiffies_relative(expires);
138 		schedule_delayed_work(&dst_gc_work, expires);
139 	}
140 
141 	spin_unlock_bh(&dst_garbage.lock);
142 	mutex_unlock(&dst_gc_mutex);
143 }
144 
145 int dst_discard(struct sk_buff *skb)
146 {
147 	kfree_skb(skb);
148 	return 0;
149 }
150 EXPORT_SYMBOL(dst_discard);
151 
152 const u32 dst_default_metrics[RTAX_MAX + 1] = {
153 	/* This initializer is needed to force linker to place this variable
154 	 * into const section. Otherwise it might end into bss section.
155 	 * We really want to avoid false sharing on this variable, and catch
156 	 * any writes on it.
157 	 */
158 	[RTAX_MAX] = 0xdeadbeef,
159 };
160 
161 
162 void *dst_alloc(struct dst_ops *ops, struct net_device *dev,
163 		int initial_ref, int initial_obsolete, unsigned short flags)
164 {
165 	struct dst_entry *dst;
166 
167 	if (ops->gc && dst_entries_get_fast(ops) > ops->gc_thresh) {
168 		if (ops->gc(ops))
169 			return NULL;
170 	}
171 	dst = kmem_cache_alloc(ops->kmem_cachep, GFP_ATOMIC);
172 	if (!dst)
173 		return NULL;
174 	dst->child = NULL;
175 	dst->dev = dev;
176 	if (dev)
177 		dev_hold(dev);
178 	dst->ops = ops;
179 	dst_init_metrics(dst, dst_default_metrics, true);
180 	dst->expires = 0UL;
181 	dst->path = dst;
182 #ifdef CONFIG_XFRM
183 	dst->xfrm = NULL;
184 #endif
185 	dst->input = dst_discard;
186 	dst->output = dst_discard;
187 	dst->error = 0;
188 	dst->obsolete = initial_obsolete;
189 	dst->header_len = 0;
190 	dst->trailer_len = 0;
191 #ifdef CONFIG_IP_ROUTE_CLASSID
192 	dst->tclassid = 0;
193 #endif
194 	atomic_set(&dst->__refcnt, initial_ref);
195 	dst->__use = 0;
196 	dst->lastuse = jiffies;
197 	dst->flags = flags;
198 	dst->pending_confirm = 0;
199 	dst->next = NULL;
200 	if (!(flags & DST_NOCOUNT))
201 		dst_entries_add(ops, 1);
202 	return dst;
203 }
204 EXPORT_SYMBOL(dst_alloc);
205 
206 static void ___dst_free(struct dst_entry *dst)
207 {
208 	/* The first case (dev==NULL) is required, when
209 	   protocol module is unloaded.
210 	 */
211 	if (dst->dev == NULL || !(dst->dev->flags&IFF_UP))
212 		dst->input = dst->output = dst_discard;
213 	dst->obsolete = DST_OBSOLETE_DEAD;
214 }
215 
216 void __dst_free(struct dst_entry *dst)
217 {
218 	spin_lock_bh(&dst_garbage.lock);
219 	___dst_free(dst);
220 	dst->next = dst_garbage.list;
221 	dst_garbage.list = dst;
222 	if (dst_garbage.timer_inc > DST_GC_INC) {
223 		dst_garbage.timer_inc = DST_GC_INC;
224 		dst_garbage.timer_expires = DST_GC_MIN;
225 		mod_delayed_work(system_wq, &dst_gc_work,
226 				 dst_garbage.timer_expires);
227 	}
228 	spin_unlock_bh(&dst_garbage.lock);
229 }
230 EXPORT_SYMBOL(__dst_free);
231 
232 struct dst_entry *dst_destroy(struct dst_entry * dst)
233 {
234 	struct dst_entry *child;
235 
236 	smp_rmb();
237 
238 again:
239 	child = dst->child;
240 
241 	if (!(dst->flags & DST_NOCOUNT))
242 		dst_entries_add(dst->ops, -1);
243 
244 	if (dst->ops->destroy)
245 		dst->ops->destroy(dst);
246 	if (dst->dev)
247 		dev_put(dst->dev);
248 	kmem_cache_free(dst->ops->kmem_cachep, dst);
249 
250 	dst = child;
251 	if (dst) {
252 		int nohash = dst->flags & DST_NOHASH;
253 
254 		if (atomic_dec_and_test(&dst->__refcnt)) {
255 			/* We were real parent of this dst, so kill child. */
256 			if (nohash)
257 				goto again;
258 		} else {
259 			/* Child is still referenced, return it for freeing. */
260 			if (nohash)
261 				return dst;
262 			/* Child is still in his hash table */
263 		}
264 	}
265 	return NULL;
266 }
267 EXPORT_SYMBOL(dst_destroy);
268 
269 void dst_release(struct dst_entry *dst)
270 {
271 	if (dst) {
272 		int newrefcnt;
273 
274 		newrefcnt = atomic_dec_return(&dst->__refcnt);
275 		WARN_ON(newrefcnt < 0);
276 		if (unlikely(dst->flags & DST_NOCACHE) && !newrefcnt) {
277 			dst = dst_destroy(dst);
278 			if (dst)
279 				__dst_free(dst);
280 		}
281 	}
282 }
283 EXPORT_SYMBOL(dst_release);
284 
285 u32 *dst_cow_metrics_generic(struct dst_entry *dst, unsigned long old)
286 {
287 	u32 *p = kmalloc(sizeof(u32) * RTAX_MAX, GFP_ATOMIC);
288 
289 	if (p) {
290 		u32 *old_p = __DST_METRICS_PTR(old);
291 		unsigned long prev, new;
292 
293 		memcpy(p, old_p, sizeof(u32) * RTAX_MAX);
294 
295 		new = (unsigned long) p;
296 		prev = cmpxchg(&dst->_metrics, old, new);
297 
298 		if (prev != old) {
299 			kfree(p);
300 			p = __DST_METRICS_PTR(prev);
301 			if (prev & DST_METRICS_READ_ONLY)
302 				p = NULL;
303 		}
304 	}
305 	return p;
306 }
307 EXPORT_SYMBOL(dst_cow_metrics_generic);
308 
309 /* Caller asserts that dst_metrics_read_only(dst) is false.  */
310 void __dst_destroy_metrics_generic(struct dst_entry *dst, unsigned long old)
311 {
312 	unsigned long prev, new;
313 
314 	new = ((unsigned long) dst_default_metrics) | DST_METRICS_READ_ONLY;
315 	prev = cmpxchg(&dst->_metrics, old, new);
316 	if (prev == old)
317 		kfree(__DST_METRICS_PTR(old));
318 }
319 EXPORT_SYMBOL(__dst_destroy_metrics_generic);
320 
321 /**
322  * skb_dst_set_noref - sets skb dst, without a reference
323  * @skb: buffer
324  * @dst: dst entry
325  *
326  * Sets skb dst, assuming a reference was not taken on dst
327  * skb_dst_drop() should not dst_release() this dst
328  */
329 void skb_dst_set_noref(struct sk_buff *skb, struct dst_entry *dst)
330 {
331 	WARN_ON(!rcu_read_lock_held() && !rcu_read_lock_bh_held());
332 	/* If dst not in cache, we must take a reference, because
333 	 * dst_release() will destroy dst as soon as its refcount becomes zero
334 	 */
335 	if (unlikely(dst->flags & DST_NOCACHE)) {
336 		dst_hold(dst);
337 		skb_dst_set(skb, dst);
338 	} else {
339 		skb->_skb_refdst = (unsigned long)dst | SKB_DST_NOREF;
340 	}
341 }
342 EXPORT_SYMBOL(skb_dst_set_noref);
343 
344 /* Dirty hack. We did it in 2.2 (in __dst_free),
345  * we have _very_ good reasons not to repeat
346  * this mistake in 2.3, but we have no choice
347  * now. _It_ _is_ _explicit_ _deliberate_
348  * _race_ _condition_.
349  *
350  * Commented and originally written by Alexey.
351  */
352 static void dst_ifdown(struct dst_entry *dst, struct net_device *dev,
353 		       int unregister)
354 {
355 	if (dst->ops->ifdown)
356 		dst->ops->ifdown(dst, dev, unregister);
357 
358 	if (dev != dst->dev)
359 		return;
360 
361 	if (!unregister) {
362 		dst->input = dst->output = dst_discard;
363 	} else {
364 		dst->dev = dev_net(dst->dev)->loopback_dev;
365 		dev_hold(dst->dev);
366 		dev_put(dev);
367 	}
368 }
369 
370 static int dst_dev_event(struct notifier_block *this, unsigned long event,
371 			 void *ptr)
372 {
373 	struct net_device *dev = ptr;
374 	struct dst_entry *dst, *last = NULL;
375 
376 	switch (event) {
377 	case NETDEV_UNREGISTER_FINAL:
378 	case NETDEV_DOWN:
379 		mutex_lock(&dst_gc_mutex);
380 		for (dst = dst_busy_list; dst; dst = dst->next) {
381 			last = dst;
382 			dst_ifdown(dst, dev, event != NETDEV_DOWN);
383 		}
384 
385 		spin_lock_bh(&dst_garbage.lock);
386 		dst = dst_garbage.list;
387 		dst_garbage.list = NULL;
388 		spin_unlock_bh(&dst_garbage.lock);
389 
390 		if (last)
391 			last->next = dst;
392 		else
393 			dst_busy_list = dst;
394 		for (; dst; dst = dst->next)
395 			dst_ifdown(dst, dev, event != NETDEV_DOWN);
396 		mutex_unlock(&dst_gc_mutex);
397 		break;
398 	}
399 	return NOTIFY_DONE;
400 }
401 
402 static struct notifier_block dst_dev_notifier = {
403 	.notifier_call	= dst_dev_event,
404 	.priority = -10, /* must be called after other network notifiers */
405 };
406 
407 void __init dst_init(void)
408 {
409 	register_netdevice_notifier(&dst_dev_notifier);
410 }
411