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
dst_gc_task(struct work_struct * work)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
140 * future 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 +
156 elapsed.tv_nsec / NSEC_PER_USEC);
157 #endif
158 }
159
dst_discard(struct sk_buff * skb)160 int dst_discard(struct sk_buff *skb)
161 {
162 kfree_skb(skb);
163 return 0;
164 }
165 EXPORT_SYMBOL(dst_discard);
166
167 const u32 dst_default_metrics[RTAX_MAX];
168
dst_alloc(struct dst_ops * ops,int initial_ref)169 void *dst_alloc(struct dst_ops *ops, int initial_ref)
170 {
171 struct dst_entry *dst;
172
173 if (ops->gc && dst_entries_get_fast(ops) > ops->gc_thresh) {
174 if (ops->gc(ops))
175 return NULL;
176 }
177 dst = kmem_cache_zalloc(ops->kmem_cachep, GFP_ATOMIC);
178 if (!dst)
179 return NULL;
180 atomic_set(&dst->__refcnt, initial_ref);
181 dst->ops = ops;
182 dst->lastuse = jiffies;
183 dst->path = dst;
184 dst->input = dst->output = dst_discard;
185 dst_init_metrics(dst, dst_default_metrics, true);
186 #if RT_CACHE_DEBUG >= 2
187 atomic_inc(&dst_total);
188 #endif
189 dst_entries_add(ops, 1);
190 return dst;
191 }
192 EXPORT_SYMBOL(dst_alloc);
193
___dst_free(struct dst_entry * dst)194 static void ___dst_free(struct dst_entry *dst)
195 {
196 /* The first case (dev==NULL) is required, when
197 protocol module is unloaded.
198 */
199 if (dst->dev == NULL || !(dst->dev->flags&IFF_UP))
200 dst->input = dst->output = dst_discard;
201 dst->obsolete = 2;
202 }
203
__dst_free(struct dst_entry * dst)204 void __dst_free(struct dst_entry *dst)
205 {
206 spin_lock_bh(&dst_garbage.lock);
207 ___dst_free(dst);
208 dst->next = dst_garbage.list;
209 dst_garbage.list = dst;
210 if (dst_garbage.timer_inc > DST_GC_INC) {
211 dst_garbage.timer_inc = DST_GC_INC;
212 dst_garbage.timer_expires = DST_GC_MIN;
213 cancel_delayed_work(&dst_gc_work);
214 schedule_delayed_work(&dst_gc_work, dst_garbage.timer_expires);
215 }
216 spin_unlock_bh(&dst_garbage.lock);
217 }
218 EXPORT_SYMBOL(__dst_free);
219
dst_destroy(struct dst_entry * dst)220 struct dst_entry *dst_destroy(struct dst_entry * dst)
221 {
222 struct dst_entry *child;
223 struct neighbour *neigh;
224 struct hh_cache *hh;
225
226 smp_rmb();
227
228 again:
229 neigh = dst->neighbour;
230 hh = dst->hh;
231 child = dst->child;
232
233 dst->hh = NULL;
234 if (hh)
235 hh_cache_put(hh);
236
237 if (neigh) {
238 dst->neighbour = NULL;
239 neigh_release(neigh);
240 }
241
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 #if RT_CACHE_DEBUG >= 2
249 atomic_dec(&dst_total);
250 #endif
251 kmem_cache_free(dst->ops->kmem_cachep, dst);
252
253 dst = child;
254 if (dst) {
255 int nohash = dst->flags & DST_NOHASH;
256
257 if (atomic_dec_and_test(&dst->__refcnt)) {
258 /* We were real parent of this dst, so kill child. */
259 if (nohash)
260 goto again;
261 } else {
262 /* Child is still referenced, return it for freeing. */
263 if (nohash)
264 return dst;
265 /* Child is still in his hash table */
266 }
267 }
268 return NULL;
269 }
270 EXPORT_SYMBOL(dst_destroy);
271
dst_release(struct dst_entry * dst)272 void dst_release(struct dst_entry *dst)
273 {
274 if (dst) {
275 int newrefcnt;
276
277 newrefcnt = atomic_dec_return(&dst->__refcnt);
278 WARN_ON(newrefcnt < 0);
279 if (unlikely(dst->flags & DST_NOCACHE) && !newrefcnt) {
280 dst = dst_destroy(dst);
281 if (dst)
282 __dst_free(dst);
283 }
284 }
285 }
286 EXPORT_SYMBOL(dst_release);
287
dst_cow_metrics_generic(struct dst_entry * dst,unsigned long old)288 u32 *dst_cow_metrics_generic(struct dst_entry *dst, unsigned long old)
289 {
290 u32 *p = kmalloc(sizeof(u32) * RTAX_MAX, GFP_ATOMIC);
291
292 if (p) {
293 u32 *old_p = __DST_METRICS_PTR(old);
294 unsigned long prev, new;
295
296 memcpy(p, old_p, sizeof(u32) * RTAX_MAX);
297
298 new = (unsigned long) p;
299 prev = cmpxchg(&dst->_metrics, old, new);
300
301 if (prev != old) {
302 kfree(p);
303 p = __DST_METRICS_PTR(prev);
304 if (prev & DST_METRICS_READ_ONLY)
305 p = NULL;
306 }
307 }
308 return p;
309 }
310 EXPORT_SYMBOL(dst_cow_metrics_generic);
311
312 /* Caller asserts that dst_metrics_read_only(dst) is false. */
__dst_destroy_metrics_generic(struct dst_entry * dst,unsigned long old)313 void __dst_destroy_metrics_generic(struct dst_entry *dst, unsigned long old)
314 {
315 unsigned long prev, new;
316
317 new = (unsigned long) dst_default_metrics;
318 prev = cmpxchg(&dst->_metrics, old, new);
319 if (prev == old)
320 kfree(__DST_METRICS_PTR(old));
321 }
322 EXPORT_SYMBOL(__dst_destroy_metrics_generic);
323
324 /**
325 * skb_dst_set_noref - sets skb dst, without a reference
326 * @skb: buffer
327 * @dst: dst entry
328 *
329 * Sets skb dst, assuming a reference was not taken on dst
330 * skb_dst_drop() should not dst_release() this dst
331 */
skb_dst_set_noref(struct sk_buff * skb,struct dst_entry * dst)332 void skb_dst_set_noref(struct sk_buff *skb, struct dst_entry *dst)
333 {
334 WARN_ON(!rcu_read_lock_held() && !rcu_read_lock_bh_held());
335 /* If dst not in cache, we must take a reference, because
336 * dst_release() will destroy dst as soon as its refcount becomes zero
337 */
338 if (unlikely(dst->flags & DST_NOCACHE)) {
339 dst_hold(dst);
340 skb_dst_set(skb, dst);
341 } else {
342 skb->_skb_refdst = (unsigned long)dst | SKB_DST_NOREF;
343 }
344 }
345 EXPORT_SYMBOL(skb_dst_set_noref);
346
347 /* Dirty hack. We did it in 2.2 (in __dst_free),
348 * we have _very_ good reasons not to repeat
349 * this mistake in 2.3, but we have no choice
350 * now. _It_ _is_ _explicit_ _deliberate_
351 * _race_ _condition_.
352 *
353 * Commented and originally written by Alexey.
354 */
dst_ifdown(struct dst_entry * dst,struct net_device * dev,int unregister)355 static void dst_ifdown(struct dst_entry *dst, struct net_device *dev,
356 int unregister)
357 {
358 if (dst->ops->ifdown)
359 dst->ops->ifdown(dst, dev, unregister);
360
361 if (dev != dst->dev)
362 return;
363
364 if (!unregister) {
365 dst->input = dst->output = dst_discard;
366 } else {
367 dst->dev = dev_net(dst->dev)->loopback_dev;
368 dev_hold(dst->dev);
369 dev_put(dev);
370 if (dst->neighbour && dst->neighbour->dev == dev) {
371 dst->neighbour->dev = dst->dev;
372 dev_hold(dst->dev);
373 dev_put(dev);
374 }
375 }
376 }
377
dst_dev_event(struct notifier_block * this,unsigned long event,void * ptr)378 static int dst_dev_event(struct notifier_block *this, unsigned long event,
379 void *ptr)
380 {
381 struct net_device *dev = ptr;
382 struct dst_entry *dst, *last = NULL;
383
384 switch (event) {
385 case NETDEV_UNREGISTER:
386 case NETDEV_DOWN:
387 mutex_lock(&dst_gc_mutex);
388 for (dst = dst_busy_list; dst; dst = dst->next) {
389 last = dst;
390 dst_ifdown(dst, dev, event != NETDEV_DOWN);
391 }
392
393 spin_lock_bh(&dst_garbage.lock);
394 dst = dst_garbage.list;
395 dst_garbage.list = NULL;
396 spin_unlock_bh(&dst_garbage.lock);
397
398 if (last)
399 last->next = dst;
400 else
401 dst_busy_list = dst;
402 for (; dst; dst = dst->next)
403 dst_ifdown(dst, dev, event != NETDEV_DOWN);
404 mutex_unlock(&dst_gc_mutex);
405 break;
406 }
407 return NOTIFY_DONE;
408 }
409
410 static struct notifier_block dst_dev_notifier = {
411 .notifier_call = dst_dev_event,
412 .priority = -10, /* must be called after other network notifiers */
413 };
414
dst_init(void)415 void __init dst_init(void)
416 {
417 register_netdevice_notifier(&dst_dev_notifier);
418 }
419