Linux Kernel  3.7.1
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dst.c
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1 /*
2  * net/core/dst.c Protocol independent destination cache.
3  *
4  * Authors: Alexey Kuznetsov, <[email protected]>
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 {
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 }
151 
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  }
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 }
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;
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 }
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 }
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 }
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 }
320 
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 }
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) {
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 }