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Linux/net/core/dst.c

  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 #include <net/lwtunnel.h>
 24 
 25 #include <net/dst.h>
 26 #include <net/dst_metadata.h>
 27 
 28 /*
 29  * Theory of operations:
 30  * 1) We use a list, protected by a spinlock, to add
 31  *    new entries from both BH and non-BH context.
 32  * 2) In order to keep spinlock held for a small delay,
 33  *    we use a second list where are stored long lived
 34  *    entries, that are handled by the garbage collect thread
 35  *    fired by a workqueue.
 36  * 3) This list is guarded by a mutex,
 37  *    so that the gc_task and dst_dev_event() can be synchronized.
 38  */
 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 
 73         mutex_lock(&dst_gc_mutex);
 74         next = dst_busy_list;
 75 
 76 loop:
 77         while ((dst = next) != NULL) {
 78                 next = dst->next;
 79                 prefetch(&next->next);
 80                 cond_resched();
 81                 if (likely(atomic_read(&dst->__refcnt))) {
 82                         last->next = dst;
 83                         last = dst;
 84                         delayed++;
 85                         continue;
 86                 }
 87                 work_performed++;
 88 
 89                 dst = dst_destroy(dst);
 90                 if (dst) {
 91                         /* NOHASH and still referenced. Unless it is already
 92                          * on gc list, invalidate it and add to gc list.
 93                          *
 94                          * Note: this is temporary. Actually, NOHASH dst's
 95                          * must be obsoleted when parent is obsoleted.
 96                          * But we do not have state "obsoleted, but
 97                          * referenced by parent", so it is right.
 98                          */
 99                         if (dst->obsolete > 0)
100                                 continue;
101 
102                         ___dst_free(dst);
103                         dst->next = next;
104                         next = dst;
105                 }
106         }
107 
108         spin_lock_bh(&dst_garbage.lock);
109         next = dst_garbage.list;
110         if (next) {
111                 dst_garbage.list = NULL;
112                 spin_unlock_bh(&dst_garbage.lock);
113                 goto loop;
114         }
115         last->next = NULL;
116         dst_busy_list = head.next;
117         if (!dst_busy_list)
118                 dst_garbage.timer_inc = DST_GC_MAX;
119         else {
120                 /*
121                  * if we freed less than 1/10 of delayed entries,
122                  * we can sleep longer.
123                  */
124                 if (work_performed <= delayed/10) {
125                         dst_garbage.timer_expires += dst_garbage.timer_inc;
126                         if (dst_garbage.timer_expires > DST_GC_MAX)
127                                 dst_garbage.timer_expires = DST_GC_MAX;
128                         dst_garbage.timer_inc += DST_GC_INC;
129                 } else {
130                         dst_garbage.timer_inc = DST_GC_INC;
131                         dst_garbage.timer_expires = DST_GC_MIN;
132                 }
133                 expires = dst_garbage.timer_expires;
134                 /*
135                  * if the next desired timer is more than 4 seconds in the
136                  * future then round the timer to whole seconds
137                  */
138                 if (expires > 4*HZ)
139                         expires = round_jiffies_relative(expires);
140                 schedule_delayed_work(&dst_gc_work, expires);
141         }
142 
143         spin_unlock_bh(&dst_garbage.lock);
144         mutex_unlock(&dst_gc_mutex);
145 }
146 
147 int dst_discard_out(struct net *net, struct sock *sk, struct sk_buff *skb)
148 {
149         kfree_skb(skb);
150         return 0;
151 }
152 EXPORT_SYMBOL(dst_discard_out);
153 
154 const u32 dst_default_metrics[RTAX_MAX + 1] = {
155         /* This initializer is needed to force linker to place this variable
156          * into const section. Otherwise it might end into bss section.
157          * We really want to avoid false sharing on this variable, and catch
158          * any writes on it.
159          */
160         [RTAX_MAX] = 0xdeadbeef,
161 };
162 
163 void dst_init(struct dst_entry *dst, struct dst_ops *ops,
164               struct net_device *dev, int initial_ref, int initial_obsolete,
165               unsigned short flags)
166 {
167         dst->child = NULL;
168         dst->dev = dev;
169         if (dev)
170                 dev_hold(dev);
171         dst->ops = ops;
172         dst_init_metrics(dst, dst_default_metrics, true);
173         dst->expires = 0UL;
174         dst->path = dst;
175         dst->from = NULL;
176 #ifdef CONFIG_XFRM
177         dst->xfrm = NULL;
178 #endif
179         dst->input = dst_discard;
180         dst->output = dst_discard_out;
181         dst->error = 0;
182         dst->obsolete = initial_obsolete;
183         dst->header_len = 0;
184         dst->trailer_len = 0;
185 #ifdef CONFIG_IP_ROUTE_CLASSID
186         dst->tclassid = 0;
187 #endif
188         dst->lwtstate = NULL;
189         atomic_set(&dst->__refcnt, initial_ref);
190         dst->__use = 0;
191         dst->lastuse = jiffies;
192         dst->flags = flags;
193         dst->pending_confirm = 0;
194         dst->next = NULL;
195         if (!(flags & DST_NOCOUNT))
196                 dst_entries_add(ops, 1);
197 }
198 EXPORT_SYMBOL(dst_init);
199 
200 void *dst_alloc(struct dst_ops *ops, struct net_device *dev,
201                 int initial_ref, int initial_obsolete, unsigned short flags)
202 {
203         struct dst_entry *dst;
204 
205         if (ops->gc && dst_entries_get_fast(ops) > ops->gc_thresh) {
206                 if (ops->gc(ops))
207                         return NULL;
208         }
209 
210         dst = kmem_cache_alloc(ops->kmem_cachep, GFP_ATOMIC);
211         if (!dst)
212                 return NULL;
213 
214         dst_init(dst, ops, dev, initial_ref, initial_obsolete, flags);
215 
216         return dst;
217 }
218 EXPORT_SYMBOL(dst_alloc);
219 
220 static void ___dst_free(struct dst_entry *dst)
221 {
222         /* The first case (dev==NULL) is required, when
223            protocol module is unloaded.
224          */
225         if (dst->dev == NULL || !(dst->dev->flags&IFF_UP)) {
226                 dst->input = dst_discard;
227                 dst->output = dst_discard_out;
228         }
229         dst->obsolete = DST_OBSOLETE_DEAD;
230 }
231 
232 void __dst_free(struct dst_entry *dst)
233 {
234         spin_lock_bh(&dst_garbage.lock);
235         ___dst_free(dst);
236         dst->next = dst_garbage.list;
237         dst_garbage.list = dst;
238         if (dst_garbage.timer_inc > DST_GC_INC) {
239                 dst_garbage.timer_inc = DST_GC_INC;
240                 dst_garbage.timer_expires = DST_GC_MIN;
241                 mod_delayed_work(system_wq, &dst_gc_work,
242                                  dst_garbage.timer_expires);
243         }
244         spin_unlock_bh(&dst_garbage.lock);
245 }
246 EXPORT_SYMBOL(__dst_free);
247 
248 struct dst_entry *dst_destroy(struct dst_entry * dst)
249 {
250         struct dst_entry *child;
251 
252         smp_rmb();
253 
254 again:
255         child = dst->child;
256 
257         if (!(dst->flags & DST_NOCOUNT))
258                 dst_entries_add(dst->ops, -1);
259 
260         if (dst->ops->destroy)
261                 dst->ops->destroy(dst);
262         if (dst->dev)
263                 dev_put(dst->dev);
264 
265         lwtstate_put(dst->lwtstate);
266 
267         if (dst->flags & DST_METADATA)
268                 kfree(dst);
269         else
270                 kmem_cache_free(dst->ops->kmem_cachep, dst);
271 
272         dst = child;
273         if (dst) {
274                 int nohash = dst->flags & DST_NOHASH;
275 
276                 if (atomic_dec_and_test(&dst->__refcnt)) {
277                         /* We were real parent of this dst, so kill child. */
278                         if (nohash)
279                                 goto again;
280                 } else {
281                         /* Child is still referenced, return it for freeing. */
282                         if (nohash)
283                                 return dst;
284                         /* Child is still in his hash table */
285                 }
286         }
287         return NULL;
288 }
289 EXPORT_SYMBOL(dst_destroy);
290 
291 static void dst_destroy_rcu(struct rcu_head *head)
292 {
293         struct dst_entry *dst = container_of(head, struct dst_entry, rcu_head);
294 
295         dst = dst_destroy(dst);
296         if (dst)
297                 __dst_free(dst);
298 }
299 
300 void dst_release(struct dst_entry *dst)
301 {
302         if (dst) {
303                 int newrefcnt;
304                 unsigned short nocache = dst->flags & DST_NOCACHE;
305 
306                 newrefcnt = atomic_dec_return(&dst->__refcnt);
307                 if (unlikely(newrefcnt < 0))
308                         net_warn_ratelimited("%s: dst:%p refcnt:%d\n",
309                                              __func__, dst, newrefcnt);
310                 if (!newrefcnt && unlikely(nocache))
311                         call_rcu(&dst->rcu_head, dst_destroy_rcu);
312         }
313 }
314 EXPORT_SYMBOL(dst_release);
315 
316 u32 *dst_cow_metrics_generic(struct dst_entry *dst, unsigned long old)
317 {
318         u32 *p = kmalloc(sizeof(u32) * RTAX_MAX, GFP_ATOMIC);
319 
320         if (p) {
321                 u32 *old_p = __DST_METRICS_PTR(old);
322                 unsigned long prev, new;
323 
324                 memcpy(p, old_p, sizeof(u32) * RTAX_MAX);
325 
326                 new = (unsigned long) p;
327                 prev = cmpxchg(&dst->_metrics, old, new);
328 
329                 if (prev != old) {
330                         kfree(p);
331                         p = __DST_METRICS_PTR(prev);
332                         if (prev & DST_METRICS_READ_ONLY)
333                                 p = NULL;
334                 }
335         }
336         return p;
337 }
338 EXPORT_SYMBOL(dst_cow_metrics_generic);
339 
340 /* Caller asserts that dst_metrics_read_only(dst) is false.  */
341 void __dst_destroy_metrics_generic(struct dst_entry *dst, unsigned long old)
342 {
343         unsigned long prev, new;
344 
345         new = ((unsigned long) dst_default_metrics) | DST_METRICS_READ_ONLY;
346         prev = cmpxchg(&dst->_metrics, old, new);
347         if (prev == old)
348                 kfree(__DST_METRICS_PTR(old));
349 }
350 EXPORT_SYMBOL(__dst_destroy_metrics_generic);
351 
352 static struct dst_ops md_dst_ops = {
353         .family =               AF_UNSPEC,
354 };
355 
356 static int dst_md_discard_out(struct net *net, struct sock *sk, struct sk_buff *skb)
357 {
358         WARN_ONCE(1, "Attempting to call output on metadata dst\n");
359         kfree_skb(skb);
360         return 0;
361 }
362 
363 static int dst_md_discard(struct sk_buff *skb)
364 {
365         WARN_ONCE(1, "Attempting to call input on metadata dst\n");
366         kfree_skb(skb);
367         return 0;
368 }
369 
370 static void __metadata_dst_init(struct metadata_dst *md_dst, u8 optslen)
371 {
372         struct dst_entry *dst;
373 
374         dst = &md_dst->dst;
375         dst_init(dst, &md_dst_ops, NULL, 1, DST_OBSOLETE_NONE,
376                  DST_METADATA | DST_NOCACHE | DST_NOCOUNT);
377 
378         dst->input = dst_md_discard;
379         dst->output = dst_md_discard_out;
380 
381         memset(dst + 1, 0, sizeof(*md_dst) + optslen - sizeof(*dst));
382 }
383 
384 struct metadata_dst *metadata_dst_alloc(u8 optslen, gfp_t flags)
385 {
386         struct metadata_dst *md_dst;
387 
388         md_dst = kmalloc(sizeof(*md_dst) + optslen, flags);
389         if (!md_dst)
390                 return NULL;
391 
392         __metadata_dst_init(md_dst, optslen);
393 
394         return md_dst;
395 }
396 EXPORT_SYMBOL_GPL(metadata_dst_alloc);
397 
398 struct metadata_dst __percpu *metadata_dst_alloc_percpu(u8 optslen, gfp_t flags)
399 {
400         int cpu;
401         struct metadata_dst __percpu *md_dst;
402 
403         md_dst = __alloc_percpu_gfp(sizeof(struct metadata_dst) + optslen,
404                                     __alignof__(struct metadata_dst), flags);
405         if (!md_dst)
406                 return NULL;
407 
408         for_each_possible_cpu(cpu)
409                 __metadata_dst_init(per_cpu_ptr(md_dst, cpu), optslen);
410 
411         return md_dst;
412 }
413 EXPORT_SYMBOL_GPL(metadata_dst_alloc_percpu);
414 
415 /* Dirty hack. We did it in 2.2 (in __dst_free),
416  * we have _very_ good reasons not to repeat
417  * this mistake in 2.3, but we have no choice
418  * now. _It_ _is_ _explicit_ _deliberate_
419  * _race_ _condition_.
420  *
421  * Commented and originally written by Alexey.
422  */
423 static void dst_ifdown(struct dst_entry *dst, struct net_device *dev,
424                        int unregister)
425 {
426         if (dst->ops->ifdown)
427                 dst->ops->ifdown(dst, dev, unregister);
428 
429         if (dev != dst->dev)
430                 return;
431 
432         if (!unregister) {
433                 dst->input = dst_discard;
434                 dst->output = dst_discard_out;
435         } else {
436                 dst->dev = dev_net(dst->dev)->loopback_dev;
437                 dev_hold(dst->dev);
438                 dev_put(dev);
439         }
440 }
441 
442 static int dst_dev_event(struct notifier_block *this, unsigned long event,
443                          void *ptr)
444 {
445         struct net_device *dev = netdev_notifier_info_to_dev(ptr);
446         struct dst_entry *dst, *last = NULL;
447 
448         switch (event) {
449         case NETDEV_UNREGISTER_FINAL:
450         case NETDEV_DOWN:
451                 mutex_lock(&dst_gc_mutex);
452                 for (dst = dst_busy_list; dst; dst = dst->next) {
453                         last = dst;
454                         dst_ifdown(dst, dev, event != NETDEV_DOWN);
455                 }
456 
457                 spin_lock_bh(&dst_garbage.lock);
458                 dst = dst_garbage.list;
459                 dst_garbage.list = NULL;
460                 spin_unlock_bh(&dst_garbage.lock);
461 
462                 if (last)
463                         last->next = dst;
464                 else
465                         dst_busy_list = dst;
466                 for (; dst; dst = dst->next)
467                         dst_ifdown(dst, dev, event != NETDEV_DOWN);
468                 mutex_unlock(&dst_gc_mutex);
469                 break;
470         }
471         return NOTIFY_DONE;
472 }
473 
474 static struct notifier_block dst_dev_notifier = {
475         .notifier_call  = dst_dev_event,
476         .priority = -10, /* must be called after other network notifiers */
477 };
478 
479 void __init dst_subsys_init(void)
480 {
481         register_netdevice_notifier(&dst_dev_notifier);
482 }
483 

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