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 struct dst_metrics dst_default_metrics = {
 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         .refcnt = ATOMIC_INIT(1),
 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.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->next = NULL;
 194         if (!(flags & DST_NOCOUNT))
 195                 dst_entries_add(ops, 1);
 196 }
 197 EXPORT_SYMBOL(dst_init);
 198
 199 void *dst_alloc(struct dst_ops *ops, struct net_device *dev,
 200                 int initial_ref, int initial_obsolete, unsigned short flags)
 201 {
 202         struct dst_entry *dst;
 203
 204         if (ops->gc && dst_entries_get_fast(ops) > ops->gc_thresh) {
 205                 if (ops->gc(ops))
 206                         return NULL;
 207         }
 208
 209         dst = kmem_cache_alloc(ops->kmem_cachep, GFP_ATOMIC);
 210         if (!dst)
 211                 return NULL;
 212
 213         dst_init(dst, ops, dev, initial_ref, initial_obsolete, flags);
 214
 215         return dst;
 216 }
 217 EXPORT_SYMBOL(dst_alloc);
 218
 219 static void ___dst_free(struct dst_entry *dst)
 220 {
 221         /* The first case (dev==NULL) is required, when
 222            protocol module is unloaded.
 223          */
 224         if (dst->dev == NULL || !(dst->dev->flags&IFF_UP)) {
 225                 dst->input = dst_discard;
 226                 dst->output = dst_discard_out;
 227         }
 228         dst->obsolete = DST_OBSOLETE_DEAD;
 229 }
 230
 231 void __dst_free(struct dst_entry *dst)
 232 {
 233         spin_lock_bh(&dst_garbage.lock);
 234         ___dst_free(dst);
 235         dst->next = dst_garbage.list;
 236         dst_garbage.list = dst;
 237         if (dst_garbage.timer_inc > DST_GC_INC) {
 238                 dst_garbage.timer_inc = DST_GC_INC;
 239                 dst_garbage.timer_expires = DST_GC_MIN;
 240                 mod_delayed_work(system_wq, &dst_gc_work,
 241                                  dst_garbage.timer_expires);
 242         }
 243         spin_unlock_bh(&dst_garbage.lock);
 244 }
 245 EXPORT_SYMBOL(__dst_free);
 246
 247 struct dst_entry *dst_destroy(struct dst_entry * dst)
 248 {
 249         struct dst_entry *child;
 250
 251         smp_rmb();
 252
 253 again:
 254         child = dst->child;
 255
 256         if (!(dst->flags & DST_NOCOUNT))
 257                 dst_entries_add(dst->ops, -1);
 258
 259         if (dst->ops->destroy)
 260                 dst->ops->destroy(dst);
 261         if (dst->dev)
 262                 dev_put(dst->dev);
 263
 264         lwtstate_put(dst->lwtstate);
 265
 266         if (dst->flags & DST_METADATA)
 267                 metadata_dst_free((struct metadata_dst *)dst);
 268         else
 269                 kmem_cache_free(dst->ops->kmem_cachep, dst);
 270
 271         dst = child;
 272         if (dst) {
 273                 int nohash = dst->flags & DST_NOHASH;
 274
 275                 if (atomic_dec_and_test(&dst->__refcnt)) {
 276                         /* We were real parent of this dst, so kill child. */
 277                         if (nohash)
 278                                 goto again;
 279                 } else {
 280                         /* Child is still referenced, return it for freeing. */
 281                         if (nohash)
 282                                 return dst;
 283                         /* Child is still in his hash table */
 284                 }
 285         }
 286         return NULL;
 287 }
 288 EXPORT_SYMBOL(dst_destroy);
 289
 290 static void dst_destroy_rcu(struct rcu_head *head)
 291 {
 292         struct dst_entry *dst = container_of(head, struct dst_entry, rcu_head);
 293
 294         dst = dst_destroy(dst);
 295         if (dst)
 296                 __dst_free(dst);
 297 }
 298
 299 void dst_release(struct dst_entry *dst)
 300 {
 301         if (dst) {
 302                 int newrefcnt;
 303                 unsigned short nocache = dst->flags & DST_NOCACHE;
 304
 305                 newrefcnt = atomic_dec_return(&dst->__refcnt);
 306                 if (unlikely(newrefcnt < 0))
 307                         net_warn_ratelimited("%s: dst:%p refcnt:%d\n",
 308                                              __func__, dst, newrefcnt);
 309                 if (!newrefcnt && unlikely(nocache))
 310                         call_rcu(&dst->rcu_head, dst_destroy_rcu);
 311         }
 312 }
 313 EXPORT_SYMBOL(dst_release);
 314
 315 u32 *dst_cow_metrics_generic(struct dst_entry *dst, unsigned long old)
 316 {
 317         struct dst_metrics *p = kmalloc(sizeof(*p), GFP_ATOMIC);
 318
 319         if (p) {
 320                 struct dst_metrics *old_p = (struct dst_metrics *)__DST_METRICS_PTR(old);
 321                 unsigned long prev, new;
 322
 323                 atomic_set(&p->refcnt, 1);
 324                 memcpy(p->metrics, old_p->metrics, sizeof(p->metrics));
 325
 326                 new = (unsigned long) p;
 327                 prev = cmpxchg(&dst->_metrics, old, new);
 328
 329                 if (prev != old) {
 330                         kfree(p);
 331                         p = (struct dst_metrics *)__DST_METRICS_PTR(prev);
 332                         if (prev & DST_METRICS_READ_ONLY)
 333                                 p = NULL;
 334                 } else if (prev & DST_METRICS_REFCOUNTED) {
 335                         if (atomic_dec_and_test(&old_p->refcnt))
 336                                 kfree(old_p);
 337                 }
 338         }
 339         BUILD_BUG_ON(offsetof(struct dst_metrics, metrics) != 0);
 340         return (u32 *)p;
 341 }
 342 EXPORT_SYMBOL(dst_cow_metrics_generic);
 343
 344 /* Caller asserts that dst_metrics_read_only(dst) is false.  */
 345 void __dst_destroy_metrics_generic(struct dst_entry *dst, unsigned long old)
 346 {
 347         unsigned long prev, new;
 348
 349         new = ((unsigned long) &dst_default_metrics) | DST_METRICS_READ_ONLY;
 350         prev = cmpxchg(&dst->_metrics, old, new);
 351         if (prev == old)
 352                 kfree(__DST_METRICS_PTR(old));
 353 }
 354 EXPORT_SYMBOL(__dst_destroy_metrics_generic);
 355
 356 static struct dst_ops md_dst_ops = {
 357         .family =               AF_UNSPEC,
 358 };
 359
 360 static int dst_md_discard_out(struct net *net, struct sock *sk, struct sk_buff *skb)
 361 {
 362         WARN_ONCE(1, "Attempting to call output on metadata dst\n");
 363         kfree_skb(skb);
 364         return 0;
 365 }
 366
 367 static int dst_md_discard(struct sk_buff *skb)
 368 {
 369         WARN_ONCE(1, "Attempting to call input on metadata dst\n");
 370         kfree_skb(skb);
 371         return 0;
 372 }
 373
 374 static void __metadata_dst_init(struct metadata_dst *md_dst, u8 optslen)
 375 {
 376         struct dst_entry *dst;
 377
 378         dst = &md_dst->dst;
 379         dst_init(dst, &md_dst_ops, NULL, 1, DST_OBSOLETE_NONE,
 380                  DST_METADATA | DST_NOCACHE | DST_NOCOUNT);
 381
 382         dst->input = dst_md_discard;
 383         dst->output = dst_md_discard_out;
 384
 385         memset(dst + 1, 0, sizeof(*md_dst) + optslen - sizeof(*dst));
 386 }
 387
 388 struct metadata_dst *metadata_dst_alloc(u8 optslen, gfp_t flags)
 389 {
 390         struct metadata_dst *md_dst;
 391
 392         md_dst = kmalloc(sizeof(*md_dst) + optslen, flags);
 393         if (!md_dst)
 394                 return NULL;
 395
 396         __metadata_dst_init(md_dst, optslen);
 397
 398         return md_dst;
 399 }
 400 EXPORT_SYMBOL_GPL(metadata_dst_alloc);
 401
 402 void metadata_dst_free(struct metadata_dst *md_dst)
 403 {
 404 #ifdef CONFIG_DST_CACHE
 405         dst_cache_destroy(&md_dst->u.tun_info.dst_cache);
 406 #endif
 407         kfree(md_dst);
 408 }
 409
 410 struct metadata_dst __percpu *metadata_dst_alloc_percpu(u8 optslen, gfp_t flags)
 411 {
 412         int cpu;
 413         struct metadata_dst __percpu *md_dst;
 414
 415         md_dst = __alloc_percpu_gfp(sizeof(struct metadata_dst) + optslen,
 416                                     __alignof__(struct metadata_dst), flags);
 417         if (!md_dst)
 418                 return NULL;
 419
 420         for_each_possible_cpu(cpu)
 421                 __metadata_dst_init(per_cpu_ptr(md_dst, cpu), optslen);
 422
 423         return md_dst;
 424 }
 425 EXPORT_SYMBOL_GPL(metadata_dst_alloc_percpu);
 426
 427 /* Dirty hack. We did it in 2.2 (in __dst_free),
 428  * we have _very_ good reasons not to repeat
 429  * this mistake in 2.3, but we have no choice
 430  * now. _It_ _is_ _explicit_ _deliberate_
 431  * _race_ _condition_.
 432  *
 433  * Commented and originally written by Alexey.
 434  */
 435 static void dst_ifdown(struct dst_entry *dst, struct net_device *dev,
 436                        int unregister)
 437 {
 438         if (dst->ops->ifdown)
 439                 dst->ops->ifdown(dst, dev, unregister);
 440
 441         if (dev != dst->dev)
 442                 return;
 443
 444         if (!unregister) {
 445                 dst->input = dst_discard;
 446                 dst->output = dst_discard_out;
 447         } else {
 448                 dst->dev = dev_net(dst->dev)->loopback_dev;
 449                 dev_hold(dst->dev);
 450                 dev_put(dev);
 451         }
 452 }
 453
 454 static int dst_dev_event(struct notifier_block *this, unsigned long event,
 455                          void *ptr)
 456 {
 457         struct net_device *dev = netdev_notifier_info_to_dev(ptr);
 458         struct dst_entry *dst, *last = NULL;
 459
 460         switch (event) {
 461         case NETDEV_UNREGISTER_FINAL:
 462         case NETDEV_DOWN:
 463                 mutex_lock(&dst_gc_mutex);
 464                 for (dst = dst_busy_list; dst; dst = dst->next) {
 465                         last = dst;
 466                         dst_ifdown(dst, dev, event != NETDEV_DOWN);
 467                 }
 468
 469                 spin_lock_bh(&dst_garbage.lock);
 470                 dst = dst_garbage.list;
 471                 dst_garbage.list = NULL;
 472                 spin_unlock_bh(&dst_garbage.lock);
 473
 474                 if (last)
 475                         last->next = dst;
 476                 else
 477                         dst_busy_list = dst;
 478                 for (; dst; dst = dst->next)
 479                         dst_ifdown(dst, dev, event != NETDEV_DOWN);
 480                 mutex_unlock(&dst_gc_mutex);
 481                 break;
 482         }
 483         return NOTIFY_DONE;
 484 }
 485
 486 static struct notifier_block dst_dev_notifier = {
 487         .notifier_call  = dst_dev_event,
 488         .priority = -10, /* must be called after other network notifiers */
 489 };
 490
 491 void __init dst_subsys_init(void)
 492 {
 493         register_netdevice_notifier(&dst_dev_notifier);
 494 }