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
  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
  37 /*
  38  * We want to keep lock & list close together
  39  * to dirty as few cache lines as possible in __dst_free().
  40  * As this is not a very strong hint, we dont force an alignment on SMP.
  41  */
  42 static struct {
  43         spinlock_t              lock;
  44         struct dst_entry        *list;
  45         unsigned long           timer_inc;
  46         unsigned long           timer_expires;
  47 } dst_garbage = {
  48         .lock = __SPIN_LOCK_UNLOCKED(dst_garbage.lock),
  49         .timer_inc = DST_GC_MAX,
  50 };
  51 static void dst_gc_task(struct work_struct *work);
  52 static void ___dst_free(struct dst_entry *dst);
  53
  54 static DECLARE_DELAYED_WORK(dst_gc_work, dst_gc_task);
  55
  56 static DEFINE_MUTEX(dst_gc_mutex);
  57 /*
  58  * long lived entries are maintained in this list, guarded by dst_gc_mutex
  59  */
  60 static struct dst_entry         *dst_busy_list;
  61
  62 static void dst_gc_task(struct work_struct *work)
  63 {
  64         int    delayed = 0;
  65         int    work_performed = 0;
  66         unsigned long expires = ~0L;
  67         struct dst_entry *dst, *next, head;
  68         struct dst_entry *last = &head;
  69
  70         mutex_lock(&dst_gc_mutex);
  71         next = dst_busy_list;
  72
  73 loop:
  74         while ((dst = next) != NULL) {
  75                 next = dst->next;
  76                 prefetch(&next->next);
  77                 cond_resched();
  78                 if (likely(atomic_read(&dst->__refcnt))) {
  79                         last->next = dst;
  80                         last = dst;
  81                         delayed++;
  82                         continue;
  83                 }
  84                 work_performed++;
  85
  86                 dst = dst_destroy(dst);
  87                 if (dst) {
  88                         /* NOHASH and still referenced. Unless it is already
  89                          * on gc list, invalidate it and add to gc list.
  90                          *
  91                          * Note: this is temporary. Actually, NOHASH dst's
  92                          * must be obsoleted when parent is obsoleted.
  93                          * But we do not have state "obsoleted, but
  94                          * referenced by parent", so it is right.
  95                          */
  96                         if (dst->obsolete > 1)
  97                                 continue;
  98
  99                         ___dst_free(dst);
 100                         dst->next = next;
 101                         next = dst;
 102                 }
 103         }
 104
 105         spin_lock_bh(&dst_garbage.lock);
 106         next = dst_garbage.list;
 107         if (next) {
 108                 dst_garbage.list = NULL;
 109                 spin_unlock_bh(&dst_garbage.lock);
 110                 goto loop;
 111         }
 112         last->next = NULL;
 113         dst_busy_list = head.next;
 114         if (!dst_busy_list)
 115                 dst_garbage.timer_inc = DST_GC_MAX;
 116         else {
 117                 /*
 118                  * if we freed less than 1/10 of delayed entries,
 119                  * we can sleep longer.
 120                  */
 121                 if (work_performed <= delayed/10) {
 122                         dst_garbage.timer_expires += dst_garbage.timer_inc;
 123                         if (dst_garbage.timer_expires > DST_GC_MAX)
 124                                 dst_garbage.timer_expires = DST_GC_MAX;
 125                         dst_garbage.timer_inc += DST_GC_INC;
 126                 } else {
 127                         dst_garbage.timer_inc = DST_GC_INC;
 128                         dst_garbage.timer_expires = DST_GC_MIN;
 129                 }
 130                 expires = dst_garbage.timer_expires;
 131                 /*
 132                  * if the next desired timer is more than 4 seconds in the
 133                  * future then round the timer to whole seconds
 134                  */
 135                 if (expires > 4*HZ)
 136                         expires = round_jiffies_relative(expires);
 137                 schedule_delayed_work(&dst_gc_work, expires);
 138         }
 139
 140         spin_unlock_bh(&dst_garbage.lock);
 141         mutex_unlock(&dst_gc_mutex);
 142 }
 143
 144 int dst_discard(struct sk_buff *skb)
 145 {
 146         kfree_skb(skb);
 147         return 0;
 148 }
 149 EXPORT_SYMBOL(dst_discard);
 150
 151 const u32 dst_default_metrics[RTAX_MAX];
 152
 153 void *dst_alloc(struct dst_ops *ops, struct net_device *dev,
 154                 int initial_ref, int initial_obsolete, int flags)
 155 {
 156         struct dst_entry *dst;
 157
 158         if (ops->gc && dst_entries_get_fast(ops) > ops->gc_thresh) {
 159                 if (ops->gc(ops))
 160                         return NULL;
 161         }
 162         dst = kmem_cache_alloc(ops->kmem_cachep, GFP_ATOMIC);
 163         if (!dst)
 164                 return NULL;
 165         dst->child = NULL;
 166         dst->dev = dev;
 167         if (dev)
 168                 dev_hold(dev);
 169         dst->ops = ops;
 170         dst_init_metrics(dst, dst_default_metrics, true);
 171         dst->expires = 0UL;
 172         dst->path = dst;
 173         dst->neighbour = NULL;
 174         dst->hh = NULL;
 175 #ifdef CONFIG_XFRM
 176         dst->xfrm = NULL;
 177 #endif
 178         dst->input = dst_discard;
 179         dst->output = dst_discard;
 180         dst->error = 0;
 181         dst->obsolete = initial_obsolete;
 182         dst->header_len = 0;
 183         dst->trailer_len = 0;
 184 #ifdef CONFIG_IP_ROUTE_CLASSID
 185         dst->tclassid = 0;
 186 #endif
 187         atomic_set(&dst->__refcnt, initial_ref);
 188         dst->__use = 0;
 189         dst->lastuse = jiffies;
 190         dst->flags = flags;
 191         dst->next = NULL;
 192         dst_entries_add(ops, 1);
 193         return dst;
 194 }
 195 EXPORT_SYMBOL(dst_alloc);
 196
 197 static void ___dst_free(struct dst_entry *dst)
 198 {
 199         /* The first case (dev==NULL) is required, when
 200            protocol module is unloaded.
 201          */
 202         if (dst->dev == NULL || !(dst->dev->flags&IFF_UP))
 203                 dst->input = dst->output = dst_discard;
 204         dst->obsolete = 2;
 205 }
 206
 207 void __dst_free(struct dst_entry *dst)
 208 {
 209         spin_lock_bh(&dst_garbage.lock);
 210         ___dst_free(dst);
 211         dst->next = dst_garbage.list;
 212         dst_garbage.list = dst;
 213         if (dst_garbage.timer_inc > DST_GC_INC) {
 214                 dst_garbage.timer_inc = DST_GC_INC;
 215                 dst_garbage.timer_expires = DST_GC_MIN;
 216                 cancel_delayed_work(&dst_gc_work);
 217                 schedule_delayed_work(&dst_gc_work, dst_garbage.timer_expires);
 218         }
 219         spin_unlock_bh(&dst_garbage.lock);
 220 }
 221 EXPORT_SYMBOL(__dst_free);
 222
 223 struct dst_entry *dst_destroy(struct dst_entry * dst)
 224 {
 225         struct dst_entry *child;
 226         struct neighbour *neigh;
 227         struct hh_cache *hh;
 228
 229         smp_rmb();
 230
 231 again:
 232         neigh = dst->neighbour;
 233         hh = dst->hh;
 234         child = dst->child;
 235
 236         dst->hh = NULL;
 237         if (hh)
 238                 hh_cache_put(hh);
 239
 240         if (neigh) {
 241                 dst->neighbour = NULL;
 242                 neigh_release(neigh);
 243         }
 244
 245         dst_entries_add(dst->ops, -1);
 246
 247         if (dst->ops->destroy)
 248                 dst->ops->destroy(dst);
 249         if (dst->dev)
 250                 dev_put(dst->dev);
 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
 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
 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.  */
 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  */
 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  */
 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
 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
 415 void __init dst_init(void)
 416 {
 417         register_netdevice_notifier(&dst_dev_notifier);
 418 }