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
  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 {
  44         spinlock_t              lock;
  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 }
 150 EXPORT_SYMBOL(dst_discard);
 151
 152 const u32 dst_default_metrics[RTAX_MAX + 1] = {
 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         }
 171         dst = kmem_cache_alloc(ops->kmem_cachep, GFP_ATOMIC);
 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 }
 204 EXPORT_SYMBOL(dst_alloc);
 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;
 213         dst->obsolete = DST_OBSOLETE_DEAD;
 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 }
 230 EXPORT_SYMBOL(__dst_free);
 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 }
 267 EXPORT_SYMBOL(dst_destroy);
 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 }
 307 EXPORT_SYMBOL(dst_cow_metrics_generic);
 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 }
 319 EXPORT_SYMBOL(__dst_destroy_metrics_generic);
 320
 321 /**
 322  * skb_dst_set_noref - sets skb dst, without a reference
 323  * @skb: buffer
 324  * @dst: dst entry
 325  *
 326  * Sets skb dst, assuming a reference was not taken on dst
 327  * skb_dst_drop() should not dst_release() this dst
 328  */
 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 }
 342 EXPORT_SYMBOL(skb_dst_set_noref);
 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) {
 377         case NETDEV_UNREGISTER_FINAL:
 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 }