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         dst->from = NULL;
 183 #ifdef CONFIG_XFRM
 184         dst->xfrm = NULL;
 185 #endif
 186         dst->input = dst_discard;
 187         dst->output = dst_discard;
 188         dst->error = 0;
 189         dst->obsolete = initial_obsolete;
 190         dst->header_len = 0;
 191         dst->trailer_len = 0;
 192 #ifdef CONFIG_IP_ROUTE_CLASSID
 193         dst->tclassid = 0;
 194 #endif
 195         atomic_set(&dst->__refcnt, initial_ref);
 196         dst->__use = 0;
 197         dst->lastuse = jiffies;
 198         dst->flags = flags;
 199         dst->pending_confirm = 0;
 200         dst->next = NULL;
 201         if (!(flags & DST_NOCOUNT))
 202                 dst_entries_add(ops, 1);
 203         return dst;
 204 }
 205 EXPORT_SYMBOL(dst_alloc);
 206
 207 static void ___dst_free(struct dst_entry *dst)
 208 {
 209         /* The first case (dev==NULL) is required, when
 210            protocol module is unloaded.
 211          */
 212         if (dst->dev == NULL || !(dst->dev->flags&IFF_UP))
 213                 dst->input = dst->output = dst_discard;
 214         dst->obsolete = DST_OBSOLETE_DEAD;
 215 }
 216
 217 void __dst_free(struct dst_entry *dst)
 218 {
 219         spin_lock_bh(&dst_garbage.lock);
 220         ___dst_free(dst);
 221         dst->next = dst_garbage.list;
 222         dst_garbage.list = dst;
 223         if (dst_garbage.timer_inc > DST_GC_INC) {
 224                 dst_garbage.timer_inc = DST_GC_INC;
 225                 dst_garbage.timer_expires = DST_GC_MIN;
 226                 mod_delayed_work(system_wq, &dst_gc_work,
 227                                  dst_garbage.timer_expires);
 228         }
 229         spin_unlock_bh(&dst_garbage.lock);
 230 }
 231 EXPORT_SYMBOL(__dst_free);
 232
 233 struct dst_entry *dst_destroy(struct dst_entry * dst)
 234 {
 235         struct dst_entry *child;
 236
 237         smp_rmb();
 238
 239 again:
 240         child = dst->child;
 241
 242         if (!(dst->flags & DST_NOCOUNT))
 243                 dst_entries_add(dst->ops, -1);
 244
 245         if (dst->ops->destroy)
 246                 dst->ops->destroy(dst);
 247         if (dst->dev)
 248                 dev_put(dst->dev);
 249         kmem_cache_free(dst->ops->kmem_cachep, dst);
 250
 251         dst = child;
 252         if (dst) {
 253                 int nohash = dst->flags & DST_NOHASH;
 254
 255                 if (atomic_dec_and_test(&dst->__refcnt)) {
 256                         /* We were real parent of this dst, so kill child. */
 257                         if (nohash)
 258                                 goto again;
 259                 } else {
 260                         /* Child is still referenced, return it for freeing. */
 261                         if (nohash)
 262                                 return dst;
 263                         /* Child is still in his hash table */
 264                 }
 265         }
 266         return NULL;
 267 }
 268 EXPORT_SYMBOL(dst_destroy);
 269
 270 void dst_release(struct dst_entry *dst)
 271 {
 272         if (dst) {
 273                 int newrefcnt;
 274
 275                 newrefcnt = atomic_dec_return(&dst->__refcnt);
 276                 WARN_ON(newrefcnt < 0);
 277                 if (unlikely(dst->flags & DST_NOCACHE) && !newrefcnt) {
 278                         dst = dst_destroy(dst);
 279                         if (dst)
 280                                 __dst_free(dst);
 281                 }
 282         }
 283 }
 284 EXPORT_SYMBOL(dst_release);
 285
 286 u32 *dst_cow_metrics_generic(struct dst_entry *dst, unsigned long old)
 287 {
 288         u32 *p = kmalloc(sizeof(u32) * RTAX_MAX, GFP_ATOMIC);
 289
 290         if (p) {
 291                 u32 *old_p = __DST_METRICS_PTR(old);
 292                 unsigned long prev, new;
 293
 294                 memcpy(p, old_p, sizeof(u32) * RTAX_MAX);
 295
 296                 new = (unsigned long) p;
 297                 prev = cmpxchg(&dst->_metrics, old, new);
 298
 299                 if (prev != old) {
 300                         kfree(p);
 301                         p = __DST_METRICS_PTR(prev);
 302                         if (prev & DST_METRICS_READ_ONLY)
 303                                 p = NULL;
 304                 }
 305         }
 306         return p;
 307 }
 308 EXPORT_SYMBOL(dst_cow_metrics_generic);
 309
 310 /* Caller asserts that dst_metrics_read_only(dst) is false.  */
 311 void __dst_destroy_metrics_generic(struct dst_entry *dst, unsigned long old)
 312 {
 313         unsigned long prev, new;
 314
 315         new = ((unsigned long) dst_default_metrics) | DST_METRICS_READ_ONLY;
 316         prev = cmpxchg(&dst->_metrics, old, new);
 317         if (prev == old)
 318                 kfree(__DST_METRICS_PTR(old));
 319 }
 320 EXPORT_SYMBOL(__dst_destroy_metrics_generic);
 321
 322 /**
 323  * skb_dst_set_noref - sets skb dst, without a reference
 324  * @skb: buffer
 325  * @dst: dst entry
 326  *
 327  * Sets skb dst, assuming a reference was not taken on dst
 328  * skb_dst_drop() should not dst_release() this dst
 329  */
 330 void skb_dst_set_noref(struct sk_buff *skb, struct dst_entry *dst)
 331 {
 332         WARN_ON(!rcu_read_lock_held() && !rcu_read_lock_bh_held());
 333         /* If dst not in cache, we must take a reference, because
 334          * dst_release() will destroy dst as soon as its refcount becomes zero
 335          */
 336         if (unlikely(dst->flags & DST_NOCACHE)) {
 337                 dst_hold(dst);
 338                 skb_dst_set(skb, dst);
 339         } else {
 340                 skb->_skb_refdst = (unsigned long)dst | SKB_DST_NOREF;
 341         }
 342 }
 343 EXPORT_SYMBOL(skb_dst_set_noref);
 344
 345 /* Dirty hack. We did it in 2.2 (in __dst_free),
 346  * we have _very_ good reasons not to repeat
 347  * this mistake in 2.3, but we have no choice
 348  * now. _It_ _is_ _explicit_ _deliberate_
 349  * _race_ _condition_.
 350  *
 351  * Commented and originally written by Alexey.
 352  */
 353 static void dst_ifdown(struct dst_entry *dst, struct net_device *dev,
 354                        int unregister)
 355 {
 356         if (dst->ops->ifdown)
 357                 dst->ops->ifdown(dst, dev, unregister);
 358
 359         if (dev != dst->dev)
 360                 return;
 361
 362         if (!unregister) {
 363                 dst->input = dst->output = dst_discard;
 364         } else {
 365                 dst->dev = dev_net(dst->dev)->loopback_dev;
 366                 dev_hold(dst->dev);
 367                 dev_put(dev);
 368         }
 369 }
 370
 371 static int dst_dev_event(struct notifier_block *this, unsigned long event,
 372                          void *ptr)
 373 {
 374         struct net_device *dev = ptr;
 375         struct dst_entry *dst, *last = NULL;
 376
 377         switch (event) {
 378         case NETDEV_UNREGISTER_FINAL:
 379         case NETDEV_DOWN:
 380                 mutex_lock(&dst_gc_mutex);
 381                 for (dst = dst_busy_list; dst; dst = dst->next) {
 382                         last = dst;
 383                         dst_ifdown(dst, dev, event != NETDEV_DOWN);
 384                 }
 385
 386                 spin_lock_bh(&dst_garbage.lock);
 387                 dst = dst_garbage.list;
 388                 dst_garbage.list = NULL;
 389                 spin_unlock_bh(&dst_garbage.lock);
 390
 391                 if (last)
 392                         last->next = dst;
 393                 else
 394                         dst_busy_list = dst;
 395                 for (; dst; dst = dst->next)
 396                         dst_ifdown(dst, dev, event != NETDEV_DOWN);
 397                 mutex_unlock(&dst_gc_mutex);
 398                 break;
 399         }
 400         return NOTIFY_DONE;
 401 }
 402
 403 static struct notifier_block dst_dev_notifier = {
 404         .notifier_call  = dst_dev_event,
 405         .priority = -10, /* must be called after other network notifiers */
 406 };
 407
 408 void __init dst_init(void)
 409 {
 410         register_netdevice_notifier(&dst_dev_notifier);
 411 }