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/netdevice.h>
  16 #include <linux/skbuff.h>
  17 #include <linux/string.h>
  18 #include <linux/types.h>
  19 #include <net/net_namespace.h>
  20
  21 #include <net/dst.h>
  22
  23 /*
  24  * Theory of operations:
  25  * 1) We use a list, protected by a spinlock, to add
  26  *    new entries from both BH and non-BH context.
  27  * 2) In order to keep spinlock held for a small delay,
  28  *    we use a second list where are stored long lived
  29  *    entries, that are handled by the garbage collect thread
  30  *    fired by a workqueue.
  31  * 3) This list is guarded by a mutex,
  32  *    so that the gc_task and dst_dev_event() can be synchronized.
  33  */
  34 #if RT_CACHE_DEBUG >= 2
  35 static atomic_t                  dst_total = ATOMIC_INIT(0);
  36 #endif
  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 #if RT_CACHE_DEBUG >= 2
  71         ktime_t time_start = ktime_get();
  72         struct timespec elapsed;
  73 #endif
  74
  75         mutex_lock(&dst_gc_mutex);
  76         next = dst_busy_list;
  77
  78 loop:
  79         while ((dst = next) != NULL) {
  80                 next = dst->next;
  81                 prefetch(&next->next);
  82                 if (likely(atomic_read(&dst->__refcnt))) {
  83                         last->next = dst;
  84                         last = dst;
  85                         delayed++;
  86                         continue;
  87                 }
  88                 work_performed++;
  89
  90                 dst = dst_destroy(dst);
  91                 if (dst) {
  92                         /* NOHASH and still referenced. Unless it is already
  93                          * on gc list, invalidate it and add to gc list.
  94                          *
  95                          * Note: this is temporary. Actually, NOHASH dst's
  96                          * must be obsoleted when parent is obsoleted.
  97                          * But we do not have state "obsoleted, but
  98                          * referenced by parent", so it is right.
  99                          */
 100                         if (dst->obsolete > 1)
 101                                 continue;
 102
 103                         ___dst_free(dst);
 104                         dst->next = next;
 105                         next = dst;
 106                 }
 107         }
 108
 109         spin_lock_bh(&dst_garbage.lock);
 110         next = dst_garbage.list;
 111         if (next) {
 112                 dst_garbage.list = NULL;
 113                 spin_unlock_bh(&dst_garbage.lock);
 114                 goto loop;
 115         }
 116         last->next = NULL;
 117         dst_busy_list = head.next;
 118         if (!dst_busy_list)
 119                 dst_garbage.timer_inc = DST_GC_MAX;
 120         else {
 121                 /*
 122                  * if we freed less than 1/10 of delayed entries,
 123                  * we can sleep longer.
 124                  */
 125                 if (work_performed <= delayed/10) {
 126                         dst_garbage.timer_expires += dst_garbage.timer_inc;
 127                         if (dst_garbage.timer_expires > DST_GC_MAX)
 128                                 dst_garbage.timer_expires = DST_GC_MAX;
 129                         dst_garbage.timer_inc += DST_GC_INC;
 130                 } else {
 131                         dst_garbage.timer_inc = DST_GC_INC;
 132                         dst_garbage.timer_expires = DST_GC_MIN;
 133                 }
 134                 expires = dst_garbage.timer_expires;
 135                 /*
 136                  * if the next desired timer is more than 4 seconds in the future
 137                  * then round the timer to whole seconds
 138                  */
 139                 if (expires > 4*HZ)
 140                         expires = round_jiffies_relative(expires);
 141                 schedule_delayed_work(&dst_gc_work, expires);
 142         }
 143
 144         spin_unlock_bh(&dst_garbage.lock);
 145         mutex_unlock(&dst_gc_mutex);
 146 #if RT_CACHE_DEBUG >= 2
 147         elapsed = ktime_to_timespec(ktime_sub(ktime_get(), time_start));
 148         printk(KERN_DEBUG "dst_total: %d delayed: %d work_perf: %d"
 149                 " expires: %lu elapsed: %lu us\n",
 150                 atomic_read(&dst_total), delayed, work_performed,
 151                 expires,
 152                 elapsed.tv_sec * USEC_PER_SEC + elapsed.tv_nsec / NSEC_PER_USEC);
 153 #endif
 154 }
 155
 156 int dst_discard(struct sk_buff *skb)
 157 {
 158         kfree_skb(skb);
 159         return 0;
 160 }
 161 EXPORT_SYMBOL(dst_discard);
 162
 163 void * dst_alloc(struct dst_ops * ops)
 164 {
 165         struct dst_entry * dst;
 166
 167         if (ops->gc && atomic_read(&ops->entries) > ops->gc_thresh) {
 168                 if (ops->gc(ops))
 169                         return NULL;
 170         }
 171         dst = kmem_cache_zalloc(ops->kmem_cachep, GFP_ATOMIC);
 172         if (!dst)
 173                 return NULL;
 174         atomic_set(&dst->__refcnt, 0);
 175         dst->ops = ops;
 176         dst->lastuse = jiffies;
 177         dst->path = dst;
 178         dst->input = dst->output = dst_discard;
 179 #if RT_CACHE_DEBUG >= 2
 180         atomic_inc(&dst_total);
 181 #endif
 182         atomic_inc(&ops->entries);
 183         return dst;
 184 }
 185
 186 static void ___dst_free(struct dst_entry * dst)
 187 {
 188         /* The first case (dev==NULL) is required, when
 189            protocol module is unloaded.
 190          */
 191         if (dst->dev == NULL || !(dst->dev->flags&IFF_UP)) {
 192                 dst->input = dst->output = dst_discard;
 193         }
 194         dst->obsolete = 2;
 195 }
 196
 197 void __dst_free(struct dst_entry * dst)
 198 {
 199         spin_lock_bh(&dst_garbage.lock);
 200         ___dst_free(dst);
 201         dst->next = dst_garbage.list;
 202         dst_garbage.list = dst;
 203         if (dst_garbage.timer_inc > DST_GC_INC) {
 204                 dst_garbage.timer_inc = DST_GC_INC;
 205                 dst_garbage.timer_expires = DST_GC_MIN;
 206                 cancel_delayed_work(&dst_gc_work);
 207                 schedule_delayed_work(&dst_gc_work, dst_garbage.timer_expires);
 208         }
 209         spin_unlock_bh(&dst_garbage.lock);
 210 }
 211
 212 struct dst_entry *dst_destroy(struct dst_entry * dst)
 213 {
 214         struct dst_entry *child;
 215         struct neighbour *neigh;
 216         struct hh_cache *hh;
 217
 218         smp_rmb();
 219
 220 again:
 221         neigh = dst->neighbour;
 222         hh = dst->hh;
 223         child = dst->child;
 224
 225         dst->hh = NULL;
 226         if (hh && atomic_dec_and_test(&hh->hh_refcnt))
 227                 kfree(hh);
 228
 229         if (neigh) {
 230                 dst->neighbour = NULL;
 231                 neigh_release(neigh);
 232         }
 233
 234         atomic_dec(&dst->ops->entries);
 235
 236         if (dst->ops->destroy)
 237                 dst->ops->destroy(dst);
 238         if (dst->dev)
 239                 dev_put(dst->dev);
 240 #if RT_CACHE_DEBUG >= 2
 241         atomic_dec(&dst_total);
 242 #endif
 243         kmem_cache_free(dst->ops->kmem_cachep, dst);
 244
 245         dst = child;
 246         if (dst) {
 247                 int nohash = dst->flags & DST_NOHASH;
 248
 249                 if (atomic_dec_and_test(&dst->__refcnt)) {
 250                         /* We were real parent of this dst, so kill child. */
 251                         if (nohash)
 252                                 goto again;
 253                 } else {
 254                         /* Child is still referenced, return it for freeing. */
 255                         if (nohash)
 256                                 return dst;
 257                         /* Child is still in his hash table */
 258                 }
 259         }
 260         return NULL;
 261 }
 262
 263 void dst_release(struct dst_entry *dst)
 264 {
 265         if (dst) {
 266                int newrefcnt;
 267
 268                 smp_mb__before_atomic_dec();
 269                newrefcnt = atomic_dec_return(&dst->__refcnt);
 270                WARN_ON(newrefcnt < 0);
 271         }
 272 }
 273 EXPORT_SYMBOL(dst_release);
 274
 275 /* Dirty hack. We did it in 2.2 (in __dst_free),
 276  * we have _very_ good reasons not to repeat
 277  * this mistake in 2.3, but we have no choice
 278  * now. _It_ _is_ _explicit_ _deliberate_
 279  * _race_ _condition_.
 280  *
 281  * Commented and originally written by Alexey.
 282  */
 283 static inline void dst_ifdown(struct dst_entry *dst, struct net_device *dev,
 284                               int unregister)
 285 {
 286         if (dst->ops->ifdown)
 287                 dst->ops->ifdown(dst, dev, unregister);
 288
 289         if (dev != dst->dev)
 290                 return;
 291
 292         if (!unregister) {
 293                 dst->input = dst->output = dst_discard;
 294         } else {
 295                 dst->dev = dev_net(dst->dev)->loopback_dev;
 296                 dev_hold(dst->dev);
 297                 dev_put(dev);
 298                 if (dst->neighbour && dst->neighbour->dev == dev) {
 299                         dst->neighbour->dev = dst->dev;
 300                         dev_hold(dst->dev);
 301                         dev_put(dev);
 302                 }
 303         }
 304 }
 305
 306 static int dst_dev_event(struct notifier_block *this, unsigned long event, void *ptr)
 307 {
 308         struct net_device *dev = ptr;
 309         struct dst_entry *dst, *last = NULL;
 310
 311         switch (event) {
 312         case NETDEV_UNREGISTER:
 313         case NETDEV_DOWN:
 314                 mutex_lock(&dst_gc_mutex);
 315                 for (dst = dst_busy_list; dst; dst = dst->next) {
 316                         last = dst;
 317                         dst_ifdown(dst, dev, event != NETDEV_DOWN);
 318                 }
 319
 320                 spin_lock_bh(&dst_garbage.lock);
 321                 dst = dst_garbage.list;
 322                 dst_garbage.list = NULL;
 323                 spin_unlock_bh(&dst_garbage.lock);
 324
 325                 if (last)
 326                         last->next = dst;
 327                 else
 328                         dst_busy_list = dst;
 329                 for (; dst; dst = dst->next) {
 330                         dst_ifdown(dst, dev, event != NETDEV_DOWN);
 331                 }
 332                 mutex_unlock(&dst_gc_mutex);
 333                 break;
 334         }
 335         return NOTIFY_DONE;
 336 }
 337
 338 static struct notifier_block dst_dev_notifier = {
 339         .notifier_call  = dst_dev_event,
 340 };
 341
 342 void __init dst_init(void)
 343 {
 344         register_netdevice_notifier(&dst_dev_notifier);
 345 }
 346
 347 EXPORT_SYMBOL(__dst_free);
 348 EXPORT_SYMBOL(dst_alloc);
 349 EXPORT_SYMBOL(dst_destroy);