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