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 #include <linux/sched.h>
  21
  22 #include <net/dst.h>
  23
  24 /*
  25  * Theory of operations:
  26  * 1) We use a list, protected by a spinlock, to add
  27  *    new entries from both BH and non-BH context.
  28  * 2) In order to keep spinlock held for a small delay,
  29  *    we use a second list where are stored long lived
  30  *    entries, that are handled by the garbage collect thread
  31  *    fired by a workqueue.
  32  * 3) This list is guarded by a mutex,
  33  *    so that the gc_task and dst_dev_event() can be synchronized.
  34  */
  35 #if RT_CACHE_DEBUG >= 2
  36 static atomic_t                  dst_total = ATOMIC_INIT(0);
  37 #endif
  38
  39 /*
  40  * We want to keep lock & list close together
  41  * to dirty as few cache lines as possible in __dst_free().
  42  * As this is not a very strong hint, we dont force an alignment on SMP.
  43  */
  44 static struct {
  45         spinlock_t              lock;
  46         struct dst_entry        *list;
  47         unsigned long           timer_inc;
  48         unsigned long           timer_expires;
  49 } dst_garbage = {
  50         .lock = __SPIN_LOCK_UNLOCKED(dst_garbage.lock),
  51         .timer_inc = DST_GC_MAX,
  52 };
  53 static void dst_gc_task(struct work_struct *work);
  54 static void ___dst_free(struct dst_entry * dst);
  55
  56 static DECLARE_DELAYED_WORK(dst_gc_work, dst_gc_task);
  57
  58 static DEFINE_MUTEX(dst_gc_mutex);
  59 /*
  60  * long lived entries are maintained in this list, guarded by dst_gc_mutex
  61  */
  62 static struct dst_entry         *dst_busy_list;
  63
  64 static void dst_gc_task(struct work_struct *work)
  65 {
  66         int    delayed = 0;
  67         int    work_performed = 0;
  68         unsigned long expires = ~0L;
  69         struct dst_entry *dst, *next, head;
  70         struct dst_entry *last = &head;
  71 #if RT_CACHE_DEBUG >= 2
  72         ktime_t time_start = ktime_get();
  73         struct timespec elapsed;
  74 #endif
  75
  76         mutex_lock(&dst_gc_mutex);
  77         next = dst_busy_list;
  78
  79 loop:
  80         while ((dst = next) != NULL) {
  81                 next = dst->next;
  82                 prefetch(&next->next);
  83                 cond_resched();
  84                 if (likely(atomic_read(&dst->__refcnt))) {
  85                         last->next = dst;
  86                         last = dst;
  87                         delayed++;
  88                         continue;
  89                 }
  90                 work_performed++;
  91
  92                 dst = dst_destroy(dst);
  93                 if (dst) {
  94                         /* NOHASH and still referenced. Unless it is already
  95                          * on gc list, invalidate it and add to gc list.
  96                          *
  97                          * Note: this is temporary. Actually, NOHASH dst's
  98                          * must be obsoleted when parent is obsoleted.
  99                          * But we do not have state "obsoleted, but
 100                          * referenced by parent", so it is right.
 101                          */
 102                         if (dst->obsolete > 1)
 103                                 continue;
 104
 105                         ___dst_free(dst);
 106                         dst->next = next;
 107                         next = dst;
 108                 }
 109         }
 110
 111         spin_lock_bh(&dst_garbage.lock);
 112         next = dst_garbage.list;
 113         if (next) {
 114                 dst_garbage.list = NULL;
 115                 spin_unlock_bh(&dst_garbage.lock);
 116                 goto loop;
 117         }
 118         last->next = NULL;
 119         dst_busy_list = head.next;
 120         if (!dst_busy_list)
 121                 dst_garbage.timer_inc = DST_GC_MAX;
 122         else {
 123                 /*
 124                  * if we freed less than 1/10 of delayed entries,
 125                  * we can sleep longer.
 126                  */
 127                 if (work_performed <= delayed/10) {
 128                         dst_garbage.timer_expires += dst_garbage.timer_inc;
 129                         if (dst_garbage.timer_expires > DST_GC_MAX)
 130                                 dst_garbage.timer_expires = DST_GC_MAX;
 131                         dst_garbage.timer_inc += DST_GC_INC;
 132                 } else {
 133                         dst_garbage.timer_inc = DST_GC_INC;
 134                         dst_garbage.timer_expires = DST_GC_MIN;
 135                 }
 136                 expires = dst_garbage.timer_expires;
 137                 /*
 138                  * if the next desired timer is more than 4 seconds in the future
 139                  * then round the timer to whole seconds
 140                  */
 141                 if (expires > 4*HZ)
 142                         expires = round_jiffies_relative(expires);
 143                 schedule_delayed_work(&dst_gc_work, expires);
 144         }
 145
 146         spin_unlock_bh(&dst_garbage.lock);
 147         mutex_unlock(&dst_gc_mutex);
 148 #if RT_CACHE_DEBUG >= 2
 149         elapsed = ktime_to_timespec(ktime_sub(ktime_get(), time_start));
 150         printk(KERN_DEBUG "dst_total: %d delayed: %d work_perf: %d"
 151                 " expires: %lu elapsed: %lu us\n",
 152                 atomic_read(&dst_total), delayed, work_performed,
 153                 expires,
 154                 elapsed.tv_sec * USEC_PER_SEC + elapsed.tv_nsec / NSEC_PER_USEC);
 155 #endif
 156 }
 157
 158 int dst_discard(struct sk_buff *skb)
 159 {
 160         kfree_skb(skb);
 161         return 0;
 162 }
 163 EXPORT_SYMBOL(dst_discard);
 164
 165 void * dst_alloc(struct dst_ops * ops)
 166 {
 167         struct dst_entry * dst;
 168
 169         if (ops->gc && atomic_read(&ops->entries) > ops->gc_thresh) {
 170                 if (ops->gc(ops))
 171                         return NULL;
 172         }
 173         dst = kmem_cache_zalloc(ops->kmem_cachep, GFP_ATOMIC);
 174         if (!dst)
 175                 return NULL;
 176         atomic_set(&dst->__refcnt, 0);
 177         dst->ops = ops;
 178         dst->lastuse = jiffies;
 179         dst->path = dst;
 180         dst->input = dst->output = dst_discard;
 181 #if RT_CACHE_DEBUG >= 2
 182         atomic_inc(&dst_total);
 183 #endif
 184         atomic_inc(&ops->entries);
 185         return dst;
 186 }
 187
 188 static void ___dst_free(struct dst_entry * dst)
 189 {
 190         /* The first case (dev==NULL) is required, when
 191            protocol module is unloaded.
 192          */
 193         if (dst->dev == NULL || !(dst->dev->flags&IFF_UP)) {
 194                 dst->input = dst->output = dst_discard;
 195         }
 196         dst->obsolete = 2;
 197 }
 198
 199 void __dst_free(struct dst_entry * dst)
 200 {
 201         spin_lock_bh(&dst_garbage.lock);
 202         ___dst_free(dst);
 203         dst->next = dst_garbage.list;
 204         dst_garbage.list = dst;
 205         if (dst_garbage.timer_inc > DST_GC_INC) {
 206                 dst_garbage.timer_inc = DST_GC_INC;
 207                 dst_garbage.timer_expires = DST_GC_MIN;
 208                 cancel_delayed_work(&dst_gc_work);
 209                 schedule_delayed_work(&dst_gc_work, dst_garbage.timer_expires);
 210         }
 211         spin_unlock_bh(&dst_garbage.lock);
 212 }
 213
 214 struct dst_entry *dst_destroy(struct dst_entry * dst)
 215 {
 216         struct dst_entry *child;
 217         struct neighbour *neigh;
 218         struct hh_cache *hh;
 219
 220         smp_rmb();
 221
 222 again:
 223         neigh = dst->neighbour;
 224         hh = dst->hh;
 225         child = dst->child;
 226
 227         dst->hh = NULL;
 228         if (hh && atomic_dec_and_test(&hh->hh_refcnt))
 229                 kfree(hh);
 230
 231         if (neigh) {
 232                 dst->neighbour = NULL;
 233                 neigh_release(neigh);
 234         }
 235
 236         atomic_dec(&dst->ops->entries);
 237
 238         if (dst->ops->destroy)
 239                 dst->ops->destroy(dst);
 240         if (dst->dev)
 241                 dev_put(dst->dev);
 242 #if RT_CACHE_DEBUG >= 2
 243         atomic_dec(&dst_total);
 244 #endif
 245         kmem_cache_free(dst->ops->kmem_cachep, dst);
 246
 247         dst = child;
 248         if (dst) {
 249                 int nohash = dst->flags & DST_NOHASH;
 250
 251                 if (atomic_dec_and_test(&dst->__refcnt)) {
 252                         /* We were real parent of this dst, so kill child. */
 253                         if (nohash)
 254                                 goto again;
 255                 } else {
 256                         /* Child is still referenced, return it for freeing. */
 257                         if (nohash)
 258                                 return dst;
 259                         /* Child is still in his hash table */
 260                 }
 261         }
 262         return NULL;
 263 }
 264
 265 void dst_release(struct dst_entry *dst)
 266 {
 267         if (dst) {
 268                int newrefcnt;
 269
 270                 smp_mb__before_atomic_dec();
 271                newrefcnt = atomic_dec_return(&dst->__refcnt);
 272                WARN_ON(newrefcnt < 0);
 273         }
 274 }
 275 EXPORT_SYMBOL(dst_release);
 276
 277 /* Dirty hack. We did it in 2.2 (in __dst_free),
 278  * we have _very_ good reasons not to repeat
 279  * this mistake in 2.3, but we have no choice
 280  * now. _It_ _is_ _explicit_ _deliberate_
 281  * _race_ _condition_.
 282  *
 283  * Commented and originally written by Alexey.
 284  */
 285 static inline void dst_ifdown(struct dst_entry *dst, struct net_device *dev,
 286                               int unregister)
 287 {
 288         if (dst->ops->ifdown)
 289                 dst->ops->ifdown(dst, dev, unregister);
 290
 291         if (dev != dst->dev)
 292                 return;
 293
 294         if (!unregister) {
 295                 dst->input = dst->output = dst_discard;
 296         } else {
 297                 dst->dev = dev_net(dst->dev)->loopback_dev;
 298                 dev_hold(dst->dev);
 299                 dev_put(dev);
 300                 if (dst->neighbour && dst->neighbour->dev == dev) {
 301                         dst->neighbour->dev = dst->dev;
 302                         dev_hold(dst->dev);
 303                         dev_put(dev);
 304                 }
 305         }
 306 }
 307
 308 static int dst_dev_event(struct notifier_block *this, unsigned long event, void *ptr)
 309 {
 310         struct net_device *dev = ptr;
 311         struct dst_entry *dst, *last = NULL;
 312
 313         switch (event) {
 314         case NETDEV_UNREGISTER:
 315         case NETDEV_DOWN:
 316                 mutex_lock(&dst_gc_mutex);
 317                 for (dst = dst_busy_list; dst; dst = dst->next) {
 318                         last = dst;
 319                         dst_ifdown(dst, dev, event != NETDEV_DOWN);
 320                 }
 321
 322                 spin_lock_bh(&dst_garbage.lock);
 323                 dst = dst_garbage.list;
 324                 dst_garbage.list = NULL;
 325                 spin_unlock_bh(&dst_garbage.lock);
 326
 327                 if (last)
 328                         last->next = dst;
 329                 else
 330                         dst_busy_list = dst;
 331                 for (; dst; dst = dst->next) {
 332                         dst_ifdown(dst, dev, event != NETDEV_DOWN);
 333                 }
 334                 mutex_unlock(&dst_gc_mutex);
 335                 break;
 336         }
 337         return NOTIFY_DONE;
 338 }
 339
 340 static struct notifier_block dst_dev_notifier = {
 341         .notifier_call  = dst_dev_event,
 342 };
 343
 344 void __init dst_init(void)
 345 {
 346         register_netdevice_notifier(&dst_dev_notifier);
 347 }
 348
 349 EXPORT_SYMBOL(__dst_free);
 350 EXPORT_SYMBOL(dst_alloc);
 351 EXPORT_SYMBOL(dst_destroy);