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 static int dst_discard(struct sk_buff *skb)
 157 {
 158         kfree_skb(skb);
 159         return 0;
 160 }
 161
 162 void * dst_alloc(struct dst_ops * ops)
 163 {
 164         struct dst_entry * dst;
 165
 166         if (ops->gc && atomic_read(&ops->entries) > ops->gc_thresh) {
 167                 if (ops->gc())
 168                         return NULL;
 169         }
 170         dst = kmem_cache_zalloc(ops->kmem_cachep, GFP_ATOMIC);
 171         if (!dst)
 172                 return NULL;
 173         atomic_set(&dst->__refcnt, 0);
 174         dst->ops = ops;
 175         dst->lastuse = jiffies;
 176         dst->path = dst;
 177         dst->input = dst->output = dst_discard;
 178 #if RT_CACHE_DEBUG >= 2
 179         atomic_inc(&dst_total);
 180 #endif
 181         atomic_inc(&ops->entries);
 182         return dst;
 183 }
 184
 185 static void ___dst_free(struct dst_entry * dst)
 186 {
 187         /* The first case (dev==NULL) is required, when
 188            protocol module is unloaded.
 189          */
 190         if (dst->dev == NULL || !(dst->dev->flags&IFF_UP)) {
 191                 dst->input = dst->output = dst_discard;
 192         }
 193         dst->obsolete = 2;
 194 }
 195
 196 void __dst_free(struct dst_entry * dst)
 197 {
 198         spin_lock_bh(&dst_garbage.lock);
 199         ___dst_free(dst);
 200         dst->next = dst_garbage.list;
 201         dst_garbage.list = dst;
 202         if (dst_garbage.timer_inc > DST_GC_INC) {
 203                 dst_garbage.timer_inc = DST_GC_INC;
 204                 dst_garbage.timer_expires = DST_GC_MIN;
 205                 schedule_delayed_work(&dst_gc_work, dst_garbage.timer_expires);
 206         }
 207         spin_unlock_bh(&dst_garbage.lock);
 208 }
 209
 210 struct dst_entry *dst_destroy(struct dst_entry * dst)
 211 {
 212         struct dst_entry *child;
 213         struct neighbour *neigh;
 214         struct hh_cache *hh;
 215
 216         smp_rmb();
 217
 218 again:
 219         neigh = dst->neighbour;
 220         hh = dst->hh;
 221         child = dst->child;
 222
 223         dst->hh = NULL;
 224         if (hh && atomic_dec_and_test(&hh->hh_refcnt))
 225                 kfree(hh);
 226
 227         if (neigh) {
 228                 dst->neighbour = NULL;
 229                 neigh_release(neigh);
 230         }
 231
 232         atomic_dec(&dst->ops->entries);
 233
 234         if (dst->ops->destroy)
 235                 dst->ops->destroy(dst);
 236         if (dst->dev)
 237                 dev_put(dst->dev);
 238 #if RT_CACHE_DEBUG >= 2
 239         atomic_dec(&dst_total);
 240 #endif
 241         kmem_cache_free(dst->ops->kmem_cachep, dst);
 242
 243         dst = child;
 244         if (dst) {
 245                 int nohash = dst->flags & DST_NOHASH;
 246
 247                 if (atomic_dec_and_test(&dst->__refcnt)) {
 248                         /* We were real parent of this dst, so kill child. */
 249                         if (nohash)
 250                                 goto again;
 251                 } else {
 252                         /* Child is still referenced, return it for freeing. */
 253                         if (nohash)
 254                                 return dst;
 255                         /* Child is still in his hash table */
 256                 }
 257         }
 258         return NULL;
 259 }
 260
 261 /* Dirty hack. We did it in 2.2 (in __dst_free),
 262  * we have _very_ good reasons not to repeat
 263  * this mistake in 2.3, but we have no choice
 264  * now. _It_ _is_ _explicit_ _deliberate_
 265  * _race_ _condition_.
 266  *
 267  * Commented and originally written by Alexey.
 268  */
 269 static inline void dst_ifdown(struct dst_entry *dst, struct net_device *dev,
 270                               int unregister)
 271 {
 272         if (dst->ops->ifdown)
 273                 dst->ops->ifdown(dst, dev, unregister);
 274
 275         if (dev != dst->dev)
 276                 return;
 277
 278         if (!unregister) {
 279                 dst->input = dst->output = dst_discard;
 280         } else {
 281                 dst->dev = &loopback_dev;
 282                 dev_hold(&loopback_dev);
 283                 dev_put(dev);
 284                 if (dst->neighbour && dst->neighbour->dev == dev) {
 285                         dst->neighbour->dev = &loopback_dev;
 286                         dev_put(dev);
 287                         dev_hold(&loopback_dev);
 288                 }
 289         }
 290 }
 291
 292 static int dst_dev_event(struct notifier_block *this, unsigned long event, void *ptr)
 293 {
 294         struct net_device *dev = ptr;
 295         struct dst_entry *dst, *last = NULL;
 296
 297         if (dev->nd_net != &init_net)
 298                 return NOTIFY_DONE;
 299
 300         switch (event) {
 301         case NETDEV_UNREGISTER:
 302         case NETDEV_DOWN:
 303                 mutex_lock(&dst_gc_mutex);
 304                 for (dst = dst_busy_list; dst; dst = dst->next) {
 305                         last = dst;
 306                         dst_ifdown(dst, dev, event != NETDEV_DOWN);
 307                 }
 308
 309                 spin_lock_bh(&dst_garbage.lock);
 310                 dst = dst_garbage.list;
 311                 dst_garbage.list = NULL;
 312                 spin_unlock_bh(&dst_garbage.lock);
 313
 314                 if (last)
 315                         last->next = dst;
 316                 else
 317                         dst_busy_list = dst;
 318                 for (; dst; dst = dst->next) {
 319                         dst_ifdown(dst, dev, event != NETDEV_DOWN);
 320                 }
 321                 mutex_unlock(&dst_gc_mutex);
 322                 break;
 323         }
 324         return NOTIFY_DONE;
 325 }
 326
 327 static struct notifier_block dst_dev_notifier = {
 328         .notifier_call  = dst_dev_event,
 329 };
 330
 331 void __init dst_init(void)
 332 {
 333         register_netdevice_notifier(&dst_dev_notifier);
 334 }
 335
 336 EXPORT_SYMBOL(__dst_free);
 337 EXPORT_SYMBOL(dst_alloc);
 338 EXPORT_SYMBOL(dst_destroy);