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/mm.h>
  13 #include <linux/module.h>
  14 #include <linux/netdevice.h>
  15 #include <linux/sched.h>
  16 #include <linux/skbuff.h>
  17 #include <linux/string.h>
  18 #include <linux/types.h>
  19
  20 #include <net/dst.h>
  21
  22 /* Locking strategy:
  23  * 1) Garbage collection state of dead destination cache
  24  *    entries is protected by dst_lock.
  25  * 2) GC is run only from BH context, and is the only remover
  26  *    of entries.
  27  * 3) Entries are added to the garbage list from both BH
  28  *    and non-BH context, so local BH disabling is needed.
  29  * 4) All operations modify state, so a spinlock is used.
  30  */
  31 static struct dst_entry         *dst_garbage_list;
  32 #if RT_CACHE_DEBUG >= 2
  33 static atomic_t                  dst_total = ATOMIC_INIT(0);
  34 #endif
  35 static DEFINE_SPINLOCK(dst_lock);
  36
  37 static unsigned long dst_gc_timer_expires;
  38 static unsigned long dst_gc_timer_inc = DST_GC_MAX;
  39 static void dst_run_gc(unsigned long);
  40 static void ___dst_free(struct dst_entry * dst);
  41
  42 static DEFINE_TIMER(dst_gc_timer, dst_run_gc, DST_GC_MIN, 0);
  43
  44 static void dst_run_gc(unsigned long dummy)
  45 {
  46         int    delayed = 0;
  47         int    work_performed;
  48         struct dst_entry * dst, **dstp;
  49
  50         if (!spin_trylock(&dst_lock)) {
  51                 mod_timer(&dst_gc_timer, jiffies + HZ/10);
  52                 return;
  53         }
  54
  55         del_timer(&dst_gc_timer);
  56         dstp = &dst_garbage_list;
  57         work_performed = 0;
  58         while ((dst = *dstp) != NULL) {
  59                 if (atomic_read(&dst->__refcnt)) {
  60                         dstp = &dst->next;
  61                         delayed++;
  62                         continue;
  63                 }
  64                 *dstp = dst->next;
  65                 work_performed = 1;
  66
  67                 dst = dst_destroy(dst);
  68                 if (dst) {
  69                         /* NOHASH and still referenced. Unless it is already
  70                          * on gc list, invalidate it and add to gc list.
  71                          *
  72                          * Note: this is temporary. Actually, NOHASH dst's
  73                          * must be obsoleted when parent is obsoleted.
  74                          * But we do not have state "obsoleted, but
  75                          * referenced by parent", so it is right.
  76                          */
  77                         if (dst->obsolete > 1)
  78                                 continue;
  79
  80                         ___dst_free(dst);
  81                         dst->next = *dstp;
  82                         *dstp = dst;
  83                         dstp = &dst->next;
  84                 }
  85         }
  86         if (!dst_garbage_list) {
  87                 dst_gc_timer_inc = DST_GC_MAX;
  88                 goto out;
  89         }
  90         if (!work_performed) {
  91                 if ((dst_gc_timer_expires += dst_gc_timer_inc) > DST_GC_MAX)
  92                         dst_gc_timer_expires = DST_GC_MAX;
  93                 dst_gc_timer_inc += DST_GC_INC;
  94         } else {
  95                 dst_gc_timer_inc = DST_GC_INC;
  96                 dst_gc_timer_expires = DST_GC_MIN;
  97         }
  98 #if RT_CACHE_DEBUG >= 2
  99         printk("dst_total: %d/%d %ld\n",
 100                atomic_read(&dst_total), delayed,  dst_gc_timer_expires);
 101 #endif
 102         /* if the next desired timer is more than 4 seconds in the future
 103          * then round the timer to whole seconds
 104          */
 105         if (dst_gc_timer_expires > 4*HZ)
 106                 mod_timer(&dst_gc_timer,
 107                         round_jiffies(jiffies + dst_gc_timer_expires));
 108         else
 109                 mod_timer(&dst_gc_timer, jiffies + dst_gc_timer_expires);
 110
 111 out:
 112         spin_unlock(&dst_lock);
 113 }
 114
 115 static int dst_discard_in(struct sk_buff *skb)
 116 {
 117         kfree_skb(skb);
 118         return 0;
 119 }
 120
 121 static int dst_discard_out(struct sk_buff *skb)
 122 {
 123         kfree_skb(skb);
 124         return 0;
 125 }
 126
 127 void * dst_alloc(struct dst_ops * ops)
 128 {
 129         struct dst_entry * dst;
 130
 131         if (ops->gc && atomic_read(&ops->entries) > ops->gc_thresh) {
 132                 if (ops->gc())
 133                         return NULL;
 134         }
 135         dst = kmem_cache_alloc(ops->kmem_cachep, GFP_ATOMIC);
 136         if (!dst)
 137                 return NULL;
 138         memset(dst, 0, ops->entry_size);
 139         atomic_set(&dst->__refcnt, 0);
 140         dst->ops = ops;
 141         dst->lastuse = jiffies;
 142         dst->path = dst;
 143         dst->input = dst_discard_in;
 144         dst->output = dst_discard_out;
 145 #if RT_CACHE_DEBUG >= 2
 146         atomic_inc(&dst_total);
 147 #endif
 148         atomic_inc(&ops->entries);
 149         return dst;
 150 }
 151
 152 static void ___dst_free(struct dst_entry * dst)
 153 {
 154         /* The first case (dev==NULL) is required, when
 155            protocol module is unloaded.
 156          */
 157         if (dst->dev == NULL || !(dst->dev->flags&IFF_UP)) {
 158                 dst->input = dst_discard_in;
 159                 dst->output = dst_discard_out;
 160         }
 161         dst->obsolete = 2;
 162 }
 163
 164 void __dst_free(struct dst_entry * dst)
 165 {
 166         spin_lock_bh(&dst_lock);
 167         ___dst_free(dst);
 168         dst->next = dst_garbage_list;
 169         dst_garbage_list = dst;
 170         if (dst_gc_timer_inc > DST_GC_INC) {
 171                 dst_gc_timer_inc = DST_GC_INC;
 172                 dst_gc_timer_expires = DST_GC_MIN;
 173                 mod_timer(&dst_gc_timer, jiffies + dst_gc_timer_expires);
 174         }
 175         spin_unlock_bh(&dst_lock);
 176 }
 177
 178 struct dst_entry *dst_destroy(struct dst_entry * dst)
 179 {
 180         struct dst_entry *child;
 181         struct neighbour *neigh;
 182         struct hh_cache *hh;
 183
 184         smp_rmb();
 185
 186 again:
 187         neigh = dst->neighbour;
 188         hh = dst->hh;
 189         child = dst->child;
 190
 191         dst->hh = NULL;
 192         if (hh && atomic_dec_and_test(&hh->hh_refcnt))
 193                 kfree(hh);
 194
 195         if (neigh) {
 196                 dst->neighbour = NULL;
 197                 neigh_release(neigh);
 198         }
 199
 200         atomic_dec(&dst->ops->entries);
 201
 202         if (dst->ops->destroy)
 203                 dst->ops->destroy(dst);
 204         if (dst->dev)
 205                 dev_put(dst->dev);
 206 #if RT_CACHE_DEBUG >= 2
 207         atomic_dec(&dst_total);
 208 #endif
 209         kmem_cache_free(dst->ops->kmem_cachep, dst);
 210
 211         dst = child;
 212         if (dst) {
 213                 int nohash = dst->flags & DST_NOHASH;
 214
 215                 if (atomic_dec_and_test(&dst->__refcnt)) {
 216                         /* We were real parent of this dst, so kill child. */
 217                         if (nohash)
 218                                 goto again;
 219                 } else {
 220                         /* Child is still referenced, return it for freeing. */
 221                         if (nohash)
 222                                 return dst;
 223                         /* Child is still in his hash table */
 224                 }
 225         }
 226         return NULL;
 227 }
 228
 229 /* Dirty hack. We did it in 2.2 (in __dst_free),
 230  * we have _very_ good reasons not to repeat
 231  * this mistake in 2.3, but we have no choice
 232  * now. _It_ _is_ _explicit_ _deliberate_
 233  * _race_ _condition_.
 234  *
 235  * Commented and originally written by Alexey.
 236  */
 237 static inline void dst_ifdown(struct dst_entry *dst, struct net_device *dev,
 238                               int unregister)
 239 {
 240         if (dst->ops->ifdown)
 241                 dst->ops->ifdown(dst, dev, unregister);
 242
 243         if (dev != dst->dev)
 244                 return;
 245
 246         if (!unregister) {
 247                 dst->input = dst_discard_in;
 248                 dst->output = dst_discard_out;
 249         } else {
 250                 dst->dev = &loopback_dev;
 251                 dev_hold(&loopback_dev);
 252                 dev_put(dev);
 253                 if (dst->neighbour && dst->neighbour->dev == dev) {
 254                         dst->neighbour->dev = &loopback_dev;
 255                         dev_put(dev);
 256                         dev_hold(&loopback_dev);
 257                 }
 258         }
 259 }
 260
 261 static int dst_dev_event(struct notifier_block *this, unsigned long event, void *ptr)
 262 {
 263         struct net_device *dev = ptr;
 264         struct dst_entry *dst;
 265
 266         switch (event) {
 267         case NETDEV_UNREGISTER:
 268         case NETDEV_DOWN:
 269                 spin_lock_bh(&dst_lock);
 270                 for (dst = dst_garbage_list; dst; dst = dst->next) {
 271                         dst_ifdown(dst, dev, event != NETDEV_DOWN);
 272                 }
 273                 spin_unlock_bh(&dst_lock);
 274                 break;
 275         }
 276         return NOTIFY_DONE;
 277 }
 278
 279 static struct notifier_block dst_dev_notifier = {
 280         .notifier_call  = dst_dev_event,
 281 };
 282
 283 void __init dst_init(void)
 284 {
 285         register_netdevice_notifier(&dst_dev_notifier);
 286 }
 287
 288 EXPORT_SYMBOL(__dst_free);
 289 EXPORT_SYMBOL(dst_alloc);
 290 EXPORT_SYMBOL(dst_destroy);