net/ipv4/inetpeer.c

   1 /*
   2  *              INETPEER - A storage for permanent information about peers
   3  *
   4  *  This source is covered by the GNU GPL, the same as all kernel sources.
   5  *
   6  *  Authors:    Andrey V. Savochkin <saw@msu.ru>
   7  */
   8
   9 #include <linux/module.h>
  10 #include <linux/types.h>
  11 #include <linux/slab.h>
  12 #include <linux/interrupt.h>
  13 #include <linux/spinlock.h>
  14 #include <linux/random.h>
  15 #include <linux/timer.h>
  16 #include <linux/time.h>
  17 #include <linux/kernel.h>
  18 #include <linux/mm.h>
  19 #include <linux/net.h>
  20 #include <net/ip.h>
  21 #include <net/inetpeer.h>
  22 #include <net/secure_seq.h>
  23
  24 /*
  25  *  Theory of operations.
  26  *  We keep one entry for each peer IP address.  The nodes contains long-living
  27  *  information about the peer which doesn't depend on routes.
  28  *  At this moment this information consists only of ID field for the next
  29  *  outgoing IP packet.  This field is incremented with each packet as encoded
  30  *  in inet_getid() function (include/net/inetpeer.h).
  31  *  At the moment of writing this notes identifier of IP packets is generated
  32  *  to be unpredictable using this code only for packets subjected
  33  *  (actually or potentially) to defragmentation.  I.e. DF packets less than
  34  *  PMTU in size uses a constant ID and do not use this code (see
  35  *  ip_select_ident() in include/net/ip.h).
  36  *
  37  *  Route cache entries hold references to our nodes.
  38  *  New cache entries get references via lookup by destination IP address in
  39  *  the avl tree.  The reference is grabbed only when it's needed i.e. only
  40  *  when we try to output IP packet which needs an unpredictable ID (see
  41  *  __ip_select_ident() in net/ipv4/route.c).
  42  *  Nodes are removed only when reference counter goes to 0.
  43  *  When it's happened the node may be removed when a sufficient amount of
  44  *  time has been passed since its last use.  The less-recently-used entry can
  45  *  also be removed if the pool is overloaded i.e. if the total amount of
  46  *  entries is greater-or-equal than the threshold.
  47  *
  48  *  Node pool is organised as an AVL tree.
  49  *  Such an implementation has been chosen not just for fun.  It's a way to
  50  *  prevent easy and efficient DoS attacks by creating hash collisions.  A huge
  51  *  amount of long living nodes in a single hash slot would significantly delay
  52  *  lookups performed with disabled BHs.
  53  *
  54  *  Serialisation issues.
  55  *  1.  Nodes may appear in the tree only with the pool lock held.
  56  *  2.  Nodes may disappear from the tree only with the pool lock held
  57  *      AND reference count being 0.
  58  *  3.  Nodes appears and disappears from unused node list only under
  59  *      "inet_peer_unused_lock".
  60  *  4.  Global variable peer_total is modified under the pool lock.
  61  *  5.  struct inet_peer fields modification:
  62  *              avl_left, avl_right, avl_parent, avl_height: pool lock
  63  *              unused: unused node list lock
  64  *              refcnt: atomically against modifications on other CPU;
  65  *                 usually under some other lock to prevent node disappearing
  66  *              dtime: unused node list lock
  67  *              daddr: unchangeable
  68  *              ip_id_count: atomic value (no lock needed)
  69  */
  70
  71 static struct kmem_cache *peer_cachep __read_mostly;
  72
  73 #define node_height(x) x->avl_height
  74
  75 #define peer_avl_empty ((struct inet_peer *)&peer_fake_node)
  76 #define peer_avl_empty_rcu ((struct inet_peer __rcu __force *)&peer_fake_node)
  77 static const struct inet_peer peer_fake_node = {
  78         .avl_left       = peer_avl_empty_rcu,
  79         .avl_right      = peer_avl_empty_rcu,
  80         .avl_height     = 0
  81 };
  82
  83 struct inet_peer_base {
  84         struct inet_peer __rcu *root;
  85         spinlock_t      lock;
  86         int             total;
  87 };
  88
  89 static struct inet_peer_base v4_peers = {
  90         .root           = peer_avl_empty_rcu,
  91         .lock           = __SPIN_LOCK_UNLOCKED(v4_peers.lock),
  92         .total          = 0,
  93 };
  94
  95 static struct inet_peer_base v6_peers = {
  96         .root           = peer_avl_empty_rcu,
  97         .lock           = __SPIN_LOCK_UNLOCKED(v6_peers.lock),
  98         .total          = 0,
  99 };
 100
 101 #define PEER_MAXDEPTH 40 /* sufficient for about 2^27 nodes */
 102
 103 /* Exported for sysctl_net_ipv4.  */
 104 int inet_peer_threshold __read_mostly = 65536 + 128;    /* start to throw entries more
 105                                          * aggressively at this stage */
 106 int inet_peer_minttl __read_mostly = 120 * HZ;  /* TTL under high load: 120 sec */
 107 int inet_peer_maxttl __read_mostly = 10 * 60 * HZ;      /* usual time to live: 10 min */
 108 int inet_peer_gc_mintime __read_mostly = 10 * HZ;
 109 int inet_peer_gc_maxtime __read_mostly = 120 * HZ;
 110
 111 static struct {
 112         struct list_head        list;
 113         spinlock_t              lock;
 114 } unused_peers = {
 115         .list                   = LIST_HEAD_INIT(unused_peers.list),
 116         .lock                   = __SPIN_LOCK_UNLOCKED(unused_peers.lock),
 117 };
 118
 119 static void peer_check_expire(unsigned long dummy);
 120 static DEFINE_TIMER(peer_periodic_timer, peer_check_expire, 0, 0);
 121
 122
 123 /* Called from ip_output.c:ip_init  */
 124 void __init inet_initpeers(void)
 125 {
 126         struct sysinfo si;
 127
 128         /* Use the straight interface to information about memory. */
 129         si_meminfo(&si);
 130         /* The values below were suggested by Alexey Kuznetsov
 131          * <kuznet@ms2.inr.ac.ru>.  I don't have any opinion about the values
 132          * myself.  --SAW
 133          */
 134         if (si.totalram <= (32768*1024)/PAGE_SIZE)
 135                 inet_peer_threshold >>= 1; /* max pool size about 1MB on IA32 */
 136         if (si.totalram <= (16384*1024)/PAGE_SIZE)
 137                 inet_peer_threshold >>= 1; /* about 512KB */
 138         if (si.totalram <= (8192*1024)/PAGE_SIZE)
 139                 inet_peer_threshold >>= 2; /* about 128KB */
 140
 141         peer_cachep = kmem_cache_create("inet_peer_cache",
 142                         sizeof(struct inet_peer),
 143                         0, SLAB_HWCACHE_ALIGN | SLAB_PANIC,
 144                         NULL);
 145
 146         /* All the timers, started at system startup tend
 147            to synchronize. Perturb it a bit.
 148          */
 149         peer_periodic_timer.expires = jiffies
 150                 + net_random() % inet_peer_gc_maxtime
 151                 + inet_peer_gc_maxtime;
 152         add_timer(&peer_periodic_timer);
 153 }
 154
 155 /* Called with or without local BH being disabled. */
 156 static void unlink_from_unused(struct inet_peer *p)
 157 {
 158         if (!list_empty(&p->unused)) {
 159                 spin_lock_bh(&unused_peers.lock);
 160                 list_del_init(&p->unused);
 161                 spin_unlock_bh(&unused_peers.lock);
 162         }
 163 }
 164
 165 static int addr_compare(const struct inetpeer_addr *a,
 166                         const struct inetpeer_addr *b)
 167 {
 168         int i, n = (a->family == AF_INET ? 1 : 4);
 169
 170         for (i = 0; i < n; i++) {
 171                 if (a->a6[i] == b->a6[i])
 172                         continue;
 173                 if (a->a6[i] < b->a6[i])
 174                         return -1;
 175                 return 1;
 176         }
 177
 178         return 0;
 179 }
 180
 181 /*
 182  * Called with local BH disabled and the pool lock held.
 183  */
 184 #define lookup(_daddr, _stack, _base)                           \
 185 ({                                                              \
 186         struct inet_peer *u;                                    \
 187         struct inet_peer __rcu **v;                             \
 188                                                                 \
 189         stackptr = _stack;                                      \
 190         *stackptr++ = &_base->root;                             \
 191         for (u = rcu_dereference_protected(_base->root,         \
 192                         lockdep_is_held(&_base->lock));         \
 193              u != peer_avl_empty; ) {                           \
 194                 int cmp = addr_compare(_daddr, &u->daddr);      \
 195                 if (cmp == 0)                                   \
 196                         break;                                  \
 197                 if (cmp == -1)                                  \
 198                         v = &u->avl_left;                       \
 199                 else                                            \
 200                         v = &u->avl_right;                      \
 201                 *stackptr++ = v;                                \
 202                 u = rcu_dereference_protected(*v,               \
 203                         lockdep_is_held(&_base->lock));         \
 204         }                                                       \
 205         u;                                                      \
 206 })
 207
 208 /*
 209  * Called with rcu_read_lock_bh()
 210  * Because we hold no lock against a writer, its quite possible we fall
 211  * in an endless loop.
 212  * But every pointer we follow is guaranteed to be valid thanks to RCU.
 213  * We exit from this function if number of links exceeds PEER_MAXDEPTH
 214  */
 215 static struct inet_peer *lookup_rcu_bh(const struct inetpeer_addr *daddr,
 216                                        struct inet_peer_base *base)
 217 {
 218         struct inet_peer *u = rcu_dereference_bh(base->root);
 219         int count = 0;
 220
 221         while (u != peer_avl_empty) {
 222                 int cmp = addr_compare(daddr, &u->daddr);
 223                 if (cmp == 0) {
 224                         /* Before taking a reference, check if this entry was
 225                          * deleted, unlink_from_pool() sets refcnt=-1 to make
 226                          * distinction between an unused entry (refcnt=0) and
 227                          * a freed one.
 228                          */
 229                         if (unlikely(!atomic_add_unless(&u->refcnt, 1, -1)))
 230                                 u = NULL;
 231                         return u;
 232                 }
 233                 if (cmp == -1)
 234                         u = rcu_dereference_bh(u->avl_left);
 235                 else
 236                         u = rcu_dereference_bh(u->avl_right);
 237                 if (unlikely(++count == PEER_MAXDEPTH))
 238                         break;
 239         }
 240         return NULL;
 241 }
 242
 243 /* Called with local BH disabled and the pool lock held. */
 244 #define lookup_rightempty(start, base)                          \
 245 ({                                                              \
 246         struct inet_peer *u;                                    \
 247         struct inet_peer __rcu **v;                             \
 248         *stackptr++ = &start->avl_left;                         \
 249         v = &start->avl_left;                                   \
 250         for (u = rcu_dereference_protected(*v,                  \
 251                         lockdep_is_held(&base->lock));          \
 252              u->avl_right != peer_avl_empty_rcu; ) {            \
 253                 v = &u->avl_right;                              \
 254                 *stackptr++ = v;                                \
 255                 u = rcu_dereference_protected(*v,               \
 256                         lockdep_is_held(&base->lock));          \
 257         }                                                       \
 258         u;                                                      \
 259 })
 260
 261 /* Called with local BH disabled and the pool lock held.
 262  * Variable names are the proof of operation correctness.
 263  * Look into mm/map_avl.c for more detail description of the ideas.
 264  */
 265 static void peer_avl_rebalance(struct inet_peer __rcu **stack[],
 266                                struct inet_peer __rcu ***stackend,
 267                                struct inet_peer_base *base)
 268 {
 269         struct inet_peer __rcu **nodep;
 270         struct inet_peer *node, *l, *r;
 271         int lh, rh;
 272
 273         while (stackend > stack) {
 274                 nodep = *--stackend;
 275                 node = rcu_dereference_protected(*nodep,
 276                                 lockdep_is_held(&base->lock));
 277                 l = rcu_dereference_protected(node->avl_left,
 278                                 lockdep_is_held(&base->lock));
 279                 r = rcu_dereference_protected(node->avl_right,
 280                                 lockdep_is_held(&base->lock));
 281                 lh = node_height(l);
 282                 rh = node_height(r);
 283                 if (lh > rh + 1) { /* l: RH+2 */
 284                         struct inet_peer *ll, *lr, *lrl, *lrr;
 285                         int lrh;
 286                         ll = rcu_dereference_protected(l->avl_left,
 287                                 lockdep_is_held(&base->lock));
 288                         lr = rcu_dereference_protected(l->avl_right,
 289                                 lockdep_is_held(&base->lock));
 290                         lrh = node_height(lr);
 291                         if (lrh <= node_height(ll)) {   /* ll: RH+1 */
 292                                 RCU_INIT_POINTER(node->avl_left, lr);   /* lr: RH or RH+1 */
 293                                 RCU_INIT_POINTER(node->avl_right, r);   /* r: RH */
 294                                 node->avl_height = lrh + 1; /* RH+1 or RH+2 */
 295                                 RCU_INIT_POINTER(l->avl_left, ll);       /* ll: RH+1 */
 296                                 RCU_INIT_POINTER(l->avl_right, node);   /* node: RH+1 or RH+2 */
 297                                 l->avl_height = node->avl_height + 1;
 298                                 RCU_INIT_POINTER(*nodep, l);
 299                         } else { /* ll: RH, lr: RH+1 */
 300                                 lrl = rcu_dereference_protected(lr->avl_left,
 301                                         lockdep_is_held(&base->lock));  /* lrl: RH or RH-1 */
 302                                 lrr = rcu_dereference_protected(lr->avl_right,
 303                                         lockdep_is_held(&base->lock));  /* lrr: RH or RH-1 */
 304                                 RCU_INIT_POINTER(node->avl_left, lrr);  /* lrr: RH or RH-1 */
 305                                 RCU_INIT_POINTER(node->avl_right, r);   /* r: RH */
 306                                 node->avl_height = rh + 1; /* node: RH+1 */
 307                                 RCU_INIT_POINTER(l->avl_left, ll);      /* ll: RH */
 308                                 RCU_INIT_POINTER(l->avl_right, lrl);    /* lrl: RH or RH-1 */
 309                                 l->avl_height = rh + 1; /* l: RH+1 */
 310                                 RCU_INIT_POINTER(lr->avl_left, l);      /* l: RH+1 */
 311                                 RCU_INIT_POINTER(lr->avl_right, node);  /* node: RH+1 */
 312                                 lr->avl_height = rh + 2;
 313                                 RCU_INIT_POINTER(*nodep, lr);
 314                         }
 315                 } else if (rh > lh + 1) { /* r: LH+2 */
 316                         struct inet_peer *rr, *rl, *rlr, *rll;
 317                         int rlh;
 318                         rr = rcu_dereference_protected(r->avl_right,
 319                                 lockdep_is_held(&base->lock));
 320                         rl = rcu_dereference_protected(r->avl_left,
 321                                 lockdep_is_held(&base->lock));
 322                         rlh = node_height(rl);
 323                         if (rlh <= node_height(rr)) {   /* rr: LH+1 */
 324                                 RCU_INIT_POINTER(node->avl_right, rl);  /* rl: LH or LH+1 */
 325                                 RCU_INIT_POINTER(node->avl_left, l);    /* l: LH */
 326                                 node->avl_height = rlh + 1; /* LH+1 or LH+2 */
 327                                 RCU_INIT_POINTER(r->avl_right, rr);     /* rr: LH+1 */
 328                                 RCU_INIT_POINTER(r->avl_left, node);    /* node: LH+1 or LH+2 */
 329                                 r->avl_height = node->avl_height + 1;
 330                                 RCU_INIT_POINTER(*nodep, r);
 331                         } else { /* rr: RH, rl: RH+1 */
 332                                 rlr = rcu_dereference_protected(rl->avl_right,
 333                                         lockdep_is_held(&base->lock));  /* rlr: LH or LH-1 */
 334                                 rll = rcu_dereference_protected(rl->avl_left,
 335                                         lockdep_is_held(&base->lock));  /* rll: LH or LH-1 */
 336                                 RCU_INIT_POINTER(node->avl_right, rll); /* rll: LH or LH-1 */
 337                                 RCU_INIT_POINTER(node->avl_left, l);    /* l: LH */
 338                                 node->avl_height = lh + 1; /* node: LH+1 */
 339                                 RCU_INIT_POINTER(r->avl_right, rr);     /* rr: LH */
 340                                 RCU_INIT_POINTER(r->avl_left, rlr);     /* rlr: LH or LH-1 */
 341                                 r->avl_height = lh + 1; /* r: LH+1 */
 342                                 RCU_INIT_POINTER(rl->avl_right, r);     /* r: LH+1 */
 343                                 RCU_INIT_POINTER(rl->avl_left, node);   /* node: LH+1 */
 344                                 rl->avl_height = lh + 2;
 345                                 RCU_INIT_POINTER(*nodep, rl);
 346                         }
 347                 } else {
 348                         node->avl_height = (lh > rh ? lh : rh) + 1;
 349                 }
 350         }
 351 }
 352
 353 /* Called with local BH disabled and the pool lock held. */
 354 #define link_to_pool(n, base)                                   \
 355 do {                                                            \
 356         n->avl_height = 1;                                      \
 357         n->avl_left = peer_avl_empty_rcu;                       \
 358         n->avl_right = peer_avl_empty_rcu;                      \
 359         /* lockless readers can catch us now */                 \
 360         rcu_assign_pointer(**--stackptr, n);                    \
 361         peer_avl_rebalance(stack, stackptr, base);              \
 362 } while (0)
 363
 364 static void inetpeer_free_rcu(struct rcu_head *head)
 365 {
 366         kmem_cache_free(peer_cachep, container_of(head, struct inet_peer, rcu));
 367 }
 368
 369 /* May be called with local BH enabled. */
 370 static void unlink_from_pool(struct inet_peer *p, struct inet_peer_base *base,
 371                              struct inet_peer __rcu **stack[PEER_MAXDEPTH])
 372 {
 373         int do_free;
 374
 375         do_free = 0;
 376
 377         spin_lock_bh(&base->lock);
 378         /* Check the reference counter.  It was artificially incremented by 1
 379          * in cleanup() function to prevent sudden disappearing.  If we can
 380          * atomically (because of lockless readers) take this last reference,
 381          * it's safe to remove the node and free it later.
 382          * We use refcnt=-1 to alert lockless readers this entry is deleted.
 383          */
 384         if (atomic_cmpxchg(&p->refcnt, 1, -1) == 1) {
 385                 struct inet_peer __rcu ***stackptr, ***delp;
 386                 if (lookup(&p->daddr, stack, base) != p)
 387                         BUG();
 388                 delp = stackptr - 1; /* *delp[0] == p */
 389                 if (p->avl_left == peer_avl_empty_rcu) {
 390                         *delp[0] = p->avl_right;
 391                         --stackptr;
 392                 } else {
 393                         /* look for a node to insert instead of p */
 394                         struct inet_peer *t;
 395                         t = lookup_rightempty(p, base);
 396                         BUG_ON(rcu_dereference_protected(*stackptr[-1],
 397                                         lockdep_is_held(&base->lock)) != t);
 398                         **--stackptr = t->avl_left;
 399                         /* t is removed, t->daddr > x->daddr for any
 400                          * x in p->avl_left subtree.
 401                          * Put t in the old place of p. */
 402                         RCU_INIT_POINTER(*delp[0], t);
 403                         t->avl_left = p->avl_left;
 404                         t->avl_right = p->avl_right;
 405                         t->avl_height = p->avl_height;
 406                         BUG_ON(delp[1] != &p->avl_left);
 407                         delp[1] = &t->avl_left; /* was &p->avl_left */
 408                 }
 409                 peer_avl_rebalance(stack, stackptr, base);
 410                 base->total--;
 411                 do_free = 1;
 412         }
 413         spin_unlock_bh(&base->lock);
 414
 415         if (do_free)
 416                 call_rcu_bh(&p->rcu, inetpeer_free_rcu);
 417         else
 418                 /* The node is used again.  Decrease the reference counter
 419                  * back.  The loop "cleanup -> unlink_from_unused
 420                  *   -> unlink_from_pool -> putpeer -> link_to_unused
 421                  *   -> cleanup (for the same node)"
 422                  * doesn't really exist because the entry will have a
 423                  * recent deletion time and will not be cleaned again soon.
 424                  */
 425                 inet_putpeer(p);
 426 }
 427
 428 static struct inet_peer_base *family_to_base(int family)
 429 {
 430         return (family == AF_INET ? &v4_peers : &v6_peers);
 431 }
 432
 433 static struct inet_peer_base *peer_to_base(struct inet_peer *p)
 434 {
 435         return family_to_base(p->daddr.family);
 436 }
 437
 438 /* May be called with local BH enabled. */
 439 static int cleanup_once(unsigned long ttl, struct inet_peer __rcu **stack[PEER_MAXDEPTH])
 440 {
 441         struct inet_peer *p = NULL;
 442
 443         /* Remove the first entry from the list of unused nodes. */
 444         spin_lock_bh(&unused_peers.lock);
 445         if (!list_empty(&unused_peers.list)) {
 446                 __u32 delta;
 447
 448                 p = list_first_entry(&unused_peers.list, struct inet_peer, unused);
 449                 delta = (__u32)jiffies - p->dtime;
 450
 451                 if (delta < ttl) {
 452                         /* Do not prune fresh entries. */
 453                         spin_unlock_bh(&unused_peers.lock);
 454                         return -1;
 455                 }
 456
 457                 list_del_init(&p->unused);
 458
 459                 /* Grab an extra reference to prevent node disappearing
 460                  * before unlink_from_pool() call. */
 461                 atomic_inc(&p->refcnt);
 462         }
 463         spin_unlock_bh(&unused_peers.lock);
 464
 465         if (p == NULL)
 466                 /* It means that the total number of USED entries has
 467                  * grown over inet_peer_threshold.  It shouldn't really
 468                  * happen because of entry limits in route cache. */
 469                 return -1;
 470
 471         unlink_from_pool(p, peer_to_base(p), stack);
 472         return 0;
 473 }
 474
 475 /* Called with or without local BH being disabled. */
 476 struct inet_peer *inet_getpeer(struct inetpeer_addr *daddr, int create)
 477 {
 478         struct inet_peer __rcu **stack[PEER_MAXDEPTH], ***stackptr;
 479         struct inet_peer_base *base = family_to_base(daddr->family);
 480         struct inet_peer *p;
 481
 482         /* Look up for the address quickly, lockless.
 483          * Because of a concurrent writer, we might not find an existing entry.
 484          */
 485         rcu_read_lock_bh();
 486         p = lookup_rcu_bh(daddr, base);
 487         rcu_read_unlock_bh();
 488
 489         if (p) {
 490                 /* The existing node has been found.
 491                  * Remove the entry from unused list if it was there.
 492                  */
 493                 unlink_from_unused(p);
 494                 return p;
 495         }
 496
 497         /* retry an exact lookup, taking the lock before.
 498          * At least, nodes should be hot in our cache.
 499          */
 500         spin_lock_bh(&base->lock);
 501         p = lookup(daddr, stack, base);
 502         if (p != peer_avl_empty) {
 503                 atomic_inc(&p->refcnt);
 504                 spin_unlock_bh(&base->lock);
 505                 /* Remove the entry from unused list if it was there. */
 506                 unlink_from_unused(p);
 507                 return p;
 508         }
 509         p = create ? kmem_cache_alloc(peer_cachep, GFP_ATOMIC) : NULL;
 510         if (p) {
 511                 p->daddr = *daddr;
 512                 atomic_set(&p->refcnt, 1);
 513                 atomic_set(&p->rid, 0);
 514                 atomic_set(&p->ip_id_count, secure_ip_id(daddr->a4));
 515                 p->tcp_ts_stamp = 0;
 516                 INIT_LIST_HEAD(&p->unused);
 517
 518
 519                 /* Link the node. */
 520                 link_to_pool(p, base);
 521                 base->total++;
 522         }
 523         spin_unlock_bh(&base->lock);
 524
 525         if (base->total >= inet_peer_threshold)
 526                 /* Remove one less-recently-used entry. */
 527                 cleanup_once(0, stack);
 528
 529         return p;
 530 }
 531
 532 static int compute_total(void)
 533 {
 534         return v4_peers.total + v6_peers.total;
 535 }
 536 EXPORT_SYMBOL_GPL(inet_getpeer);
 537
 538 /* Called with local BH disabled. */
 539 static void peer_check_expire(unsigned long dummy)
 540 {
 541         unsigned long now = jiffies;
 542         int ttl, total;
 543         struct inet_peer __rcu **stack[PEER_MAXDEPTH];
 544
 545         total = compute_total();
 546         if (total >= inet_peer_threshold)
 547                 ttl = inet_peer_minttl;
 548         else
 549                 ttl = inet_peer_maxttl
 550                                 - (inet_peer_maxttl - inet_peer_minttl) / HZ *
 551                                         total / inet_peer_threshold * HZ;
 552         while (!cleanup_once(ttl, stack)) {
 553                 if (jiffies != now)
 554                         break;
 555         }
 556
 557         /* Trigger the timer after inet_peer_gc_mintime .. inet_peer_gc_maxtime
 558          * interval depending on the total number of entries (more entries,
 559          * less interval). */
 560         total = compute_total();
 561         if (total >= inet_peer_threshold)
 562                 peer_periodic_timer.expires = jiffies + inet_peer_gc_mintime;
 563         else
 564                 peer_periodic_timer.expires = jiffies
 565                         + inet_peer_gc_maxtime
 566                         - (inet_peer_gc_maxtime - inet_peer_gc_mintime) / HZ *
 567                                 total / inet_peer_threshold * HZ;
 568         add_timer(&peer_periodic_timer);
 569 }
 570
 571 void inet_putpeer(struct inet_peer *p)
 572 {
 573         local_bh_disable();
 574
 575         if (atomic_dec_and_lock(&p->refcnt, &unused_peers.lock)) {
 576                 list_add_tail(&p->unused, &unused_peers.list);
 577                 p->dtime = (__u32)jiffies;
 578                 spin_unlock(&unused_peers.lock);
 579         }
 580
 581         local_bh_enable();
 582 }
 583 EXPORT_SYMBOL_GPL(inet_putpeer);