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