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 <linux/workqueue.h>
  21 #include <net/ip.h>
  22 #include <net/inetpeer.h>
  23 #include <net/secure_seq.h>
  24
  25 /*
  26  *  Theory of operations.
  27  *  We keep one entry for each peer IP address.  The nodes contains long-living
  28  *  information about the peer which doesn't depend on routes.
  29  *
  30  *  Nodes are removed only when reference counter goes to 0.
  31  *  When it's happened the node may be removed when a sufficient amount of
  32  *  time has been passed since its last use.  The less-recently-used entry can
  33  *  also be removed if the pool is overloaded i.e. if the total amount of
  34  *  entries is greater-or-equal than the threshold.
  35  *
  36  *  Node pool is organised as an AVL tree.
  37  *  Such an implementation has been chosen not just for fun.  It's a way to
  38  *  prevent easy and efficient DoS attacks by creating hash collisions.  A huge
  39  *  amount of long living nodes in a single hash slot would significantly delay
  40  *  lookups performed with disabled BHs.
  41  *
  42  *  Serialisation issues.
  43  *  1.  Nodes may appear in the tree only with the pool lock held.
  44  *  2.  Nodes may disappear from the tree only with the pool lock held
  45  *      AND reference count being 0.
  46  *  3.  Global variable peer_total is modified under the pool lock.
  47  *  4.  struct inet_peer fields modification:
  48  *              avl_left, avl_right, avl_parent, avl_height: pool lock
  49  *              refcnt: atomically against modifications on other CPU;
  50  *                 usually under some other lock to prevent node disappearing
  51  *              daddr: unchangeable
  52  */
  53
  54 static struct kmem_cache *peer_cachep __read_mostly;
  55
  56 static LIST_HEAD(gc_list);
  57 static const int gc_delay = 60 * HZ;
  58 static struct delayed_work gc_work;
  59 static DEFINE_SPINLOCK(gc_lock);
  60
  61 #define node_height(x) x->avl_height
  62
  63 #define peer_avl_empty ((struct inet_peer *)&peer_fake_node)
  64 #define peer_avl_empty_rcu ((struct inet_peer __rcu __force *)&peer_fake_node)
  65 static const struct inet_peer peer_fake_node = {
  66         .avl_left       = peer_avl_empty_rcu,
  67         .avl_right      = peer_avl_empty_rcu,
  68         .avl_height     = 0
  69 };
  70
  71 struct inet_peer_base {
  72         struct inet_peer __rcu *root;
  73         seqlock_t       lock;
  74         int             total;
  75 };
  76
  77 static struct inet_peer_base v4_peers = {
  78         .root           = peer_avl_empty_rcu,
  79         .lock           = __SEQLOCK_UNLOCKED(v4_peers.lock),
  80         .total          = 0,
  81 };
  82
  83 static struct inet_peer_base v6_peers = {
  84         .root           = peer_avl_empty_rcu,
  85         .lock           = __SEQLOCK_UNLOCKED(v6_peers.lock),
  86         .total          = 0,
  87 };
  88
  89 #define PEER_MAXDEPTH 40 /* sufficient for about 2^27 nodes */
  90
  91 /* Exported for sysctl_net_ipv4.  */
  92 int inet_peer_threshold __read_mostly = 65536 + 128;    /* start to throw entries more
  93                                          * aggressively at this stage */
  94 int inet_peer_minttl __read_mostly = 120 * HZ;  /* TTL under high load: 120 sec */
  95 int inet_peer_maxttl __read_mostly = 10 * 60 * HZ;      /* usual time to live: 10 min */
  96
  97 static void inetpeer_gc_worker(struct work_struct *work)
  98 {
  99         struct inet_peer *p, *n;
 100         LIST_HEAD(list);
 101
 102         spin_lock_bh(&gc_lock);
 103         list_replace_init(&gc_list, &list);
 104         spin_unlock_bh(&gc_lock);
 105
 106         if (list_empty(&list))
 107                 return;
 108
 109         list_for_each_entry_safe(p, n, &list, gc_list) {
 110
 111                 if(need_resched())
 112                         cond_resched();
 113
 114                 if (p->avl_left != peer_avl_empty) {
 115                         list_add_tail(&p->avl_left->gc_list, &list);
 116                         p->avl_left = peer_avl_empty;
 117                 }
 118
 119                 if (p->avl_right != peer_avl_empty) {
 120                         list_add_tail(&p->avl_right->gc_list, &list);
 121                         p->avl_right = peer_avl_empty;
 122                 }
 123
 124                 n = list_entry(p->gc_list.next, struct inet_peer, gc_list);
 125
 126                 if (!atomic_read(&p->refcnt)) {
 127                         list_del(&p->gc_list);
 128                         kmem_cache_free(peer_cachep, p);
 129                 }
 130         }
 131
 132         if (list_empty(&list))
 133                 return;
 134
 135         spin_lock_bh(&gc_lock);
 136         list_splice(&list, &gc_list);
 137         spin_unlock_bh(&gc_lock);
 138
 139         schedule_delayed_work(&gc_work, gc_delay);
 140 }
 141
 142 /* Called from ip_output.c:ip_init  */
 143 void __init inet_initpeers(void)
 144 {
 145         struct sysinfo si;
 146
 147         /* Use the straight interface to information about memory. */
 148         si_meminfo(&si);
 149         /* The values below were suggested by Alexey Kuznetsov
 150          * <kuznet@ms2.inr.ac.ru>.  I don't have any opinion about the values
 151          * myself.  --SAW
 152          */
 153         if (si.totalram <= (32768*1024)/PAGE_SIZE)
 154                 inet_peer_threshold >>= 1; /* max pool size about 1MB on IA32 */
 155         if (si.totalram <= (16384*1024)/PAGE_SIZE)
 156                 inet_peer_threshold >>= 1; /* about 512KB */
 157         if (si.totalram <= (8192*1024)/PAGE_SIZE)
 158                 inet_peer_threshold >>= 2; /* about 128KB */
 159
 160         peer_cachep = kmem_cache_create("inet_peer_cache",
 161                         sizeof(struct inet_peer),
 162                         0, SLAB_HWCACHE_ALIGN | SLAB_PANIC,
 163                         NULL);
 164
 165         INIT_DELAYED_WORK_DEFERRABLE(&gc_work, inetpeer_gc_worker);
 166 }
 167
 168 static int addr_compare(const struct inetpeer_addr *a,
 169                         const struct inetpeer_addr *b)
 170 {
 171         int i, n = (a->family == AF_INET ? 1 : 4);
 172
 173         for (i = 0; i < n; i++) {
 174                 if (a->addr.a6[i] == b->addr.a6[i])
 175                         continue;
 176                 if (a->addr.a6[i] < b->addr.a6[i])
 177                         return -1;
 178                 return 1;
 179         }
 180
 181         return 0;
 182 }
 183
 184 #define rcu_deref_locked(X, BASE)                               \
 185         rcu_dereference_protected(X, lockdep_is_held(&(BASE)->lock.lock))
 186
 187 /*
 188  * Called with local BH disabled and the pool lock held.
 189  */
 190 #define lookup(_daddr, _stack, _base)                           \
 191 ({                                                              \
 192         struct inet_peer *u;                                    \
 193         struct inet_peer __rcu **v;                             \
 194                                                                 \
 195         stackptr = _stack;                                      \
 196         *stackptr++ = &_base->root;                             \
 197         for (u = rcu_deref_locked(_base->root, _base);          \
 198              u != peer_avl_empty; ) {                           \
 199                 int cmp = addr_compare(_daddr, &u->daddr);      \
 200                 if (cmp == 0)                                   \
 201                         break;                                  \
 202                 if (cmp == -1)                                  \
 203                         v = &u->avl_left;                       \
 204                 else                                            \
 205                         v = &u->avl_right;                      \
 206                 *stackptr++ = v;                                \
 207                 u = rcu_deref_locked(*v, _base);                \
 208         }                                                       \
 209         u;                                                      \
 210 })
 211
 212 /*
 213  * Called with rcu_read_lock()
 214  * Because we hold no lock against a writer, its quite possible we fall
 215  * in an endless loop.
 216  * But every pointer we follow is guaranteed to be valid thanks to RCU.
 217  * We exit from this function if number of links exceeds PEER_MAXDEPTH
 218  */
 219 static struct inet_peer *lookup_rcu(const struct inetpeer_addr *daddr,
 220                                     struct inet_peer_base *base)
 221 {
 222         struct inet_peer *u = rcu_dereference(base->root);
 223         int count = 0;
 224
 225         while (u != peer_avl_empty) {
 226                 int cmp = addr_compare(daddr, &u->daddr);
 227                 if (cmp == 0) {
 228                         /* Before taking a reference, check if this entry was
 229                          * deleted (refcnt=-1)
 230                          */
 231                         if (!atomic_add_unless(&u->refcnt, 1, -1))
 232                                 u = NULL;
 233                         return u;
 234                 }
 235                 if (cmp == -1)
 236                         u = rcu_dereference(u->avl_left);
 237                 else
 238                         u = rcu_dereference(u->avl_right);
 239                 if (unlikely(++count == PEER_MAXDEPTH))
 240                         break;
 241         }
 242         return NULL;
 243 }
 244
 245 /* Called with local BH disabled and the pool lock held. */
 246 #define lookup_rightempty(start, base)                          \
 247 ({                                                              \
 248         struct inet_peer *u;                                    \
 249         struct inet_peer __rcu **v;                             \
 250         *stackptr++ = &start->avl_left;                         \
 251         v = &start->avl_left;                                   \
 252         for (u = rcu_deref_locked(*v, base);                    \
 253              u->avl_right != peer_avl_empty_rcu; ) {            \
 254                 v = &u->avl_right;                              \
 255                 *stackptr++ = v;                                \
 256                 u = rcu_deref_locked(*v, base);                 \
 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_deref_locked(*nodep, base);
 276                 l = rcu_deref_locked(node->avl_left, base);
 277                 r = rcu_deref_locked(node->avl_right, base);
 278                 lh = node_height(l);
 279                 rh = node_height(r);
 280                 if (lh > rh + 1) { /* l: RH+2 */
 281                         struct inet_peer *ll, *lr, *lrl, *lrr;
 282                         int lrh;
 283                         ll = rcu_deref_locked(l->avl_left, base);
 284                         lr = rcu_deref_locked(l->avl_right, base);
 285                         lrh = node_height(lr);
 286                         if (lrh <= node_height(ll)) {   /* ll: RH+1 */
 287                                 RCU_INIT_POINTER(node->avl_left, lr);   /* lr: RH or RH+1 */
 288                                 RCU_INIT_POINTER(node->avl_right, r);   /* r: RH */
 289                                 node->avl_height = lrh + 1; /* RH+1 or RH+2 */
 290                                 RCU_INIT_POINTER(l->avl_left, ll);       /* ll: RH+1 */
 291                                 RCU_INIT_POINTER(l->avl_right, node);   /* node: RH+1 or RH+2 */
 292                                 l->avl_height = node->avl_height + 1;
 293                                 RCU_INIT_POINTER(*nodep, l);
 294                         } else { /* ll: RH, lr: RH+1 */
 295                                 lrl = rcu_deref_locked(lr->avl_left, base);/* lrl: RH or RH-1 */
 296                                 lrr = rcu_deref_locked(lr->avl_right, base);/* lrr: RH or RH-1 */
 297                                 RCU_INIT_POINTER(node->avl_left, lrr);  /* lrr: RH or RH-1 */
 298                                 RCU_INIT_POINTER(node->avl_right, r);   /* r: RH */
 299                                 node->avl_height = rh + 1; /* node: RH+1 */
 300                                 RCU_INIT_POINTER(l->avl_left, ll);      /* ll: RH */
 301                                 RCU_INIT_POINTER(l->avl_right, lrl);    /* lrl: RH or RH-1 */
 302                                 l->avl_height = rh + 1; /* l: RH+1 */
 303                                 RCU_INIT_POINTER(lr->avl_left, l);      /* l: RH+1 */
 304                                 RCU_INIT_POINTER(lr->avl_right, node);  /* node: RH+1 */
 305                                 lr->avl_height = rh + 2;
 306                                 RCU_INIT_POINTER(*nodep, lr);
 307                         }
 308                 } else if (rh > lh + 1) { /* r: LH+2 */
 309                         struct inet_peer *rr, *rl, *rlr, *rll;
 310                         int rlh;
 311                         rr = rcu_deref_locked(r->avl_right, base);
 312                         rl = rcu_deref_locked(r->avl_left, base);
 313                         rlh = node_height(rl);
 314                         if (rlh <= node_height(rr)) {   /* rr: LH+1 */
 315                                 RCU_INIT_POINTER(node->avl_right, rl);  /* rl: LH or LH+1 */
 316                                 RCU_INIT_POINTER(node->avl_left, l);    /* l: LH */
 317                                 node->avl_height = rlh + 1; /* LH+1 or LH+2 */
 318                                 RCU_INIT_POINTER(r->avl_right, rr);     /* rr: LH+1 */
 319                                 RCU_INIT_POINTER(r->avl_left, node);    /* node: LH+1 or LH+2 */
 320                                 r->avl_height = node->avl_height + 1;
 321                                 RCU_INIT_POINTER(*nodep, r);
 322                         } else { /* rr: RH, rl: RH+1 */
 323                                 rlr = rcu_deref_locked(rl->avl_right, base);/* rlr: LH or LH-1 */
 324                                 rll = rcu_deref_locked(rl->avl_left, base);/* rll: LH or LH-1 */
 325                                 RCU_INIT_POINTER(node->avl_right, rll); /* rll: LH or LH-1 */
 326                                 RCU_INIT_POINTER(node->avl_left, l);    /* l: LH */
 327                                 node->avl_height = lh + 1; /* node: LH+1 */
 328                                 RCU_INIT_POINTER(r->avl_right, rr);     /* rr: LH */
 329                                 RCU_INIT_POINTER(r->avl_left, rlr);     /* rlr: LH or LH-1 */
 330                                 r->avl_height = lh + 1; /* r: LH+1 */
 331                                 RCU_INIT_POINTER(rl->avl_right, r);     /* r: LH+1 */
 332                                 RCU_INIT_POINTER(rl->avl_left, node);   /* node: LH+1 */
 333                                 rl->avl_height = lh + 2;
 334                                 RCU_INIT_POINTER(*nodep, rl);
 335                         }
 336                 } else {
 337                         node->avl_height = (lh > rh ? lh : rh) + 1;
 338                 }
 339         }
 340 }
 341
 342 /* Called with local BH disabled and the pool lock held. */
 343 #define link_to_pool(n, base)                                   \
 344 do {                                                            \
 345         n->avl_height = 1;                                      \
 346         n->avl_left = peer_avl_empty_rcu;                       \
 347         n->avl_right = peer_avl_empty_rcu;                      \
 348         /* lockless readers can catch us now */                 \
 349         rcu_assign_pointer(**--stackptr, n);                    \
 350         peer_avl_rebalance(stack, stackptr, base);              \
 351 } while (0)
 352
 353 static void inetpeer_free_rcu(struct rcu_head *head)
 354 {
 355         kmem_cache_free(peer_cachep, container_of(head, struct inet_peer, rcu));
 356 }
 357
 358 static void unlink_from_pool(struct inet_peer *p, struct inet_peer_base *base,
 359                              struct inet_peer __rcu **stack[PEER_MAXDEPTH])
 360 {
 361         struct inet_peer __rcu ***stackptr, ***delp;
 362
 363         if (lookup(&p->daddr, stack, base) != p)
 364                 BUG();
 365         delp = stackptr - 1; /* *delp[0] == p */
 366         if (p->avl_left == peer_avl_empty_rcu) {
 367                 *delp[0] = p->avl_right;
 368                 --stackptr;
 369         } else {
 370                 /* look for a node to insert instead of p */
 371                 struct inet_peer *t;
 372                 t = lookup_rightempty(p, base);
 373                 BUG_ON(rcu_deref_locked(*stackptr[-1], base) != t);
 374                 **--stackptr = t->avl_left;
 375                 /* t is removed, t->daddr > x->daddr for any
 376                  * x in p->avl_left subtree.
 377                  * Put t in the old place of p. */
 378                 RCU_INIT_POINTER(*delp[0], t);
 379                 t->avl_left = p->avl_left;
 380                 t->avl_right = p->avl_right;
 381                 t->avl_height = p->avl_height;
 382                 BUG_ON(delp[1] != &p->avl_left);
 383                 delp[1] = &t->avl_left; /* was &p->avl_left */
 384         }
 385         peer_avl_rebalance(stack, stackptr, base);
 386         base->total--;
 387         call_rcu(&p->rcu, inetpeer_free_rcu);
 388 }
 389
 390 static struct inet_peer_base *family_to_base(int family)
 391 {
 392         return family == AF_INET ? &v4_peers : &v6_peers;
 393 }
 394
 395 /* perform garbage collect on all items stacked during a lookup */
 396 static int inet_peer_gc(struct inet_peer_base *base,
 397                         struct inet_peer __rcu **stack[PEER_MAXDEPTH],
 398                         struct inet_peer __rcu ***stackptr)
 399 {
 400         struct inet_peer *p, *gchead = NULL;
 401         __u32 delta, ttl;
 402         int cnt = 0;
 403
 404         if (base->total >= inet_peer_threshold)
 405                 ttl = 0; /* be aggressive */
 406         else
 407                 ttl = inet_peer_maxttl
 408                                 - (inet_peer_maxttl - inet_peer_minttl) / HZ *
 409                                         base->total / inet_peer_threshold * HZ;
 410         stackptr--; /* last stack slot is peer_avl_empty */
 411         while (stackptr > stack) {
 412                 stackptr--;
 413                 p = rcu_deref_locked(**stackptr, base);
 414                 if (atomic_read(&p->refcnt) == 0) {
 415                         smp_rmb();
 416                         delta = (__u32)jiffies - p->dtime;
 417                         if (delta >= ttl &&
 418                             atomic_cmpxchg(&p->refcnt, 0, -1) == 0) {
 419                                 p->gc_next = gchead;
 420                                 gchead = p;
 421                         }
 422                 }
 423         }
 424         while ((p = gchead) != NULL) {
 425                 gchead = p->gc_next;
 426                 cnt++;
 427                 unlink_from_pool(p, base, stack);
 428         }
 429         return cnt;
 430 }
 431
 432 struct inet_peer *inet_getpeer(const struct inetpeer_addr *daddr, int create)
 433 {
 434         struct inet_peer __rcu **stack[PEER_MAXDEPTH], ***stackptr;
 435         struct inet_peer_base *base = family_to_base(daddr->family);
 436         struct inet_peer *p;
 437         unsigned int sequence;
 438         int invalidated, gccnt = 0;
 439
 440         /* Attempt a lockless lookup first.
 441          * Because of a concurrent writer, we might not find an existing entry.
 442          */
 443         rcu_read_lock();
 444         sequence = read_seqbegin(&base->lock);
 445         p = lookup_rcu(daddr, base);
 446         invalidated = read_seqretry(&base->lock, sequence);
 447         rcu_read_unlock();
 448
 449         if (p)
 450                 return p;
 451
 452         /* If no writer did a change during our lookup, we can return early. */
 453         if (!create && !invalidated)
 454                 return NULL;
 455
 456         /* retry an exact lookup, taking the lock before.
 457          * At least, nodes should be hot in our cache.
 458          */
 459         write_seqlock_bh(&base->lock);
 460 relookup:
 461         p = lookup(daddr, stack, base);
 462         if (p != peer_avl_empty) {
 463                 atomic_inc(&p->refcnt);
 464                 write_sequnlock_bh(&base->lock);
 465                 return p;
 466         }
 467         if (!gccnt) {
 468                 gccnt = inet_peer_gc(base, stack, stackptr);
 469                 if (gccnt && create)
 470                         goto relookup;
 471         }
 472         p = create ? kmem_cache_alloc(peer_cachep, GFP_ATOMIC) : NULL;
 473         if (p) {
 474                 p->daddr = *daddr;
 475                 atomic_set(&p->refcnt, 1);
 476                 atomic_set(&p->rid, 0);
 477                 p->tcp_ts_stamp = 0;
 478                 p->metrics[RTAX_LOCK-1] = INETPEER_METRICS_NEW;
 479                 p->rate_tokens = 0;
 480                 p->rate_last = 0;
 481                 p->pmtu_expires = 0;
 482                 p->pmtu_orig = 0;
 483                 memset(&p->redirect_learned, 0, sizeof(p->redirect_learned));
 484                 INIT_LIST_HEAD(&p->gc_list);
 485
 486                 /* Link the node. */
 487                 link_to_pool(p, base);
 488                 base->total++;
 489         }
 490         write_sequnlock_bh(&base->lock);
 491
 492         return p;
 493 }
 494 EXPORT_SYMBOL_GPL(inet_getpeer);
 495
 496 void inet_putpeer(struct inet_peer *p)
 497 {
 498         p->dtime = (__u32)jiffies;
 499         smp_mb__before_atomic_dec();
 500         atomic_dec(&p->refcnt);
 501 }
 502 EXPORT_SYMBOL_GPL(inet_putpeer);
 503
 504 /*
 505  *      Check transmit rate limitation for given message.
 506  *      The rate information is held in the inet_peer entries now.
 507  *      This function is generic and could be used for other purposes
 508  *      too. It uses a Token bucket filter as suggested by Alexey Kuznetsov.
 509  *
 510  *      Note that the same inet_peer fields are modified by functions in
 511  *      route.c too, but these work for packet destinations while xrlim_allow
 512  *      works for icmp destinations. This means the rate limiting information
 513  *      for one "ip object" is shared - and these ICMPs are twice limited:
 514  *      by source and by destination.
 515  *
 516  *      RFC 1812: 4.3.2.8 SHOULD be able to limit error message rate
 517  *                        SHOULD allow setting of rate limits
 518  *
 519  *      Shared between ICMPv4 and ICMPv6.
 520  */
 521 #define XRLIM_BURST_FACTOR 6
 522 bool inet_peer_xrlim_allow(struct inet_peer *peer, int timeout)
 523 {
 524         unsigned long now, token;
 525         bool rc = false;
 526
 527         if (!peer)
 528                 return true;
 529
 530         token = peer->rate_tokens;
 531         now = jiffies;
 532         token += now - peer->rate_last;
 533         peer->rate_last = now;
 534         if (token > XRLIM_BURST_FACTOR * timeout)
 535                 token = XRLIM_BURST_FACTOR * timeout;
 536         if (token >= timeout) {
 537                 token -= timeout;
 538                 rc = true;
 539         }
 540         peer->rate_tokens = token;
 541         return rc;
 542 }
 543 EXPORT_SYMBOL(inet_peer_xrlim_allow);
 544
 545 static void inetpeer_inval_rcu(struct rcu_head *head)
 546 {
 547         struct inet_peer *p = container_of(head, struct inet_peer, gc_rcu);
 548
 549         spin_lock_bh(&gc_lock);
 550         list_add_tail(&p->gc_list, &gc_list);
 551         spin_unlock_bh(&gc_lock);
 552
 553         schedule_delayed_work(&gc_work, gc_delay);
 554 }
 555
 556 void inetpeer_invalidate_tree(int family)
 557 {
 558         struct inet_peer *old, *new, *prev;
 559         struct inet_peer_base *base = family_to_base(family);
 560
 561         write_seqlock_bh(&base->lock);
 562
 563         old = base->root;
 564         if (old == peer_avl_empty_rcu)
 565                 goto out;
 566
 567         new = peer_avl_empty_rcu;
 568
 569         prev = cmpxchg(&base->root, old, new);
 570         if (prev == old) {
 571                 base->total = 0;
 572                 call_rcu(&prev->gc_rcu, inetpeer_inval_rcu);
 573         }
 574
 575 out:
 576         write_sequnlock_bh(&base->lock);
 577 }
 578 EXPORT_SYMBOL(inetpeer_invalidate_tree);