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 void inet_peer_base_init(struct inet_peer_base *bp)
  72 {
  73         bp->root = peer_avl_empty_rcu;
  74         seqlock_init(&bp->lock);
  75         bp->flush_seq = ~0U;
  76         bp->total = 0;
  77 }
  78 EXPORT_SYMBOL_GPL(inet_peer_base_init);
  79
  80 static atomic_t v4_seq = ATOMIC_INIT(0);
  81 static atomic_t v6_seq = ATOMIC_INIT(0);
  82
  83 static atomic_t *inetpeer_seq_ptr(int family)
  84 {
  85         return (family == AF_INET ? &v4_seq : &v6_seq);
  86 }
  87
  88 static inline void flush_check(struct inet_peer_base *base, int family)
  89 {
  90         atomic_t *fp = inetpeer_seq_ptr(family);
  91
  92         if (unlikely(base->flush_seq != atomic_read(fp))) {
  93                 inetpeer_invalidate_tree(base);
  94                 base->flush_seq = atomic_read(fp);
  95         }
  96 }
  97
  98 #define PEER_MAXDEPTH 40 /* sufficient for about 2^27 nodes */
  99
 100 /* Exported for sysctl_net_ipv4.  */
 101 int inet_peer_threshold __read_mostly = 65536 + 128;    /* start to throw entries more
 102                                          * aggressively at this stage */
 103 int inet_peer_minttl __read_mostly = 120 * HZ;  /* TTL under high load: 120 sec */
 104 int inet_peer_maxttl __read_mostly = 10 * 60 * HZ;      /* usual time to live: 10 min */
 105
 106 static void inetpeer_gc_worker(struct work_struct *work)
 107 {
 108         struct inet_peer *p, *n, *c;
 109         LIST_HEAD(list);
 110
 111         spin_lock_bh(&gc_lock);
 112         list_replace_init(&gc_list, &list);
 113         spin_unlock_bh(&gc_lock);
 114
 115         if (list_empty(&list))
 116                 return;
 117
 118         list_for_each_entry_safe(p, n, &list, gc_list) {
 119
 120                 if (need_resched())
 121                         cond_resched();
 122
 123                 c = rcu_dereference_protected(p->avl_left, 1);
 124                 if (c != peer_avl_empty) {
 125                         list_add_tail(&c->gc_list, &list);
 126                         p->avl_left = peer_avl_empty_rcu;
 127                 }
 128
 129                 c = rcu_dereference_protected(p->avl_right, 1);
 130                 if (c != peer_avl_empty) {
 131                         list_add_tail(&c->gc_list, &list);
 132                         p->avl_right = peer_avl_empty_rcu;
 133                 }
 134
 135                 n = list_entry(p->gc_list.next, struct inet_peer, gc_list);
 136
 137                 if (!atomic_read(&p->refcnt)) {
 138                         list_del(&p->gc_list);
 139                         kmem_cache_free(peer_cachep, p);
 140                 }
 141         }
 142
 143         if (list_empty(&list))
 144                 return;
 145
 146         spin_lock_bh(&gc_lock);
 147         list_splice(&list, &gc_list);
 148         spin_unlock_bh(&gc_lock);
 149
 150         schedule_delayed_work(&gc_work, gc_delay);
 151 }
 152
 153 /* Called from ip_output.c:ip_init  */
 154 void __init inet_initpeers(void)
 155 {
 156         struct sysinfo si;
 157
 158         /* Use the straight interface to information about memory. */
 159         si_meminfo(&si);
 160         /* The values below were suggested by Alexey Kuznetsov
 161          * <kuznet@ms2.inr.ac.ru>.  I don't have any opinion about the values
 162          * myself.  --SAW
 163          */
 164         if (si.totalram <= (32768*1024)/PAGE_SIZE)
 165                 inet_peer_threshold >>= 1; /* max pool size about 1MB on IA32 */
 166         if (si.totalram <= (16384*1024)/PAGE_SIZE)
 167                 inet_peer_threshold >>= 1; /* about 512KB */
 168         if (si.totalram <= (8192*1024)/PAGE_SIZE)
 169                 inet_peer_threshold >>= 2; /* about 128KB */
 170
 171         peer_cachep = kmem_cache_create("inet_peer_cache",
 172                         sizeof(struct inet_peer),
 173                         0, SLAB_HWCACHE_ALIGN | SLAB_PANIC,
 174                         NULL);
 175
 176         INIT_DEFERRABLE_WORK(&gc_work, inetpeer_gc_worker);
 177 }
 178
 179 static int addr_compare(const struct inetpeer_addr *a,
 180                         const struct inetpeer_addr *b)
 181 {
 182         int i, n = (a->family == AF_INET ? 1 : 4);
 183
 184         for (i = 0; i < n; i++) {
 185                 if (a->addr.a6[i] == b->addr.a6[i])
 186                         continue;
 187                 if ((__force u32)a->addr.a6[i] < (__force u32)b->addr.a6[i])
 188                         return -1;
 189                 return 1;
 190         }
 191
 192         return 0;
 193 }
 194
 195 #define rcu_deref_locked(X, BASE)                               \
 196         rcu_dereference_protected(X, lockdep_is_held(&(BASE)->lock.lock))
 197
 198 /*
 199  * Called with local BH disabled and the pool lock held.
 200  */
 201 #define lookup(_daddr, _stack, _base)                           \
 202 ({                                                              \
 203         struct inet_peer *u;                                    \
 204         struct inet_peer __rcu **v;                             \
 205                                                                 \
 206         stackptr = _stack;                                      \
 207         *stackptr++ = &_base->root;                             \
 208         for (u = rcu_deref_locked(_base->root, _base);          \
 209              u != peer_avl_empty;) {                            \
 210                 int cmp = addr_compare(_daddr, &u->daddr);      \
 211                 if (cmp == 0)                                   \
 212                         break;                                  \
 213                 if (cmp == -1)                                  \
 214                         v = &u->avl_left;                       \
 215                 else                                            \
 216                         v = &u->avl_right;                      \
 217                 *stackptr++ = v;                                \
 218                 u = rcu_deref_locked(*v, _base);                \
 219         }                                                       \
 220         u;                                                      \
 221 })
 222
 223 /*
 224  * Called with rcu_read_lock()
 225  * Because we hold no lock against a writer, its quite possible we fall
 226  * in an endless loop.
 227  * But every pointer we follow is guaranteed to be valid thanks to RCU.
 228  * We exit from this function if number of links exceeds PEER_MAXDEPTH
 229  */
 230 static struct inet_peer *lookup_rcu(const struct inetpeer_addr *daddr,
 231                                     struct inet_peer_base *base)
 232 {
 233         struct inet_peer *u = rcu_dereference(base->root);
 234         int count = 0;
 235
 236         while (u != peer_avl_empty) {
 237                 int cmp = addr_compare(daddr, &u->daddr);
 238                 if (cmp == 0) {
 239                         /* Before taking a reference, check if this entry was
 240                          * deleted (refcnt=-1)
 241                          */
 242                         if (!atomic_add_unless(&u->refcnt, 1, -1))
 243                                 u = NULL;
 244                         return u;
 245                 }
 246                 if (cmp == -1)
 247                         u = rcu_dereference(u->avl_left);
 248                 else
 249                         u = rcu_dereference(u->avl_right);
 250                 if (unlikely(++count == PEER_MAXDEPTH))
 251                         break;
 252         }
 253         return NULL;
 254 }
 255
 256 /* Called with local BH disabled and the pool lock held. */
 257 #define lookup_rightempty(start, base)                          \
 258 ({                                                              \
 259         struct inet_peer *u;                                    \
 260         struct inet_peer __rcu **v;                             \
 261         *stackptr++ = &start->avl_left;                         \
 262         v = &start->avl_left;                                   \
 263         for (u = rcu_deref_locked(*v, base);                    \
 264              u->avl_right != peer_avl_empty_rcu;) {             \
 265                 v = &u->avl_right;                              \
 266                 *stackptr++ = v;                                \
 267                 u = rcu_deref_locked(*v, base);                 \
 268         }                                                       \
 269         u;                                                      \
 270 })
 271
 272 /* Called with local BH disabled and the pool lock held.
 273  * Variable names are the proof of operation correctness.
 274  * Look into mm/map_avl.c for more detail description of the ideas.
 275  */
 276 static void peer_avl_rebalance(struct inet_peer __rcu **stack[],
 277                                struct inet_peer __rcu ***stackend,
 278                                struct inet_peer_base *base)
 279 {
 280         struct inet_peer __rcu **nodep;
 281         struct inet_peer *node, *l, *r;
 282         int lh, rh;
 283
 284         while (stackend > stack) {
 285                 nodep = *--stackend;
 286                 node = rcu_deref_locked(*nodep, base);
 287                 l = rcu_deref_locked(node->avl_left, base);
 288                 r = rcu_deref_locked(node->avl_right, base);
 289                 lh = node_height(l);
 290                 rh = node_height(r);
 291                 if (lh > rh + 1) { /* l: RH+2 */
 292                         struct inet_peer *ll, *lr, *lrl, *lrr;
 293                         int lrh;
 294                         ll = rcu_deref_locked(l->avl_left, base);
 295                         lr = rcu_deref_locked(l->avl_right, base);
 296                         lrh = node_height(lr);
 297                         if (lrh <= node_height(ll)) {   /* ll: RH+1 */
 298                                 RCU_INIT_POINTER(node->avl_left, lr);   /* lr: RH or RH+1 */
 299                                 RCU_INIT_POINTER(node->avl_right, r);   /* r: RH */
 300                                 node->avl_height = lrh + 1; /* RH+1 or RH+2 */
 301                                 RCU_INIT_POINTER(l->avl_left, ll);       /* ll: RH+1 */
 302                                 RCU_INIT_POINTER(l->avl_right, node);   /* node: RH+1 or RH+2 */
 303                                 l->avl_height = node->avl_height + 1;
 304                                 RCU_INIT_POINTER(*nodep, l);
 305                         } else { /* ll: RH, lr: RH+1 */
 306                                 lrl = rcu_deref_locked(lr->avl_left, base);/* lrl: RH or RH-1 */
 307                                 lrr = rcu_deref_locked(lr->avl_right, base);/* lrr: RH or RH-1 */
 308                                 RCU_INIT_POINTER(node->avl_left, lrr);  /* lrr: RH or RH-1 */
 309                                 RCU_INIT_POINTER(node->avl_right, r);   /* r: RH */
 310                                 node->avl_height = rh + 1; /* node: RH+1 */
 311                                 RCU_INIT_POINTER(l->avl_left, ll);      /* ll: RH */
 312                                 RCU_INIT_POINTER(l->avl_right, lrl);    /* lrl: RH or RH-1 */
 313                                 l->avl_height = rh + 1; /* l: RH+1 */
 314                                 RCU_INIT_POINTER(lr->avl_left, l);      /* l: RH+1 */
 315                                 RCU_INIT_POINTER(lr->avl_right, node);  /* node: RH+1 */
 316                                 lr->avl_height = rh + 2;
 317                                 RCU_INIT_POINTER(*nodep, lr);
 318                         }
 319                 } else if (rh > lh + 1) { /* r: LH+2 */
 320                         struct inet_peer *rr, *rl, *rlr, *rll;
 321                         int rlh;
 322                         rr = rcu_deref_locked(r->avl_right, base);
 323                         rl = rcu_deref_locked(r->avl_left, base);
 324                         rlh = node_height(rl);
 325                         if (rlh <= node_height(rr)) {   /* rr: LH+1 */
 326                                 RCU_INIT_POINTER(node->avl_right, rl);  /* rl: LH or LH+1 */
 327                                 RCU_INIT_POINTER(node->avl_left, l);    /* l: LH */
 328                                 node->avl_height = rlh + 1; /* LH+1 or LH+2 */
 329                                 RCU_INIT_POINTER(r->avl_right, rr);     /* rr: LH+1 */
 330                                 RCU_INIT_POINTER(r->avl_left, node);    /* node: LH+1 or LH+2 */
 331                                 r->avl_height = node->avl_height + 1;
 332                                 RCU_INIT_POINTER(*nodep, r);
 333                         } else { /* rr: RH, rl: RH+1 */
 334                                 rlr = rcu_deref_locked(rl->avl_right, base);/* rlr: LH or LH-1 */
 335                                 rll = rcu_deref_locked(rl->avl_left, base);/* 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 static void unlink_from_pool(struct inet_peer *p, struct inet_peer_base *base,
 370                              struct inet_peer __rcu **stack[PEER_MAXDEPTH])
 371 {
 372         struct inet_peer __rcu ***stackptr, ***delp;
 373
 374         if (lookup(&p->daddr, stack, base) != p)
 375                 BUG();
 376         delp = stackptr - 1; /* *delp[0] == p */
 377         if (p->avl_left == peer_avl_empty_rcu) {
 378                 *delp[0] = p->avl_right;
 379                 --stackptr;
 380         } else {
 381                 /* look for a node to insert instead of p */
 382                 struct inet_peer *t;
 383                 t = lookup_rightempty(p, base);
 384                 BUG_ON(rcu_deref_locked(*stackptr[-1], base) != t);
 385                 **--stackptr = t->avl_left;
 386                 /* t is removed, t->daddr > x->daddr for any
 387                  * x in p->avl_left subtree.
 388                  * Put t in the old place of p. */
 389                 RCU_INIT_POINTER(*delp[0], t);
 390                 t->avl_left = p->avl_left;
 391                 t->avl_right = p->avl_right;
 392                 t->avl_height = p->avl_height;
 393                 BUG_ON(delp[1] != &p->avl_left);
 394                 delp[1] = &t->avl_left; /* was &p->avl_left */
 395         }
 396         peer_avl_rebalance(stack, stackptr, base);
 397         base->total--;
 398         call_rcu(&p->rcu, inetpeer_free_rcu);
 399 }
 400
 401 /* perform garbage collect on all items stacked during a lookup */
 402 static int inet_peer_gc(struct inet_peer_base *base,
 403                         struct inet_peer __rcu **stack[PEER_MAXDEPTH],
 404                         struct inet_peer __rcu ***stackptr)
 405 {
 406         struct inet_peer *p, *gchead = NULL;
 407         __u32 delta, ttl;
 408         int cnt = 0;
 409
 410         if (base->total >= inet_peer_threshold)
 411                 ttl = 0; /* be aggressive */
 412         else
 413                 ttl = inet_peer_maxttl
 414                                 - (inet_peer_maxttl - inet_peer_minttl) / HZ *
 415                                         base->total / inet_peer_threshold * HZ;
 416         stackptr--; /* last stack slot is peer_avl_empty */
 417         while (stackptr > stack) {
 418                 stackptr--;
 419                 p = rcu_deref_locked(**stackptr, base);
 420                 if (atomic_read(&p->refcnt) == 0) {
 421                         smp_rmb();
 422                         delta = (__u32)jiffies - p->dtime;
 423                         if (delta >= ttl &&
 424                             atomic_cmpxchg(&p->refcnt, 0, -1) == 0) {
 425                                 p->gc_next = gchead;
 426                                 gchead = p;
 427                         }
 428                 }
 429         }
 430         while ((p = gchead) != NULL) {
 431                 gchead = p->gc_next;
 432                 cnt++;
 433                 unlink_from_pool(p, base, stack);
 434         }
 435         return cnt;
 436 }
 437
 438 struct inet_peer *inet_getpeer(struct inet_peer_base *base,
 439                                const struct inetpeer_addr *daddr,
 440                                int create)
 441 {
 442         struct inet_peer __rcu **stack[PEER_MAXDEPTH], ***stackptr;
 443         struct inet_peer *p;
 444         unsigned int sequence;
 445         int invalidated, gccnt = 0;
 446
 447         flush_check(base, daddr->family);
 448
 449         /* Attempt a lockless lookup first.
 450          * Because of a concurrent writer, we might not find an existing entry.
 451          */
 452         rcu_read_lock();
 453         sequence = read_seqbegin(&base->lock);
 454         p = lookup_rcu(daddr, base);
 455         invalidated = read_seqretry(&base->lock, sequence);
 456         rcu_read_unlock();
 457
 458         if (p)
 459                 return p;
 460
 461         /* If no writer did a change during our lookup, we can return early. */
 462         if (!create && !invalidated)
 463                 return NULL;
 464
 465         /* retry an exact lookup, taking the lock before.
 466          * At least, nodes should be hot in our cache.
 467          */
 468         write_seqlock_bh(&base->lock);
 469 relookup:
 470         p = lookup(daddr, stack, base);
 471         if (p != peer_avl_empty) {
 472                 atomic_inc(&p->refcnt);
 473                 write_sequnlock_bh(&base->lock);
 474                 return p;
 475         }
 476         if (!gccnt) {
 477                 gccnt = inet_peer_gc(base, stack, stackptr);
 478                 if (gccnt && create)
 479                         goto relookup;
 480         }
 481         p = create ? kmem_cache_alloc(peer_cachep, GFP_ATOMIC) : NULL;
 482         if (p) {
 483                 p->daddr = *daddr;
 484                 atomic_set(&p->refcnt, 1);
 485                 atomic_set(&p->rid, 0);
 486                 p->metrics[RTAX_LOCK-1] = INETPEER_METRICS_NEW;
 487                 p->rate_tokens = 0;
 488                 /* 60*HZ is arbitrary, but chosen enough high so that the first
 489                  * calculation of tokens is at its maximum.
 490                  */
 491                 p->rate_last = jiffies - 60*HZ;
 492                 INIT_LIST_HEAD(&p->gc_list);
 493
 494                 /* Link the node. */
 495                 link_to_pool(p, base);
 496                 base->total++;
 497         }
 498         write_sequnlock_bh(&base->lock);
 499
 500         return p;
 501 }
 502 EXPORT_SYMBOL_GPL(inet_getpeer);
 503
 504 void inet_putpeer(struct inet_peer *p)
 505 {
 506         p->dtime = (__u32)jiffies;
 507         smp_mb__before_atomic_dec();
 508         atomic_dec(&p->refcnt);
 509 }
 510 EXPORT_SYMBOL_GPL(inet_putpeer);
 511
 512 /*
 513  *      Check transmit rate limitation for given message.
 514  *      The rate information is held in the inet_peer entries now.
 515  *      This function is generic and could be used for other purposes
 516  *      too. It uses a Token bucket filter as suggested by Alexey Kuznetsov.
 517  *
 518  *      Note that the same inet_peer fields are modified by functions in
 519  *      route.c too, but these work for packet destinations while xrlim_allow
 520  *      works for icmp destinations. This means the rate limiting information
 521  *      for one "ip object" is shared - and these ICMPs are twice limited:
 522  *      by source and by destination.
 523  *
 524  *      RFC 1812: 4.3.2.8 SHOULD be able to limit error message rate
 525  *                        SHOULD allow setting of rate limits
 526  *
 527  *      Shared between ICMPv4 and ICMPv6.
 528  */
 529 #define XRLIM_BURST_FACTOR 6
 530 bool inet_peer_xrlim_allow(struct inet_peer *peer, int timeout)
 531 {
 532         unsigned long now, token;
 533         bool rc = false;
 534
 535         if (!peer)
 536                 return true;
 537
 538         token = peer->rate_tokens;
 539         now = jiffies;
 540         token += now - peer->rate_last;
 541         peer->rate_last = now;
 542         if (token > XRLIM_BURST_FACTOR * timeout)
 543                 token = XRLIM_BURST_FACTOR * timeout;
 544         if (token >= timeout) {
 545                 token -= timeout;
 546                 rc = true;
 547         }
 548         peer->rate_tokens = token;
 549         return rc;
 550 }
 551 EXPORT_SYMBOL(inet_peer_xrlim_allow);
 552
 553 static void inetpeer_inval_rcu(struct rcu_head *head)
 554 {
 555         struct inet_peer *p = container_of(head, struct inet_peer, gc_rcu);
 556
 557         spin_lock_bh(&gc_lock);
 558         list_add_tail(&p->gc_list, &gc_list);
 559         spin_unlock_bh(&gc_lock);
 560
 561         schedule_delayed_work(&gc_work, gc_delay);
 562 }
 563
 564 void inetpeer_invalidate_tree(struct inet_peer_base *base)
 565 {
 566         struct inet_peer *root;
 567
 568         write_seqlock_bh(&base->lock);
 569
 570         root = rcu_deref_locked(base->root, base);
 571         if (root != peer_avl_empty) {
 572                 base->root = peer_avl_empty_rcu;
 573                 base->total = 0;
 574                 call_rcu(&root->gc_rcu, inetpeer_inval_rcu);
 575         }
 576
 577         write_sequnlock_bh(&base->lock);
 578 }
 579 EXPORT_SYMBOL(inetpeer_invalidate_tree);