fs/lockd/host.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * linux/fs/lockd/host.c
   4  *
   5  * Management for NLM peer hosts. The nlm_host struct is shared
   6  * between client and server implementation. The only reason to
   7  * do so is to reduce code bloat.
   8  *
   9  * Copyright (C) 1996, Olaf Kirch <okir@monad.swb.de>
  10  */
  11
  12 #include <linux/types.h>
  13 #include <linux/slab.h>
  14 #include <linux/in.h>
  15 #include <linux/in6.h>
  16 #include <linux/sunrpc/clnt.h>
  17 #include <linux/sunrpc/addr.h>
  18 #include <linux/sunrpc/svc.h>
  19 #include <linux/lockd/lockd.h>
  20 #include <linux/mutex.h>
  21
  22 #include <linux/sunrpc/svc_xprt.h>
  23
  24 #include <net/ipv6.h>
  25
  26 #include "netns.h"
  27
  28 #define NLMDBG_FACILITY         NLMDBG_HOSTCACHE
  29 #define NLM_HOST_NRHASH         32
  30 #define NLM_HOST_REBIND         (60 * HZ)
  31 #define NLM_HOST_EXPIRE         (300 * HZ)
  32 #define NLM_HOST_COLLECT        (120 * HZ)
  33
  34 static struct hlist_head        nlm_server_hosts[NLM_HOST_NRHASH];
  35 static struct hlist_head        nlm_client_hosts[NLM_HOST_NRHASH];
  36
  37 #define for_each_host(host, chain, table) \
  38         for ((chain) = (table); \
  39              (chain) < (table) + NLM_HOST_NRHASH; ++(chain)) \
  40                 hlist_for_each_entry((host), (chain), h_hash)
  41
  42 #define for_each_host_safe(host, next, chain, table) \
  43         for ((chain) = (table); \
  44              (chain) < (table) + NLM_HOST_NRHASH; ++(chain)) \
  45                 hlist_for_each_entry_safe((host), (next), \
  46                                                 (chain), h_hash)
  47
  48 static unsigned long            nrhosts;
  49 static DEFINE_MUTEX(nlm_host_mutex);
  50
  51 static void                     nlm_gc_hosts(struct net *net);
  52
  53 struct nlm_lookup_host_info {
  54         const int               server;         /* search for server|client */
  55         const struct sockaddr   *sap;           /* address to search for */
  56         const size_t            salen;          /* it's length */
  57         const unsigned short    protocol;       /* transport to search for*/
  58         const u32               version;        /* NLM version to search for */
  59         const char              *hostname;      /* remote's hostname */
  60         const size_t            hostname_len;   /* it's length */
  61         const int               noresvport;     /* use non-priv port */
  62         struct net              *net;           /* network namespace to bind */
  63         const struct cred       *cred;
  64 };
  65
  66 /*
  67  * Hash function must work well on big- and little-endian platforms
  68  */
  69 static unsigned int __nlm_hash32(const __be32 n)
  70 {
  71         unsigned int hash = (__force u32)n ^ ((__force u32)n >> 16);
  72         return hash ^ (hash >> 8);
  73 }
  74
  75 static unsigned int __nlm_hash_addr4(const struct sockaddr *sap)
  76 {
  77         const struct sockaddr_in *sin = (struct sockaddr_in *)sap;
  78         return __nlm_hash32(sin->sin_addr.s_addr);
  79 }
  80
  81 static unsigned int __nlm_hash_addr6(const struct sockaddr *sap)
  82 {
  83         const struct sockaddr_in6 *sin6 = (struct sockaddr_in6 *)sap;
  84         const struct in6_addr addr = sin6->sin6_addr;
  85         return __nlm_hash32(addr.s6_addr32[0]) ^
  86                __nlm_hash32(addr.s6_addr32[1]) ^
  87                __nlm_hash32(addr.s6_addr32[2]) ^
  88                __nlm_hash32(addr.s6_addr32[3]);
  89 }
  90
  91 static unsigned int nlm_hash_address(const struct sockaddr *sap)
  92 {
  93         unsigned int hash;
  94
  95         switch (sap->sa_family) {
  96         case AF_INET:
  97                 hash = __nlm_hash_addr4(sap);
  98                 break;
  99         case AF_INET6:
 100                 hash = __nlm_hash_addr6(sap);
 101                 break;
 102         default:
 103                 hash = 0;
 104         }
 105         return hash & (NLM_HOST_NRHASH - 1);
 106 }
 107
 108 /*
 109  * Allocate and initialize an nlm_host.  Common to both client and server.
 110  */
 111 static struct nlm_host *nlm_alloc_host(struct nlm_lookup_host_info *ni,
 112                                        struct nsm_handle *nsm)
 113 {
 114         struct nlm_host *host = NULL;
 115         unsigned long now = jiffies;
 116
 117         if (nsm != NULL)
 118                 refcount_inc(&nsm->sm_count);
 119         else {
 120                 host = NULL;
 121                 nsm = nsm_get_handle(ni->net, ni->sap, ni->salen,
 122                                         ni->hostname, ni->hostname_len);
 123                 if (unlikely(nsm == NULL)) {
 124                         dprintk("lockd: %s failed; no nsm handle\n",
 125                                 __func__);
 126                         goto out;
 127                 }
 128         }
 129
 130         host = kmalloc(sizeof(*host), GFP_KERNEL);
 131         if (unlikely(host == NULL)) {
 132                 dprintk("lockd: %s failed; no memory\n", __func__);
 133                 nsm_release(nsm);
 134                 goto out;
 135         }
 136
 137         memcpy(nlm_addr(host), ni->sap, ni->salen);
 138         host->h_addrlen    = ni->salen;
 139         rpc_set_port(nlm_addr(host), 0);
 140         host->h_srcaddrlen = 0;
 141
 142         host->h_rpcclnt    = NULL;
 143         host->h_name       = nsm->sm_name;
 144         host->h_version    = ni->version;
 145         host->h_proto      = ni->protocol;
 146         host->h_reclaiming = 0;
 147         host->h_server     = ni->server;
 148         host->h_noresvport = ni->noresvport;
 149         host->h_inuse      = 0;
 150         init_waitqueue_head(&host->h_gracewait);
 151         init_rwsem(&host->h_rwsem);
 152         host->h_state      = 0;
 153         host->h_nsmstate   = 0;
 154         host->h_pidcount   = 0;
 155         refcount_set(&host->h_count, 1);
 156         mutex_init(&host->h_mutex);
 157         host->h_nextrebind = now + NLM_HOST_REBIND;
 158         host->h_expires    = now + NLM_HOST_EXPIRE;
 159         INIT_LIST_HEAD(&host->h_lockowners);
 160         spin_lock_init(&host->h_lock);
 161         INIT_LIST_HEAD(&host->h_granted);
 162         INIT_LIST_HEAD(&host->h_reclaim);
 163         host->h_nsmhandle  = nsm;
 164         host->h_addrbuf    = nsm->sm_addrbuf;
 165         host->net          = ni->net;
 166         host->h_cred       = get_cred(ni->cred);
 167         strscpy(host->nodename, utsname()->nodename, sizeof(host->nodename));
 168
 169 out:
 170         return host;
 171 }
 172
 173 /*
 174  * Destroy an nlm_host and free associated resources
 175  *
 176  * Caller must hold nlm_host_mutex.
 177  */
 178 static void nlm_destroy_host_locked(struct nlm_host *host)
 179 {
 180         struct rpc_clnt *clnt;
 181         struct lockd_net *ln = net_generic(host->net, lockd_net_id);
 182
 183         dprintk("lockd: destroy host %s\n", host->h_name);
 184
 185         hlist_del_init(&host->h_hash);
 186
 187         nsm_unmonitor(host);
 188         nsm_release(host->h_nsmhandle);
 189
 190         clnt = host->h_rpcclnt;
 191         if (clnt != NULL)
 192                 rpc_shutdown_client(clnt);
 193         put_cred(host->h_cred);
 194         kfree(host);
 195
 196         ln->nrhosts--;
 197         nrhosts--;
 198 }
 199
 200 /**
 201  * nlmclnt_lookup_host - Find an NLM host handle matching a remote server
 202  * @sap: network address of server
 203  * @salen: length of server address
 204  * @protocol: transport protocol to use
 205  * @version: NLM protocol version
 206  * @hostname: '\0'-terminated hostname of server
 207  * @noresvport: 1 if non-privileged port should be used
 208  * @net: pointer to net namespace
 209  * @cred: pointer to cred
 210  *
 211  * Returns an nlm_host structure that matches the passed-in
 212  * [server address, transport protocol, NLM version, server hostname].
 213  * If one doesn't already exist in the host cache, a new handle is
 214  * created and returned.
 215  */
 216 struct nlm_host *nlmclnt_lookup_host(const struct sockaddr *sap,
 217                                      const size_t salen,
 218                                      const unsigned short protocol,
 219                                      const u32 version,
 220                                      const char *hostname,
 221                                      int noresvport,
 222                                      struct net *net,
 223                                      const struct cred *cred)
 224 {
 225         struct nlm_lookup_host_info ni = {
 226                 .server         = 0,
 227                 .sap            = sap,
 228                 .salen          = salen,
 229                 .protocol       = protocol,
 230                 .version        = version,
 231                 .hostname       = hostname,
 232                 .hostname_len   = strlen(hostname),
 233                 .noresvport     = noresvport,
 234                 .net            = net,
 235                 .cred           = cred,
 236         };
 237         struct hlist_head *chain;
 238         struct nlm_host *host;
 239         struct nsm_handle *nsm = NULL;
 240         struct lockd_net *ln = net_generic(net, lockd_net_id);
 241
 242         dprintk("lockd: %s(host='%s', vers=%u, proto=%s)\n", __func__,
 243                         (hostname ? hostname : "<none>"), version,
 244                         (protocol == IPPROTO_UDP ? "udp" : "tcp"));
 245
 246         mutex_lock(&nlm_host_mutex);
 247
 248         chain = &nlm_client_hosts[nlm_hash_address(sap)];
 249         hlist_for_each_entry(host, chain, h_hash) {
 250                 if (host->net != net)
 251                         continue;
 252                 if (!rpc_cmp_addr(nlm_addr(host), sap))
 253                         continue;
 254
 255                 /* Same address. Share an NSM handle if we already have one */
 256                 if (nsm == NULL)
 257                         nsm = host->h_nsmhandle;
 258
 259                 if (host->h_proto != protocol)
 260                         continue;
 261                 if (host->h_version != version)
 262                         continue;
 263
 264                 nlm_get_host(host);
 265                 dprintk("lockd: %s found host %s (%s)\n", __func__,
 266                         host->h_name, host->h_addrbuf);
 267                 goto out;
 268         }
 269
 270         host = nlm_alloc_host(&ni, nsm);
 271         if (unlikely(host == NULL))
 272                 goto out;
 273
 274         hlist_add_head(&host->h_hash, chain);
 275         ln->nrhosts++;
 276         nrhosts++;
 277
 278         dprintk("lockd: %s created host %s (%s)\n", __func__,
 279                 host->h_name, host->h_addrbuf);
 280
 281 out:
 282         mutex_unlock(&nlm_host_mutex);
 283         return host;
 284 }
 285
 286 /**
 287  * nlmclnt_release_host - release client nlm_host
 288  * @host: nlm_host to release
 289  *
 290  */
 291 void nlmclnt_release_host(struct nlm_host *host)
 292 {
 293         if (host == NULL)
 294                 return;
 295
 296         dprintk("lockd: release client host %s\n", host->h_name);
 297
 298         WARN_ON_ONCE(host->h_server);
 299
 300         if (refcount_dec_and_mutex_lock(&host->h_count, &nlm_host_mutex)) {
 301                 WARN_ON_ONCE(!list_empty(&host->h_lockowners));
 302                 WARN_ON_ONCE(!list_empty(&host->h_granted));
 303                 WARN_ON_ONCE(!list_empty(&host->h_reclaim));
 304
 305                 nlm_destroy_host_locked(host);
 306                 mutex_unlock(&nlm_host_mutex);
 307         }
 308 }
 309
 310 /**
 311  * nlmsvc_lookup_host - Find an NLM host handle matching a remote client
 312  * @rqstp: incoming NLM request
 313  * @hostname: name of client host
 314  * @hostname_len: length of client hostname
 315  *
 316  * Returns an nlm_host structure that matches the [client address,
 317  * transport protocol, NLM version, client hostname] of the passed-in
 318  * NLM request.  If one doesn't already exist in the host cache, a
 319  * new handle is created and returned.
 320  *
 321  * Before possibly creating a new nlm_host, construct a sockaddr
 322  * for a specific source address in case the local system has
 323  * multiple network addresses.  The family of the address in
 324  * rq_daddr is guaranteed to be the same as the family of the
 325  * address in rq_addr, so it's safe to use the same family for
 326  * the source address.
 327  */
 328 struct nlm_host *nlmsvc_lookup_host(const struct svc_rqst *rqstp,
 329                                     const char *hostname,
 330                                     const size_t hostname_len)
 331 {
 332         struct hlist_head *chain;
 333         struct nlm_host *host = NULL;
 334         struct nsm_handle *nsm = NULL;
 335         struct sockaddr *src_sap = svc_daddr(rqstp);
 336         size_t src_len = rqstp->rq_daddrlen;
 337         struct net *net = SVC_NET(rqstp);
 338         struct nlm_lookup_host_info ni = {
 339                 .server         = 1,
 340                 .sap            = svc_addr(rqstp),
 341                 .salen          = rqstp->rq_addrlen,
 342                 .protocol       = rqstp->rq_prot,
 343                 .version        = rqstp->rq_vers,
 344                 .hostname       = hostname,
 345                 .hostname_len   = hostname_len,
 346                 .net            = net,
 347         };
 348         struct lockd_net *ln = net_generic(net, lockd_net_id);
 349
 350         dprintk("lockd: %s(host='%.*s', vers=%u, proto=%s)\n", __func__,
 351                         (int)hostname_len, hostname, rqstp->rq_vers,
 352                         (rqstp->rq_prot == IPPROTO_UDP ? "udp" : "tcp"));
 353
 354         mutex_lock(&nlm_host_mutex);
 355
 356         if (time_after_eq(jiffies, ln->next_gc))
 357                 nlm_gc_hosts(net);
 358
 359         chain = &nlm_server_hosts[nlm_hash_address(ni.sap)];
 360         hlist_for_each_entry(host, chain, h_hash) {
 361                 if (host->net != net)
 362                         continue;
 363                 if (!rpc_cmp_addr(nlm_addr(host), ni.sap))
 364                         continue;
 365
 366                 /* Same address. Share an NSM handle if we already have one */
 367                 if (nsm == NULL)
 368                         nsm = host->h_nsmhandle;
 369
 370                 if (host->h_proto != ni.protocol)
 371                         continue;
 372                 if (host->h_version != ni.version)
 373                         continue;
 374                 if (!rpc_cmp_addr(nlm_srcaddr(host), src_sap))
 375                         continue;
 376
 377                 /* Move to head of hash chain. */
 378                 hlist_del(&host->h_hash);
 379                 hlist_add_head(&host->h_hash, chain);
 380
 381                 nlm_get_host(host);
 382                 dprintk("lockd: %s found host %s (%s)\n",
 383                         __func__, host->h_name, host->h_addrbuf);
 384                 goto out;
 385         }
 386
 387         host = nlm_alloc_host(&ni, nsm);
 388         if (unlikely(host == NULL))
 389                 goto out;
 390
 391         memcpy(nlm_srcaddr(host), src_sap, src_len);
 392         host->h_srcaddrlen = src_len;
 393         hlist_add_head(&host->h_hash, chain);
 394         ln->nrhosts++;
 395         nrhosts++;
 396
 397         refcount_inc(&host->h_count);
 398
 399         dprintk("lockd: %s created host %s (%s)\n",
 400                 __func__, host->h_name, host->h_addrbuf);
 401
 402 out:
 403         mutex_unlock(&nlm_host_mutex);
 404         return host;
 405 }
 406
 407 /**
 408  * nlmsvc_release_host - release server nlm_host
 409  * @host: nlm_host to release
 410  *
 411  * Host is destroyed later in nlm_gc_host().
 412  */
 413 void nlmsvc_release_host(struct nlm_host *host)
 414 {
 415         if (host == NULL)
 416                 return;
 417
 418         dprintk("lockd: release server host %s\n", host->h_name);
 419
 420         WARN_ON_ONCE(!host->h_server);
 421         refcount_dec(&host->h_count);
 422 }
 423
 424 /*
 425  * Create the NLM RPC client for an NLM peer
 426  */
 427 struct rpc_clnt *
 428 nlm_bind_host(struct nlm_host *host)
 429 {
 430         struct rpc_clnt *clnt;
 431
 432         dprintk("lockd: nlm_bind_host %s (%s)\n",
 433                         host->h_name, host->h_addrbuf);
 434
 435         /* Lock host handle */
 436         mutex_lock(&host->h_mutex);
 437
 438         /* If we've already created an RPC client, check whether
 439          * RPC rebind is required
 440          */
 441         if ((clnt = host->h_rpcclnt) != NULL) {
 442                 nlm_rebind_host(host);
 443         } else {
 444                 unsigned long increment = nlmsvc_timeout;
 445                 struct rpc_timeout timeparms = {
 446                         .to_initval     = increment,
 447                         .to_increment   = increment,
 448                         .to_maxval      = increment * 6UL,
 449                         .to_retries     = 5U,
 450                 };
 451                 struct rpc_create_args args = {
 452                         .net            = host->net,
 453                         .protocol       = host->h_proto,
 454                         .address        = nlm_addr(host),
 455                         .addrsize       = host->h_addrlen,
 456                         .timeout        = &timeparms,
 457                         .servername     = host->h_name,
 458                         .program        = &nlm_program,
 459                         .version        = host->h_version,
 460                         .authflavor     = RPC_AUTH_UNIX,
 461                         .flags          = (RPC_CLNT_CREATE_NOPING |
 462                                            RPC_CLNT_CREATE_AUTOBIND |
 463                                            RPC_CLNT_CREATE_REUSEPORT),
 464                         .cred           = host->h_cred,
 465                 };
 466
 467                 /*
 468                  * lockd retries server side blocks automatically so we want
 469                  * those to be soft RPC calls. Client side calls need to be
 470                  * hard RPC tasks.
 471                  */
 472                 if (!host->h_server)
 473                         args.flags |= RPC_CLNT_CREATE_HARDRTRY;
 474                 if (host->h_noresvport)
 475                         args.flags |= RPC_CLNT_CREATE_NONPRIVPORT;
 476                 if (host->h_srcaddrlen)
 477                         args.saddress = nlm_srcaddr(host);
 478
 479                 clnt = rpc_create(&args);
 480                 if (!IS_ERR(clnt))
 481                         host->h_rpcclnt = clnt;
 482                 else {
 483                         printk("lockd: couldn't create RPC handle for %s\n", host->h_name);
 484                         clnt = NULL;
 485                 }
 486         }
 487
 488         mutex_unlock(&host->h_mutex);
 489         return clnt;
 490 }
 491
 492 /**
 493  * nlm_rebind_host - If needed, force a portmap lookup of the peer's lockd port
 494  * @host: NLM host handle for peer
 495  *
 496  * This is not needed when using a connection-oriented protocol, such as TCP.
 497  * The existing autobind mechanism is sufficient to force a rebind when
 498  * required, e.g. on connection state transitions.
 499  */
 500 void
 501 nlm_rebind_host(struct nlm_host *host)
 502 {
 503         if (host->h_proto != IPPROTO_UDP)
 504                 return;
 505
 506         if (host->h_rpcclnt && time_after_eq(jiffies, host->h_nextrebind)) {
 507                 rpc_force_rebind(host->h_rpcclnt);
 508                 host->h_nextrebind = jiffies + NLM_HOST_REBIND;
 509         }
 510 }
 511
 512 /*
 513  * Increment NLM host count
 514  */
 515 struct nlm_host * nlm_get_host(struct nlm_host *host)
 516 {
 517         if (host) {
 518                 dprintk("lockd: get host %s\n", host->h_name);
 519                 refcount_inc(&host->h_count);
 520                 host->h_expires = jiffies + NLM_HOST_EXPIRE;
 521         }
 522         return host;
 523 }
 524
 525 static struct nlm_host *next_host_state(struct hlist_head *cache,
 526                                         struct nsm_handle *nsm,
 527                                         const struct nlm_reboot *info)
 528 {
 529         struct nlm_host *host;
 530         struct hlist_head *chain;
 531
 532         mutex_lock(&nlm_host_mutex);
 533         for_each_host(host, chain, cache) {
 534                 if (host->h_nsmhandle == nsm
 535                     && host->h_nsmstate != info->state) {
 536                         host->h_nsmstate = info->state;
 537                         host->h_state++;
 538
 539                         nlm_get_host(host);
 540                         mutex_unlock(&nlm_host_mutex);
 541                         return host;
 542                 }
 543         }
 544
 545         mutex_unlock(&nlm_host_mutex);
 546         return NULL;
 547 }
 548
 549 /**
 550  * nlm_host_rebooted - Release all resources held by rebooted host
 551  * @net:  network namespace
 552  * @info: pointer to decoded results of NLM_SM_NOTIFY call
 553  *
 554  * We were notified that the specified host has rebooted.  Release
 555  * all resources held by that peer.
 556  */
 557 void nlm_host_rebooted(const struct net *net, const struct nlm_reboot *info)
 558 {
 559         struct nsm_handle *nsm;
 560         struct nlm_host *host;
 561
 562         nsm = nsm_reboot_lookup(net, info);
 563         if (unlikely(nsm == NULL))
 564                 return;
 565
 566         /* Mark all hosts tied to this NSM state as having rebooted.
 567          * We run the loop repeatedly, because we drop the host table
 568          * lock for this.
 569          * To avoid processing a host several times, we match the nsmstate.
 570          */
 571         while ((host = next_host_state(nlm_server_hosts, nsm, info)) != NULL) {
 572                 nlmsvc_free_host_resources(host);
 573                 nlmsvc_release_host(host);
 574         }
 575         while ((host = next_host_state(nlm_client_hosts, nsm, info)) != NULL) {
 576                 nlmclnt_recovery(host);
 577                 nlmclnt_release_host(host);
 578         }
 579
 580         nsm_release(nsm);
 581 }
 582
 583 static void nlm_complain_hosts(struct net *net)
 584 {
 585         struct hlist_head *chain;
 586         struct nlm_host *host;
 587
 588         if (net) {
 589                 struct lockd_net *ln = net_generic(net, lockd_net_id);
 590
 591                 if (ln->nrhosts == 0)
 592                         return;
 593                 pr_warn("lockd: couldn't shutdown host module for net %x!\n",
 594                         net->ns.inum);
 595                 dprintk("lockd: %lu hosts left in net %x:\n", ln->nrhosts,
 596                         net->ns.inum);
 597         } else {
 598                 if (nrhosts == 0)
 599                         return;
 600                 printk(KERN_WARNING "lockd: couldn't shutdown host module!\n");
 601                 dprintk("lockd: %lu hosts left:\n", nrhosts);
 602         }
 603
 604         for_each_host(host, chain, nlm_server_hosts) {
 605                 if (net && host->net != net)
 606                         continue;
 607                 dprintk("       %s (cnt %d use %d exp %ld net %x)\n",
 608                         host->h_name, refcount_read(&host->h_count),
 609                         host->h_inuse, host->h_expires, host->net->ns.inum);
 610         }
 611 }
 612
 613 void
 614 nlm_shutdown_hosts_net(struct net *net)
 615 {
 616         struct hlist_head *chain;
 617         struct nlm_host *host;
 618
 619         mutex_lock(&nlm_host_mutex);
 620
 621         /* First, make all hosts eligible for gc */
 622         dprintk("lockd: nuking all hosts in net %x...\n",
 623                 net ? net->ns.inum : 0);
 624         for_each_host(host, chain, nlm_server_hosts) {
 625                 if (net && host->net != net)
 626                         continue;
 627                 host->h_expires = jiffies - 1;
 628                 if (host->h_rpcclnt) {
 629                         rpc_shutdown_client(host->h_rpcclnt);
 630                         host->h_rpcclnt = NULL;
 631                 }
 632                 nlmsvc_free_host_resources(host);
 633         }
 634
 635         /* Then, perform a garbage collection pass */
 636         nlm_gc_hosts(net);
 637         nlm_complain_hosts(net);
 638         mutex_unlock(&nlm_host_mutex);
 639 }
 640
 641 /*
 642  * Shut down the hosts module.
 643  * Note that this routine is called only at server shutdown time.
 644  */
 645 void
 646 nlm_shutdown_hosts(void)
 647 {
 648         dprintk("lockd: shutting down host module\n");
 649         nlm_shutdown_hosts_net(NULL);
 650 }
 651
 652 /*
 653  * Garbage collect any unused NLM hosts.
 654  * This GC combines reference counting for async operations with
 655  * mark & sweep for resources held by remote clients.
 656  */
 657 static void
 658 nlm_gc_hosts(struct net *net)
 659 {
 660         struct hlist_head *chain;
 661         struct hlist_node *next;
 662         struct nlm_host *host;
 663
 664         dprintk("lockd: host garbage collection for net %x\n",
 665                 net ? net->ns.inum : 0);
 666         for_each_host(host, chain, nlm_server_hosts) {
 667                 if (net && host->net != net)
 668                         continue;
 669                 host->h_inuse = 0;
 670         }
 671
 672         /* Mark all hosts that hold locks, blocks or shares */
 673         nlmsvc_mark_resources(net);
 674
 675         for_each_host_safe(host, next, chain, nlm_server_hosts) {
 676                 if (net && host->net != net)
 677                         continue;
 678                 if (host->h_inuse || time_before(jiffies, host->h_expires)) {
 679                         dprintk("nlm_gc_hosts skipping %s "
 680                                 "(cnt %d use %d exp %ld net %x)\n",
 681                                 host->h_name, refcount_read(&host->h_count),
 682                                 host->h_inuse, host->h_expires,
 683                                 host->net->ns.inum);
 684                         continue;
 685                 }
 686                 if (refcount_dec_if_one(&host->h_count))
 687                         nlm_destroy_host_locked(host);
 688         }
 689
 690         if (net) {
 691                 struct lockd_net *ln = net_generic(net, lockd_net_id);
 692
 693                 ln->next_gc = jiffies + NLM_HOST_COLLECT;
 694         }
 695 }