lustre/ptlrpc/pinger.c

   1 /*
   2  * GPL HEADER START
   3  *
   4  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   5  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License version 2 only,
   8  * as published by the Free Software Foundation.
   9  *
  10  * This program is distributed in the hope that it will be useful, but
  11  * WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13  * General Public License version 2 for more details (a copy is included
  14  * in the LICENSE file that accompanied this code).
  15  *
  16  * You should have received a copy of the GNU General Public License
  17  * version 2 along with this program; If not, see
  18  * http://www.gnu.org/licenses/gpl-2.0.html
  19  *
  20  * GPL HEADER END
  21  */
  22 /*
  23  * Copyright (c) 2003, 2010, Oracle and/or its affiliates. All rights reserved.
  24  * Use is subject to license terms.
  25  *
  26  * Copyright (c) 2011, 2015, Intel Corporation.
  27  */
  28 /*
  29  * This file is part of Lustre, http://www.lustre.org/
  30  * Lustre is a trademark of Sun Microsystems, Inc.
  31  *
  32  * lustre/ptlrpc/pinger.c
  33  *
  34  * Portal-RPC reconnection and replay operations, for use in recovery.
  35  */
  36
  37 #define DEBUG_SUBSYSTEM S_RPC
  38
  39 #include <linux/kthread.h>
  40 #include <linux/workqueue.h>
  41 #include <obd_support.h>
  42 #include <obd_class.h>
  43 #include "ptlrpc_internal.h"
  44
  45 static int suppress_pings;
  46 module_param(suppress_pings, int, 0644);
  47 MODULE_PARM_DESC(suppress_pings, "Suppress pings");
  48
  49 struct mutex pinger_mutex;
  50 static struct list_head pinger_imports =
  51                 LIST_HEAD_INIT(pinger_imports);
  52 static struct list_head timeout_list =
  53                 LIST_HEAD_INIT(timeout_list);
  54
  55 int ptlrpc_pinger_suppress_pings()
  56 {
  57         return suppress_pings;
  58 }
  59 EXPORT_SYMBOL(ptlrpc_pinger_suppress_pings);
  60
  61 struct ptlrpc_request *
  62 ptlrpc_prep_ping(struct obd_import *imp)
  63 {
  64         struct ptlrpc_request *req;
  65
  66         req = ptlrpc_request_alloc_pack(imp, &RQF_OBD_PING,
  67                                         LUSTRE_OBD_VERSION, OBD_PING);
  68         if (req) {
  69                 ptlrpc_request_set_replen(req);
  70                 req->rq_no_resend = req->rq_no_delay = 1;
  71         }
  72         return req;
  73 }
  74
  75 int ptlrpc_obd_ping(struct obd_device *obd)
  76 {
  77         int rc;
  78         struct ptlrpc_request *req;
  79         ENTRY;
  80
  81         req = ptlrpc_prep_ping(obd->u.cli.cl_import);
  82         if (req == NULL)
  83                 RETURN(-ENOMEM);
  84
  85         req->rq_send_state = LUSTRE_IMP_FULL;
  86
  87         rc = ptlrpc_queue_wait(req);
  88
  89         ptlrpc_req_finished(req);
  90
  91         RETURN(rc);
  92 }
  93 EXPORT_SYMBOL(ptlrpc_obd_ping);
  94
  95 static int ptlrpc_ping(struct obd_import *imp)
  96 {
  97         struct ptlrpc_request   *req;
  98         ENTRY;
  99
 100         req = ptlrpc_prep_ping(imp);
 101         if (req == NULL) {
 102                 CERROR("OOM trying to ping %s->%s\n",
 103                        imp->imp_obd->obd_uuid.uuid,
 104                        obd2cli_tgt(imp->imp_obd));
 105                 RETURN(-ENOMEM);
 106         }
 107
 108         DEBUG_REQ(D_INFO, req, "pinging %s->%s",
 109                   imp->imp_obd->obd_uuid.uuid, obd2cli_tgt(imp->imp_obd));
 110         ptlrpcd_add_req(req);
 111
 112         RETURN(0);
 113 }
 114
 115 static void ptlrpc_update_next_ping(struct obd_import *imp, int soon)
 116 {
 117 #ifdef ENABLE_PINGER
 118         time64_t time = soon ? PING_INTERVAL_SHORT : PING_INTERVAL;
 119
 120         if (imp->imp_state == LUSTRE_IMP_DISCON) {
 121                 time64_t dtime = max_t(time64_t, CONNECTION_SWITCH_MIN,
 122                                        AT_OFF ? 0 :
 123                                        at_get(&imp->imp_at.iat_net_latency));
 124                 time = min(time, dtime);
 125         }
 126         imp->imp_next_ping = ktime_get_seconds() + time;
 127 #endif /* ENABLE_PINGER */
 128 }
 129
 130 void ptlrpc_ping_import_soon(struct obd_import *imp)
 131 {
 132         imp->imp_next_ping = ktime_get_seconds();
 133 }
 134
 135 static inline int imp_is_deactive(struct obd_import *imp)
 136 {
 137         return (imp->imp_deactive ||
 138                 OBD_FAIL_CHECK(OBD_FAIL_PTLRPC_IMP_DEACTIVE));
 139 }
 140
 141 static inline time64_t ptlrpc_next_reconnect(struct obd_import *imp)
 142 {
 143         if (imp->imp_server_timeout)
 144                 return ktime_get_seconds() + (obd_timeout >> 1);
 145         else
 146                 return ktime_get_seconds() + obd_timeout;
 147 }
 148
 149 static time64_t pinger_check_timeout(time64_t time)
 150 {
 151         struct timeout_item *item;
 152         time64_t timeout = PING_INTERVAL;
 153
 154         /* This list is sorted in increasing timeout order */
 155         mutex_lock(&pinger_mutex);
 156         list_for_each_entry(item, &timeout_list, ti_chain) {
 157                 time64_t ti_timeout = item->ti_timeout;
 158
 159                 if (timeout > ti_timeout)
 160                         timeout = ti_timeout;
 161                 break;
 162         }
 163         mutex_unlock(&pinger_mutex);
 164
 165         return time + timeout - ktime_get_seconds();
 166 }
 167
 168 static bool ir_up;
 169
 170 void ptlrpc_pinger_ir_up(void)
 171 {
 172         CDEBUG(D_HA, "IR up\n");
 173         ir_up = true;
 174 }
 175 EXPORT_SYMBOL(ptlrpc_pinger_ir_up);
 176
 177 void ptlrpc_pinger_ir_down(void)
 178 {
 179         CDEBUG(D_HA, "IR down\n");
 180         ir_up = false;
 181 }
 182 EXPORT_SYMBOL(ptlrpc_pinger_ir_down);
 183
 184 static void ptlrpc_pinger_process_import(struct obd_import *imp,
 185                                          time64_t this_ping)
 186 {
 187         int level;
 188         int force;
 189         int force_next;
 190         int suppress;
 191
 192         spin_lock(&imp->imp_lock);
 193
 194         level = imp->imp_state;
 195         force = imp->imp_force_verify;
 196         force_next = imp->imp_force_next_verify;
 197         /*
 198          * This will be used below only if the import is "FULL".
 199          */
 200         suppress = ir_up && OCD_HAS_FLAG(&imp->imp_connect_data, PINGLESS);
 201
 202         imp->imp_force_verify = 0;
 203
 204         if (imp->imp_next_ping - 5 >= this_ping && !force) {
 205                 spin_unlock(&imp->imp_lock);
 206                 return;
 207         }
 208
 209         imp->imp_force_next_verify = 0;
 210
 211         spin_unlock(&imp->imp_lock);
 212
 213         CDEBUG(level == LUSTRE_IMP_FULL ? D_INFO : D_HA, "%s->%s: level %s/%u "
 214                "force %u force_next %u deactive %u pingable %u suppress %u\n",
 215                imp->imp_obd->obd_uuid.uuid, obd2cli_tgt(imp->imp_obd),
 216                ptlrpc_import_state_name(level), level, force, force_next,
 217                imp->imp_deactive, imp->imp_pingable, suppress);
 218
 219         if (level == LUSTRE_IMP_DISCON && !imp_is_deactive(imp)) {
 220                 /* wait for a while before trying recovery again */
 221                 imp->imp_next_ping = ptlrpc_next_reconnect(imp);
 222                 if (!imp->imp_no_pinger_recover)
 223                         ptlrpc_initiate_recovery(imp);
 224         } else if (level != LUSTRE_IMP_FULL ||
 225                    imp->imp_obd->obd_no_recov ||
 226                    imp_is_deactive(imp)) {
 227                 CDEBUG(D_HA, "%s->%s: not pinging (in recovery "
 228                        "or recovery disabled: %s)\n",
 229                        imp->imp_obd->obd_uuid.uuid, obd2cli_tgt(imp->imp_obd),
 230                        ptlrpc_import_state_name(level));
 231                 if (force) {
 232                         spin_lock(&imp->imp_lock);
 233                         imp->imp_force_verify = 1;
 234                         spin_unlock(&imp->imp_lock);
 235                 }
 236         } else if ((imp->imp_pingable && !suppress) || force_next || force) {
 237                 ptlrpc_ping(imp);
 238         }
 239 }
 240
 241 static struct workqueue_struct *pinger_wq;
 242 static void ptlrpc_pinger_main(struct work_struct *ws);
 243 static DECLARE_DELAYED_WORK(ping_work, ptlrpc_pinger_main);
 244
 245 static void ptlrpc_pinger_main(struct work_struct *ws)
 246 {
 247         time64_t this_ping = ktime_get_seconds();
 248         time64_t time_to_next_wake;
 249         struct timeout_item *item;
 250         struct obd_import *imp;
 251         struct list_head *iter;
 252
 253         do {
 254                 mutex_lock(&pinger_mutex);
 255                 list_for_each_entry(item, &timeout_list, ti_chain)
 256                         item->ti_cb(item, item->ti_cb_data);
 257
 258                 list_for_each(iter, &pinger_imports) {
 259                         imp = list_entry(iter, struct obd_import,
 260                                          imp_pinger_chain);
 261
 262                         ptlrpc_pinger_process_import(imp, this_ping);
 263                         /* obd_timeout might have changed */
 264                         if (imp->imp_pingable && imp->imp_next_ping &&
 265                             imp->imp_next_ping > this_ping + PING_INTERVAL)
 266                                 ptlrpc_update_next_ping(imp, 0);
 267                 }
 268                 mutex_unlock(&pinger_mutex);
 269                 /* update memory usage info */
 270                 obd_update_maxusage();
 271
 272                 /* Wait until the next ping time, or until we're stopped. */
 273                 time_to_next_wake = pinger_check_timeout(this_ping);
 274                 /* The ping sent by ptlrpc_send_rpc may get sent out
 275                  * say .01 second after this.
 276                  * ptlrpc_pinger_sending_on_import will then set the
 277                  * next ping time to next_ping + .01 sec, which means
 278                  * we will SKIP the next ping at next_ping, and the
 279                  * ping will get sent 2 timeouts from now!  Beware. */
 280                 CDEBUG(D_INFO, "next wakeup in %lld (%lld)\n",
 281                        time_to_next_wake, this_ping + PING_INTERVAL);
 282         } while (time_to_next_wake <= 0);
 283
 284         queue_delayed_work(pinger_wq, &ping_work,
 285                            cfs_time_seconds(max(time_to_next_wake, 1LL)));
 286 }
 287
 288 int ptlrpc_start_pinger(void)
 289 {
 290 #ifdef ENABLE_PINGER
 291         if (pinger_wq)
 292                 return -EALREADY;
 293
 294         pinger_wq = alloc_workqueue("ptlrpc_pinger", 0, 1);
 295         if (!pinger_wq) {
 296                 CERROR("cannot start pinger workqueue\n");
 297                 return -ENOMEM;
 298         }
 299
 300         queue_delayed_work(pinger_wq, &ping_work, 0);
 301
 302         if (suppress_pings)
 303                 CWARN("Pings will be suppressed at the request of the "
 304                       "administrator.  The configuration shall meet the "
 305                       "additional requirements described in the manual.  "
 306                       "(Search for the \"suppress_pings\" kernel module "
 307                       "parameter.)\n");
 308 #endif
 309         return 0;
 310 }
 311
 312 int ptlrpc_pinger_remove_timeouts(void);
 313
 314 int ptlrpc_stop_pinger(void)
 315 {
 316 #ifdef ENABLE_PINGER
 317         if (!pinger_wq)
 318                 return -EALREADY;
 319
 320         ptlrpc_pinger_remove_timeouts();
 321
 322         cancel_delayed_work_sync(&ping_work);
 323         destroy_workqueue(pinger_wq);
 324         pinger_wq = NULL;
 325 #endif
 326         return 0;
 327 }
 328
 329 void ptlrpc_pinger_sending_on_import(struct obd_import *imp)
 330 {
 331         ptlrpc_update_next_ping(imp, 0);
 332 }
 333
 334 void ptlrpc_pinger_commit_expected(struct obd_import *imp)
 335 {
 336         ptlrpc_update_next_ping(imp, 1);
 337         assert_spin_locked(&imp->imp_lock);
 338         /*
 339          * Avoid reading stale imp_connect_data.  When not sure if pings are
 340          * expected or not on next connection, we assume they are not and force
 341          * one anyway to guarantee the chance of updating
 342          * imp_peer_committed_transno.
 343          */
 344         if (imp->imp_state != LUSTRE_IMP_FULL ||
 345             OCD_HAS_FLAG(&imp->imp_connect_data, PINGLESS))
 346                 imp->imp_force_next_verify = 1;
 347 }
 348
 349 int ptlrpc_pinger_add_import(struct obd_import *imp)
 350 {
 351         ENTRY;
 352         if (!list_empty(&imp->imp_pinger_chain))
 353                 RETURN(-EALREADY);
 354
 355         mutex_lock(&pinger_mutex);
 356         CDEBUG(D_HA, "adding pingable import %s->%s\n",
 357                imp->imp_obd->obd_uuid.uuid, obd2cli_tgt(imp->imp_obd));
 358         /* if we add to pinger we want recovery on this import */
 359         imp->imp_obd->obd_no_recov = 0;
 360         ptlrpc_update_next_ping(imp, 0);
 361         /* XXX sort, blah blah */
 362         list_add_tail(&imp->imp_pinger_chain, &pinger_imports);
 363         class_import_get(imp);
 364
 365         ptlrpc_pinger_wake_up();
 366         mutex_unlock(&pinger_mutex);
 367
 368         RETURN(0);
 369 }
 370 EXPORT_SYMBOL(ptlrpc_pinger_add_import);
 371
 372 int ptlrpc_pinger_del_import(struct obd_import *imp)
 373 {
 374         ENTRY;
 375
 376         if (list_empty(&imp->imp_pinger_chain))
 377                 RETURN(-ENOENT);
 378
 379         mutex_lock(&pinger_mutex);
 380         list_del_init(&imp->imp_pinger_chain);
 381         CDEBUG(D_HA, "removing pingable import %s->%s\n",
 382                imp->imp_obd->obd_uuid.uuid, obd2cli_tgt(imp->imp_obd));
 383         /* if we remove from pinger we don't want recovery on this import */
 384         imp->imp_obd->obd_no_recov = 1;
 385         class_import_put(imp);
 386         mutex_unlock(&pinger_mutex);
 387         RETURN(0);
 388 }
 389 EXPORT_SYMBOL(ptlrpc_pinger_del_import);
 390
 391 /**
 392  * Register a timeout callback to the pinger list, and the callback will
 393  * be called when timeout happens.
 394  */
 395 static struct timeout_item *ptlrpc_new_timeout(time64_t time,
 396                                                enum timeout_event event,
 397                                                timeout_cb_t cb, void *data)
 398 {
 399         struct timeout_item *ti;
 400
 401         OBD_ALLOC_PTR(ti);
 402         if (!ti)
 403                 return(NULL);
 404
 405         INIT_LIST_HEAD(&ti->ti_obd_list);
 406         INIT_LIST_HEAD(&ti->ti_chain);
 407         ti->ti_timeout = time;
 408         ti->ti_event = event;
 409         ti->ti_cb = cb;
 410         ti->ti_cb_data = data;
 411
 412         return ti;
 413 }
 414
 415 /**
 416  * Register timeout event on the the pinger thread.
 417  * Note: the timeout list is an sorted list with increased timeout value.
 418  */
 419 static struct timeout_item*
 420 ptlrpc_pinger_register_timeout(time64_t time, enum timeout_event event,
 421                                timeout_cb_t cb, void *data)
 422 {
 423         struct timeout_item *item, *tmp;
 424
 425         LASSERT(mutex_is_locked(&pinger_mutex));
 426
 427         list_for_each_entry(item, &timeout_list, ti_chain)
 428                 if (item->ti_event == event)
 429                         goto out;
 430
 431         item = ptlrpc_new_timeout(time, event, cb, data);
 432         if (item) {
 433                 list_for_each_entry_reverse(tmp, &timeout_list, ti_chain) {
 434                         if (tmp->ti_timeout < time) {
 435                                 list_add(&item->ti_chain, &tmp->ti_chain);
 436                                 goto out;
 437                         }
 438                 }
 439                 list_add(&item->ti_chain, &timeout_list);
 440         }
 441 out:
 442         return item;
 443 }
 444
 445 /* Add a client_obd to the timeout event list, when timeout(@time)
 446  * happens, the callback(@cb) will be called.
 447  */
 448 int ptlrpc_add_timeout_client(time64_t time, enum timeout_event event,
 449                               timeout_cb_t cb, void *data,
 450                               struct list_head *obd_list)
 451 {
 452         struct timeout_item *ti;
 453
 454         mutex_lock(&pinger_mutex);
 455         ti = ptlrpc_pinger_register_timeout(time, event, cb, data);
 456         if (!ti) {
 457                 mutex_unlock(&pinger_mutex);
 458                 return (-EINVAL);
 459         }
 460         list_add(obd_list, &ti->ti_obd_list);
 461         mutex_unlock(&pinger_mutex);
 462         return 0;
 463 }
 464 EXPORT_SYMBOL(ptlrpc_add_timeout_client);
 465
 466 int ptlrpc_del_timeout_client(struct list_head *obd_list,
 467                               enum timeout_event event)
 468 {
 469         struct timeout_item *ti = NULL, *item;
 470
 471         if (list_empty(obd_list))
 472                 return 0;
 473         mutex_lock(&pinger_mutex);
 474         list_del_init(obd_list);
 475         /**
 476          * If there are no obd attached to the timeout event
 477          * list, remove this timeout event from the pinger
 478          */
 479         list_for_each_entry(item, &timeout_list, ti_chain) {
 480                 if (item->ti_event == event) {
 481                         ti = item;
 482                         break;
 483                 }
 484         }
 485         LASSERTF(ti != NULL, "ti is NULL !\n");
 486         if (list_empty(&ti->ti_obd_list)) {
 487                 list_del(&ti->ti_chain);
 488                 OBD_FREE_PTR(ti);
 489         }
 490         mutex_unlock(&pinger_mutex);
 491         return 0;
 492 }
 493 EXPORT_SYMBOL(ptlrpc_del_timeout_client);
 494
 495 int ptlrpc_pinger_remove_timeouts(void)
 496 {
 497         struct timeout_item *item, *tmp;
 498
 499         mutex_lock(&pinger_mutex);
 500         list_for_each_entry_safe(item, tmp, &timeout_list, ti_chain) {
 501                 LASSERT(list_empty(&item->ti_obd_list));
 502                 list_del(&item->ti_chain);
 503                 OBD_FREE_PTR(item);
 504         }
 505         mutex_unlock(&pinger_mutex);
 506         return 0;
 507 }
 508
 509 void ptlrpc_pinger_wake_up()
 510 {
 511 #ifdef ENABLE_PINGER
 512         mod_delayed_work(pinger_wq, &ping_work, 0);
 513 #endif
 514 }
 515
 516 /* Ping evictor thread */
 517 #define PET_READY     1
 518 #define PET_TERMINATE 2
 519
 520 static int               pet_refcount = 0;
 521 static int               pet_state;
 522 static wait_queue_head_t pet_waitq;
 523 static struct list_head  pet_list;
 524 static DEFINE_SPINLOCK(pet_lock);
 525
 526 int ping_evictor_wake(struct obd_export *exp)
 527 {
 528         struct obd_device *obd;
 529
 530         spin_lock(&pet_lock);
 531         if (pet_state != PET_READY) {
 532                 /* eventually the new obd will call here again. */
 533                 spin_unlock(&pet_lock);
 534                 return 1;
 535         }
 536
 537         obd = class_exp2obd(exp);
 538         if (list_empty(&obd->obd_evict_list)) {
 539                 class_incref(obd, "evictor", obd);
 540                 list_add(&obd->obd_evict_list, &pet_list);
 541         }
 542         spin_unlock(&pet_lock);
 543
 544         wake_up(&pet_waitq);
 545         return 0;
 546 }
 547
 548 static int ping_evictor_main(void *arg)
 549 {
 550         struct obd_device *obd;
 551         struct obd_export *exp;
 552         struct l_wait_info lwi = { 0 };
 553         time64_t expire_time;
 554
 555         ENTRY;
 556         unshare_fs_struct();
 557
 558         CDEBUG(D_HA, "Starting Ping Evictor\n");
 559         pet_state = PET_READY;
 560         while (1) {
 561                 l_wait_event(pet_waitq, (!list_empty(&pet_list)) ||
 562                             (pet_state == PET_TERMINATE), &lwi);
 563
 564                 /* loop until all obd's will be removed */
 565                 if ((pet_state == PET_TERMINATE) && list_empty(&pet_list))
 566                         break;
 567
 568                 /* we only get here if pet_exp != NULL, and the end of this
 569                  * loop is the only place which sets it NULL again, so lock
 570                  * is not strictly necessary. */
 571                 spin_lock(&pet_lock);
 572                 obd = list_entry(pet_list.next, struct obd_device,
 573                                  obd_evict_list);
 574                 spin_unlock(&pet_lock);
 575
 576                 expire_time = ktime_get_real_seconds() - PING_EVICT_TIMEOUT;
 577
 578                 CDEBUG(D_HA, "evicting all exports of obd %s older than %lld\n",
 579                        obd->obd_name, expire_time);
 580
 581                 /* Exports can't be deleted out of the list while we hold
 582                  * the obd lock (class_unlink_export), which means we can't
 583                  * lose the last ref on the export.  If they've already been
 584                  * removed from the list, we won't find them here. */
 585                 spin_lock(&obd->obd_dev_lock);
 586                 while (!list_empty(&obd->obd_exports_timed)) {
 587                         exp = list_entry(obd->obd_exports_timed.next,
 588                                          struct obd_export,
 589                                          exp_obd_chain_timed);
 590                         if (expire_time > exp->exp_last_request_time) {
 591                                 class_export_get(exp);
 592                                 spin_unlock(&obd->obd_dev_lock);
 593                                 LCONSOLE_WARN("%s: haven't heard from client %s"
 594                                               " (at %s) in %lld seconds. I think"
 595                                               " it's dead, and I am evicting"
 596                                               " it. exp %p, cur %lld expire %lld"
 597                                               " last %lld\n",
 598                                               obd->obd_name,
 599                                               obd_uuid2str(&exp->exp_client_uuid),
 600                                               obd_export_nid2str(exp),
 601                                               ktime_get_real_seconds() -
 602                                               exp->exp_last_request_time,
 603                                               exp, ktime_get_real_seconds(),
 604                                               expire_time,
 605                                               exp->exp_last_request_time);
 606                                 CDEBUG(D_HA, "Last request was at %lld\n",
 607                                        exp->exp_last_request_time);
 608                                 class_fail_export(exp);
 609                                 class_export_put(exp);
 610                                 spin_lock(&obd->obd_dev_lock);
 611                         } else {
 612                                 /* List is sorted, so everyone below is ok */
 613                                 break;
 614                         }
 615                 }
 616                 spin_unlock(&obd->obd_dev_lock);
 617
 618                 spin_lock(&pet_lock);
 619                 list_del_init(&obd->obd_evict_list);
 620                 spin_unlock(&pet_lock);
 621
 622                 class_decref(obd, "evictor", obd);
 623         }
 624         CDEBUG(D_HA, "Exiting Ping Evictor\n");
 625
 626         RETURN(0);
 627 }
 628
 629 void ping_evictor_start(void)
 630 {
 631         struct task_struct *task;
 632
 633         if (++pet_refcount > 1)
 634                 return;
 635
 636         INIT_LIST_HEAD(&pet_list);
 637         init_waitqueue_head(&pet_waitq);
 638
 639         task = kthread_run(ping_evictor_main, NULL, "ll_evictor");
 640         if (IS_ERR(task)) {
 641                 pet_refcount--;
 642                 CERROR("Cannot start ping evictor thread: %ld\n",
 643                         PTR_ERR(task));
 644         }
 645 }
 646 EXPORT_SYMBOL(ping_evictor_start);
 647
 648 void ping_evictor_stop(void)
 649 {
 650         if (--pet_refcount > 0)
 651                 return;
 652
 653         pet_state = PET_TERMINATE;
 654         wake_up(&pet_waitq);
 655 }
 656 EXPORT_SYMBOL(ping_evictor_stop);