kernel/rcu/rcuperf.c

   1 /*
   2  * Read-Copy Update module-based performance-test facility
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License as published by
   6  * the Free Software Foundation; either version 2 of the License, or
   7  * (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, you can access it online at
  16  * http://www.gnu.org/licenses/gpl-2.0.html.
  17  *
  18  * Copyright (C) IBM Corporation, 2015
  19  *
  20  * Authors: Paul E. McKenney <paulmck@us.ibm.com>
  21  */
  22 #include <linux/types.h>
  23 #include <linux/kernel.h>
  24 #include <linux/init.h>
  25 #include <linux/module.h>
  26 #include <linux/kthread.h>
  27 #include <linux/err.h>
  28 #include <linux/spinlock.h>
  29 #include <linux/smp.h>
  30 #include <linux/rcupdate.h>
  31 #include <linux/interrupt.h>
  32 #include <linux/sched.h>
  33 #include <uapi/linux/sched/types.h>
  34 #include <linux/atomic.h>
  35 #include <linux/bitops.h>
  36 #include <linux/completion.h>
  37 #include <linux/moduleparam.h>
  38 #include <linux/percpu.h>
  39 #include <linux/notifier.h>
  40 #include <linux/reboot.h>
  41 #include <linux/freezer.h>
  42 #include <linux/cpu.h>
  43 #include <linux/delay.h>
  44 #include <linux/stat.h>
  45 #include <linux/srcu.h>
  46 #include <linux/slab.h>
  47 #include <asm/byteorder.h>
  48 #include <linux/torture.h>
  49 #include <linux/vmalloc.h>
  50
  51 MODULE_LICENSE("GPL");
  52 MODULE_AUTHOR("Paul E. McKenney <paulmck@linux.vnet.ibm.com>");
  53
  54 #define PERF_FLAG "-perf:"
  55 #define PERFOUT_STRING(s) \
  56         pr_alert("%s" PERF_FLAG " %s\n", perf_type, s)
  57 #define VERBOSE_PERFOUT_STRING(s) \
  58         do { if (verbose) pr_alert("%s" PERF_FLAG " %s\n", perf_type, s); } while (0)
  59 #define VERBOSE_PERFOUT_ERRSTRING(s) \
  60         do { if (verbose) pr_alert("%s" PERF_FLAG "!!! %s\n", perf_type, s); } while (0)
  61
  62 torture_param(bool, gp_exp, false, "Use expedited GP wait primitives");
  63 torture_param(int, holdoff, 10, "Holdoff time before test start (s)");
  64 torture_param(int, nreaders, -1, "Number of RCU reader threads");
  65 torture_param(int, nwriters, -1, "Number of RCU updater threads");
  66 torture_param(bool, shutdown, false, "Shutdown at end of performance tests.");
  67 torture_param(bool, verbose, true, "Enable verbose debugging printk()s");
  68
  69 static char *perf_type = "rcu";
  70 module_param(perf_type, charp, 0444);
  71 MODULE_PARM_DESC(perf_type, "Type of RCU to performance-test (rcu, rcu_bh, ...)");
  72
  73 static int nrealreaders;
  74 static int nrealwriters;
  75 static struct task_struct **writer_tasks;
  76 static struct task_struct **reader_tasks;
  77 static struct task_struct *shutdown_task;
  78
  79 static u64 **writer_durations;
  80 static int *writer_n_durations;
  81 static atomic_t n_rcu_perf_reader_started;
  82 static atomic_t n_rcu_perf_writer_started;
  83 static atomic_t n_rcu_perf_writer_finished;
  84 static wait_queue_head_t shutdown_wq;
  85 static u64 t_rcu_perf_writer_started;
  86 static u64 t_rcu_perf_writer_finished;
  87 static unsigned long b_rcu_perf_writer_started;
  88 static unsigned long b_rcu_perf_writer_finished;
  89
  90 static int rcu_perf_writer_state;
  91 #define RTWS_INIT               0
  92 #define RTWS_EXP_SYNC           1
  93 #define RTWS_SYNC               2
  94 #define RTWS_IDLE               2
  95 #define RTWS_STOPPING           3
  96
  97 #define MAX_MEAS 10000
  98 #define MIN_MEAS 100
  99
 100 static int perf_runnable = IS_ENABLED(MODULE);
 101 module_param(perf_runnable, int, 0444);
 102 MODULE_PARM_DESC(perf_runnable, "Start rcuperf at boot");
 103
 104 /*
 105  * Operations vector for selecting different types of tests.
 106  */
 107
 108 struct rcu_perf_ops {
 109         int ptype;
 110         void (*init)(void);
 111         void (*cleanup)(void);
 112         int (*readlock)(void);
 113         void (*readunlock)(int idx);
 114         unsigned long (*started)(void);
 115         unsigned long (*completed)(void);
 116         unsigned long (*exp_completed)(void);
 117         void (*sync)(void);
 118         void (*exp_sync)(void);
 119         const char *name;
 120 };
 121
 122 static struct rcu_perf_ops *cur_ops;
 123
 124 /*
 125  * Definitions for rcu perf testing.
 126  */
 127
 128 static int rcu_perf_read_lock(void) __acquires(RCU)
 129 {
 130         rcu_read_lock();
 131         return 0;
 132 }
 133
 134 static void rcu_perf_read_unlock(int idx) __releases(RCU)
 135 {
 136         rcu_read_unlock();
 137 }
 138
 139 static unsigned long __maybe_unused rcu_no_completed(void)
 140 {
 141         return 0;
 142 }
 143
 144 static void rcu_sync_perf_init(void)
 145 {
 146 }
 147
 148 static struct rcu_perf_ops rcu_ops = {
 149         .ptype          = RCU_FLAVOR,
 150         .init           = rcu_sync_perf_init,
 151         .readlock       = rcu_perf_read_lock,
 152         .readunlock     = rcu_perf_read_unlock,
 153         .started        = rcu_batches_started,
 154         .completed      = rcu_batches_completed,
 155         .exp_completed  = rcu_exp_batches_completed,
 156         .sync           = synchronize_rcu,
 157         .exp_sync       = synchronize_rcu_expedited,
 158         .name           = "rcu"
 159 };
 160
 161 /*
 162  * Definitions for rcu_bh perf testing.
 163  */
 164
 165 static int rcu_bh_perf_read_lock(void) __acquires(RCU_BH)
 166 {
 167         rcu_read_lock_bh();
 168         return 0;
 169 }
 170
 171 static void rcu_bh_perf_read_unlock(int idx) __releases(RCU_BH)
 172 {
 173         rcu_read_unlock_bh();
 174 }
 175
 176 static struct rcu_perf_ops rcu_bh_ops = {
 177         .ptype          = RCU_BH_FLAVOR,
 178         .init           = rcu_sync_perf_init,
 179         .readlock       = rcu_bh_perf_read_lock,
 180         .readunlock     = rcu_bh_perf_read_unlock,
 181         .started        = rcu_batches_started_bh,
 182         .completed      = rcu_batches_completed_bh,
 183         .exp_completed  = rcu_exp_batches_completed_sched,
 184         .sync           = synchronize_rcu_bh,
 185         .exp_sync       = synchronize_rcu_bh_expedited,
 186         .name           = "rcu_bh"
 187 };
 188
 189 /*
 190  * Definitions for srcu perf testing.
 191  */
 192
 193 DEFINE_STATIC_SRCU(srcu_ctl_perf);
 194 static struct srcu_struct *srcu_ctlp = &srcu_ctl_perf;
 195
 196 static int srcu_perf_read_lock(void) __acquires(srcu_ctlp)
 197 {
 198         return srcu_read_lock(srcu_ctlp);
 199 }
 200
 201 static void srcu_perf_read_unlock(int idx) __releases(srcu_ctlp)
 202 {
 203         srcu_read_unlock(srcu_ctlp, idx);
 204 }
 205
 206 static unsigned long srcu_perf_completed(void)
 207 {
 208         return srcu_batches_completed(srcu_ctlp);
 209 }
 210
 211 static void srcu_perf_synchronize(void)
 212 {
 213         synchronize_srcu(srcu_ctlp);
 214 }
 215
 216 static void srcu_perf_synchronize_expedited(void)
 217 {
 218         synchronize_srcu_expedited(srcu_ctlp);
 219 }
 220
 221 static struct rcu_perf_ops srcu_ops = {
 222         .ptype          = SRCU_FLAVOR,
 223         .init           = rcu_sync_perf_init,
 224         .readlock       = srcu_perf_read_lock,
 225         .readunlock     = srcu_perf_read_unlock,
 226         .started        = NULL,
 227         .completed      = srcu_perf_completed,
 228         .exp_completed  = srcu_perf_completed,
 229         .sync           = srcu_perf_synchronize,
 230         .exp_sync       = srcu_perf_synchronize_expedited,
 231         .name           = "srcu"
 232 };
 233
 234 /*
 235  * Definitions for sched perf testing.
 236  */
 237
 238 static int sched_perf_read_lock(void)
 239 {
 240         preempt_disable();
 241         return 0;
 242 }
 243
 244 static void sched_perf_read_unlock(int idx)
 245 {
 246         preempt_enable();
 247 }
 248
 249 static struct rcu_perf_ops sched_ops = {
 250         .ptype          = RCU_SCHED_FLAVOR,
 251         .init           = rcu_sync_perf_init,
 252         .readlock       = sched_perf_read_lock,
 253         .readunlock     = sched_perf_read_unlock,
 254         .started        = rcu_batches_started_sched,
 255         .completed      = rcu_batches_completed_sched,
 256         .exp_completed  = rcu_exp_batches_completed_sched,
 257         .sync           = synchronize_sched,
 258         .exp_sync       = synchronize_sched_expedited,
 259         .name           = "sched"
 260 };
 261
 262 #ifdef CONFIG_TASKS_RCU
 263
 264 /*
 265  * Definitions for RCU-tasks perf testing.
 266  */
 267
 268 static int tasks_perf_read_lock(void)
 269 {
 270         return 0;
 271 }
 272
 273 static void tasks_perf_read_unlock(int idx)
 274 {
 275 }
 276
 277 static struct rcu_perf_ops tasks_ops = {
 278         .ptype          = RCU_TASKS_FLAVOR,
 279         .init           = rcu_sync_perf_init,
 280         .readlock       = tasks_perf_read_lock,
 281         .readunlock     = tasks_perf_read_unlock,
 282         .started        = rcu_no_completed,
 283         .completed      = rcu_no_completed,
 284         .sync           = synchronize_rcu_tasks,
 285         .exp_sync       = synchronize_rcu_tasks,
 286         .name           = "tasks"
 287 };
 288
 289 #define RCUPERF_TASKS_OPS &tasks_ops,
 290
 291 static bool __maybe_unused torturing_tasks(void)
 292 {
 293         return cur_ops == &tasks_ops;
 294 }
 295
 296 #else /* #ifdef CONFIG_TASKS_RCU */
 297
 298 #define RCUPERF_TASKS_OPS
 299
 300 static bool __maybe_unused torturing_tasks(void)
 301 {
 302         return false;
 303 }
 304
 305 #endif /* #else #ifdef CONFIG_TASKS_RCU */
 306
 307 /*
 308  * If performance tests complete, wait for shutdown to commence.
 309  */
 310 static void rcu_perf_wait_shutdown(void)
 311 {
 312         cond_resched_rcu_qs();
 313         if (atomic_read(&n_rcu_perf_writer_finished) < nrealwriters)
 314                 return;
 315         while (!torture_must_stop())
 316                 schedule_timeout_uninterruptible(1);
 317 }
 318
 319 /*
 320  * RCU perf reader kthread.  Repeatedly does empty RCU read-side
 321  * critical section, minimizing update-side interference.
 322  */
 323 static int
 324 rcu_perf_reader(void *arg)
 325 {
 326         unsigned long flags;
 327         int idx;
 328         long me = (long)arg;
 329
 330         VERBOSE_PERFOUT_STRING("rcu_perf_reader task started");
 331         set_cpus_allowed_ptr(current, cpumask_of(me % nr_cpu_ids));
 332         set_user_nice(current, MAX_NICE);
 333         atomic_inc(&n_rcu_perf_reader_started);
 334
 335         do {
 336                 local_irq_save(flags);
 337                 idx = cur_ops->readlock();
 338                 cur_ops->readunlock(idx);
 339                 local_irq_restore(flags);
 340                 rcu_perf_wait_shutdown();
 341         } while (!torture_must_stop());
 342         torture_kthread_stopping("rcu_perf_reader");
 343         return 0;
 344 }
 345
 346 /*
 347  * RCU perf writer kthread.  Repeatedly does a grace period.
 348  */
 349 static int
 350 rcu_perf_writer(void *arg)
 351 {
 352         int i = 0;
 353         int i_max;
 354         long me = (long)arg;
 355         struct sched_param sp;
 356         bool started = false, done = false, alldone = false;
 357         u64 t;
 358         u64 *wdp;
 359         u64 *wdpp = writer_durations[me];
 360
 361         VERBOSE_PERFOUT_STRING("rcu_perf_writer task started");
 362         WARN_ON(!wdpp);
 363         set_cpus_allowed_ptr(current, cpumask_of(me % nr_cpu_ids));
 364         sp.sched_priority = 1;
 365         sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
 366
 367         if (holdoff)
 368                 schedule_timeout_uninterruptible(holdoff * HZ);
 369
 370         t = ktime_get_mono_fast_ns();
 371         if (atomic_inc_return(&n_rcu_perf_writer_started) >= nrealwriters) {
 372                 t_rcu_perf_writer_started = t;
 373                 if (gp_exp) {
 374                         b_rcu_perf_writer_started =
 375                                 cur_ops->exp_completed() / 2;
 376                 } else {
 377                         b_rcu_perf_writer_started =
 378                                 cur_ops->completed();
 379                 }
 380         }
 381
 382         do {
 383                 wdp = &wdpp[i];
 384                 *wdp = ktime_get_mono_fast_ns();
 385                 if (gp_exp) {
 386                         rcu_perf_writer_state = RTWS_EXP_SYNC;
 387                         cur_ops->exp_sync();
 388                 } else {
 389                         rcu_perf_writer_state = RTWS_SYNC;
 390                         cur_ops->sync();
 391                 }
 392                 rcu_perf_writer_state = RTWS_IDLE;
 393                 t = ktime_get_mono_fast_ns();
 394                 *wdp = t - *wdp;
 395                 i_max = i;
 396                 if (!started &&
 397                     atomic_read(&n_rcu_perf_writer_started) >= nrealwriters)
 398                         started = true;
 399                 if (!done && i >= MIN_MEAS) {
 400                         done = true;
 401                         sp.sched_priority = 0;
 402                         sched_setscheduler_nocheck(current,
 403                                                    SCHED_NORMAL, &sp);
 404                         pr_alert("%s%s rcu_perf_writer %ld has %d measurements\n",
 405                                  perf_type, PERF_FLAG, me, MIN_MEAS);
 406                         if (atomic_inc_return(&n_rcu_perf_writer_finished) >=
 407                             nrealwriters) {
 408                                 schedule_timeout_interruptible(10);
 409                                 rcu_ftrace_dump(DUMP_ALL);
 410                                 PERFOUT_STRING("Test complete");
 411                                 t_rcu_perf_writer_finished = t;
 412                                 if (gp_exp) {
 413                                         b_rcu_perf_writer_finished =
 414                                                 cur_ops->exp_completed() / 2;
 415                                 } else {
 416                                         b_rcu_perf_writer_finished =
 417                                                 cur_ops->completed();
 418                                 }
 419                                 if (shutdown) {
 420                                         smp_mb(); /* Assign before wake. */
 421                                         wake_up(&shutdown_wq);
 422                                 }
 423                         }
 424                 }
 425                 if (done && !alldone &&
 426                     atomic_read(&n_rcu_perf_writer_finished) >= nrealwriters)
 427                         alldone = true;
 428                 if (started && !alldone && i < MAX_MEAS - 1)
 429                         i++;
 430                 rcu_perf_wait_shutdown();
 431         } while (!torture_must_stop());
 432         rcu_perf_writer_state = RTWS_STOPPING;
 433         writer_n_durations[me] = i_max;
 434         torture_kthread_stopping("rcu_perf_writer");
 435         return 0;
 436 }
 437
 438 static inline void
 439 rcu_perf_print_module_parms(struct rcu_perf_ops *cur_ops, const char *tag)
 440 {
 441         pr_alert("%s" PERF_FLAG
 442                  "--- %s: nreaders=%d nwriters=%d verbose=%d shutdown=%d\n",
 443                  perf_type, tag, nrealreaders, nrealwriters, verbose, shutdown);
 444 }
 445
 446 static void
 447 rcu_perf_cleanup(void)
 448 {
 449         int i;
 450         int j;
 451         int ngps = 0;
 452         u64 *wdp;
 453         u64 *wdpp;
 454
 455         if (torture_cleanup_begin())
 456                 return;
 457
 458         if (reader_tasks) {
 459                 for (i = 0; i < nrealreaders; i++)
 460                         torture_stop_kthread(rcu_perf_reader,
 461                                              reader_tasks[i]);
 462                 kfree(reader_tasks);
 463         }
 464
 465         if (writer_tasks) {
 466                 for (i = 0; i < nrealwriters; i++) {
 467                         torture_stop_kthread(rcu_perf_writer,
 468                                              writer_tasks[i]);
 469                         if (!writer_n_durations)
 470                                 continue;
 471                         j = writer_n_durations[i];
 472                         pr_alert("%s%s writer %d gps: %d\n",
 473                                  perf_type, PERF_FLAG, i, j);
 474                         ngps += j;
 475                 }
 476                 pr_alert("%s%s start: %llu end: %llu duration: %llu gps: %d batches: %ld\n",
 477                          perf_type, PERF_FLAG,
 478                          t_rcu_perf_writer_started, t_rcu_perf_writer_finished,
 479                          t_rcu_perf_writer_finished -
 480                          t_rcu_perf_writer_started,
 481                          ngps,
 482                          b_rcu_perf_writer_finished -
 483                          b_rcu_perf_writer_started);
 484                 for (i = 0; i < nrealwriters; i++) {
 485                         if (!writer_durations)
 486                                 break;
 487                         if (!writer_n_durations)
 488                                 continue;
 489                         wdpp = writer_durations[i];
 490                         if (!wdpp)
 491                                 continue;
 492                         for (j = 0; j <= writer_n_durations[i]; j++) {
 493                                 wdp = &wdpp[j];
 494                                 pr_alert("%s%s %4d writer-duration: %5d %llu\n",
 495                                         perf_type, PERF_FLAG,
 496                                         i, j, *wdp);
 497                                 if (j % 100 == 0)
 498                                         schedule_timeout_uninterruptible(1);
 499                         }
 500                         kfree(writer_durations[i]);
 501                 }
 502                 kfree(writer_tasks);
 503                 kfree(writer_durations);
 504                 kfree(writer_n_durations);
 505         }
 506
 507         /* Do flavor-specific cleanup operations.  */
 508         if (cur_ops->cleanup != NULL)
 509                 cur_ops->cleanup();
 510
 511         torture_cleanup_end();
 512 }
 513
 514 /*
 515  * Return the number if non-negative.  If -1, the number of CPUs.
 516  * If less than -1, that much less than the number of CPUs, but
 517  * at least one.
 518  */
 519 static int compute_real(int n)
 520 {
 521         int nr;
 522
 523         if (n >= 0) {
 524                 nr = n;
 525         } else {
 526                 nr = num_online_cpus() + 1 + n;
 527                 if (nr <= 0)
 528                         nr = 1;
 529         }
 530         return nr;
 531 }
 532
 533 /*
 534  * RCU perf shutdown kthread.  Just waits to be awakened, then shuts
 535  * down system.
 536  */
 537 static int
 538 rcu_perf_shutdown(void *arg)
 539 {
 540         do {
 541                 wait_event(shutdown_wq,
 542                            atomic_read(&n_rcu_perf_writer_finished) >=
 543                            nrealwriters);
 544         } while (atomic_read(&n_rcu_perf_writer_finished) < nrealwriters);
 545         smp_mb(); /* Wake before output. */
 546         rcu_perf_cleanup();
 547         kernel_power_off();
 548         return -EINVAL;
 549 }
 550
 551 static int __init
 552 rcu_perf_init(void)
 553 {
 554         long i;
 555         int firsterr = 0;
 556         static struct rcu_perf_ops *perf_ops[] = {
 557                 &rcu_ops, &rcu_bh_ops, &srcu_ops, &sched_ops,
 558                 RCUPERF_TASKS_OPS
 559         };
 560
 561         if (!torture_init_begin(perf_type, verbose, &perf_runnable))
 562                 return -EBUSY;
 563
 564         /* Process args and tell the world that the perf'er is on the job. */
 565         for (i = 0; i < ARRAY_SIZE(perf_ops); i++) {
 566                 cur_ops = perf_ops[i];
 567                 if (strcmp(perf_type, cur_ops->name) == 0)
 568                         break;
 569         }
 570         if (i == ARRAY_SIZE(perf_ops)) {
 571                 pr_alert("rcu-perf: invalid perf type: \"%s\"\n",
 572                          perf_type);
 573                 pr_alert("rcu-perf types:");
 574                 for (i = 0; i < ARRAY_SIZE(perf_ops); i++)
 575                         pr_alert(" %s", perf_ops[i]->name);
 576                 pr_alert("\n");
 577                 firsterr = -EINVAL;
 578                 goto unwind;
 579         }
 580         if (cur_ops->init)
 581                 cur_ops->init();
 582
 583         nrealwriters = compute_real(nwriters);
 584         nrealreaders = compute_real(nreaders);
 585         atomic_set(&n_rcu_perf_reader_started, 0);
 586         atomic_set(&n_rcu_perf_writer_started, 0);
 587         atomic_set(&n_rcu_perf_writer_finished, 0);
 588         rcu_perf_print_module_parms(cur_ops, "Start of test");
 589
 590         /* Start up the kthreads. */
 591
 592         if (shutdown) {
 593                 init_waitqueue_head(&shutdown_wq);
 594                 firsterr = torture_create_kthread(rcu_perf_shutdown, NULL,
 595                                                   shutdown_task);
 596                 if (firsterr)
 597                         goto unwind;
 598                 schedule_timeout_uninterruptible(1);
 599         }
 600         reader_tasks = kcalloc(nrealreaders, sizeof(reader_tasks[0]),
 601                                GFP_KERNEL);
 602         if (reader_tasks == NULL) {
 603                 VERBOSE_PERFOUT_ERRSTRING("out of memory");
 604                 firsterr = -ENOMEM;
 605                 goto unwind;
 606         }
 607         for (i = 0; i < nrealreaders; i++) {
 608                 firsterr = torture_create_kthread(rcu_perf_reader, (void *)i,
 609                                                   reader_tasks[i]);
 610                 if (firsterr)
 611                         goto unwind;
 612         }
 613         while (atomic_read(&n_rcu_perf_reader_started) < nrealreaders)
 614                 schedule_timeout_uninterruptible(1);
 615         writer_tasks = kcalloc(nrealwriters, sizeof(reader_tasks[0]),
 616                                GFP_KERNEL);
 617         writer_durations = kcalloc(nrealwriters, sizeof(*writer_durations),
 618                                    GFP_KERNEL);
 619         writer_n_durations =
 620                 kcalloc(nrealwriters, sizeof(*writer_n_durations),
 621                         GFP_KERNEL);
 622         if (!writer_tasks || !writer_durations || !writer_n_durations) {
 623                 VERBOSE_PERFOUT_ERRSTRING("out of memory");
 624                 firsterr = -ENOMEM;
 625                 goto unwind;
 626         }
 627         if (rcu_gp_is_expedited() && !rcu_gp_is_normal() && !gp_exp) {
 628                 VERBOSE_PERFOUT_ERRSTRING("All grace periods expedited, no normal ones to measure!");
 629                 firsterr = -EINVAL;
 630                 goto unwind;
 631         }
 632         if (rcu_gp_is_normal() && gp_exp) {
 633                 VERBOSE_PERFOUT_ERRSTRING("All grace periods normal, no expedited ones to measure!");
 634                 firsterr = -EINVAL;
 635                 goto unwind;
 636         }
 637         for (i = 0; i < nrealwriters; i++) {
 638                 writer_durations[i] =
 639                         kcalloc(MAX_MEAS, sizeof(*writer_durations[i]),
 640                                 GFP_KERNEL);
 641                 if (!writer_durations[i]) {
 642                         firsterr = -ENOMEM;
 643                         goto unwind;
 644                 }
 645                 firsterr = torture_create_kthread(rcu_perf_writer, (void *)i,
 646                                                   writer_tasks[i]);
 647                 if (firsterr)
 648                         goto unwind;
 649         }
 650         torture_init_end();
 651         return 0;
 652
 653 unwind:
 654         torture_init_end();
 655         rcu_perf_cleanup();
 656         return firsterr;
 657 }
 658
 659 module_init(rcu_perf_init);
 660 module_exit(rcu_perf_cleanup);