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