kernel/rcutorture.c

   1 /*
   2  * Read-Copy Update /proc-based torture 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, write to the Free Software
  16  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  17  *
  18  * Copyright (C) IBM Corporation, 2005
  19  *
  20  * Authors: Paul E. McKenney <paulmck@us.ibm.com>
  21  *
  22  * See also:  Documentation/RCU/torture.txt
  23  */
  24 #include <linux/types.h>
  25 #include <linux/kernel.h>
  26 #include <linux/init.h>
  27 #include <linux/module.h>
  28 #include <linux/kthread.h>
  29 #include <linux/err.h>
  30 #include <linux/spinlock.h>
  31 #include <linux/smp.h>
  32 #include <linux/rcupdate.h>
  33 #include <linux/interrupt.h>
  34 #include <linux/sched.h>
  35 #include <asm/atomic.h>
  36 #include <linux/bitops.h>
  37 #include <linux/module.h>
  38 #include <linux/completion.h>
  39 #include <linux/moduleparam.h>
  40 #include <linux/percpu.h>
  41 #include <linux/notifier.h>
  42 #include <linux/cpu.h>
  43 #include <linux/random.h>
  44 #include <linux/delay.h>
  45 #include <linux/byteorder/swabb.h>
  46 #include <linux/stat.h>
  47
  48 MODULE_LICENSE("GPL");
  49
  50 static int nreaders = -1;       /* # reader threads, defaults to 4*ncpus */
  51 static int stat_interval;       /* Interval between stats, in seconds. */
  52                                 /*  Defaults to "only at end of test". */
  53 static int verbose;             /* Print more debug info. */
  54 static int test_no_idle_hz;     /* Test RCU's support for tickless idle CPUs. */
  55 static int shuffle_interval = 5; /* Interval between shuffles (in sec)*/
  56
  57 MODULE_PARM(nreaders, "i");
  58 MODULE_PARM_DESC(nreaders, "Number of RCU reader threads");
  59 MODULE_PARM(stat_interval, "i");
  60 MODULE_PARM_DESC(stat_interval, "Number of seconds between stats printk()s");
  61 MODULE_PARM(verbose, "i");
  62 MODULE_PARM_DESC(verbose, "Enable verbose debugging printk()s");
  63 MODULE_PARM(test_no_idle_hz, "i");
  64 MODULE_PARM_DESC(test_no_idle_hz, "Test support for tickless idle CPUs");
  65 MODULE_PARM(shuffle_interval, "i");
  66 MODULE_PARM_DESC(shuffle_interval, "Number of seconds between shuffles");
  67 #define TORTURE_FLAG "rcutorture: "
  68 #define PRINTK_STRING(s) \
  69         do { printk(KERN_ALERT TORTURE_FLAG s "\n"); } while (0)
  70 #define VERBOSE_PRINTK_STRING(s) \
  71         do { if (verbose) printk(KERN_ALERT TORTURE_FLAG s "\n"); } while (0)
  72 #define VERBOSE_PRINTK_ERRSTRING(s) \
  73         do { if (verbose) printk(KERN_ALERT TORTURE_FLAG "!!! " s "\n"); } while (0)
  74
  75 static char printk_buf[4096];
  76
  77 static int nrealreaders;
  78 static struct task_struct *writer_task;
  79 static struct task_struct **reader_tasks;
  80 static struct task_struct *stats_task;
  81 static struct task_struct *shuffler_task;
  82
  83 #define RCU_TORTURE_PIPE_LEN 10
  84
  85 struct rcu_torture {
  86         struct rcu_head rtort_rcu;
  87         int rtort_pipe_count;
  88         struct list_head rtort_free;
  89         int rtort_mbtest;
  90 };
  91
  92 static int fullstop = 0;        /* stop generating callbacks at test end. */
  93 static LIST_HEAD(rcu_torture_freelist);
  94 static struct rcu_torture *rcu_torture_current = NULL;
  95 static long rcu_torture_current_version = 0;
  96 static struct rcu_torture rcu_tortures[10 * RCU_TORTURE_PIPE_LEN];
  97 static DEFINE_SPINLOCK(rcu_torture_lock);
  98 static DEFINE_PER_CPU(long [RCU_TORTURE_PIPE_LEN + 1], rcu_torture_count) =
  99         { 0 };
 100 static DEFINE_PER_CPU(long [RCU_TORTURE_PIPE_LEN + 1], rcu_torture_batch) =
 101         { 0 };
 102 static atomic_t rcu_torture_wcount[RCU_TORTURE_PIPE_LEN + 1];
 103 atomic_t n_rcu_torture_alloc;
 104 atomic_t n_rcu_torture_alloc_fail;
 105 atomic_t n_rcu_torture_free;
 106 atomic_t n_rcu_torture_mberror;
 107 atomic_t n_rcu_torture_error;
 108
 109 /*
 110  * Allocate an element from the rcu_tortures pool.
 111  */
 112 static struct rcu_torture *
 113 rcu_torture_alloc(void)
 114 {
 115         struct list_head *p;
 116
 117         spin_lock_bh(&rcu_torture_lock);
 118         if (list_empty(&rcu_torture_freelist)) {
 119                 atomic_inc(&n_rcu_torture_alloc_fail);
 120                 spin_unlock_bh(&rcu_torture_lock);
 121                 return NULL;
 122         }
 123         atomic_inc(&n_rcu_torture_alloc);
 124         p = rcu_torture_freelist.next;
 125         list_del_init(p);
 126         spin_unlock_bh(&rcu_torture_lock);
 127         return container_of(p, struct rcu_torture, rtort_free);
 128 }
 129
 130 /*
 131  * Free an element to the rcu_tortures pool.
 132  */
 133 static void
 134 rcu_torture_free(struct rcu_torture *p)
 135 {
 136         atomic_inc(&n_rcu_torture_free);
 137         spin_lock_bh(&rcu_torture_lock);
 138         list_add_tail(&p->rtort_free, &rcu_torture_freelist);
 139         spin_unlock_bh(&rcu_torture_lock);
 140 }
 141
 142 static void
 143 rcu_torture_cb(struct rcu_head *p)
 144 {
 145         int i;
 146         struct rcu_torture *rp = container_of(p, struct rcu_torture, rtort_rcu);
 147
 148         if (fullstop) {
 149                 /* Test is ending, just drop callbacks on the floor. */
 150                 /* The next initialization will pick up the pieces. */
 151                 return;
 152         }
 153         i = rp->rtort_pipe_count;
 154         if (i > RCU_TORTURE_PIPE_LEN)
 155                 i = RCU_TORTURE_PIPE_LEN;
 156         atomic_inc(&rcu_torture_wcount[i]);
 157         if (++rp->rtort_pipe_count >= RCU_TORTURE_PIPE_LEN) {
 158                 rp->rtort_mbtest = 0;
 159                 rcu_torture_free(rp);
 160         } else
 161                 call_rcu(p, rcu_torture_cb);
 162 }
 163
 164 struct rcu_random_state {
 165         unsigned long rrs_state;
 166         unsigned long rrs_count;
 167 };
 168
 169 #define RCU_RANDOM_MULT 39916801  /* prime */
 170 #define RCU_RANDOM_ADD  479001701 /* prime */
 171 #define RCU_RANDOM_REFRESH 10000
 172
 173 #define DEFINE_RCU_RANDOM(name) struct rcu_random_state name = { 0, 0 }
 174
 175 /*
 176  * Crude but fast random-number generator.  Uses a linear congruential
 177  * generator, with occasional help from get_random_bytes().
 178  */
 179 static long
 180 rcu_random(struct rcu_random_state *rrsp)
 181 {
 182         long refresh;
 183
 184         if (--rrsp->rrs_count < 0) {
 185                 get_random_bytes(&refresh, sizeof(refresh));
 186                 rrsp->rrs_state += refresh;
 187                 rrsp->rrs_count = RCU_RANDOM_REFRESH;
 188         }
 189         rrsp->rrs_state = rrsp->rrs_state * RCU_RANDOM_MULT + RCU_RANDOM_ADD;
 190         return swahw32(rrsp->rrs_state);
 191 }
 192
 193 /*
 194  * RCU torture writer kthread.  Repeatedly substitutes a new structure
 195  * for that pointed to by rcu_torture_current, freeing the old structure
 196  * after a series of grace periods (the "pipeline").
 197  */
 198 static int
 199 rcu_torture_writer(void *arg)
 200 {
 201         int i;
 202         long oldbatch = rcu_batches_completed();
 203         struct rcu_torture *rp;
 204         struct rcu_torture *old_rp;
 205         static DEFINE_RCU_RANDOM(rand);
 206
 207         VERBOSE_PRINTK_STRING("rcu_torture_writer task started");
 208         set_user_nice(current, 19);
 209
 210         do {
 211                 schedule_timeout_uninterruptible(1);
 212                 if (rcu_batches_completed() == oldbatch)
 213                         continue;
 214                 if ((rp = rcu_torture_alloc()) == NULL)
 215                         continue;
 216                 rp->rtort_pipe_count = 0;
 217                 udelay(rcu_random(&rand) & 0x3ff);
 218                 old_rp = rcu_torture_current;
 219                 rp->rtort_mbtest = 1;
 220                 rcu_assign_pointer(rcu_torture_current, rp);
 221                 smp_wmb();
 222                 if (old_rp != NULL) {
 223                         i = old_rp->rtort_pipe_count;
 224                         if (i > RCU_TORTURE_PIPE_LEN)
 225                                 i = RCU_TORTURE_PIPE_LEN;
 226                         atomic_inc(&rcu_torture_wcount[i]);
 227                         old_rp->rtort_pipe_count++;
 228                         call_rcu(&old_rp->rtort_rcu, rcu_torture_cb);
 229                 }
 230                 rcu_torture_current_version++;
 231                 oldbatch = rcu_batches_completed();
 232         } while (!kthread_should_stop() && !fullstop);
 233         VERBOSE_PRINTK_STRING("rcu_torture_writer task stopping");
 234         while (!kthread_should_stop())
 235                 schedule_timeout_uninterruptible(1);
 236         return 0;
 237 }
 238
 239 /*
 240  * RCU torture reader kthread.  Repeatedly dereferences rcu_torture_current,
 241  * incrementing the corresponding element of the pipeline array.  The
 242  * counter in the element should never be greater than 1, otherwise, the
 243  * RCU implementation is broken.
 244  */
 245 static int
 246 rcu_torture_reader(void *arg)
 247 {
 248         int completed;
 249         DEFINE_RCU_RANDOM(rand);
 250         struct rcu_torture *p;
 251         int pipe_count;
 252
 253         VERBOSE_PRINTK_STRING("rcu_torture_reader task started");
 254         set_user_nice(current, 19);
 255
 256         do {
 257                 rcu_read_lock();
 258                 completed = rcu_batches_completed();
 259                 p = rcu_dereference(rcu_torture_current);
 260                 if (p == NULL) {
 261                         /* Wait for rcu_torture_writer to get underway */
 262                         rcu_read_unlock();
 263                         schedule_timeout_interruptible(HZ);
 264                         continue;
 265                 }
 266                 if (p->rtort_mbtest == 0)
 267                         atomic_inc(&n_rcu_torture_mberror);
 268                 udelay(rcu_random(&rand) & 0x7f);
 269                 preempt_disable();
 270                 pipe_count = p->rtort_pipe_count;
 271                 if (pipe_count > RCU_TORTURE_PIPE_LEN) {
 272                         /* Should not happen, but... */
 273                         pipe_count = RCU_TORTURE_PIPE_LEN;
 274                 }
 275                 ++__get_cpu_var(rcu_torture_count)[pipe_count];
 276                 completed = rcu_batches_completed() - completed;
 277                 if (completed > RCU_TORTURE_PIPE_LEN) {
 278                         /* Should not happen, but... */
 279                         completed = RCU_TORTURE_PIPE_LEN;
 280                 }
 281                 ++__get_cpu_var(rcu_torture_batch)[completed];
 282                 preempt_enable();
 283                 rcu_read_unlock();
 284                 schedule();
 285         } while (!kthread_should_stop() && !fullstop);
 286         VERBOSE_PRINTK_STRING("rcu_torture_reader task stopping");
 287         while (!kthread_should_stop())
 288                 schedule_timeout_uninterruptible(1);
 289         return 0;
 290 }
 291
 292 /*
 293  * Create an RCU-torture statistics message in the specified buffer.
 294  */
 295 static int
 296 rcu_torture_printk(char *page)
 297 {
 298         int cnt = 0;
 299         int cpu;
 300         int i;
 301         long pipesummary[RCU_TORTURE_PIPE_LEN + 1] = { 0 };
 302         long batchsummary[RCU_TORTURE_PIPE_LEN + 1] = { 0 };
 303
 304         for_each_cpu(cpu) {
 305                 for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++) {
 306                         pipesummary[i] += per_cpu(rcu_torture_count, cpu)[i];
 307                         batchsummary[i] += per_cpu(rcu_torture_batch, cpu)[i];
 308                 }
 309         }
 310         for (i = RCU_TORTURE_PIPE_LEN - 1; i >= 0; i--) {
 311                 if (pipesummary[i] != 0)
 312                         break;
 313         }
 314         cnt += sprintf(&page[cnt], "rcutorture: ");
 315         cnt += sprintf(&page[cnt],
 316                        "rtc: %p ver: %ld tfle: %d rta: %d rtaf: %d rtf: %d "
 317                        "rtmbe: %d",
 318                        rcu_torture_current,
 319                        rcu_torture_current_version,
 320                        list_empty(&rcu_torture_freelist),
 321                        atomic_read(&n_rcu_torture_alloc),
 322                        atomic_read(&n_rcu_torture_alloc_fail),
 323                        atomic_read(&n_rcu_torture_free),
 324                        atomic_read(&n_rcu_torture_mberror));
 325         if (atomic_read(&n_rcu_torture_mberror) != 0)
 326                 cnt += sprintf(&page[cnt], " !!!");
 327         cnt += sprintf(&page[cnt], "\nrcutorture: ");
 328         if (i > 1) {
 329                 cnt += sprintf(&page[cnt], "!!! ");
 330                 atomic_inc(&n_rcu_torture_error);
 331         }
 332         cnt += sprintf(&page[cnt], "Reader Pipe: ");
 333         for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++)
 334                 cnt += sprintf(&page[cnt], " %ld", pipesummary[i]);
 335         cnt += sprintf(&page[cnt], "\nrcutorture: ");
 336         cnt += sprintf(&page[cnt], "Reader Batch: ");
 337         for (i = 0; i < RCU_TORTURE_PIPE_LEN; i++)
 338                 cnt += sprintf(&page[cnt], " %ld", batchsummary[i]);
 339         cnt += sprintf(&page[cnt], "\nrcutorture: ");
 340         cnt += sprintf(&page[cnt], "Free-Block Circulation: ");
 341         for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++) {
 342                 cnt += sprintf(&page[cnt], " %d",
 343                                atomic_read(&rcu_torture_wcount[i]));
 344         }
 345         cnt += sprintf(&page[cnt], "\n");
 346         return cnt;
 347 }
 348
 349 /*
 350  * Print torture statistics.  Caller must ensure that there is only
 351  * one call to this function at a given time!!!  This is normally
 352  * accomplished by relying on the module system to only have one copy
 353  * of the module loaded, and then by giving the rcu_torture_stats
 354  * kthread full control (or the init/cleanup functions when rcu_torture_stats
 355  * thread is not running).
 356  */
 357 static void
 358 rcu_torture_stats_print(void)
 359 {
 360         int cnt;
 361
 362         cnt = rcu_torture_printk(printk_buf);
 363         printk(KERN_ALERT "%s", printk_buf);
 364 }
 365
 366 /*
 367  * Periodically prints torture statistics, if periodic statistics printing
 368  * was specified via the stat_interval module parameter.
 369  *
 370  * No need to worry about fullstop here, since this one doesn't reference
 371  * volatile state or register callbacks.
 372  */
 373 static int
 374 rcu_torture_stats(void *arg)
 375 {
 376         VERBOSE_PRINTK_STRING("rcu_torture_stats task started");
 377         do {
 378                 schedule_timeout_interruptible(stat_interval * HZ);
 379                 rcu_torture_stats_print();
 380         } while (!kthread_should_stop());
 381         VERBOSE_PRINTK_STRING("rcu_torture_stats task stopping");
 382         return 0;
 383 }
 384
 385 static int rcu_idle_cpu;        /* Force all torture tasks off this CPU */
 386
 387 /* Shuffle tasks such that we allow @rcu_idle_cpu to become idle. A special case
 388  * is when @rcu_idle_cpu = -1, when we allow the tasks to run on all CPUs.
 389  */
 390 void rcu_torture_shuffle_tasks(void)
 391 {
 392         cpumask_t tmp_mask = CPU_MASK_ALL;
 393         int i;
 394
 395         lock_cpu_hotplug();
 396
 397         /* No point in shuffling if there is only one online CPU (ex: UP) */
 398         if (num_online_cpus() == 1) {
 399                 unlock_cpu_hotplug();
 400                 return;
 401         }
 402
 403         if (rcu_idle_cpu != -1)
 404                 cpu_clear(rcu_idle_cpu, tmp_mask);
 405
 406         set_cpus_allowed(current, tmp_mask);
 407
 408         if (reader_tasks != NULL) {
 409                 for (i = 0; i < nrealreaders; i++)
 410                         if (reader_tasks[i])
 411                                 set_cpus_allowed(reader_tasks[i], tmp_mask);
 412         }
 413
 414         if (writer_task)
 415                 set_cpus_allowed(writer_task, tmp_mask);
 416
 417         if (stats_task)
 418                 set_cpus_allowed(stats_task, tmp_mask);
 419
 420         if (rcu_idle_cpu == -1)
 421                 rcu_idle_cpu = num_online_cpus() - 1;
 422         else
 423                 rcu_idle_cpu--;
 424
 425         unlock_cpu_hotplug();
 426 }
 427
 428 /* Shuffle tasks across CPUs, with the intent of allowing each CPU in the
 429  * system to become idle at a time and cut off its timer ticks. This is meant
 430  * to test the support for such tickless idle CPU in RCU.
 431  */
 432 static int
 433 rcu_torture_shuffle(void *arg)
 434 {
 435         VERBOSE_PRINTK_STRING("rcu_torture_shuffle task started");
 436         do {
 437                 schedule_timeout_interruptible(shuffle_interval * HZ);
 438                 rcu_torture_shuffle_tasks();
 439         } while (!kthread_should_stop());
 440         VERBOSE_PRINTK_STRING("rcu_torture_shuffle task stopping");
 441         return 0;
 442 }
 443
 444 static void
 445 rcu_torture_cleanup(void)
 446 {
 447         int i;
 448
 449         fullstop = 1;
 450         if (shuffler_task != NULL) {
 451                 VERBOSE_PRINTK_STRING("Stopping rcu_torture_shuffle task");
 452                 kthread_stop(shuffler_task);
 453         }
 454         shuffler_task = NULL;
 455
 456         if (writer_task != NULL) {
 457                 VERBOSE_PRINTK_STRING("Stopping rcu_torture_writer task");
 458                 kthread_stop(writer_task);
 459         }
 460         writer_task = NULL;
 461
 462         if (reader_tasks != NULL) {
 463                 for (i = 0; i < nrealreaders; i++) {
 464                         if (reader_tasks[i] != NULL) {
 465                                 VERBOSE_PRINTK_STRING(
 466                                         "Stopping rcu_torture_reader task");
 467                                 kthread_stop(reader_tasks[i]);
 468                         }
 469                         reader_tasks[i] = NULL;
 470                 }
 471                 kfree(reader_tasks);
 472                 reader_tasks = NULL;
 473         }
 474         rcu_torture_current = NULL;
 475
 476         if (stats_task != NULL) {
 477                 VERBOSE_PRINTK_STRING("Stopping rcu_torture_stats task");
 478                 kthread_stop(stats_task);
 479         }
 480         stats_task = NULL;
 481
 482         /* Wait for all RCU callbacks to fire.  */
 483         rcu_barrier();
 484
 485         rcu_torture_stats_print();  /* -After- the stats thread is stopped! */
 486         printk(KERN_ALERT TORTURE_FLAG
 487                "--- End of test: %s\n",
 488                atomic_read(&n_rcu_torture_error) == 0 ? "SUCCESS" : "FAILURE");
 489 }
 490
 491 static int
 492 rcu_torture_init(void)
 493 {
 494         int i;
 495         int cpu;
 496         int firsterr = 0;
 497
 498         /* Process args and tell the world that the torturer is on the job. */
 499
 500         if (nreaders >= 0)
 501                 nrealreaders = nreaders;
 502         else
 503                 nrealreaders = 2 * num_online_cpus();
 504         printk(KERN_ALERT TORTURE_FLAG "--- Start of test: nreaders=%d "
 505                 "stat_interval=%d verbose=%d test_no_idle_hz=%d "
 506                 "shuffle_interval = %d\n",
 507                 nrealreaders, stat_interval, verbose, test_no_idle_hz,
 508                 shuffle_interval);
 509         fullstop = 0;
 510
 511         /* Set up the freelist. */
 512
 513         INIT_LIST_HEAD(&rcu_torture_freelist);
 514         for (i = 0; i < sizeof(rcu_tortures) / sizeof(rcu_tortures[0]); i++) {
 515                 rcu_tortures[i].rtort_mbtest = 0;
 516                 list_add_tail(&rcu_tortures[i].rtort_free,
 517                               &rcu_torture_freelist);
 518         }
 519
 520         /* Initialize the statistics so that each run gets its own numbers. */
 521
 522         rcu_torture_current = NULL;
 523         rcu_torture_current_version = 0;
 524         atomic_set(&n_rcu_torture_alloc, 0);
 525         atomic_set(&n_rcu_torture_alloc_fail, 0);
 526         atomic_set(&n_rcu_torture_free, 0);
 527         atomic_set(&n_rcu_torture_mberror, 0);
 528         atomic_set(&n_rcu_torture_error, 0);
 529         for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++)
 530                 atomic_set(&rcu_torture_wcount[i], 0);
 531         for_each_cpu(cpu) {
 532                 for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++) {
 533                         per_cpu(rcu_torture_count, cpu)[i] = 0;
 534                         per_cpu(rcu_torture_batch, cpu)[i] = 0;
 535                 }
 536         }
 537
 538         /* Start up the kthreads. */
 539
 540         VERBOSE_PRINTK_STRING("Creating rcu_torture_writer task");
 541         writer_task = kthread_run(rcu_torture_writer, NULL,
 542                                   "rcu_torture_writer");
 543         if (IS_ERR(writer_task)) {
 544                 firsterr = PTR_ERR(writer_task);
 545                 VERBOSE_PRINTK_ERRSTRING("Failed to create writer");
 546                 writer_task = NULL;
 547                 goto unwind;
 548         }
 549         reader_tasks = kmalloc(nrealreaders * sizeof(reader_tasks[0]),
 550                                GFP_KERNEL);
 551         if (reader_tasks == NULL) {
 552                 VERBOSE_PRINTK_ERRSTRING("out of memory");
 553                 firsterr = -ENOMEM;
 554                 goto unwind;
 555         }
 556         for (i = 0; i < nrealreaders; i++) {
 557                 VERBOSE_PRINTK_STRING("Creating rcu_torture_reader task");
 558                 reader_tasks[i] = kthread_run(rcu_torture_reader, NULL,
 559                                               "rcu_torture_reader");
 560                 if (IS_ERR(reader_tasks[i])) {
 561                         firsterr = PTR_ERR(reader_tasks[i]);
 562                         VERBOSE_PRINTK_ERRSTRING("Failed to create reader");
 563                         reader_tasks[i] = NULL;
 564                         goto unwind;
 565                 }
 566         }
 567         if (stat_interval > 0) {
 568                 VERBOSE_PRINTK_STRING("Creating rcu_torture_stats task");
 569                 stats_task = kthread_run(rcu_torture_stats, NULL,
 570                                         "rcu_torture_stats");
 571                 if (IS_ERR(stats_task)) {
 572                         firsterr = PTR_ERR(stats_task);
 573                         VERBOSE_PRINTK_ERRSTRING("Failed to create stats");
 574                         stats_task = NULL;
 575                         goto unwind;
 576                 }
 577         }
 578         if (test_no_idle_hz) {
 579                 rcu_idle_cpu = num_online_cpus() - 1;
 580                 /* Create the shuffler thread */
 581                 shuffler_task = kthread_run(rcu_torture_shuffle, NULL,
 582                                           "rcu_torture_shuffle");
 583                 if (IS_ERR(shuffler_task)) {
 584                         firsterr = PTR_ERR(shuffler_task);
 585                         VERBOSE_PRINTK_ERRSTRING("Failed to create shuffler");
 586                         shuffler_task = NULL;
 587                         goto unwind;
 588                 }
 589         }
 590         return 0;
 591
 592 unwind:
 593         rcu_torture_cleanup();
 594         return firsterr;
 595 }
 596
 597 module_init(rcu_torture_init);
 598 module_exit(rcu_torture_cleanup);