[PATCH] rcutorture: add ops vector and Classic RCU ops
[linux-2.6.git] / kernel / rcutorture.c
1 /*
2  * Read-Copy Update module-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 static char *torture_type = "rcu"; /* What to torture. */
57
58 module_param(nreaders, int, 0);
59 MODULE_PARM_DESC(nreaders, "Number of RCU reader threads");
60 module_param(stat_interval, int, 0);
61 MODULE_PARM_DESC(stat_interval, "Number of seconds between stats printk()s");
62 module_param(verbose, bool, 0);
63 MODULE_PARM_DESC(verbose, "Enable verbose debugging printk()s");
64 module_param(test_no_idle_hz, bool, 0);
65 MODULE_PARM_DESC(test_no_idle_hz, "Test support for tickless idle CPUs");
66 module_param(shuffle_interval, int, 0);
67 MODULE_PARM_DESC(shuffle_interval, "Number of seconds between shuffles");
68 module_param(torture_type, charp, 0);
69 MODULE_PARM_DESC(torture_type, "Type of RCU to torture (rcu)");
70
71 #define TORTURE_FLAG "-torture:"
72 #define PRINTK_STRING(s) \
73         do { printk(KERN_ALERT "%s" TORTURE_FLAG s "\n", torture_type); } while (0)
74 #define VERBOSE_PRINTK_STRING(s) \
75         do { if (verbose) printk(KERN_ALERT "%s" TORTURE_FLAG s "\n", torture_type); } while (0)
76 #define VERBOSE_PRINTK_ERRSTRING(s) \
77         do { if (verbose) printk(KERN_ALERT "%s" TORTURE_FLAG "!!! " s "\n", torture_type); } while (0)
78
79 static char printk_buf[4096];
80
81 static int nrealreaders;
82 static struct task_struct *writer_task;
83 static struct task_struct **reader_tasks;
84 static struct task_struct *stats_task;
85 static struct task_struct *shuffler_task;
86
87 #define RCU_TORTURE_PIPE_LEN 10
88
89 struct rcu_torture {
90         struct rcu_head rtort_rcu;
91         int rtort_pipe_count;
92         struct list_head rtort_free;
93         int rtort_mbtest;
94 };
95
96 static int fullstop = 0;        /* stop generating callbacks at test end. */
97 static LIST_HEAD(rcu_torture_freelist);
98 static struct rcu_torture *rcu_torture_current = NULL;
99 static long rcu_torture_current_version = 0;
100 static struct rcu_torture rcu_tortures[10 * RCU_TORTURE_PIPE_LEN];
101 static DEFINE_SPINLOCK(rcu_torture_lock);
102 static DEFINE_PER_CPU(long [RCU_TORTURE_PIPE_LEN + 1], rcu_torture_count) =
103         { 0 };
104 static DEFINE_PER_CPU(long [RCU_TORTURE_PIPE_LEN + 1], rcu_torture_batch) =
105         { 0 };
106 static atomic_t rcu_torture_wcount[RCU_TORTURE_PIPE_LEN + 1];
107 atomic_t n_rcu_torture_alloc;
108 atomic_t n_rcu_torture_alloc_fail;
109 atomic_t n_rcu_torture_free;
110 atomic_t n_rcu_torture_mberror;
111 atomic_t n_rcu_torture_error;
112
113 /*
114  * Allocate an element from the rcu_tortures pool.
115  */
116 static struct rcu_torture *
117 rcu_torture_alloc(void)
118 {
119         struct list_head *p;
120
121         spin_lock_bh(&rcu_torture_lock);
122         if (list_empty(&rcu_torture_freelist)) {
123                 atomic_inc(&n_rcu_torture_alloc_fail);
124                 spin_unlock_bh(&rcu_torture_lock);
125                 return NULL;
126         }
127         atomic_inc(&n_rcu_torture_alloc);
128         p = rcu_torture_freelist.next;
129         list_del_init(p);
130         spin_unlock_bh(&rcu_torture_lock);
131         return container_of(p, struct rcu_torture, rtort_free);
132 }
133
134 /*
135  * Free an element to the rcu_tortures pool.
136  */
137 static void
138 rcu_torture_free(struct rcu_torture *p)
139 {
140         atomic_inc(&n_rcu_torture_free);
141         spin_lock_bh(&rcu_torture_lock);
142         list_add_tail(&p->rtort_free, &rcu_torture_freelist);
143         spin_unlock_bh(&rcu_torture_lock);
144 }
145
146 struct rcu_random_state {
147         unsigned long rrs_state;
148         unsigned long rrs_count;
149 };
150
151 #define RCU_RANDOM_MULT 39916801  /* prime */
152 #define RCU_RANDOM_ADD  479001701 /* prime */
153 #define RCU_RANDOM_REFRESH 10000
154
155 #define DEFINE_RCU_RANDOM(name) struct rcu_random_state name = { 0, 0 }
156
157 /*
158  * Crude but fast random-number generator.  Uses a linear congruential
159  * generator, with occasional help from get_random_bytes().
160  */
161 static long
162 rcu_random(struct rcu_random_state *rrsp)
163 {
164         long refresh;
165
166         if (--rrsp->rrs_count < 0) {
167                 get_random_bytes(&refresh, sizeof(refresh));
168                 rrsp->rrs_state += refresh;
169                 rrsp->rrs_count = RCU_RANDOM_REFRESH;
170         }
171         rrsp->rrs_state = rrsp->rrs_state * RCU_RANDOM_MULT + RCU_RANDOM_ADD;
172         return swahw32(rrsp->rrs_state);
173 }
174
175 /*
176  * Operations vector for selecting different types of tests.
177  */
178
179 struct rcu_torture_ops {
180         void (*init)(void);
181         void (*cleanup)(void);
182         int (*readlock)(void);
183         void (*readunlock)(int idx);
184         int (*completed)(void);
185         void (*deferredfree)(struct rcu_torture *p);
186         int (*stats)(char *page);
187         char *name;
188 };
189 static struct rcu_torture_ops *cur_ops = NULL;
190
191 /*
192  * Definitions for rcu torture testing.
193  */
194
195 static int rcu_torture_read_lock(void)
196 {
197         rcu_read_lock();
198         return 0;
199 }
200
201 static void rcu_torture_read_unlock(int idx)
202 {
203         rcu_read_unlock();
204 }
205
206 static int rcu_torture_completed(void)
207 {
208         return rcu_batches_completed();
209 }
210
211 static void
212 rcu_torture_cb(struct rcu_head *p)
213 {
214         int i;
215         struct rcu_torture *rp = container_of(p, struct rcu_torture, rtort_rcu);
216
217         if (fullstop) {
218                 /* Test is ending, just drop callbacks on the floor. */
219                 /* The next initialization will pick up the pieces. */
220                 return;
221         }
222         i = rp->rtort_pipe_count;
223         if (i > RCU_TORTURE_PIPE_LEN)
224                 i = RCU_TORTURE_PIPE_LEN;
225         atomic_inc(&rcu_torture_wcount[i]);
226         if (++rp->rtort_pipe_count >= RCU_TORTURE_PIPE_LEN) {
227                 rp->rtort_mbtest = 0;
228                 rcu_torture_free(rp);
229         } else
230                 cur_ops->deferredfree(rp);
231 }
232
233 static void rcu_torture_deferred_free(struct rcu_torture *p)
234 {
235         call_rcu(&p->rtort_rcu, rcu_torture_cb);
236 }
237
238 static struct rcu_torture_ops rcu_ops = {
239         .init = NULL,
240         .cleanup = NULL,
241         .readlock = rcu_torture_read_lock,
242         .readunlock = rcu_torture_read_unlock,
243         .completed = rcu_torture_completed,
244         .deferredfree = rcu_torture_deferred_free,
245         .stats = NULL,
246         .name = "rcu"
247 };
248
249 static struct rcu_torture_ops *torture_ops[] =
250         { &rcu_ops, NULL };
251
252 /*
253  * RCU torture writer kthread.  Repeatedly substitutes a new structure
254  * for that pointed to by rcu_torture_current, freeing the old structure
255  * after a series of grace periods (the "pipeline").
256  */
257 static int
258 rcu_torture_writer(void *arg)
259 {
260         int i;
261         long oldbatch = rcu_batches_completed();
262         struct rcu_torture *rp;
263         struct rcu_torture *old_rp;
264         static DEFINE_RCU_RANDOM(rand);
265
266         VERBOSE_PRINTK_STRING("rcu_torture_writer task started");
267         set_user_nice(current, 19);
268
269         do {
270                 schedule_timeout_uninterruptible(1);
271                 if ((rp = rcu_torture_alloc()) == NULL)
272                         continue;
273                 rp->rtort_pipe_count = 0;
274                 udelay(rcu_random(&rand) & 0x3ff);
275                 old_rp = rcu_torture_current;
276                 rp->rtort_mbtest = 1;
277                 rcu_assign_pointer(rcu_torture_current, rp);
278                 smp_wmb();
279                 if (old_rp != NULL) {
280                         i = old_rp->rtort_pipe_count;
281                         if (i > RCU_TORTURE_PIPE_LEN)
282                                 i = RCU_TORTURE_PIPE_LEN;
283                         atomic_inc(&rcu_torture_wcount[i]);
284                         old_rp->rtort_pipe_count++;
285                         cur_ops->deferredfree(old_rp);
286                 }
287                 rcu_torture_current_version++;
288                 oldbatch = cur_ops->completed();
289         } while (!kthread_should_stop() && !fullstop);
290         VERBOSE_PRINTK_STRING("rcu_torture_writer task stopping");
291         while (!kthread_should_stop())
292                 schedule_timeout_uninterruptible(1);
293         return 0;
294 }
295
296 /*
297  * RCU torture reader kthread.  Repeatedly dereferences rcu_torture_current,
298  * incrementing the corresponding element of the pipeline array.  The
299  * counter in the element should never be greater than 1, otherwise, the
300  * RCU implementation is broken.
301  */
302 static int
303 rcu_torture_reader(void *arg)
304 {
305         int completed;
306         int idx;
307         DEFINE_RCU_RANDOM(rand);
308         struct rcu_torture *p;
309         int pipe_count;
310
311         VERBOSE_PRINTK_STRING("rcu_torture_reader task started");
312         set_user_nice(current, 19);
313
314         do {
315                 idx = cur_ops->readlock();
316                 completed = cur_ops->completed();
317                 p = rcu_dereference(rcu_torture_current);
318                 if (p == NULL) {
319                         /* Wait for rcu_torture_writer to get underway */
320                         cur_ops->readunlock(idx);
321                         schedule_timeout_interruptible(HZ);
322                         continue;
323                 }
324                 if (p->rtort_mbtest == 0)
325                         atomic_inc(&n_rcu_torture_mberror);
326                 udelay(rcu_random(&rand) & 0x7f);
327                 preempt_disable();
328                 pipe_count = p->rtort_pipe_count;
329                 if (pipe_count > RCU_TORTURE_PIPE_LEN) {
330                         /* Should not happen, but... */
331                         pipe_count = RCU_TORTURE_PIPE_LEN;
332                 }
333                 ++__get_cpu_var(rcu_torture_count)[pipe_count];
334                 completed = cur_ops->completed() - completed;
335                 if (completed > RCU_TORTURE_PIPE_LEN) {
336                         /* Should not happen, but... */
337                         completed = RCU_TORTURE_PIPE_LEN;
338                 }
339                 ++__get_cpu_var(rcu_torture_batch)[completed];
340                 preempt_enable();
341                 cur_ops->readunlock(idx);
342                 schedule();
343         } while (!kthread_should_stop() && !fullstop);
344         VERBOSE_PRINTK_STRING("rcu_torture_reader task stopping");
345         while (!kthread_should_stop())
346                 schedule_timeout_uninterruptible(1);
347         return 0;
348 }
349
350 /*
351  * Create an RCU-torture statistics message in the specified buffer.
352  */
353 static int
354 rcu_torture_printk(char *page)
355 {
356         int cnt = 0;
357         int cpu;
358         int i;
359         long pipesummary[RCU_TORTURE_PIPE_LEN + 1] = { 0 };
360         long batchsummary[RCU_TORTURE_PIPE_LEN + 1] = { 0 };
361
362         for_each_possible_cpu(cpu) {
363                 for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++) {
364                         pipesummary[i] += per_cpu(rcu_torture_count, cpu)[i];
365                         batchsummary[i] += per_cpu(rcu_torture_batch, cpu)[i];
366                 }
367         }
368         for (i = RCU_TORTURE_PIPE_LEN - 1; i >= 0; i--) {
369                 if (pipesummary[i] != 0)
370                         break;
371         }
372         cnt += sprintf(&page[cnt], "%s%s ", torture_type, TORTURE_FLAG);
373         cnt += sprintf(&page[cnt],
374                        "rtc: %p ver: %ld tfle: %d rta: %d rtaf: %d rtf: %d "
375                        "rtmbe: %d",
376                        rcu_torture_current,
377                        rcu_torture_current_version,
378                        list_empty(&rcu_torture_freelist),
379                        atomic_read(&n_rcu_torture_alloc),
380                        atomic_read(&n_rcu_torture_alloc_fail),
381                        atomic_read(&n_rcu_torture_free),
382                        atomic_read(&n_rcu_torture_mberror));
383         if (atomic_read(&n_rcu_torture_mberror) != 0)
384                 cnt += sprintf(&page[cnt], " !!!");
385         cnt += sprintf(&page[cnt], "\n%s%s ", torture_type, TORTURE_FLAG);
386         if (i > 1) {
387                 cnt += sprintf(&page[cnt], "!!! ");
388                 atomic_inc(&n_rcu_torture_error);
389         }
390         cnt += sprintf(&page[cnt], "Reader Pipe: ");
391         for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++)
392                 cnt += sprintf(&page[cnt], " %ld", pipesummary[i]);
393         cnt += sprintf(&page[cnt], "\n%s%s ", torture_type, TORTURE_FLAG);
394         cnt += sprintf(&page[cnt], "Reader Batch: ");
395         for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++)
396                 cnt += sprintf(&page[cnt], " %ld", batchsummary[i]);
397         cnt += sprintf(&page[cnt], "\n%s%s ", torture_type, TORTURE_FLAG);
398         cnt += sprintf(&page[cnt], "Free-Block Circulation: ");
399         for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++) {
400                 cnt += sprintf(&page[cnt], " %d",
401                                atomic_read(&rcu_torture_wcount[i]));
402         }
403         cnt += sprintf(&page[cnt], "\n");
404         if (cur_ops->stats != NULL)
405                 cnt += cur_ops->stats(&page[cnt]);
406         return cnt;
407 }
408
409 /*
410  * Print torture statistics.  Caller must ensure that there is only
411  * one call to this function at a given time!!!  This is normally
412  * accomplished by relying on the module system to only have one copy
413  * of the module loaded, and then by giving the rcu_torture_stats
414  * kthread full control (or the init/cleanup functions when rcu_torture_stats
415  * thread is not running).
416  */
417 static void
418 rcu_torture_stats_print(void)
419 {
420         int cnt;
421
422         cnt = rcu_torture_printk(printk_buf);
423         printk(KERN_ALERT "%s", printk_buf);
424 }
425
426 /*
427  * Periodically prints torture statistics, if periodic statistics printing
428  * was specified via the stat_interval module parameter.
429  *
430  * No need to worry about fullstop here, since this one doesn't reference
431  * volatile state or register callbacks.
432  */
433 static int
434 rcu_torture_stats(void *arg)
435 {
436         VERBOSE_PRINTK_STRING("rcu_torture_stats task started");
437         do {
438                 schedule_timeout_interruptible(stat_interval * HZ);
439                 rcu_torture_stats_print();
440         } while (!kthread_should_stop());
441         VERBOSE_PRINTK_STRING("rcu_torture_stats task stopping");
442         return 0;
443 }
444
445 static int rcu_idle_cpu;        /* Force all torture tasks off this CPU */
446
447 /* Shuffle tasks such that we allow @rcu_idle_cpu to become idle. A special case
448  * is when @rcu_idle_cpu = -1, when we allow the tasks to run on all CPUs.
449  */
450 void rcu_torture_shuffle_tasks(void)
451 {
452         cpumask_t tmp_mask = CPU_MASK_ALL;
453         int i;
454
455         lock_cpu_hotplug();
456
457         /* No point in shuffling if there is only one online CPU (ex: UP) */
458         if (num_online_cpus() == 1) {
459                 unlock_cpu_hotplug();
460                 return;
461         }
462
463         if (rcu_idle_cpu != -1)
464                 cpu_clear(rcu_idle_cpu, tmp_mask);
465
466         set_cpus_allowed(current, tmp_mask);
467
468         if (reader_tasks != NULL) {
469                 for (i = 0; i < nrealreaders; i++)
470                         if (reader_tasks[i])
471                                 set_cpus_allowed(reader_tasks[i], tmp_mask);
472         }
473
474         if (writer_task)
475                 set_cpus_allowed(writer_task, tmp_mask);
476
477         if (stats_task)
478                 set_cpus_allowed(stats_task, tmp_mask);
479
480         if (rcu_idle_cpu == -1)
481                 rcu_idle_cpu = num_online_cpus() - 1;
482         else
483                 rcu_idle_cpu--;
484
485         unlock_cpu_hotplug();
486 }
487
488 /* Shuffle tasks across CPUs, with the intent of allowing each CPU in the
489  * system to become idle at a time and cut off its timer ticks. This is meant
490  * to test the support for such tickless idle CPU in RCU.
491  */
492 static int
493 rcu_torture_shuffle(void *arg)
494 {
495         VERBOSE_PRINTK_STRING("rcu_torture_shuffle task started");
496         do {
497                 schedule_timeout_interruptible(shuffle_interval * HZ);
498                 rcu_torture_shuffle_tasks();
499         } while (!kthread_should_stop());
500         VERBOSE_PRINTK_STRING("rcu_torture_shuffle task stopping");
501         return 0;
502 }
503
504 static inline void
505 rcu_torture_print_module_parms(char *tag)
506 {
507         printk(KERN_ALERT "%s" TORTURE_FLAG "--- %s: nreaders=%d "
508                 "stat_interval=%d verbose=%d test_no_idle_hz=%d "
509                 "shuffle_interval = %d\n",
510                 torture_type, tag, nrealreaders, stat_interval, verbose,
511                 test_no_idle_hz, shuffle_interval);
512 }
513
514 static void
515 rcu_torture_cleanup(void)
516 {
517         int i;
518
519         fullstop = 1;
520         if (shuffler_task != NULL) {
521                 VERBOSE_PRINTK_STRING("Stopping rcu_torture_shuffle task");
522                 kthread_stop(shuffler_task);
523         }
524         shuffler_task = NULL;
525
526         if (writer_task != NULL) {
527                 VERBOSE_PRINTK_STRING("Stopping rcu_torture_writer task");
528                 kthread_stop(writer_task);
529         }
530         writer_task = NULL;
531
532         if (reader_tasks != NULL) {
533                 for (i = 0; i < nrealreaders; i++) {
534                         if (reader_tasks[i] != NULL) {
535                                 VERBOSE_PRINTK_STRING(
536                                         "Stopping rcu_torture_reader task");
537                                 kthread_stop(reader_tasks[i]);
538                         }
539                         reader_tasks[i] = NULL;
540                 }
541                 kfree(reader_tasks);
542                 reader_tasks = NULL;
543         }
544         rcu_torture_current = NULL;
545
546         if (stats_task != NULL) {
547                 VERBOSE_PRINTK_STRING("Stopping rcu_torture_stats task");
548                 kthread_stop(stats_task);
549         }
550         stats_task = NULL;
551
552         /* Wait for all RCU callbacks to fire.  */
553         rcu_barrier();
554
555         rcu_torture_stats_print();  /* -After- the stats thread is stopped! */
556
557         if (cur_ops->cleanup != NULL)
558                 cur_ops->cleanup();
559         if (atomic_read(&n_rcu_torture_error))
560                 rcu_torture_print_module_parms("End of test: FAILURE");
561         else
562                 rcu_torture_print_module_parms("End of test: SUCCESS");
563 }
564
565 static int
566 rcu_torture_init(void)
567 {
568         int i;
569         int cpu;
570         int firsterr = 0;
571
572         /* Process args and tell the world that the torturer is on the job. */
573
574         for (i = 0; cur_ops = torture_ops[i], cur_ops != NULL; i++) {
575                 cur_ops = torture_ops[i];
576                 if (strcmp(torture_type, cur_ops->name) == 0) {
577                         break;
578                 }
579         }
580         if (cur_ops == NULL) {
581                 printk(KERN_ALERT "rcutorture: invalid torture type: \"%s\"\n",
582                        torture_type);
583                 return (-EINVAL);
584         }
585         if (cur_ops->init != NULL)
586                 cur_ops->init(); /* no "goto unwind" prior to this point!!! */
587
588         if (nreaders >= 0)
589                 nrealreaders = nreaders;
590         else
591                 nrealreaders = 2 * num_online_cpus();
592         rcu_torture_print_module_parms("Start of test");
593         fullstop = 0;
594
595         /* Set up the freelist. */
596
597         INIT_LIST_HEAD(&rcu_torture_freelist);
598         for (i = 0; i < sizeof(rcu_tortures) / sizeof(rcu_tortures[0]); i++) {
599                 rcu_tortures[i].rtort_mbtest = 0;
600                 list_add_tail(&rcu_tortures[i].rtort_free,
601                               &rcu_torture_freelist);
602         }
603
604         /* Initialize the statistics so that each run gets its own numbers. */
605
606         rcu_torture_current = NULL;
607         rcu_torture_current_version = 0;
608         atomic_set(&n_rcu_torture_alloc, 0);
609         atomic_set(&n_rcu_torture_alloc_fail, 0);
610         atomic_set(&n_rcu_torture_free, 0);
611         atomic_set(&n_rcu_torture_mberror, 0);
612         atomic_set(&n_rcu_torture_error, 0);
613         for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++)
614                 atomic_set(&rcu_torture_wcount[i], 0);
615         for_each_possible_cpu(cpu) {
616                 for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++) {
617                         per_cpu(rcu_torture_count, cpu)[i] = 0;
618                         per_cpu(rcu_torture_batch, cpu)[i] = 0;
619                 }
620         }
621
622         /* Start up the kthreads. */
623
624         VERBOSE_PRINTK_STRING("Creating rcu_torture_writer task");
625         writer_task = kthread_run(rcu_torture_writer, NULL,
626                                   "rcu_torture_writer");
627         if (IS_ERR(writer_task)) {
628                 firsterr = PTR_ERR(writer_task);
629                 VERBOSE_PRINTK_ERRSTRING("Failed to create writer");
630                 writer_task = NULL;
631                 goto unwind;
632         }
633         reader_tasks = kmalloc(nrealreaders * sizeof(reader_tasks[0]),
634                                GFP_KERNEL);
635         if (reader_tasks == NULL) {
636                 VERBOSE_PRINTK_ERRSTRING("out of memory");
637                 firsterr = -ENOMEM;
638                 goto unwind;
639         }
640         for (i = 0; i < nrealreaders; i++) {
641                 VERBOSE_PRINTK_STRING("Creating rcu_torture_reader task");
642                 reader_tasks[i] = kthread_run(rcu_torture_reader, NULL,
643                                               "rcu_torture_reader");
644                 if (IS_ERR(reader_tasks[i])) {
645                         firsterr = PTR_ERR(reader_tasks[i]);
646                         VERBOSE_PRINTK_ERRSTRING("Failed to create reader");
647                         reader_tasks[i] = NULL;
648                         goto unwind;
649                 }
650         }
651         if (stat_interval > 0) {
652                 VERBOSE_PRINTK_STRING("Creating rcu_torture_stats task");
653                 stats_task = kthread_run(rcu_torture_stats, NULL,
654                                         "rcu_torture_stats");
655                 if (IS_ERR(stats_task)) {
656                         firsterr = PTR_ERR(stats_task);
657                         VERBOSE_PRINTK_ERRSTRING("Failed to create stats");
658                         stats_task = NULL;
659                         goto unwind;
660                 }
661         }
662         if (test_no_idle_hz) {
663                 rcu_idle_cpu = num_online_cpus() - 1;
664                 /* Create the shuffler thread */
665                 shuffler_task = kthread_run(rcu_torture_shuffle, NULL,
666                                           "rcu_torture_shuffle");
667                 if (IS_ERR(shuffler_task)) {
668                         firsterr = PTR_ERR(shuffler_task);
669                         VERBOSE_PRINTK_ERRSTRING("Failed to create shuffler");
670                         shuffler_task = NULL;
671                         goto unwind;
672                 }
673         }
674         return 0;
675
676 unwind:
677         rcu_torture_cleanup();
678         return firsterr;
679 }
680
681 module_init(rcu_torture_init);
682 module_exit(rcu_torture_cleanup);