generic: use new set_cpus_allowed_ptr function
[linux-2.6.git] / kernel / rcutorture.c
index 23446e9..47894f9 100644 (file)
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  *
- * Copyright (C) IBM Corporation, 2005
+ * Copyright (C) IBM Corporation, 2005, 2006
  *
  * Authors: Paul E. McKenney <paulmck@us.ibm.com>
+ *          Josh Triplett <josh@freedesktop.org>
  *
  * See also:  Documentation/RCU/torture.txt
  */
 #include <linux/sched.h>
 #include <asm/atomic.h>
 #include <linux/bitops.h>
-#include <linux/module.h>
 #include <linux/completion.h>
 #include <linux/moduleparam.h>
 #include <linux/percpu.h>
 #include <linux/notifier.h>
+#include <linux/freezer.h>
 #include <linux/cpu.h>
-#include <linux/random.h>
 #include <linux/delay.h>
 #include <linux/byteorder/swabb.h>
 #include <linux/stat.h>
+#include <linux/srcu.h>
 
 MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Paul E. McKenney <paulmck@us.ibm.com> and "
+              "Josh Triplett <josh@freedesktop.org>");
 
 static int nreaders = -1;      /* # reader threads, defaults to 2*ncpus */
+static int nfakewriters = 4;   /* # fake writer threads */
 static int stat_interval;      /* Interval between stats, in seconds. */
                                /*  Defaults to "only at end of test". */
 static int verbose;            /* Print more debug info. */
 static int test_no_idle_hz;    /* Test RCU's support for tickless idle CPUs. */
 static int shuffle_interval = 5; /* Interval between shuffles (in sec)*/
-static char *torture_type = "rcu"; /* What to torture. */
+static char *torture_type = "rcu"; /* What RCU implementation to torture. */
 
-module_param(nreaders, int, 0);
+module_param(nreaders, int, 0444);
 MODULE_PARM_DESC(nreaders, "Number of RCU reader threads");
-module_param(stat_interval, int, 0);
+module_param(nfakewriters, int, 0444);
+MODULE_PARM_DESC(nfakewriters, "Number of RCU fake writer threads");
+module_param(stat_interval, int, 0444);
 MODULE_PARM_DESC(stat_interval, "Number of seconds between stats printk()s");
-module_param(verbose, bool, 0);
+module_param(verbose, bool, 0444);
 MODULE_PARM_DESC(verbose, "Enable verbose debugging printk()s");
-module_param(test_no_idle_hz, bool, 0);
+module_param(test_no_idle_hz, bool, 0444);
 MODULE_PARM_DESC(test_no_idle_hz, "Test support for tickless idle CPUs");
-module_param(shuffle_interval, int, 0);
+module_param(shuffle_interval, int, 0444);
 MODULE_PARM_DESC(shuffle_interval, "Number of seconds between shuffles");
-module_param(torture_type, charp, 0);
-MODULE_PARM_DESC(torture_type, "Type of RCU to torture (rcu, rcu_bh)");
+module_param(torture_type, charp, 0444);
+MODULE_PARM_DESC(torture_type, "Type of RCU to torture (rcu, rcu_bh, srcu)");
 
 #define TORTURE_FLAG "-torture:"
 #define PRINTK_STRING(s) \
@@ -80,6 +86,7 @@ static char printk_buf[4096];
 
 static int nrealreaders;
 static struct task_struct *writer_task;
+static struct task_struct **fakewriter_tasks;
 static struct task_struct **reader_tasks;
 static struct task_struct *stats_task;
 static struct task_struct *shuffler_task;
@@ -104,11 +111,12 @@ static DEFINE_PER_CPU(long [RCU_TORTURE_PIPE_LEN + 1], rcu_torture_count) =
 static DEFINE_PER_CPU(long [RCU_TORTURE_PIPE_LEN + 1], rcu_torture_batch) =
        { 0 };
 static atomic_t rcu_torture_wcount[RCU_TORTURE_PIPE_LEN + 1];
-atomic_t n_rcu_torture_alloc;
-atomic_t n_rcu_torture_alloc_fail;
-atomic_t n_rcu_torture_free;
-atomic_t n_rcu_torture_mberror;
-atomic_t n_rcu_torture_error;
+static atomic_t n_rcu_torture_alloc;
+static atomic_t n_rcu_torture_alloc_fail;
+static atomic_t n_rcu_torture_free;
+static atomic_t n_rcu_torture_mberror;
+static atomic_t n_rcu_torture_error;
+static struct list_head rcu_torture_removed;
 
 /*
  * Allocate an element from the rcu_tortures pool.
@@ -145,7 +153,7 @@ rcu_torture_free(struct rcu_torture *p)
 
 struct rcu_random_state {
        unsigned long rrs_state;
-       unsigned long rrs_count;
+       long rrs_count;
 };
 
 #define RCU_RANDOM_MULT 39916801  /* prime */
@@ -156,16 +164,14 @@ struct rcu_random_state {
 
 /*
  * Crude but fast random-number generator.  Uses a linear congruential
- * generator, with occasional help from get_random_bytes().
+ * generator, with occasional help from cpu_clock().
  */
-static long
+static unsigned long
 rcu_random(struct rcu_random_state *rrsp)
 {
-       long refresh;
-
        if (--rrsp->rrs_count < 0) {
-               get_random_bytes(&refresh, sizeof(refresh));
-               rrsp->rrs_state += refresh;
+               rrsp->rrs_state +=
+                       (unsigned long)cpu_clock(raw_smp_processor_id());
                rrsp->rrs_count = RCU_RANDOM_REFRESH;
        }
        rrsp->rrs_state = rrsp->rrs_state * RCU_RANDOM_MULT + RCU_RANDOM_ADD;
@@ -180,9 +186,11 @@ struct rcu_torture_ops {
        void (*init)(void);
        void (*cleanup)(void);
        int (*readlock)(void);
+       void (*readdelay)(struct rcu_random_state *rrsp);
        void (*readunlock)(int idx);
        int (*completed)(void);
        void (*deferredfree)(struct rcu_torture *p);
+       void (*sync)(void);
        int (*stats)(char *page);
        char *name;
 };
@@ -198,6 +206,18 @@ static int rcu_torture_read_lock(void) __acquires(RCU)
        return 0;
 }
 
+static void rcu_read_delay(struct rcu_random_state *rrsp)
+{
+       long delay;
+       const long longdelay = 200;
+
+       /* We want there to be long-running readers, but not all the time. */
+
+       delay = rcu_random(rrsp) % (nrealreaders * 2 * longdelay);
+       if (!delay)
+               udelay(longdelay);
+}
+
 static void rcu_torture_read_unlock(int idx) __releases(RCU)
 {
        rcu_read_unlock();
@@ -239,13 +259,54 @@ static struct rcu_torture_ops rcu_ops = {
        .init = NULL,
        .cleanup = NULL,
        .readlock = rcu_torture_read_lock,
+       .readdelay = rcu_read_delay,
        .readunlock = rcu_torture_read_unlock,
        .completed = rcu_torture_completed,
        .deferredfree = rcu_torture_deferred_free,
+       .sync = synchronize_rcu,
        .stats = NULL,
        .name = "rcu"
 };
 
+static void rcu_sync_torture_deferred_free(struct rcu_torture *p)
+{
+       int i;
+       struct rcu_torture *rp;
+       struct rcu_torture *rp1;
+
+       cur_ops->sync();
+       list_add(&p->rtort_free, &rcu_torture_removed);
+       list_for_each_entry_safe(rp, rp1, &rcu_torture_removed, rtort_free) {
+               i = rp->rtort_pipe_count;
+               if (i > RCU_TORTURE_PIPE_LEN)
+                       i = RCU_TORTURE_PIPE_LEN;
+               atomic_inc(&rcu_torture_wcount[i]);
+               if (++rp->rtort_pipe_count >= RCU_TORTURE_PIPE_LEN) {
+                       rp->rtort_mbtest = 0;
+                       list_del(&rp->rtort_free);
+                       rcu_torture_free(rp);
+               }
+       }
+}
+
+static void rcu_sync_torture_init(void)
+{
+       INIT_LIST_HEAD(&rcu_torture_removed);
+}
+
+static struct rcu_torture_ops rcu_sync_ops = {
+       .init = rcu_sync_torture_init,
+       .cleanup = NULL,
+       .readlock = rcu_torture_read_lock,
+       .readdelay = rcu_read_delay,
+       .readunlock = rcu_torture_read_unlock,
+       .completed = rcu_torture_completed,
+       .deferredfree = rcu_sync_torture_deferred_free,
+       .sync = synchronize_rcu,
+       .stats = NULL,
+       .name = "rcu_sync"
+};
+
 /*
  * Definitions for rcu_bh torture testing.
  */
@@ -271,19 +332,172 @@ static void rcu_bh_torture_deferred_free(struct rcu_torture *p)
        call_rcu_bh(&p->rtort_rcu, rcu_torture_cb);
 }
 
+struct rcu_bh_torture_synchronize {
+       struct rcu_head head;
+       struct completion completion;
+};
+
+static void rcu_bh_torture_wakeme_after_cb(struct rcu_head *head)
+{
+       struct rcu_bh_torture_synchronize *rcu;
+
+       rcu = container_of(head, struct rcu_bh_torture_synchronize, head);
+       complete(&rcu->completion);
+}
+
+static void rcu_bh_torture_synchronize(void)
+{
+       struct rcu_bh_torture_synchronize rcu;
+
+       init_completion(&rcu.completion);
+       call_rcu_bh(&rcu.head, rcu_bh_torture_wakeme_after_cb);
+       wait_for_completion(&rcu.completion);
+}
+
 static struct rcu_torture_ops rcu_bh_ops = {
        .init = NULL,
        .cleanup = NULL,
        .readlock = rcu_bh_torture_read_lock,
+       .readdelay = rcu_read_delay,  /* just reuse rcu's version. */
        .readunlock = rcu_bh_torture_read_unlock,
        .completed = rcu_bh_torture_completed,
        .deferredfree = rcu_bh_torture_deferred_free,
+       .sync = rcu_bh_torture_synchronize,
        .stats = NULL,
        .name = "rcu_bh"
 };
 
-static struct rcu_torture_ops *torture_ops[] =
-       { &rcu_ops, &rcu_bh_ops, NULL };
+static struct rcu_torture_ops rcu_bh_sync_ops = {
+       .init = rcu_sync_torture_init,
+       .cleanup = NULL,
+       .readlock = rcu_bh_torture_read_lock,
+       .readdelay = rcu_read_delay,  /* just reuse rcu's version. */
+       .readunlock = rcu_bh_torture_read_unlock,
+       .completed = rcu_bh_torture_completed,
+       .deferredfree = rcu_sync_torture_deferred_free,
+       .sync = rcu_bh_torture_synchronize,
+       .stats = NULL,
+       .name = "rcu_bh_sync"
+};
+
+/*
+ * Definitions for srcu torture testing.
+ */
+
+static struct srcu_struct srcu_ctl;
+
+static void srcu_torture_init(void)
+{
+       init_srcu_struct(&srcu_ctl);
+       rcu_sync_torture_init();
+}
+
+static void srcu_torture_cleanup(void)
+{
+       synchronize_srcu(&srcu_ctl);
+       cleanup_srcu_struct(&srcu_ctl);
+}
+
+static int srcu_torture_read_lock(void) __acquires(&srcu_ctl)
+{
+       return srcu_read_lock(&srcu_ctl);
+}
+
+static void srcu_read_delay(struct rcu_random_state *rrsp)
+{
+       long delay;
+       const long uspertick = 1000000 / HZ;
+       const long longdelay = 10;
+
+       /* We want there to be long-running readers, but not all the time. */
+
+       delay = rcu_random(rrsp) % (nrealreaders * 2 * longdelay * uspertick);
+       if (!delay)
+               schedule_timeout_interruptible(longdelay);
+}
+
+static void srcu_torture_read_unlock(int idx) __releases(&srcu_ctl)
+{
+       srcu_read_unlock(&srcu_ctl, idx);
+}
+
+static int srcu_torture_completed(void)
+{
+       return srcu_batches_completed(&srcu_ctl);
+}
+
+static void srcu_torture_synchronize(void)
+{
+       synchronize_srcu(&srcu_ctl);
+}
+
+static int srcu_torture_stats(char *page)
+{
+       int cnt = 0;
+       int cpu;
+       int idx = srcu_ctl.completed & 0x1;
+
+       cnt += sprintf(&page[cnt], "%s%s per-CPU(idx=%d):",
+                      torture_type, TORTURE_FLAG, idx);
+       for_each_possible_cpu(cpu) {
+               cnt += sprintf(&page[cnt], " %d(%d,%d)", cpu,
+                              per_cpu_ptr(srcu_ctl.per_cpu_ref, cpu)->c[!idx],
+                              per_cpu_ptr(srcu_ctl.per_cpu_ref, cpu)->c[idx]);
+       }
+       cnt += sprintf(&page[cnt], "\n");
+       return cnt;
+}
+
+static struct rcu_torture_ops srcu_ops = {
+       .init = srcu_torture_init,
+       .cleanup = srcu_torture_cleanup,
+       .readlock = srcu_torture_read_lock,
+       .readdelay = srcu_read_delay,
+       .readunlock = srcu_torture_read_unlock,
+       .completed = srcu_torture_completed,
+       .deferredfree = rcu_sync_torture_deferred_free,
+       .sync = srcu_torture_synchronize,
+       .stats = srcu_torture_stats,
+       .name = "srcu"
+};
+
+/*
+ * Definitions for sched torture testing.
+ */
+
+static int sched_torture_read_lock(void)
+{
+       preempt_disable();
+       return 0;
+}
+
+static void sched_torture_read_unlock(int idx)
+{
+       preempt_enable();
+}
+
+static int sched_torture_completed(void)
+{
+       return 0;
+}
+
+static void sched_torture_synchronize(void)
+{
+       synchronize_sched();
+}
+
+static struct rcu_torture_ops sched_ops = {
+       .init = rcu_sync_torture_init,
+       .cleanup = NULL,
+       .readlock = sched_torture_read_lock,
+       .readdelay = rcu_read_delay,  /* just reuse rcu's version. */
+       .readunlock = sched_torture_read_unlock,
+       .completed = sched_torture_completed,
+       .deferredfree = rcu_sync_torture_deferred_free,
+       .sync = sched_torture_synchronize,
+       .stats = NULL,
+       .name = "sched"
+};
 
 /*
  * RCU torture writer kthread.  Repeatedly substitutes a new structure
@@ -312,7 +526,7 @@ rcu_torture_writer(void *arg)
                rp->rtort_mbtest = 1;
                rcu_assign_pointer(rcu_torture_current, rp);
                smp_wmb();
-               if (old_rp != NULL) {
+               if (old_rp) {
                        i = old_rp->rtort_pipe_count;
                        if (i > RCU_TORTURE_PIPE_LEN)
                                i = RCU_TORTURE_PIPE_LEN;
@@ -330,6 +544,30 @@ rcu_torture_writer(void *arg)
 }
 
 /*
+ * RCU torture fake writer kthread.  Repeatedly calls sync, with a random
+ * delay between calls.
+ */
+static int
+rcu_torture_fakewriter(void *arg)
+{
+       DEFINE_RCU_RANDOM(rand);
+
+       VERBOSE_PRINTK_STRING("rcu_torture_fakewriter task started");
+       set_user_nice(current, 19);
+
+       do {
+               schedule_timeout_uninterruptible(1 + rcu_random(&rand)%10);
+               udelay(rcu_random(&rand) & 0x3ff);
+               cur_ops->sync();
+       } while (!kthread_should_stop() && !fullstop);
+
+       VERBOSE_PRINTK_STRING("rcu_torture_fakewriter task stopping");
+       while (!kthread_should_stop())
+               schedule_timeout_uninterruptible(1);
+       return 0;
+}
+
+/*
  * RCU torture reader kthread.  Repeatedly dereferences rcu_torture_current,
  * incrementing the corresponding element of the pipeline array.  The
  * counter in the element should never be greater than 1, otherwise, the
@@ -359,7 +597,7 @@ rcu_torture_reader(void *arg)
                }
                if (p->rtort_mbtest == 0)
                        atomic_inc(&n_rcu_torture_mberror);
-               udelay(rcu_random(&rand) & 0x7f);
+               cur_ops->readdelay(&rand);
                preempt_disable();
                pipe_count = p->rtort_pipe_count;
                if (pipe_count > RCU_TORTURE_PIPE_LEN) {
@@ -437,7 +675,7 @@ rcu_torture_printk(char *page)
                               atomic_read(&rcu_torture_wcount[i]));
        }
        cnt += sprintf(&page[cnt], "\n");
-       if (cur_ops->stats != NULL)
+       if (cur_ops->stats)
                cnt += cur_ops->stats(&page[cnt]);
        return cnt;
 }
@@ -483,42 +721,51 @@ static int rcu_idle_cpu;  /* Force all torture tasks off this CPU */
 /* Shuffle tasks such that we allow @rcu_idle_cpu to become idle. A special case
  * is when @rcu_idle_cpu = -1, when we allow the tasks to run on all CPUs.
  */
-void rcu_torture_shuffle_tasks(void)
+static void rcu_torture_shuffle_tasks(void)
 {
-       cpumask_t tmp_mask = CPU_MASK_ALL;
+       cpumask_t tmp_mask;
        int i;
 
-       lock_cpu_hotplug();
+       cpus_setall(tmp_mask);
+       get_online_cpus();
 
        /* No point in shuffling if there is only one online CPU (ex: UP) */
        if (num_online_cpus() == 1) {
-               unlock_cpu_hotplug();
+               put_online_cpus();
                return;
        }
 
        if (rcu_idle_cpu != -1)
                cpu_clear(rcu_idle_cpu, tmp_mask);
 
-       set_cpus_allowed(current, tmp_mask);
+       set_cpus_allowed_ptr(current, &tmp_mask);
 
-       if (reader_tasks != NULL) {
+       if (reader_tasks) {
                for (i = 0; i < nrealreaders; i++)
                        if (reader_tasks[i])
-                               set_cpus_allowed(reader_tasks[i], tmp_mask);
+                               set_cpus_allowed_ptr(reader_tasks[i],
+                                                    &tmp_mask);
+       }
+
+       if (fakewriter_tasks) {
+               for (i = 0; i < nfakewriters; i++)
+                       if (fakewriter_tasks[i])
+                               set_cpus_allowed_ptr(fakewriter_tasks[i],
+                                                    &tmp_mask);
        }
 
        if (writer_task)
-               set_cpus_allowed(writer_task, tmp_mask);
+               set_cpus_allowed_ptr(writer_task, &tmp_mask);
 
        if (stats_task)
-               set_cpus_allowed(stats_task, tmp_mask);
+               set_cpus_allowed_ptr(stats_task, &tmp_mask);
 
        if (rcu_idle_cpu == -1)
                rcu_idle_cpu = num_online_cpus() - 1;
        else
                rcu_idle_cpu--;
 
-       unlock_cpu_hotplug();
+       put_online_cpus();
 }
 
 /* Shuffle tasks across CPUs, with the intent of allowing each CPU in the
@@ -540,11 +787,12 @@ rcu_torture_shuffle(void *arg)
 static inline void
 rcu_torture_print_module_parms(char *tag)
 {
-       printk(KERN_ALERT "%s" TORTURE_FLAG "--- %s: nreaders=%d "
+       printk(KERN_ALERT "%s" TORTURE_FLAG
+               "--- %s: nreaders=%d nfakewriters=%d "
                "stat_interval=%d verbose=%d test_no_idle_hz=%d "
                "shuffle_interval = %d\n",
-               torture_type, tag, nrealreaders, stat_interval, verbose,
-               test_no_idle_hz, shuffle_interval);
+               torture_type, tag, nrealreaders, nfakewriters,
+               stat_interval, verbose, test_no_idle_hz, shuffle_interval);
 }
 
 static void
@@ -553,21 +801,21 @@ rcu_torture_cleanup(void)
        int i;
 
        fullstop = 1;
-       if (shuffler_task != NULL) {
+       if (shuffler_task) {
                VERBOSE_PRINTK_STRING("Stopping rcu_torture_shuffle task");
                kthread_stop(shuffler_task);
        }
        shuffler_task = NULL;
 
-       if (writer_task != NULL) {
+       if (writer_task) {
                VERBOSE_PRINTK_STRING("Stopping rcu_torture_writer task");
                kthread_stop(writer_task);
        }
        writer_task = NULL;
 
-       if (reader_tasks != NULL) {
+       if (reader_tasks) {
                for (i = 0; i < nrealreaders; i++) {
-                       if (reader_tasks[i] != NULL) {
+                       if (reader_tasks[i]) {
                                VERBOSE_PRINTK_STRING(
                                        "Stopping rcu_torture_reader task");
                                kthread_stop(reader_tasks[i]);
@@ -579,7 +827,20 @@ rcu_torture_cleanup(void)
        }
        rcu_torture_current = NULL;
 
-       if (stats_task != NULL) {
+       if (fakewriter_tasks) {
+               for (i = 0; i < nfakewriters; i++) {
+                       if (fakewriter_tasks[i]) {
+                               VERBOSE_PRINTK_STRING(
+                                       "Stopping rcu_torture_fakewriter task");
+                               kthread_stop(fakewriter_tasks[i]);
+                       }
+                       fakewriter_tasks[i] = NULL;
+               }
+               kfree(fakewriter_tasks);
+               fakewriter_tasks = NULL;
+       }
+
+       if (stats_task) {
                VERBOSE_PRINTK_STRING("Stopping rcu_torture_stats task");
                kthread_stop(stats_task);
        }
@@ -590,7 +851,7 @@ rcu_torture_cleanup(void)
 
        rcu_torture_stats_print();  /* -After- the stats thread is stopped! */
 
-       if (cur_ops->cleanup != NULL)
+       if (cur_ops->cleanup)
                cur_ops->cleanup();
        if (atomic_read(&n_rcu_torture_error))
                rcu_torture_print_module_parms("End of test: FAILURE");
@@ -598,27 +859,28 @@ rcu_torture_cleanup(void)
                rcu_torture_print_module_parms("End of test: SUCCESS");
 }
 
-static int
+static int __init
 rcu_torture_init(void)
 {
        int i;
        int cpu;
        int firsterr = 0;
+       static struct rcu_torture_ops *torture_ops[] =
+               { &rcu_ops, &rcu_sync_ops, &rcu_bh_ops, &rcu_bh_sync_ops,
+                 &srcu_ops, &sched_ops, };
 
        /* Process args and tell the world that the torturer is on the job. */
-
-       for (i = 0; cur_ops = torture_ops[i], cur_ops != NULL; i++) {
+       for (i = 0; i < ARRAY_SIZE(torture_ops); i++) {
                cur_ops = torture_ops[i];
-               if (strcmp(torture_type, cur_ops->name) == 0) {
+               if (strcmp(torture_type, cur_ops->name) == 0)
                        break;
-               }
        }
-       if (cur_ops == NULL) {
+       if (i == ARRAY_SIZE(torture_ops)) {
                printk(KERN_ALERT "rcutorture: invalid torture type: \"%s\"\n",
                       torture_type);
                return (-EINVAL);
        }
-       if (cur_ops->init != NULL)
+       if (cur_ops->init)
                cur_ops->init(); /* no "goto unwind" prior to this point!!! */
 
        if (nreaders >= 0)
@@ -631,7 +893,7 @@ rcu_torture_init(void)
        /* Set up the freelist. */
 
        INIT_LIST_HEAD(&rcu_torture_freelist);
-       for (i = 0; i < sizeof(rcu_tortures) / sizeof(rcu_tortures[0]); i++) {
+       for (i = 0; i < ARRAY_SIZE(rcu_tortures); i++) {
                rcu_tortures[i].rtort_mbtest = 0;
                list_add_tail(&rcu_tortures[i].rtort_free,
                              &rcu_torture_freelist);
@@ -666,7 +928,25 @@ rcu_torture_init(void)
                writer_task = NULL;
                goto unwind;
        }
-       reader_tasks = kmalloc(nrealreaders * sizeof(reader_tasks[0]),
+       fakewriter_tasks = kzalloc(nfakewriters * sizeof(fakewriter_tasks[0]),
+                                  GFP_KERNEL);
+       if (fakewriter_tasks == NULL) {
+               VERBOSE_PRINTK_ERRSTRING("out of memory");
+               firsterr = -ENOMEM;
+               goto unwind;
+       }
+       for (i = 0; i < nfakewriters; i++) {
+               VERBOSE_PRINTK_STRING("Creating rcu_torture_fakewriter task");
+               fakewriter_tasks[i] = kthread_run(rcu_torture_fakewriter, NULL,
+                                                 "rcu_torture_fakewriter");
+               if (IS_ERR(fakewriter_tasks[i])) {
+                       firsterr = PTR_ERR(fakewriter_tasks[i]);
+                       VERBOSE_PRINTK_ERRSTRING("Failed to create fakewriter");
+                       fakewriter_tasks[i] = NULL;
+                       goto unwind;
+               }
+       }
+       reader_tasks = kzalloc(nrealreaders * sizeof(reader_tasks[0]),
                               GFP_KERNEL);
        if (reader_tasks == NULL) {
                VERBOSE_PRINTK_ERRSTRING("out of memory");