1 files changed, 323 insertions, 69 deletions

diff --git a/kernel/locking/locktorture.c b/kernel/locking/locktorture.c
index 0955b885d0dc..540d5dfe1112 100644
--- a/kernel/locking/locktorture.c
+++ b/kernel/locking/locktorture.c
@@ -27,6 +27,7 @@
 #include <linux/kthread.h>
 #include <linux/err.h>
 #include <linux/spinlock.h>
+#include <linux/mutex.h>
 #include <linux/smp.h>
 #include <linux/interrupt.h>
 #include <linux/sched.h>
@@ -51,6 +52,8 @@ MODULE_AUTHOR("Paul E. McKenney <paulmck@us.ibm.com>");
 
 torture_param(int, nwriters_stress, -1,
              "Number of write-locking stress-test threads");
+torture_param(int, nreaders_stress, -1,
+             "Number of read-locking stress-test threads");
 torture_param(int, onoff_holdoff, 0, "Time after boot before CPU hotplugs (s)");
 torture_param(int, onoff_interval, 0,
              "Time between CPU hotplugs (s), 0=disable");
@@ -66,30 +69,28 @@ torture_param(bool, verbose, true,
 static char *torture_type = "spin_lock";
 module_param(torture_type, charp, 0444);
 MODULE_PARM_DESC(torture_type,
-                 "Type of lock to torture (spin_lock, spin_lock_irq, ...)");
-
-static atomic_t n_lock_torture_errors;
+                 "Type of lock to torture (spin_lock, spin_lock_irq, mutex_lock, ...)");
 
 static struct task_struct *stats_task;
 static struct task_struct **writer_tasks;
+static struct task_struct **reader_tasks;
 
-static int nrealwriters_stress;
 static bool lock_is_write_held;
+static bool lock_is_read_held;
 
-struct lock_writer_stress_stats {
-        long n_write_lock_fail;
-        long n_write_lock_acquired;
+struct lock_stress_stats {
+        long n_lock_fail;
+        long n_lock_acquired;
 };
-static struct lock_writer_stress_stats *lwsa;
 
 #if defined(MODULE)
 #define LOCKTORTURE_RUNNABLE_INIT 1
 #else
 #define LOCKTORTURE_RUNNABLE_INIT 0
 #endif
-int locktorture_runnable = LOCKTORTURE_RUNNABLE_INIT;
-module_param(locktorture_runnable, int, 0444);
-MODULE_PARM_DESC(locktorture_runnable, "Start locktorture at module init");
+int torture_runnable = LOCKTORTURE_RUNNABLE_INIT;
+module_param(torture_runnable, int, 0444);
+MODULE_PARM_DESC(torture_runnable, "Start locktorture at module init");
 
 /* Forward reference. */
 static void lock_torture_cleanup(void);
@@ -102,12 +103,25 @@ struct lock_torture_ops {
         int (*writelock)(void);
         void (*write_delay)(struct torture_random_state *trsp);
         void (*writeunlock)(void);
+        int (*readlock)(void);
+        void (*read_delay)(struct torture_random_state *trsp);
+        void (*readunlock)(void);
         unsigned long flags;
         const char *name;
 };
 
-static struct lock_torture_ops *cur_ops;
-
+struct lock_torture_cxt {
+        int nrealwriters_stress;
+        int nrealreaders_stress;
+        bool debug_lock;
+        atomic_t n_lock_torture_errors;
+        struct lock_torture_ops *cur_ops;
+        struct lock_stress_stats *lwsa; /* writer statistics */
+        struct lock_stress_stats *lrsa; /* reader statistics */
+};
+static struct lock_torture_cxt cxt = { 0, 0, false,
+                                       ATOMIC_INIT(0),
+                                       NULL, NULL};
 /*
  * Definitions for lock torture testing.
  */
@@ -123,10 +137,10 @@ static void torture_lock_busted_write_delay(struct torture_random_state *trsp)
 
         /* We want a long delay occasionally to force massive contention.  */
         if (!(torture_random(trsp) %
-              (nrealwriters_stress * 2000 * longdelay_us)))
+              (cxt.nrealwriters_stress * 2000 * longdelay_us)))
                 mdelay(longdelay_us);
 #ifdef CONFIG_PREEMPT
-        if (!(torture_random(trsp) % (nrealwriters_stress * 20000)))
+        if (!(torture_random(trsp) % (cxt.nrealwriters_stress * 20000)))
                 preempt_schedule();  /* Allow test to be preempted. */
 #endif
 }
@@ -140,6 +154,9 @@ static struct lock_torture_ops lock_busted_ops = {
         .writelock      = torture_lock_busted_write_lock,
         .write_delay    = torture_lock_busted_write_delay,
         .writeunlock    = torture_lock_busted_write_unlock,
+        .readlock       = NULL,
+        .read_delay     = NULL,
+        .readunlock     = NULL,
         .name           = "lock_busted"
 };
 
@@ -160,13 +177,13 @@ static void torture_spin_lock_write_delay(struct torture_random_state *trsp)
          * we want a long delay occasionally to force massive contention.
          */
         if (!(torture_random(trsp) %
-              (nrealwriters_stress * 2000 * longdelay_us)))
+              (cxt.nrealwriters_stress * 2000 * longdelay_us)))
                 mdelay(longdelay_us);
         if (!(torture_random(trsp) %
-              (nrealwriters_stress * 2 * shortdelay_us)))
+              (cxt.nrealwriters_stress * 2 * shortdelay_us)))
                 udelay(shortdelay_us);
 #ifdef CONFIG_PREEMPT
-        if (!(torture_random(trsp) % (nrealwriters_stress * 20000)))
+        if (!(torture_random(trsp) % (cxt.nrealwriters_stress * 20000)))
                 preempt_schedule();  /* Allow test to be preempted. */
 #endif
 }
@@ -180,6 +197,9 @@ static struct lock_torture_ops spin_lock_ops = {
         .writelock      = torture_spin_lock_write_lock,
         .write_delay    = torture_spin_lock_write_delay,
         .writeunlock    = torture_spin_lock_write_unlock,
+        .readlock       = NULL,
+        .read_delay     = NULL,
+        .readunlock     = NULL,
         .name           = "spin_lock"
 };
 
@@ -189,30 +209,137 @@ __acquires(torture_spinlock_irq)
         unsigned long flags;
 
         spin_lock_irqsave(&torture_spinlock, flags);
-        cur_ops->flags = flags;
+        cxt.cur_ops->flags = flags;
         return 0;
 }
 
 static void torture_lock_spin_write_unlock_irq(void)
 __releases(torture_spinlock)
 {
-        spin_unlock_irqrestore(&torture_spinlock, cur_ops->flags);
+        spin_unlock_irqrestore(&torture_spinlock, cxt.cur_ops->flags);
 }
 
 static struct lock_torture_ops spin_lock_irq_ops = {
         .writelock      = torture_spin_lock_write_lock_irq,
         .write_delay    = torture_spin_lock_write_delay,
         .writeunlock    = torture_lock_spin_write_unlock_irq,
+        .readlock       = NULL,
+        .read_delay     = NULL,
+        .readunlock     = NULL,
         .name           = "spin_lock_irq"
 };
 
+static DEFINE_MUTEX(torture_mutex);
+
+static int torture_mutex_lock(void) __acquires(torture_mutex)
+{
+        mutex_lock(&torture_mutex);
+        return 0;
+}
+
+static void torture_mutex_delay(struct torture_random_state *trsp)
+{
+        const unsigned long longdelay_ms = 100;
+
+        /* We want a long delay occasionally to force massive contention.  */
+        if (!(torture_random(trsp) %
+              (cxt.nrealwriters_stress * 2000 * longdelay_ms)))
+                mdelay(longdelay_ms * 5);
+        else
+                mdelay(longdelay_ms / 5);
+#ifdef CONFIG_PREEMPT
+        if (!(torture_random(trsp) % (cxt.nrealwriters_stress * 20000)))
+                preempt_schedule();  /* Allow test to be preempted. */
+#endif
+}
+
+static void torture_mutex_unlock(void) __releases(torture_mutex)
+{
+        mutex_unlock(&torture_mutex);
+}
+
+static struct lock_torture_ops mutex_lock_ops = {
+        .writelock      = torture_mutex_lock,
+        .write_delay    = torture_mutex_delay,
+        .writeunlock    = torture_mutex_unlock,
+        .readlock       = NULL,
+        .read_delay     = NULL,
+        .readunlock     = NULL,
+        .name           = "mutex_lock"
+};
+
+static DECLARE_RWSEM(torture_rwsem);
+static int torture_rwsem_down_write(void) __acquires(torture_rwsem)
+{
+        down_write(&torture_rwsem);
+        return 0;
+}
+
+static void torture_rwsem_write_delay(struct torture_random_state *trsp)
+{
+        const unsigned long longdelay_ms = 100;
+
+        /* We want a long delay occasionally to force massive contention.  */
+        if (!(torture_random(trsp) %
+              (cxt.nrealwriters_stress * 2000 * longdelay_ms)))
+                mdelay(longdelay_ms * 10);
+        else
+                mdelay(longdelay_ms / 10);
+#ifdef CONFIG_PREEMPT
+        if (!(torture_random(trsp) % (cxt.nrealwriters_stress * 20000)))
+                preempt_schedule();  /* Allow test to be preempted. */
+#endif
+}
+
+static void torture_rwsem_up_write(void) __releases(torture_rwsem)
+{
+        up_write(&torture_rwsem);
+}
+
+static int torture_rwsem_down_read(void) __acquires(torture_rwsem)
+{
+        down_read(&torture_rwsem);
+        return 0;
+}
+
+static void torture_rwsem_read_delay(struct torture_random_state *trsp)
+{
+        const unsigned long longdelay_ms = 100;
+
+        /* We want a long delay occasionally to force massive contention.  */
+        if (!(torture_random(trsp) %
+              (cxt.nrealwriters_stress * 2000 * longdelay_ms)))
+                mdelay(longdelay_ms * 2);
+        else
+                mdelay(longdelay_ms / 2);
+#ifdef CONFIG_PREEMPT
+        if (!(torture_random(trsp) % (cxt.nrealreaders_stress * 20000)))
+                preempt_schedule();  /* Allow test to be preempted. */
+#endif
+}
+
+static void torture_rwsem_up_read(void) __releases(torture_rwsem)
+{
+        up_read(&torture_rwsem);
+}
+
+static struct lock_torture_ops rwsem_lock_ops = {
+        .writelock      = torture_rwsem_down_write,
+        .write_delay    = torture_rwsem_write_delay,
+        .writeunlock    = torture_rwsem_up_write,
+        .readlock       = torture_rwsem_down_read,
+        .read_delay     = torture_rwsem_read_delay,
+        .readunlock     = torture_rwsem_up_read,
+        .name           = "rwsem_lock"
+};
+
 /*
  * Lock torture writer kthread.  Repeatedly acquires and releases
  * the lock, checking for duplicate acquisitions.
  */
 static int lock_torture_writer(void *arg)
 {
-        struct lock_writer_stress_stats *lwsp = arg;
+        struct lock_stress_stats *lwsp = arg;
         static DEFINE_TORTURE_RANDOM(rand);
 
         VERBOSE_TOROUT_STRING("lock_torture_writer task started");
@@ -221,14 +348,14 @@ static int lock_torture_writer(void *arg)
         do {
                 if ((torture_random(&rand) & 0xfffff) == 0)
                         schedule_timeout_uninterruptible(1);
-                cur_ops->writelock();
+                cxt.cur_ops->writelock();
                 if (WARN_ON_ONCE(lock_is_write_held))
-                        lwsp->n_write_lock_fail++;
+                        lwsp->n_lock_fail++;
                 lock_is_write_held = 1;
-                lwsp->n_write_lock_acquired++;
-                cur_ops->write_delay(&rand);
+                lwsp->n_lock_acquired++;
+                cxt.cur_ops->write_delay(&rand);
                 lock_is_write_held = 0;
-                cur_ops->writeunlock();
+                cxt.cur_ops->writeunlock();
                 stutter_wait("lock_torture_writer");
         } while (!torture_must_stop());
         torture_kthread_stopping("lock_torture_writer");
@@ -236,32 +363,61 @@ static int lock_torture_writer(void *arg)
 }
 
 /*
+ * Lock torture reader kthread.  Repeatedly acquires and releases
+ * the reader lock.
+ */
+static int lock_torture_reader(void *arg)
+{
+        struct lock_stress_stats *lrsp = arg;
+        static DEFINE_TORTURE_RANDOM(rand);
+
+        VERBOSE_TOROUT_STRING("lock_torture_reader task started");
+        set_user_nice(current, MAX_NICE);
+
+        do {
+                if ((torture_random(&rand) & 0xfffff) == 0)
+                        schedule_timeout_uninterruptible(1);
+                cxt.cur_ops->readlock();
+                lock_is_read_held = 1;
+                lrsp->n_lock_acquired++;
+                cxt.cur_ops->read_delay(&rand);
+                lock_is_read_held = 0;
+                cxt.cur_ops->readunlock();
+                stutter_wait("lock_torture_reader");
+        } while (!torture_must_stop());
+        torture_kthread_stopping("lock_torture_reader");
+        return 0;
+}
+
+/*
  * Create an lock-torture-statistics message in the specified buffer.
  */
-static void lock_torture_printk(char *page)
+static void __torture_print_stats(char *page,
+                                  struct lock_stress_stats *statp, bool write)
 {
         bool fail = 0;
-        int i;
+        int i, n_stress;
         long max = 0;
-        long min = lwsa[0].n_write_lock_acquired;
+        long min = statp[0].n_lock_acquired;
         long long sum = 0;
 
-        for (i = 0; i < nrealwriters_stress; i++) {
-                if (lwsa[i].n_write_lock_fail)
+        n_stress = write ? cxt.nrealwriters_stress : cxt.nrealreaders_stress;
+        for (i = 0; i < n_stress; i++) {
+                if (statp[i].n_lock_fail)
                         fail = true;
-                sum += lwsa[i].n_write_lock_acquired;
-                if (max < lwsa[i].n_write_lock_fail)
-                        max = lwsa[i].n_write_lock_fail;
-                if (min > lwsa[i].n_write_lock_fail)
-                        min = lwsa[i].n_write_lock_fail;
+                sum += statp[i].n_lock_acquired;
+                if (max < statp[i].n_lock_fail)
+                        max = statp[i].n_lock_fail;
+                if (min > statp[i].n_lock_fail)
+                        min = statp[i].n_lock_fail;
         }
-        page += sprintf(page, "%s%s ", torture_type, TORTURE_FLAG);
         page += sprintf(page,
-                        "Writes:  Total: %lld  Max/Min: %ld/%ld %s  Fail: %d %s\n",
+                        "%s:  Total: %lld  Max/Min: %ld/%ld %s  Fail: %d %s\n",
+                        write ? "Writes" : "Reads ",
                         sum, max, min, max / 2 > min ? "???" : "",
                         fail, fail ? "!!!" : "");
         if (fail)
-                atomic_inc(&n_lock_torture_errors);
+                atomic_inc(&cxt.n_lock_torture_errors);
 }
 
 /*
@@ -274,18 +430,35 @@ static void lock_torture_printk(char *page)
  */
 static void lock_torture_stats_print(void)
 {
-        int size = nrealwriters_stress * 200 + 8192;
+        int size = cxt.nrealwriters_stress * 200 + 8192;
         char *buf;
 
+        if (cxt.cur_ops->readlock)
+                size += cxt.nrealreaders_stress * 200 + 8192;
+
         buf = kmalloc(size, GFP_KERNEL);
         if (!buf) {
                 pr_err("lock_torture_stats_print: Out of memory, need: %d",
                        size);
                 return;
         }
-        lock_torture_printk(buf);
+
+        __torture_print_stats(buf, cxt.lwsa, true);
         pr_alert("%s", buf);
         kfree(buf);
+
+        if (cxt.cur_ops->readlock) {
+                buf = kmalloc(size, GFP_KERNEL);
+                if (!buf) {
+                        pr_err("lock_torture_stats_print: Out of memory, need: %d",
+                               size);
+                        return;
+                }
+
+                __torture_print_stats(buf, cxt.lrsa, false);
+                pr_alert("%s", buf);
+                kfree(buf);
+        }
 }
 
 /*
@@ -312,9 +485,10 @@ lock_torture_print_module_parms(struct lock_torture_ops *cur_ops,
                                 const char *tag)
 {
         pr_alert("%s" TORTURE_FLAG
-                 "--- %s: nwriters_stress=%d stat_interval=%d verbose=%d shuffle_interval=%d stutter=%d shutdown_secs=%d onoff_interval=%d onoff_holdoff=%d\n",
-                 torture_type, tag, nrealwriters_stress, stat_interval, verbose,
-                 shuffle_interval, stutter, shutdown_secs,
+                 "--- %s%s: nwriters_stress=%d nreaders_stress=%d stat_interval=%d verbose=%d shuffle_interval=%d stutter=%d shutdown_secs=%d onoff_interval=%d onoff_holdoff=%d\n",
+                 torture_type, tag, cxt.debug_lock ? " [debug]": "",
+                 cxt.nrealwriters_stress, cxt.nrealreaders_stress, stat_interval,
+                 verbose, shuffle_interval, stutter, shutdown_secs,
                  onoff_interval, onoff_holdoff);
 }
 
@@ -322,46 +496,56 @@ static void lock_torture_cleanup(void)
 {
         int i;
 
-        if (torture_cleanup())
+        if (torture_cleanup_begin())
                 return;
 
         if (writer_tasks) {
-                for (i = 0; i < nrealwriters_stress; i++)
+                for (i = 0; i < cxt.nrealwriters_stress; i++)
                         torture_stop_kthread(lock_torture_writer,
                                              writer_tasks[i]);
                 kfree(writer_tasks);
                 writer_tasks = NULL;
         }
 
+        if (reader_tasks) {
+                for (i = 0; i < cxt.nrealreaders_stress; i++)
+                        torture_stop_kthread(lock_torture_reader,
+                                             reader_tasks[i]);
+                kfree(reader_tasks);
+                reader_tasks = NULL;
+        }
+
         torture_stop_kthread(lock_torture_stats, stats_task);
         lock_torture_stats_print();  /* -After- the stats thread is stopped! */
 
-        if (atomic_read(&n_lock_torture_errors))
-                lock_torture_print_module_parms(cur_ops,
+        if (atomic_read(&cxt.n_lock_torture_errors))
+                lock_torture_print_module_parms(cxt.cur_ops,
                                                 "End of test: FAILURE");
         else if (torture_onoff_failures())
-                lock_torture_print_module_parms(cur_ops,
+                lock_torture_print_module_parms(cxt.cur_ops,
                                                 "End of test: LOCK_HOTPLUG");
         else
-                lock_torture_print_module_parms(cur_ops,
+                lock_torture_print_module_parms(cxt.cur_ops,
                                                 "End of test: SUCCESS");
+        torture_cleanup_end();
 }
 
 static int __init lock_torture_init(void)
 {
-        int i;
+        int i, j;
         int firsterr = 0;
         static struct lock_torture_ops *torture_ops[] = {
                 &lock_busted_ops, &spin_lock_ops, &spin_lock_irq_ops,
+                &mutex_lock_ops, &rwsem_lock_ops,
         };
 
-        if (!torture_init_begin(torture_type, verbose, &locktorture_runnable))
+        if (!torture_init_begin(torture_type, verbose, &torture_runnable))
                 return -EBUSY;
 
         /* Process args and tell the world that the torturer is on the job. */
         for (i = 0; i < ARRAY_SIZE(torture_ops); i++) {
-                cur_ops = torture_ops[i];
-                if (strcmp(torture_type, cur_ops->name) == 0)
+                cxt.cur_ops = torture_ops[i];
+                if (strcmp(torture_type, cxt.cur_ops->name) == 0)
                         break;
         }
         if (i == ARRAY_SIZE(torture_ops)) {
@@ -374,31 +558,68 @@ static int __init lock_torture_init(void)
                 torture_init_end();
                 return -EINVAL;
         }
-        if (cur_ops->init)
-                cur_ops->init(); /* no "goto unwind" prior to this point!!! */
+        if (cxt.cur_ops->init)
+                cxt.cur_ops->init(); /* no "goto unwind" prior to this point!!! */
 
         if (nwriters_stress >= 0)
-                nrealwriters_stress = nwriters_stress;
+                cxt.nrealwriters_stress = nwriters_stress;
         else
-                nrealwriters_stress = 2 * num_online_cpus();
-        lock_torture_print_module_parms(cur_ops, "Start of test");
+                cxt.nrealwriters_stress = 2 * num_online_cpus();
+
+#ifdef CONFIG_DEBUG_MUTEXES
+        if (strncmp(torture_type, "mutex", 5) == 0)
+                cxt.debug_lock = true;
+#endif
+#ifdef CONFIG_DEBUG_SPINLOCK
+        if (strncmp(torture_type, "spin", 4) == 0)
+                cxt.debug_lock = true;
+#endif
 
         /* Initialize the statistics so that each run gets its own numbers. */
 
         lock_is_write_held = 0;
-        lwsa = kmalloc(sizeof(*lwsa) * nrealwriters_stress, GFP_KERNEL);
-        if (lwsa == NULL) {
-                VERBOSE_TOROUT_STRING("lwsa: Out of memory");
+        cxt.lwsa = kmalloc(sizeof(*cxt.lwsa) * cxt.nrealwriters_stress, GFP_KERNEL);
+        if (cxt.lwsa == NULL) {
+                VERBOSE_TOROUT_STRING("cxt.lwsa: Out of memory");
                 firsterr = -ENOMEM;
                 goto unwind;
         }
-        for (i = 0; i < nrealwriters_stress; i++) {
-                lwsa[i].n_write_lock_fail = 0;
-                lwsa[i].n_write_lock_acquired = 0;
+        for (i = 0; i < cxt.nrealwriters_stress; i++) {
+                cxt.lwsa[i].n_lock_fail = 0;
+                cxt.lwsa[i].n_lock_acquired = 0;
         }
 
-        /* Start up the kthreads. */
+        if (cxt.cur_ops->readlock) {
+                if (nreaders_stress >= 0)
+                        cxt.nrealreaders_stress = nreaders_stress;
+                else {
+                        /*
+                         * By default distribute evenly the number of
+                         * readers and writers. We still run the same number
+                         * of threads as the writer-only locks default.
+                         */
+                        if (nwriters_stress < 0) /* user doesn't care */
+                                cxt.nrealwriters_stress = num_online_cpus();
+                        cxt.nrealreaders_stress = cxt.nrealwriters_stress;
+                }
+
+                lock_is_read_held = 0;
+                cxt.lrsa = kmalloc(sizeof(*cxt.lrsa) * cxt.nrealreaders_stress, GFP_KERNEL);
+                if (cxt.lrsa == NULL) {
+                        VERBOSE_TOROUT_STRING("cxt.lrsa: Out of memory");
+                        firsterr = -ENOMEM;
+                        kfree(cxt.lwsa);
+                        goto unwind;
+                }
+
+                for (i = 0; i < cxt.nrealreaders_stress; i++) {
+                        cxt.lrsa[i].n_lock_fail = 0;
+                        cxt.lrsa[i].n_lock_acquired = 0;
+                }
+        }
+        lock_torture_print_module_parms(cxt.cur_ops, "Start of test");
 
+        /* Prepare torture context. */
         if (onoff_interval > 0) {
                 firsterr = torture_onoff_init(onoff_holdoff * HZ,
                                               onoff_interval * HZ);
@@ -422,18 +643,51 @@ static int __init lock_torture_init(void)
                         goto unwind;
         }
 
-        writer_tasks = kzalloc(nrealwriters_stress * sizeof(writer_tasks[0]),
+        writer_tasks = kzalloc(cxt.nrealwriters_stress * sizeof(writer_tasks[0]),
                                GFP_KERNEL);
         if (writer_tasks == NULL) {
                 VERBOSE_TOROUT_ERRSTRING("writer_tasks: Out of memory");
                 firsterr = -ENOMEM;
                 goto unwind;
         }
-        for (i = 0; i < nrealwriters_stress; i++) {
-                firsterr = torture_create_kthread(lock_torture_writer, &lwsa[i],
+
+        if (cxt.cur_ops->readlock) {
+                reader_tasks = kzalloc(cxt.nrealreaders_stress * sizeof(reader_tasks[0]),
+                                       GFP_KERNEL);
+                if (reader_tasks == NULL) {
+                        VERBOSE_TOROUT_ERRSTRING("reader_tasks: Out of memory");
+                        firsterr = -ENOMEM;
+                        goto unwind;
+                }
+        }
+
+        /*
+         * Create the kthreads and start torturing (oh, those poor little locks).
+         *
+         * TODO: Note that we interleave writers with readers, giving writers a
+         * slight advantage, by creating its kthread first. This can be modified
+         * for very specific needs, or even let the user choose the policy, if
+         * ever wanted.
+         */
+        for (i = 0, j = 0; i < cxt.nrealwriters_stress ||
+                    j < cxt.nrealreaders_stress; i++, j++) {
+                if (i >= cxt.nrealwriters_stress)
+                        goto create_reader;
+
+                /* Create writer. */
+                firsterr = torture_create_kthread(lock_torture_writer, &cxt.lwsa[i],
                                                   writer_tasks[i]);
                 if (firsterr)
                         goto unwind;
+
+        create_reader:
+                if (cxt.cur_ops->readlock == NULL || (j >= cxt.nrealreaders_stress))
+                        continue;
+                /* Create reader. */
+                firsterr = torture_create_kthread(lock_torture_reader, &cxt.lrsa[j],
+                                                  reader_tasks[j]);
+                if (firsterr)
+                        goto unwind;
         }
         if (stat_interval > 0) {
                 firsterr = torture_create_kthread(lock_torture_stats, NULL,