rcutorture: Abstract torture_shuffle()

The torture_shuffle() function forces each CPU in turn to go idle
periodically in order to check for problems interacting with per-CPU
variables and with dyntick-idle mode.  Because this sort of debugging
is not specific to RCU, this commit abstracts that functionality.
This in turn requires abstracting some additional infrastructure.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

3 files changed, 171 insertions, 109 deletions

diff --git a/include/linux/torture.h b/include/linux/torture.h
index 8474d776c864..544a2c33c1ae 100644
--- a/include/linux/torture.h
+++ b/include/linux/torture.h
@@ -69,6 +69,11 @@ struct torture_random_state {
 #define DEFINE_TORTURE_RANDOM(name) struct torture_random_state name = { 0, 0 }
 unsigned long torture_random(struct torture_random_state *trsp);
 
+/* Task shuffler, which causes CPUs to occasionally go idle. */
+void torture_shuffle_task_register(struct task_struct *tp);
+int torture_shuffle_init(long shuffint);
+void torture_shuffle_cleanup(void);
+
 /* Shutdown task absorption, for when the tasks cannot safely be killed. */
 void torture_shutdown_absorb(const char *title);
 
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index a868758a6f9c..0380696f1844 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -106,7 +106,6 @@ 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;
 static struct task_struct *stutter_task;
 static struct task_struct *fqs_task;
 static struct task_struct *boost_tasks[NR_CPUS];
@@ -161,7 +160,6 @@ static int max_online;
 static long n_barrier_attempts;
 static long n_barrier_successes;
 static struct list_head rcu_torture_removed;
-static cpumask_var_t shuffle_tmp_mask;
 
 static int stutter_pause_test;
 
@@ -1080,90 +1078,6 @@ rcu_torture_stats(void *arg)
 	return 0;
 }
 
-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.
- */
-static void rcu_torture_shuffle_tasks(void)
-{
-	int i;
-
-	cpumask_setall(shuffle_tmp_mask);
-	get_online_cpus();
-
-	/* No point in shuffling if there is only one online CPU (ex: UP) */
-	if (num_online_cpus() == 1) {
-		put_online_cpus();
-		return;
-	}
-
-	if (rcu_idle_cpu != -1)
-		cpumask_clear_cpu(rcu_idle_cpu, shuffle_tmp_mask);
-
-	set_cpus_allowed_ptr(current, shuffle_tmp_mask);
-
-	if (reader_tasks) {
-		for (i = 0; i < nrealreaders; i++)
-			if (reader_tasks[i])
-				set_cpus_allowed_ptr(reader_tasks[i],
-						     shuffle_tmp_mask);
-	}
-	if (fakewriter_tasks) {
-		for (i = 0; i < nfakewriters; i++)
-			if (fakewriter_tasks[i])
-				set_cpus_allowed_ptr(fakewriter_tasks[i],
-						     shuffle_tmp_mask);
-	}
-	if (writer_task)
-		set_cpus_allowed_ptr(writer_task, shuffle_tmp_mask);
-	if (stats_task)
-		set_cpus_allowed_ptr(stats_task, shuffle_tmp_mask);
-	if (stutter_task)
-		set_cpus_allowed_ptr(stutter_task, shuffle_tmp_mask);
-	if (fqs_task)
-		set_cpus_allowed_ptr(fqs_task, shuffle_tmp_mask);
-	if (shutdown_task)
-		set_cpus_allowed_ptr(shutdown_task, shuffle_tmp_mask);
-#ifdef CONFIG_HOTPLUG_CPU
-	if (onoff_task)
-		set_cpus_allowed_ptr(onoff_task, shuffle_tmp_mask);
-#endif /* #ifdef CONFIG_HOTPLUG_CPU */
-	if (stall_task)
-		set_cpus_allowed_ptr(stall_task, shuffle_tmp_mask);
-	if (barrier_cbs_tasks)
-		for (i = 0; i < n_barrier_cbs; i++)
-			if (barrier_cbs_tasks[i])
-				set_cpus_allowed_ptr(barrier_cbs_tasks[i],
-						     shuffle_tmp_mask);
-	if (barrier_task)
-		set_cpus_allowed_ptr(barrier_task, shuffle_tmp_mask);
-
-	if (rcu_idle_cpu == -1)
-		rcu_idle_cpu = num_online_cpus() - 1;
-	else
-		rcu_idle_cpu--;
-
-	put_online_cpus();
-}
-
-/* Shuffle tasks across CPUs, with the intent of allowing each CPU in the
- * system to become idle at a time and cut off its timer ticks. This is meant
- * to test the support for such tickless idle CPU in RCU.
- */
-static int
-rcu_torture_shuffle(void *arg)
-{
-	VERBOSE_TOROUT_STRING("rcu_torture_shuffle task started");
-	do {
-		schedule_timeout_interruptible(shuffle_interval * HZ);
-		rcu_torture_shuffle_tasks();
-		torture_shutdown_absorb("rcu_torture_shuffle");
-	} while (!kthread_should_stop());
-	VERBOSE_TOROUT_STRING("rcu_torture_shuffle task stopping");
-	return 0;
-}
-
 /* Cause the rcutorture test to "stutter", starting and stopping all
  * threads periodically.
  */
@@ -1397,6 +1311,7 @@ rcu_torture_onoff_init(void)
 		onoff_task = NULL;
 		return ret;
 	}
+	torture_shuffle_task_register(onoff_task);
 	return 0;
 }
 
@@ -1468,6 +1383,7 @@ static int __init rcu_torture_stall_init(void)
 		stall_task = NULL;
 		return ret;
 	}
+	torture_shuffle_task_register(stall_task);
 	return 0;
 }
 
@@ -1594,6 +1510,7 @@ static int rcu_torture_barrier_init(void)
 			barrier_cbs_tasks[i] = NULL;
 			return ret;
 		}
+		torture_shuffle_task_register(barrier_cbs_tasks[i]);
 	}
 	barrier_task = kthread_run(rcu_torture_barrier, NULL,
 				   "rcu_torture_barrier");
@@ -1602,6 +1519,7 @@ static int rcu_torture_barrier_init(void)
 		VERBOSE_TOROUT_ERRSTRING("Failed to create rcu_torture_barrier");
 		barrier_task = NULL;
 	}
+	torture_shuffle_task_register(barrier_task);
 	return 0;
 }
 
@@ -1674,6 +1592,8 @@ rcu_torture_cleanup(void)
 	fullstop = FULLSTOP_RMMOD;
 	mutex_unlock(&fullstop_mutex);
 	unregister_reboot_notifier(&rcutorture_shutdown_nb);
+
+	torture_shuffle_cleanup(); /* Must be first task cleaned up. */
 	rcu_torture_barrier_cleanup();
 	rcu_torture_stall_cleanup();
 	if (stutter_task) {
@@ -1681,12 +1601,6 @@ rcu_torture_cleanup(void)
 		kthread_stop(stutter_task);
 	}
 	stutter_task = NULL;
-	if (shuffler_task) {
-		VERBOSE_TOROUT_STRING("Stopping rcu_torture_shuffle task");
-		kthread_stop(shuffler_task);
-		free_cpumask_var(shuffle_tmp_mask);
-	}
-	shuffler_task = NULL;
 
 	if (writer_task) {
 		VERBOSE_TOROUT_STRING("Stopping rcu_torture_writer task");
@@ -1904,6 +1818,7 @@ rcu_torture_init(void)
 		writer_task = NULL;
 		goto unwind;
 	}
+	torture_shuffle_task_register(writer_task);
 	wake_up_process(writer_task);
 	fakewriter_tasks = kzalloc(nfakewriters * sizeof(fakewriter_tasks[0]),
 				   GFP_KERNEL);
@@ -1922,6 +1837,7 @@ rcu_torture_init(void)
 			fakewriter_tasks[i] = NULL;
 			goto unwind;
 		}
+		torture_shuffle_task_register(fakewriter_tasks[i]);
 	}
 	reader_tasks = kzalloc(nrealreaders * sizeof(reader_tasks[0]),
 			       GFP_KERNEL);
@@ -1940,6 +1856,7 @@ rcu_torture_init(void)
 			reader_tasks[i] = NULL;
 			goto unwind;
 		}
+		torture_shuffle_task_register(reader_tasks[i]);
 	}
 	if (stat_interval > 0) {
 		VERBOSE_TOROUT_STRING("Creating rcu_torture_stats task");
@@ -1951,26 +1868,12 @@ rcu_torture_init(void)
 			stats_task = NULL;
 			goto unwind;
 		}
+		torture_shuffle_task_register(stats_task);
 	}
 	if (test_no_idle_hz) {
-		rcu_idle_cpu = num_online_cpus() - 1;
-
-		if (!alloc_cpumask_var(&shuffle_tmp_mask, GFP_KERNEL)) {
-			firsterr = -ENOMEM;
-			VERBOSE_TOROUT_ERRSTRING("Failed to alloc mask");
+		firsterr = torture_shuffle_init(shuffle_interval * HZ);
+		if (firsterr)
 			goto unwind;
-		}
-
-		/* Create the shuffler thread */
-		shuffler_task = kthread_run(rcu_torture_shuffle, NULL,
-					  "rcu_torture_shuffle");
-		if (IS_ERR(shuffler_task)) {
-			free_cpumask_var(shuffle_tmp_mask);
-			firsterr = PTR_ERR(shuffler_task);
-			VERBOSE_TOROUT_ERRSTRING("Failed to create shuffler");
-			shuffler_task = NULL;
-			goto unwind;
-		}
 	}
 	if (stutter < 0)
 		stutter = 0;
@@ -1984,6 +1887,7 @@ rcu_torture_init(void)
 			stutter_task = NULL;
 			goto unwind;
 		}
+		torture_shuffle_task_register(stutter_task);
 	}
 	if (fqs_duration < 0)
 		fqs_duration = 0;
@@ -1997,6 +1901,7 @@ rcu_torture_init(void)
 			fqs_task = NULL;
 			goto unwind;
 		}
+		torture_shuffle_task_register(fqs_task);
 	}
 	if (test_boost_interval < 1)
 		test_boost_interval = 1;
@@ -2027,6 +1932,7 @@ rcu_torture_init(void)
 			shutdown_task = NULL;
 			goto unwind;
 		}
+		torture_shuffle_task_register(shutdown_task);
 		wake_up_process(shutdown_task);
 	}
 	i = rcu_torture_onoff_init();
diff --git a/kernel/torture.c b/kernel/torture.c
index f05042036ae8..26058f20ee83 100644
--- a/kernel/torture.c
+++ b/kernel/torture.c
@@ -76,6 +76,157 @@ torture_random(struct torture_random_state *trsp)
 EXPORT_SYMBOL_GPL(torture_random);
 
 /*
+ * Variables for shuffling.  The idea is to ensure that each CPU stays
+ * idle for an extended period to test interactions with dyntick idle,
+ * as well as interactions with any per-CPU varibles.
+ */
+struct shuffle_task {
+	struct list_head st_l;
+	struct task_struct *st_t;
+};
+
+static long shuffle_interval;	/* In jiffies. */
+static struct task_struct *shuffler_task;
+static cpumask_var_t shuffle_tmp_mask;
+static int shuffle_idle_cpu;	/* Force all torture tasks off this CPU */
+static struct list_head shuffle_task_list = LIST_HEAD_INIT(shuffle_task_list);
+static DEFINE_MUTEX(shuffle_task_mutex);
+
+/*
+ * Register a task to be shuffled.  If there is no memory, just splat
+ * and don't bother registering.
+ */
+void torture_shuffle_task_register(struct task_struct *tp)
+{
+	struct shuffle_task *stp;
+
+	if (WARN_ON_ONCE(tp == NULL))
+		return;
+	stp = kmalloc(sizeof(*stp), GFP_KERNEL);
+	if (WARN_ON_ONCE(stp == NULL))
+		return;
+	stp->st_t = tp;
+	mutex_lock(&shuffle_task_mutex);
+	list_add(&stp->st_l, &shuffle_task_list);
+	mutex_unlock(&shuffle_task_mutex);
+}
+EXPORT_SYMBOL_GPL(torture_shuffle_task_register);
+
+/*
+ * Unregister all tasks, for example, at the end of the torture run.
+ */
+static void torture_shuffle_task_unregister_all(void)
+{
+	struct shuffle_task *stp;
+	struct shuffle_task *p;
+
+	mutex_lock(&shuffle_task_mutex);
+	list_for_each_entry_safe(stp, p, &shuffle_task_list, st_l) {
+		list_del(&stp->st_l);
+		kfree(stp);
+	}
+	mutex_unlock(&shuffle_task_mutex);
+}
+
+/* Shuffle tasks such that we allow shuffle_idle_cpu to become idle.
+ * A special case is when shuffle_idle_cpu = -1, in which case we allow
+ * the tasks to run on all CPUs.
+ */
+static void torture_shuffle_tasks(void)
+{
+	struct shuffle_task *stp;
+
+	cpumask_setall(shuffle_tmp_mask);
+	get_online_cpus();
+
+	/* No point in shuffling if there is only one online CPU (ex: UP) */
+	if (num_online_cpus() == 1) {
+		put_online_cpus();
+		return;
+	}
+
+	/* Advance to the next CPU.  Upon overflow, don't idle any CPUs. */
+	shuffle_idle_cpu = cpumask_next(shuffle_idle_cpu, shuffle_tmp_mask);
+	if (shuffle_idle_cpu >= nr_cpu_ids)
+		shuffle_idle_cpu = -1;
+	if (shuffle_idle_cpu != -1) {
+		cpumask_clear_cpu(shuffle_idle_cpu, shuffle_tmp_mask);
+		if (cpumask_empty(shuffle_tmp_mask)) {
+			put_online_cpus();
+			return;
+		}
+	}
+
+	mutex_lock(&shuffle_task_mutex);
+	list_for_each_entry(stp, &shuffle_task_list, st_l)
+		set_cpus_allowed_ptr(stp->st_t, shuffle_tmp_mask);
+	mutex_unlock(&shuffle_task_mutex);
+
+	put_online_cpus();
+}
+
+/* Shuffle tasks across CPUs, with the intent of allowing each CPU in the
+ * system to become idle at a time and cut off its timer ticks. This is meant
+ * to test the support for such tickless idle CPU in RCU.
+ */
+static int torture_shuffle(void *arg)
+{
+	VERBOSE_TOROUT_STRING("torture_shuffle task started");
+	do {
+		schedule_timeout_interruptible(shuffle_interval);
+		torture_shuffle_tasks();
+		torture_shutdown_absorb("torture_shuffle");
+	} while (!torture_must_stop());
+	VERBOSE_TOROUT_STRING("torture_shuffle task stopping");
+	return 0;
+}
+
+/*
+ * Start the shuffler, with shuffint in jiffies.
+ */
+int torture_shuffle_init(long shuffint)
+{
+	int ret;
+
+	shuffle_interval = shuffint;
+
+	shuffle_idle_cpu = -1;
+
+	if (!alloc_cpumask_var(&shuffle_tmp_mask, GFP_KERNEL)) {
+		VERBOSE_TOROUT_ERRSTRING("Failed to alloc mask");
+		return -ENOMEM;
+	}
+
+	/* Create the shuffler thread */
+	shuffler_task = kthread_run(torture_shuffle, NULL, "torture_shuffle");
+	if (IS_ERR(shuffler_task)) {
+		ret = PTR_ERR(shuffler_task);
+		free_cpumask_var(shuffle_tmp_mask);
+		VERBOSE_TOROUT_ERRSTRING("Failed to create shuffler");
+		shuffler_task = NULL;
+		return ret;
+	}
+	torture_shuffle_task_register(shuffler_task);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(torture_shuffle_init);
+
+/*
+ * Stop the shuffling.
+ */
+void torture_shuffle_cleanup(void)
+{
+	torture_shuffle_task_unregister_all();
+	if (shuffler_task) {
+		VERBOSE_TOROUT_STRING("Stopping torture_shuffle task");
+		kthread_stop(shuffler_task);
+		free_cpumask_var(shuffle_tmp_mask);
+	}
+	shuffler_task = NULL;
+}
+EXPORT_SYMBOL_GPL(torture_shuffle_cleanup);
+
+/*
  * Absorb kthreads into a kernel function that won't return, so that
  * they won't ever access module text or data again.
  */