Date:	Wed, 15 Jun 2016 15:28:21 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
	rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
	dvhart@...ux.intel.com, fweisbec@...il.com, oleg@...hat.com,
	bobby.prani@...il.com,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 1/8] waketorture: Add a wakeup-torture module

This commit adds a wakeup-torture module to assist tracking down an
elusive lost-wakeup problem.

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 kernel/rcu/Makefile      |   3 +-
 kernel/rcu/waketorture.c | 371 +++++++++++++++++++++++++++++++++++++++++++++++
 lib/Kconfig.debug        |  17 +++
 3 files changed, 390 insertions(+), 1 deletion(-)
 create mode 100644 kernel/rcu/waketorture.c

diff --git a/kernel/rcu/Makefile b/kernel/rcu/Makefile
index 18dfc485225c..42cd319920b1 100644
--- a/kernel/rcu/Makefile
+++ b/kernel/rcu/Makefile
@@ -4,9 +4,10 @@ KCOV_INSTRUMENT := n
 
 obj-y += update.o sync.o
 obj-$(CONFIG_SRCU) += srcu.o
-obj-$(CONFIG_RCU_TORTURE_TEST) += rcutorture.o
 obj-$(CONFIG_RCU_PERF_TEST) += rcuperf.o
+obj-$(CONFIG_RCU_TORTURE_TEST) += rcutorture.o
 obj-$(CONFIG_TREE_RCU) += tree.o
 obj-$(CONFIG_PREEMPT_RCU) += tree.o
 obj-$(CONFIG_TREE_RCU_TRACE) += tree_trace.o
 obj-$(CONFIG_TINY_RCU) += tiny.o
+obj-$(CONFIG_WAKE_TORTURE_TEST) += waketorture.o
diff --git a/kernel/rcu/waketorture.c b/kernel/rcu/waketorture.c
new file mode 100644
index 000000000000..75bc547206cc
--- /dev/null
+++ b/kernel/rcu/waketorture.c
@@ -0,0 +1,371 @@
+/*
+ * Specific stress-testing of wakeup logic in the presence of hotplug
+ * operations.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, you can access it online at
+ * http://www.gnu.org/licenses/gpl-2.0.html.
+ *
+ * Copyright (C) IBM Corporation, 2016
+ *
+ * Author: Paul E. McKenney <paulmck@...ibm.com>
+ */
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/kthread.h>
+#include <linux/err.h>
+#include <linux/spinlock.h>
+#include <linux/smp.h>
+#include <linux/rcupdate.h>
+#include <linux/interrupt.h>
+#include <linux/sched.h>
+#include <linux/atomic.h>
+#include <linux/bitops.h>
+#include <linux/completion.h>
+#include <linux/moduleparam.h>
+#include <linux/percpu.h>
+#include <linux/notifier.h>
+#include <linux/reboot.h>
+#include <linux/freezer.h>
+#include <linux/cpu.h>
+#include <linux/delay.h>
+#include <linux/stat.h>
+#include <linux/srcu.h>
+#include <linux/slab.h>
+#include <linux/trace_clock.h>
+#include <asm/byteorder.h>
+#include <linux/torture.h>
+#include <linux/vmalloc.h>
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Paul E. McKenney <paulmck@...ibm.com>");
+
+
+torture_param(int, nwaiters, -1, "Number of timed-wait threads");
+torture_param(int, onoff_holdoff, 0, "Time after boot before CPU hotplugs (s)");
+torture_param(int, onoff_interval, 0,
+	     "Time between CPU hotplugs (jiffies), 0=disable");
+torture_param(int, shutdown_secs, 0, "Shutdown time (s), <= zero to disable.");
+torture_param(int, stat_interval, 60,
+	     "Number of seconds between stats printk()s");
+torture_param(bool, verbose, true,
+	     "Enable verbose debugging printk()s");
+torture_param(int, wait_duration, 3,
+	     "Number of jiffies to wait each iteration");
+torture_param(int, wait_grace, 20,
+	     "Number of jiffies before complaining about long wait");
+
+static char *torture_type = "sti";
+module_param(torture_type, charp, 0444);
+MODULE_PARM_DESC(torture_type, "Type of wait to torture (sti, stui, ...)");
+
+static int nrealwaiters;
+static struct task_struct **waiter_tasks;
+static struct task_struct *stats_task;
+
+/* Yes, these cache-thrash, and it is inherent to the concurrency design. */
+static bool *waiter_done;		/* Waiter is done, don't wake. */
+static unsigned long *waiter_iter;	/* Number of wait iterations. */
+static bool *waiter_cts;		/* Waiter already checked. */
+static unsigned long *waiter_kicks;	/* Number of waiter starvations. */
+static unsigned long *waiter_ts;	/* Jiffies last run. */
+DEFINE_MUTEX(waiter_mutex);
+
+static int torture_runnable = IS_ENABLED(MODULE);
+module_param(torture_runnable, int, 0444);
+MODULE_PARM_DESC(torture_runnable, "Start waketorture at boot");
+
+/*
+ * Operations vector for selecting different types of tests.
+ */
+
+struct wake_torture_ops {
+	signed long (*wait)(signed long timeout);
+	const char *name;
+};
+
+static struct wake_torture_ops *cur_ops;
+
+/*
+ * Definitions for schedule_timeout_interruptible() torture testing.
+ */
+
+static struct wake_torture_ops sti_ops = {
+	.wait		= schedule_timeout_interruptible,
+	.name		= "sti"
+};
+
+/*
+ * Definitions for schedule_timeout_uninterruptible() torture testing.
+ */
+
+static struct wake_torture_ops stui_ops = {
+	.wait		= schedule_timeout_uninterruptible,
+	.name		= "stui"
+};
+
+/*
+ * Has the specified waiter thread run recently?
+ */
+static bool kthread_ran_recently(int tnum)
+{
+	smp_mb(); /* Ensure waiter_cts[] read before waiter_ts[].  [A] */
+	return time_before(READ_ONCE(waiter_ts[tnum]), jiffies + wait_grace);
+}
+
+/*
+ * Wakeup torture fake writer kthread.  Repeatedly calls sync, with a random
+ * delay between calls.
+ */
+static int wake_torture_waiter(void *arg)
+{
+	int i;
+	long me = (long)arg;
+
+	VERBOSE_TOROUT_STRING("wake_torture_waiter task started");
+	set_user_nice(current, MAX_NICE);
+
+	do {
+		waiter_ts[me] = jiffies;
+		smp_mb(); /* Ensure waiter_ts[] written before waiter_cts[]. */
+			  /* Pairs with [A]. */
+		waiter_cts[me] = false;
+		cur_ops->wait(wait_duration);
+		waiter_iter[me]++;
+		for (i = 0; i < nrealwaiters; i++) {
+			if (waiter_done[i] ||
+			    waiter_cts[i] ||
+			    kthread_ran_recently(i))
+				continue;
+			if (!mutex_trylock(&waiter_mutex)) {
+				break; /* Keep lock contention to dull roar. */
+			} else if (waiter_done[i] ||
+				   waiter_cts[i] ||
+				   kthread_ran_recently(i)) {
+				mutex_unlock(&waiter_mutex);
+			} else {
+				waiter_cts[i] = true;
+				waiter_kicks[i]++;
+				pr_alert("%s%s wake_torture_waiter(): P%d failing to awaken!\n", torture_type, TORTURE_FLAG, waiter_tasks[i]->pid);
+				rcu_ftrace_dump(DUMP_ALL);
+				wake_up_process(waiter_tasks[i]);
+				mutex_unlock(&waiter_mutex);
+			}
+		}
+		torture_shutdown_absorb("wake_torture_waiter");
+	} while (!torture_must_stop());
+	mutex_lock(&waiter_mutex);
+	waiter_done[me] = true;
+	mutex_unlock(&waiter_mutex);
+	torture_kthread_stopping("wake_torture_waiter");
+	return 0;
+}
+
+/*
+ * Print torture statistics.  Caller must ensure that there is only one
+ * call to this function at a given time!!!  This is normally accomplished
+ * by relying on the module system to only have one copy of the module
+ * loaded, and then by giving the wake_torture_stats kthread full control
+ * (or the init/cleanup functions when wake_torture_stats thread is not
+ * running).
+ *
+ * Note that some care is required because this can be called once during
+ * cleanup processing after a failed startup attempt.
+ */
+static void
+wake_torture_stats_print(void)
+{
+	int i;
+	bool tardy = false;
+
+	if (!waiter_done || !waiter_iter || !waiter_cts ||
+	    !waiter_kicks || !waiter_ts) {
+		TOROUT_STRING("Partial initialization, no stats print.\n");
+		return;
+	}
+	for (i = 0; i < nrealwaiters; i++)
+		if (waiter_kicks[i]) {
+			if (!tardy)
+				pr_alert("%s" TORTURE_FLAG " Tardy kthreads:",
+					 torture_type);
+			tardy = true;
+			pr_cont("  P%d%c: %lud/%lu",
+				waiter_tasks && waiter_tasks[i]
+					? waiter_tasks[i]->pid
+					: -1,
+				"!."[kthread_ran_recently(i)],
+				waiter_kicks[i], waiter_iter[i]);
+		}
+	if (tardy)
+		pr_cont("\n");
+	else
+		TOROUT_STRING(" No tardy kthreads");
+}
+
+/*
+ * Periodically prints torture statistics, if periodic statistics printing
+ * was specified via the stat_interval module parameter.
+ */
+static int
+wake_torture_stats(void *arg)
+{
+	VERBOSE_TOROUT_STRING("wake_torture_stats task started");
+	do {
+		schedule_timeout_interruptible(stat_interval * HZ);
+		wake_torture_stats_print();
+		torture_shutdown_absorb("wake_torture_stats");
+	} while (!torture_must_stop());
+	torture_kthread_stopping("wake_torture_stats");
+	return 0;
+}
+
+static inline void
+wake_torture_print_module_parms(struct wake_torture_ops *cur_ops,
+				const char *tag)
+{
+	pr_alert("%s" TORTURE_FLAG
+		 "--- %s: nwaiters=%d onoff_holdoff=%d onoff_interval=%d shutdown_secs=%d stat_interval=%d verbose=%d wait_duration=%d wait_grace=%d\n",
+		 torture_type, tag,
+		 nrealwaiters, onoff_holdoff, onoff_interval,
+		 shutdown_secs, stat_interval, verbose,
+		 wait_duration, wait_grace);
+}
+
+static void
+wake_torture_cleanup(void)
+{
+	int i;
+	bool success;
+
+	(void)torture_cleanup_begin();
+
+	if (waiter_tasks) {
+		for (i = 0; i < nrealwaiters; i++)
+			torture_stop_kthread(wake_torture_waiter,
+					     waiter_tasks[i]);
+		kfree(waiter_tasks);
+	}
+
+	torture_stop_kthread(wake_torture_stats, stats_task);
+
+	wake_torture_stats_print();  /* -After- the stats thread is stopped! */
+
+	success = !!waiter_kicks;
+	for (i = 0; i < nrealwaiters; i++)
+		if (!success || waiter_kicks[i]) {
+			success = false;
+			break;
+		}
+
+	kfree(waiter_done);
+	kfree(waiter_iter);
+	kfree(waiter_cts);
+	kfree(waiter_kicks);
+	kfree(waiter_ts);
+
+	wake_torture_print_module_parms(cur_ops,
+					success ? "End of test: SUCCESS"
+						: "End of test: FAILURE");
+	torture_cleanup_end();
+}
+
+static int __init
+wake_torture_init(void)
+{
+	int i;
+	int firsterr = 0;
+	static struct wake_torture_ops *torture_ops[] = { &sti_ops, &stui_ops };
+
+	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)
+			break;
+	}
+	if (i == ARRAY_SIZE(torture_ops)) {
+		pr_alert("wake-torture: invalid torture type: \"%s\"\n",
+			 torture_type);
+		pr_alert("wake-torture types:");
+		for (i = 0; i < ARRAY_SIZE(torture_ops); i++)
+			pr_alert(" %s", torture_ops[i]->name);
+		pr_alert("\n");
+		firsterr = -EINVAL;
+		goto unwind;
+	}
+
+	if (nwaiters >= 0) {
+		nrealwaiters = nwaiters;
+	} else {
+		nrealwaiters = num_online_cpus() - 2 - nwaiters;
+		if (nrealwaiters <= 0)
+			nrealwaiters = 1;
+	}
+	wake_torture_print_module_parms(cur_ops, "Start of test");
+
+	/* Initialize the statistics so that each run gets its own numbers. */
+
+	waiter_done = kcalloc(nrealwaiters, sizeof(*waiter_done), GFP_KERNEL);
+	waiter_iter = kcalloc(nrealwaiters, sizeof(*waiter_iter), GFP_KERNEL);
+	waiter_cts = kcalloc(nrealwaiters, sizeof(*waiter_cts), GFP_KERNEL);
+	waiter_kicks = kcalloc(nrealwaiters, sizeof(*waiter_kicks), GFP_KERNEL);
+	waiter_ts = kcalloc(nrealwaiters, sizeof(*waiter_ts), GFP_KERNEL);
+	if (!waiter_done || !waiter_iter || !waiter_cts || !waiter_kicks ||
+	    !waiter_ts) {
+		VERBOSE_TOROUT_ERRSTRING("out of memory");
+		firsterr = -ENOMEM;
+		goto unwind;
+	}
+
+	/* Start up the kthreads. */
+
+	waiter_tasks = kcalloc(nrealwaiters, sizeof(waiter_tasks[0]),
+			       GFP_KERNEL);
+	if (!waiter_tasks) {
+		VERBOSE_TOROUT_ERRSTRING("out of memory");
+		firsterr = -ENOMEM;
+		goto unwind;
+	}
+	for (i = 0; i < nrealwaiters; i++) {
+		firsterr = torture_create_kthread(wake_torture_waiter,
+						  NULL, waiter_tasks[i]);
+		if (firsterr)
+			goto unwind;
+	}
+	if (stat_interval > 0) {
+		firsterr = torture_create_kthread(wake_torture_stats, NULL,
+						  stats_task);
+		if (firsterr)
+			goto unwind;
+	}
+	firsterr = torture_shutdown_init(shutdown_secs, wake_torture_cleanup);
+	if (firsterr)
+		goto unwind;
+	firsterr = torture_onoff_init(onoff_holdoff * HZ, onoff_interval);
+	if (firsterr)
+		goto unwind;
+	torture_init_end();
+	return 0;
+
+unwind:
+	torture_init_end();
+	wake_torture_cleanup();
+	return firsterr;
+}
+
+module_init(wake_torture_init);
+module_exit(wake_torture_cleanup);
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 805b7048a1bd..f0dcb4c0fe96 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1399,6 +1399,23 @@ config RCU_TORTURE_TEST_SLOW_CLEANUP_DELAY
 	  This option specifies the number of jiffies to wait between
 	  each rcu_node structure cleanup operation.
 
+config WAKE_TORTURE_TEST
+	tristate "Torture test for wakeups and CPU hotplug"
+	depends on DEBUG_KERNEL
+	depends on 64BIT
+	select TORTURE_TEST
+	default n
+	help
+	  This option provides a kernel module that runs torture tests
+	  on wakeups from timed waits in the presence of CPU hotplug.
+	  The kernel module may be built after the fact on the running
+	  kernel to be tested, if desired.
+
+	  Say Y here if you want wakeup torture tests to be built into
+	  the kernel.
+	  Say M if you want the wakeup torture tests to build as a module.
+	  Say N if you are unsure.
+
 config RCU_CPU_STALL_TIMEOUT
 	int "RCU CPU stall timeout in seconds"
 	depends on RCU_STALL_COMMON
-- 
2.5.2

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