[PATCH RFC tip/core/rcu 0/8] Waketorture, not for inclusion

[PATCH RFC tip/core/rcu 0/8] Waketorture, not for inclusion

[Paul E. McKenney]

Hello!

And for your amusement, this series provides a waketorture module.  It is
intended to increase the probability of a heisenbug or three I have been
chasing for longer than I care to admit.  Should it someday actually
significantly increase that probability, I might consider submitting it
for acceptance.  In the meantime, for your amusement:

1.	Add a wakeup-torture module.

2.	Update scripting to accommodate waketorture.

3.	Don't kick kthreads unless grace period or request.

4.	Add utilization measurement.

5.	Add hrtimer support for fine-grained event scheduling.

6.	Make waketorture always hotplug the same CPU.

7.	Make waketorture kill test if no hotpluggable CPUs.

8.	Affinity waiter tasks away from hotpluggable CPU.

							Thanx, Paul

------------------------------------------------------------------------

 kernel/rcu/Makefile                                              |    3 
 kernel/rcu/tree.c                                                |    3 
 kernel/rcu/waketorture.c                                         |  567 +++++++++-
 lib/Kconfig.debug                                                |   18 
 tools/testing/selftests/rcutorture/bin/kvm-recheck-wake.sh       |   39 
 tools/testing/selftests/rcutorture/bin/kvm-recheck.sh            |    2 
 tools/testing/selftests/rcutorture/bin/kvm.sh                    |    2 
 tools/testing/selftests/rcutorture/configs/wake/CFLIST           |    1 
 tools/testing/selftests/rcutorture/configs/wake/CFcommon         |    2 
 tools/testing/selftests/rcutorture/configs/wake/SH               |   19 
 tools/testing/selftests/rcutorture/configs/wake/SH.boot          |    1 
 tools/testing/selftests/rcutorture/configs/wake/STI              |   19 
 tools/testing/selftests/rcutorture/configs/wake/STI.boot         |    1 
 tools/testing/selftests/rcutorture/configs/wake/ver_functions.sh |   43 
 14 files changed, 701 insertions(+), 19 deletions(-)

[PATCH tip/core/rcu 1/8] waketorture: Add a wakeup-torture module

[Paul E. McKenney]

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

Signed-off-by: Paul E. McKenney <paulmck@linux.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@us.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@us.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

[PATCH tip/core/rcu 2/8] waketorture: Update scripting to accommodate waketorture

[Paul E. McKenney]

This commit adds the scripting changes to add support for the shiny
new waketorture kernel module.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 .../selftests/rcutorture/bin/kvm-recheck-wake.sh   | 39 ++++++++++++++++++++
 .../selftests/rcutorture/bin/kvm-recheck.sh        |  2 +-
 tools/testing/selftests/rcutorture/bin/kvm.sh      |  2 +-
 .../selftests/rcutorture/configs/wake/CFLIST       |  1 +
 .../selftests/rcutorture/configs/wake/CFcommon     |  2 +
 .../testing/selftests/rcutorture/configs/wake/STI  | 19 ++++++++++
 .../selftests/rcutorture/configs/wake/STI.boot     |  1 +
 .../rcutorture/configs/wake/ver_functions.sh       | 43 ++++++++++++++++++++++
 8 files changed, 107 insertions(+), 2 deletions(-)
 create mode 100755 tools/testing/selftests/rcutorture/bin/kvm-recheck-wake.sh
 create mode 100644 tools/testing/selftests/rcutorture/configs/wake/CFLIST
 create mode 100644 tools/testing/selftests/rcutorture/configs/wake/CFcommon
 create mode 100644 tools/testing/selftests/rcutorture/configs/wake/STI
 create mode 100644 tools/testing/selftests/rcutorture/configs/wake/STI.boot
 create mode 100644 tools/testing/selftests/rcutorture/configs/wake/ver_functions.sh

diff --git a/tools/testing/selftests/rcutorture/bin/kvm-recheck-wake.sh b/tools/testing/selftests/rcutorture/bin/kvm-recheck-wake.sh
new file mode 100755
index 000000000000..fc9ee1920acb
--- /dev/null
+++ b/tools/testing/selftests/rcutorture/bin/kvm-recheck-wake.sh
@@ -0,0 +1,39 @@
+#!/bin/bash
+#
+# Analyze a given results directory for waketorture diagnostics.
+#
+# Usage: kvm-recheck-wake resdir
+#
+# 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
+#
+# Authors: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
+
+i="$1"
+if test -d $i
+then
+	:
+else
+	echo Unreadable results directory: $i
+	exit 1
+fi
+PATH=`pwd`/tools/testing/selftests/rcutorture/bin:$PATH; export PATH
+. tools/testing/selftests/rcutorture/bin/functions.sh
+
+configfile=`echo $i | sed -e 's/^.*\///'`
+
+sed -e 's/^\[[^]]*]//' < $i/console.log | grep -e -torture |
+	grep "Tardy kthreads" | tail -1
diff --git a/tools/testing/selftests/rcutorture/bin/kvm-recheck.sh b/tools/testing/selftests/rcutorture/bin/kvm-recheck.sh
index f659346d3358..060c1eec73f4 100755
--- a/tools/testing/selftests/rcutorture/bin/kvm-recheck.sh
+++ b/tools/testing/selftests/rcutorture/bin/kvm-recheck.sh
@@ -48,7 +48,7 @@ do
 				cat $i/Make.oldconfig.err
 			fi
 			parse-build.sh $i/Make.out $configfile
-			if test "$TORTURE_SUITE" != rcuperf
+			if test "$TORTURE_SUITE" != rcuperf -a "$TORTURE_SUITE" != wake
 			then
 				parse-torture.sh $i/console.log $configfile
 			fi
diff --git a/tools/testing/selftests/rcutorture/bin/kvm.sh b/tools/testing/selftests/rcutorture/bin/kvm.sh
index 0aed965f0062..0109ddf7b666 100755
--- a/tools/testing/selftests/rcutorture/bin/kvm.sh
+++ b/tools/testing/selftests/rcutorture/bin/kvm.sh
@@ -163,7 +163,7 @@ do
 		shift
 		;;
 	--torture)
-		checkarg --torture "(suite name)" "$#" "$2" '^\(lock\|rcu\|rcuperf\)$' '^--'
+		checkarg --torture "(suite name)" "$#" "$2" '^\(lock\|rcu\|rcuperf\|wake\)$' '^--'
 		TORTURE_SUITE=$2
 		shift
 		;;
diff --git a/tools/testing/selftests/rcutorture/configs/wake/CFLIST b/tools/testing/selftests/rcutorture/configs/wake/CFLIST
new file mode 100644
index 000000000000..850c262a6226
--- /dev/null
+++ b/tools/testing/selftests/rcutorture/configs/wake/CFLIST
@@ -0,0 +1 @@
+STI
diff --git a/tools/testing/selftests/rcutorture/configs/wake/CFcommon b/tools/testing/selftests/rcutorture/configs/wake/CFcommon
new file mode 100644
index 000000000000..ffba1816cb6c
--- /dev/null
+++ b/tools/testing/selftests/rcutorture/configs/wake/CFcommon
@@ -0,0 +1,2 @@
+CONFIG_WAKE_TORTURE_TEST=y
+CONFIG_PRINTK_TIME=y
diff --git a/tools/testing/selftests/rcutorture/configs/wake/STI b/tools/testing/selftests/rcutorture/configs/wake/STI
new file mode 100644
index 000000000000..7a17c503b382
--- /dev/null
+++ b/tools/testing/selftests/rcutorture/configs/wake/STI
@@ -0,0 +1,19 @@
+CONFIG_SMP=y
+CONFIG_NR_CPUS=16
+CONFIG_PREEMPT_NONE=n
+CONFIG_PREEMPT_VOLUNTARY=n
+CONFIG_PREEMPT=y
+#CHECK#CONFIG_PREEMPT_RCU=y
+CONFIG_HZ_PERIODIC=y
+CONFIG_NO_HZ_IDLE=n
+CONFIG_NO_HZ_FULL=n
+CONFIG_RCU_TRACE=y
+CONFIG_HOTPLUG_CPU=y
+CONFIG_RCU_FANOUT=2
+CONFIG_RCU_FANOUT_LEAF=2
+CONFIG_RCU_NOCB_CPU=n
+CONFIG_DEBUG_LOCK_ALLOC=n
+CONFIG_RCU_BOOST=y
+CONFIG_RCU_KTHREAD_PRIO=2
+CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
+CONFIG_RCU_EXPERT=y
diff --git a/tools/testing/selftests/rcutorture/configs/wake/STI.boot b/tools/testing/selftests/rcutorture/configs/wake/STI.boot
new file mode 100644
index 000000000000..67ac1ad46672
--- /dev/null
+++ b/tools/testing/selftests/rcutorture/configs/wake/STI.boot
@@ -0,0 +1 @@
+rcupdate.rcu_expedited waketorture.torture_type=sti
diff --git a/tools/testing/selftests/rcutorture/configs/wake/ver_functions.sh b/tools/testing/selftests/rcutorture/configs/wake/ver_functions.sh
new file mode 100644
index 000000000000..7331a1884d99
--- /dev/null
+++ b/tools/testing/selftests/rcutorture/configs/wake/ver_functions.sh
@@ -0,0 +1,43 @@
+#!/bin/bash
+#
+# Kernel-version-dependent shell functions for the rest of the scripts.
+#
+# 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
+#
+# Authors: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
+
+# waketorture_param_onoff bootparam-string config-file
+#
+# Adds onoff waketorture module parameters to kernels having it.
+waketorture_param_onoff () {
+	if ! bootparam_hotplug_cpu "$1" && configfrag_hotplug_cpu "$2"
+	then
+		echo CPU-hotplug kernel, adding waketorture onoff. 1>&2
+		echo waketorture.onoff_interval=50 waketorture.onoff_holdoff=30
+	fi
+}
+
+# per_version_boot_params bootparam-string config-file seconds
+#
+# Adds per-version torture-module parameters to kernels supporting them.
+per_version_boot_params () {
+	echo $1 `waketorture_param_onoff "$1" "$2"` \
+		waketorture.stat_interval=15 \
+		waketorture.shutdown_secs=$3 \
+		waketorture.torture_runnable=1 \
+		waketorture.verbose=1
+}
-- 
2.5.2

[PATCH tip/core/rcu 3/8] waketorture: Don't kick unless grace period or request

[Paul E. McKenney]

The current code can result in spurious kicks when there are no grace
periods in progress and no grace-period-related requests.  This is
sort of OK for a diagnostic aid, but the resulting ftrace-dump messages
in dmesg are annoying.  This commit therefore avoids spurious kicks
in the common case.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/tree.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index f433959e9322..88d3f9590322 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1306,7 +1306,8 @@ static void rcu_stall_kick_kthreads(struct rcu_state *rsp)
 	if (!rcu_kick_kthreads)
 		return;
 	j = READ_ONCE(rsp->jiffies_kick_kthreads);
-	if (time_after(jiffies, j) && rsp->gp_kthread) {
+	if (time_after(jiffies, j) && rsp->gp_kthread &&
+	    (rcu_gp_in_progress(rsp) || READ_ONCE(rsp->gp_flags))) {
 		WARN_ONCE(1, "Kicking %s grace-period kthread\n", rsp->name);
 		rcu_ftrace_dump(DUMP_ALL);
 		wake_up_process(rsp->gp_kthread);
-- 
2.5.2

[PATCH tip/core/rcu 4/8] waketorture: Add utilization measurement

[Paul E. McKenney]

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/waketorture.c | 29 ++++++++++++++++++++++++++++-
 lib/Kconfig.debug        |  1 +
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/waketorture.c b/kernel/rcu/waketorture.c
index 75bc547206cc..3068a5c858c8 100644
--- a/kernel/rcu/waketorture.c
+++ b/kernel/rcu/waketorture.c
@@ -81,7 +81,9 @@ 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 DEFINE_MUTEX(waiter_mutex);
+static DEFINE_PER_CPU(u64, waiter_cputime); /* Nanoseconds. */
+static u64 starttime;
 
 static int torture_runnable = IS_ENABLED(MODULE);
 module_param(torture_runnable, int, 0444);
@@ -133,16 +135,23 @@ static int wake_torture_waiter(void *arg)
 {
 	int i;
 	long me = (long)arg;
+	u64 ts;
 
 	VERBOSE_TOROUT_STRING("wake_torture_waiter task started");
 	set_user_nice(current, MAX_NICE);
 
+	preempt_disable();
+	ts = trace_clock_local();
 	do {
 		waiter_ts[me] = jiffies;
 		smp_mb(); /* Ensure waiter_ts[] written before waiter_cts[]. */
 			  /* Pairs with [A]. */
 		waiter_cts[me] = false;
+		__this_cpu_add(waiter_cputime, trace_clock_local() - ts);
+		preempt_enable();
 		cur_ops->wait(wait_duration);
+		preempt_disable();
+		ts = trace_clock_local();
 		waiter_iter[me]++;
 		for (i = 0; i < nrealwaiters; i++) {
 			if (waiter_done[i] ||
@@ -164,8 +173,14 @@ static int wake_torture_waiter(void *arg)
 				mutex_unlock(&waiter_mutex);
 			}
 		}
+		__this_cpu_add(waiter_cputime, trace_clock_local() - ts);
+		preempt_enable();
 		torture_shutdown_absorb("wake_torture_waiter");
+		preempt_disable();
+		ts = trace_clock_local();
 	} while (!torture_must_stop());
+	__this_cpu_add(waiter_cputime, trace_clock_local() - ts);
+	preempt_enable();
 	mutex_lock(&waiter_mutex);
 	waiter_done[me] = true;
 	mutex_unlock(&waiter_mutex);
@@ -189,6 +204,8 @@ wake_torture_stats_print(void)
 {
 	int i;
 	bool tardy = false;
+	u64 timediff;
+	u64 timetot;
 
 	if (!waiter_done || !waiter_iter || !waiter_cts ||
 	    !waiter_kicks || !waiter_ts) {
@@ -212,6 +229,15 @@ wake_torture_stats_print(void)
 		pr_cont("\n");
 	else
 		TOROUT_STRING(" No tardy kthreads");
+	timediff = (trace_clock_global() - starttime) / 1000;
+	timetot = 0;
+	for_each_possible_cpu(i)
+		timetot += READ_ONCE(per_cpu(waiter_cputime, i));
+	timetot /= nr_cpu_ids;
+	timetot /= timediff;
+	pr_alert("%s" TORTURE_FLAG " timediff: %llu utilization: %llu.%llu nr_cpu_ids: %d\n",
+		 torture_type, timediff,
+		 timetot / 1000ULL, timetot % 1000ULL, nr_cpu_ids);
 }
 
 /*
@@ -290,6 +316,7 @@ wake_torture_init(void)
 
 	if (!torture_init_begin(torture_type, verbose, &torture_runnable))
 		return -EBUSY;
+	starttime = trace_clock_global();
 
 	/* Process args and tell the world that the torturer is on the job. */
 	for (i = 0; i < ARRAY_SIZE(torture_ops); i++) {
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index f0dcb4c0fe96..c8fb7dad5062 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1403,6 +1403,7 @@ config WAKE_TORTURE_TEST
 	tristate "Torture test for wakeups and CPU hotplug"
 	depends on DEBUG_KERNEL
 	depends on 64BIT
+	depends on TRACE_CLOCK
 	select TORTURE_TEST
 	default n
 	help
-- 
2.5.2

[PATCH tip/core/rcu 5/8] waketorture: Add hrtimer support

[Paul E. McKenney]

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/waketorture.c                           | 50 ++++++++++++++++++----
 tools/testing/selftests/rcutorture/configs/wake/SH | 19 ++++++++
 .../selftests/rcutorture/configs/wake/SH.boot      |  1 +
 3 files changed, 61 insertions(+), 9 deletions(-)
 create mode 100644 tools/testing/selftests/rcutorture/configs/wake/SH
 create mode 100644 tools/testing/selftests/rcutorture/configs/wake/SH.boot

diff --git a/kernel/rcu/waketorture.c b/kernel/rcu/waketorture.c
index 3068a5c858c8..bf04c65296bd 100644
--- a/kernel/rcu/waketorture.c
+++ b/kernel/rcu/waketorture.c
@@ -62,12 +62,12 @@ 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_duration, 127,
+	     "Number of microseconds to wait each iteration");
 torture_param(int, wait_grace, 20,
 	     "Number of jiffies before complaining about long wait");
 
-static char *torture_type = "sti";
+static char *torture_type = "sh";
 module_param(torture_type, charp, 0444);
 MODULE_PARM_DESC(torture_type, "Type of wait to torture (sti, stui, ...)");
 
@@ -94,18 +94,40 @@ MODULE_PARM_DESC(torture_runnable, "Start waketorture at boot");
  */
 
 struct wake_torture_ops {
-	signed long (*wait)(signed long timeout);
+	void (*wait)(void);
 	const char *name;
 };
 
 static struct wake_torture_ops *cur_ops;
 
 /*
+ * Definitions for schedule_hrtimeout() torture testing.
+ */
+
+static void wait_schedule_hrtimeout(void)
+{
+	ktime_t wait = ns_to_ktime(wait_duration * 1000);
+
+	set_current_state(TASK_UNINTERRUPTIBLE);
+	schedule_hrtimeout(&wait, HRTIMER_MODE_REL);
+}
+
+static struct wake_torture_ops sh_ops = {
+	.wait		= wait_schedule_hrtimeout,
+	.name		= "sh"
+};
+
+/*
  * Definitions for schedule_timeout_interruptible() torture testing.
  */
 
+static void wait_schedule_timeout_interruptible(void)
+{
+	schedule_timeout_interruptible((wait_duration + 999) / 1000);
+}
+
 static struct wake_torture_ops sti_ops = {
-	.wait		= schedule_timeout_interruptible,
+	.wait		= wait_schedule_timeout_interruptible,
 	.name		= "sti"
 };
 
@@ -113,8 +135,13 @@ static struct wake_torture_ops sti_ops = {
  * Definitions for schedule_timeout_uninterruptible() torture testing.
  */
 
+static void wait_schedule_timeout_uninterruptible(void)
+{
+	schedule_timeout_uninterruptible((wait_duration + 999) / 1000);
+}
+
 static struct wake_torture_ops stui_ops = {
-	.wait		= schedule_timeout_uninterruptible,
+	.wait		= wait_schedule_timeout_uninterruptible,
 	.name		= "stui"
 };
 
@@ -149,7 +176,7 @@ static int wake_torture_waiter(void *arg)
 		waiter_cts[me] = false;
 		__this_cpu_add(waiter_cputime, trace_clock_local() - ts);
 		preempt_enable();
-		cur_ops->wait(wait_duration);
+		cur_ops->wait();
 		preempt_disable();
 		ts = trace_clock_local();
 		waiter_iter[me]++;
@@ -167,7 +194,10 @@ static int wake_torture_waiter(void *arg)
 			} 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);
+				pr_alert("%s%s wake_torture_waiter(): P%d (%#lx) failing to awaken!\n",
+					 torture_type, TORTURE_FLAG,
+					 waiter_tasks[i]->pid,
+					 waiter_tasks[i]->state);
 				rcu_ftrace_dump(DUMP_ALL);
 				wake_up_process(waiter_tasks[i]);
 				mutex_unlock(&waiter_mutex);
@@ -312,7 +342,9 @@ wake_torture_init(void)
 {
 	int i;
 	int firsterr = 0;
-	static struct wake_torture_ops *torture_ops[] = { &sti_ops, &stui_ops };
+	static struct wake_torture_ops *torture_ops[] = {
+		&sh_ops, &sti_ops, &stui_ops
+	};
 
 	if (!torture_init_begin(torture_type, verbose, &torture_runnable))
 		return -EBUSY;
diff --git a/tools/testing/selftests/rcutorture/configs/wake/SH b/tools/testing/selftests/rcutorture/configs/wake/SH
new file mode 100644
index 000000000000..7a17c503b382
--- /dev/null
+++ b/tools/testing/selftests/rcutorture/configs/wake/SH
@@ -0,0 +1,19 @@
+CONFIG_SMP=y
+CONFIG_NR_CPUS=16
+CONFIG_PREEMPT_NONE=n
+CONFIG_PREEMPT_VOLUNTARY=n
+CONFIG_PREEMPT=y
+#CHECK#CONFIG_PREEMPT_RCU=y
+CONFIG_HZ_PERIODIC=y
+CONFIG_NO_HZ_IDLE=n
+CONFIG_NO_HZ_FULL=n
+CONFIG_RCU_TRACE=y
+CONFIG_HOTPLUG_CPU=y
+CONFIG_RCU_FANOUT=2
+CONFIG_RCU_FANOUT_LEAF=2
+CONFIG_RCU_NOCB_CPU=n
+CONFIG_DEBUG_LOCK_ALLOC=n
+CONFIG_RCU_BOOST=y
+CONFIG_RCU_KTHREAD_PRIO=2
+CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
+CONFIG_RCU_EXPERT=y
diff --git a/tools/testing/selftests/rcutorture/configs/wake/SH.boot b/tools/testing/selftests/rcutorture/configs/wake/SH.boot
new file mode 100644
index 000000000000..a631c878cb27
--- /dev/null
+++ b/tools/testing/selftests/rcutorture/configs/wake/SH.boot
@@ -0,0 +1 @@
+rcupdate.rcu_expedited waketorture.torture_type=sh
-- 
2.5.2

[PATCH tip/core/rcu 6/8] torture: Make waketorture always hotplug the same CPU

[Paul E. McKenney]

This commit causes waketorture to always hotplug the same CPU,
namely, the highest-numbered CPU that can be hotplugged.  This
will be used by later commits to force race conditions with
higher probability.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/waketorture.c | 88 ++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 85 insertions(+), 3 deletions(-)

diff --git a/kernel/rcu/waketorture.c b/kernel/rcu/waketorture.c
index bf04c65296bd..8568688607ac 100644
--- a/kernel/rcu/waketorture.c
+++ b/kernel/rcu/waketorture.c
@@ -74,6 +74,7 @@ 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;
+static struct task_struct *onoff_task;
 
 /* Yes, these cache-thrash, and it is inherent to the concurrency design. */
 static bool *waiter_done;		/* Waiter is done, don't wake. */
@@ -85,6 +86,18 @@ static DEFINE_MUTEX(waiter_mutex);
 static DEFINE_PER_CPU(u64, waiter_cputime); /* Nanoseconds. */
 static u64 starttime;
 
+static int onoff_cpu = -1;
+static long n_offline_attempts;
+static long n_offline_successes;
+static unsigned long sum_offline;
+static int min_offline = -1;
+static int max_offline;
+static long n_online_attempts;
+static long n_online_successes;
+static unsigned long sum_online;
+static int min_online = -1;
+static int max_online;
+
 static int torture_runnable = IS_ENABLED(MODULE);
 module_param(torture_runnable, int, 0444);
 MODULE_PARM_DESC(torture_runnable, "Start waketorture at boot");
@@ -219,6 +232,67 @@ static int wake_torture_waiter(void *arg)
 }
 
 /*
+ * Find a hotpluggable CPU and repeatedly take it online and offline.
+ */
+static int wake_torture_onoff(void *args)
+{
+	int cpu;
+
+	VERBOSE_TOROUT_STRING("wake_torture_onoff task started");
+	if (onoff_holdoff > 0) {
+		VERBOSE_TOROUT_STRING("wake_torture_onoff begin holdoff");
+		schedule_timeout_interruptible(onoff_holdoff * HZ);
+		VERBOSE_TOROUT_STRING("wake_torture_onoff end holdoff");
+	}
+	for_each_online_cpu(cpu) {
+		if (cpu_is_hotpluggable(cpu))
+			onoff_cpu = cpu;
+	}
+	pr_alert("%s" TORTURE_FLAG " wake_torture_onoff: onoff_cpu: %d\n", torture_type, onoff_cpu);
+	if (onoff_cpu < 0)
+		VERBOSE_TOROUT_STRING("wake_torture_onoff: no hotpluggable CPUs!");
+	while (!torture_must_stop() && onoff_cpu >= 0) {
+		if (!torture_offline(onoff_cpu,
+				    &n_offline_attempts, &n_offline_successes,
+				    &sum_offline, &min_offline, &max_offline))
+			torture_online(onoff_cpu,
+				       &n_online_attempts, &n_online_successes,
+				       &sum_online, &min_online, &max_online);
+		schedule_timeout_interruptible(onoff_interval);
+	}
+	torture_kthread_stopping("wake_torture_onoff");
+	return 0;
+}
+
+/*
+ * Initiate waketorture-specific online-offline handling, which
+ * focuses on a single CPU.
+ */
+static int wake_torture_onoff_init(void)
+{
+	int ret = 0;
+
+	if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
+		return ret;
+	if (onoff_interval <= 0)
+		return 0;
+	ret = torture_create_kthread(wake_torture_onoff, NULL, onoff_task);
+	return ret;
+}
+
+/*
+ * Clean up after waketorture-specific online-offline handling.
+ */
+static void wake_torture_onoff_cleanup(void)
+{
+	if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
+		return;
+	VERBOSE_TOROUT_STRING("Stopping wake_torture_onoff task");
+	kthread_stop(onoff_task);
+	onoff_task = NULL;
+}
+
+/*
  * 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
@@ -265,9 +339,14 @@ wake_torture_stats_print(void)
 		timetot += READ_ONCE(per_cpu(waiter_cputime, i));
 	timetot /= nr_cpu_ids;
 	timetot /= timediff;
-	pr_alert("%s" TORTURE_FLAG " timediff: %llu utilization: %llu.%llu nr_cpu_ids: %d\n",
+	pr_alert("%s" TORTURE_FLAG " timediff: %llu utilization: %llu.%llu nr_cpu_ids: %d onoff: %ld/%ld:%ld/%ld %d,%d:%d,%d %lu:%lu (HZ=%d)\n",
 		 torture_type, timediff,
-		 timetot / 1000ULL, timetot % 1000ULL, nr_cpu_ids);
+		 timetot / 1000ULL, timetot % 1000ULL, nr_cpu_ids,
+		 n_online_successes, n_online_attempts,
+		 n_offline_successes, n_offline_attempts,
+		 min_online, max_online,
+		 min_offline, max_offline,
+		 sum_online, sum_offline, HZ);
 }
 
 /*
@@ -307,6 +386,9 @@ wake_torture_cleanup(void)
 
 	(void)torture_cleanup_begin();
 
+	if (onoff_task)
+		wake_torture_onoff_cleanup();
+
 	if (waiter_tasks) {
 		for (i = 0; i < nrealwaiters; i++)
 			torture_stop_kthread(wake_torture_waiter,
@@ -414,7 +496,7 @@ wake_torture_init(void)
 	firsterr = torture_shutdown_init(shutdown_secs, wake_torture_cleanup);
 	if (firsterr)
 		goto unwind;
-	firsterr = torture_onoff_init(onoff_holdoff * HZ, onoff_interval);
+	firsterr = wake_torture_onoff_init();
 	if (firsterr)
 		goto unwind;
 	torture_init_end();
-- 
2.5.2

[PATCH tip/core/rcu 7/8] torture: Make waketorture kill test if no hotpluggable CPUs

[Paul E. McKenney]

This commit shuts down the kernel if a shutdown time was specified and
if there were no hotpluggable CPUs.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/waketorture.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/waketorture.c b/kernel/rcu/waketorture.c
index 8568688607ac..f9843eb3f7b7 100644
--- a/kernel/rcu/waketorture.c
+++ b/kernel/rcu/waketorture.c
@@ -248,9 +248,15 @@ static int wake_torture_onoff(void *args)
 		if (cpu_is_hotpluggable(cpu))
 			onoff_cpu = cpu;
 	}
-	pr_alert("%s" TORTURE_FLAG " wake_torture_onoff: onoff_cpu: %d\n", torture_type, onoff_cpu);
-	if (onoff_cpu < 0)
+	if (onoff_cpu < 0) {
 		VERBOSE_TOROUT_STRING("wake_torture_onoff: no hotpluggable CPUs!");
+		if (shutdown_secs > 0) {
+			VERBOSE_TOROUT_STRING("wake_torture_onoff: Shutting down");
+			kernel_power_off();
+			VERBOSE_TOROUT_STRING("wake_torture_onoff: Survived kernel_power_off()?");
+		}
+	}
+	pr_alert("%s" TORTURE_FLAG " wake_torture_onoff: onoff_cpu: %d\n", torture_type, onoff_cpu);
 	while (!torture_must_stop() && onoff_cpu >= 0) {
 		if (!torture_offline(onoff_cpu,
 				    &n_offline_attempts, &n_offline_successes,
-- 
2.5.2

[PATCH tip/core/rcu 8/8] torture: Affinity waiter tasks away from hotpluggable CPU

[Paul E. McKenney]

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/waketorture.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/kernel/rcu/waketorture.c b/kernel/rcu/waketorture.c
index f9843eb3f7b7..68be40400f51 100644
--- a/kernel/rcu/waketorture.c
+++ b/kernel/rcu/waketorture.c
@@ -236,7 +236,9 @@ static int wake_torture_waiter(void *arg)
  */
 static int wake_torture_onoff(void *args)
 {
+	cpumask_var_t cm;
 	int cpu;
+	int i;
 
 	VERBOSE_TOROUT_STRING("wake_torture_onoff task started");
 	if (onoff_holdoff > 0) {
@@ -244,6 +246,11 @@ static int wake_torture_onoff(void *args)
 		schedule_timeout_interruptible(onoff_holdoff * HZ);
 		VERBOSE_TOROUT_STRING("wake_torture_onoff end holdoff");
 	}
+
+	/*
+	 * Find the last hotpluggable CPU, and affinity the waiter
+	 * tasks elsewhere.
+	 */
 	for_each_online_cpu(cpu) {
 		if (cpu_is_hotpluggable(cpu))
 			onoff_cpu = cpu;
@@ -257,6 +264,18 @@ static int wake_torture_onoff(void *args)
 		}
 	}
 	pr_alert("%s" TORTURE_FLAG " wake_torture_onoff: onoff_cpu: %d\n", torture_type, onoff_cpu);
+	if (!zalloc_cpumask_var(&cm, GFP_KERNEL)) {
+		VERBOSE_TOROUT_STRING("wake_torture_onoff: Out of memory, no affinity");
+	} else {
+		cpumask_copy(cm, cpu_online_mask);
+		cpumask_clear_cpu(onoff_cpu, cm);
+		if (cpumask_weight(cm) == 0)
+			cpumask_setall(cm);
+		for (i = 0; i < nrealwaiters; i++)
+			set_cpus_allowed_ptr(waiter_tasks[i], cm);
+	}
+
+	/* Cycle the victim CPU online and offline! */
 	while (!torture_must_stop() && onoff_cpu >= 0) {
 		if (!torture_offline(onoff_cpu,
 				    &n_offline_attempts, &n_offline_successes,
-- 
2.5.2