[PATCH rcu v2 00/10] RCU torture test and tool updates for v6.4

[PATCH rcu v2 00/10] RCU torture test and tool updates for v6.4

[Boqun Feng]

Hi,

I of course took the opportunity at my first time to make a mistake: two
patches were missing in v1.. please note that patch #9 and #10 are newly
added.

Previous version:

v1: https://lore.kernel.org/rcu/20230315235454.2993-1-boqun.feng@gmail.com/

Changes since v1:

*	Add two missing patches.
*	Fix checkpatch warnings.

You will also be able to find the series at:

	https://github.com/fbq/linux rcu/rcutorture.2023.03.20a

top commit is:

	6bc6e6b27524
	
List of changes:

Bhaskar Chowdhury (1):
  tools: rcu: Add usage function and check for argument

Paul E. McKenney (7):
  rcutorture: Add test_nmis module parameter
  rcutorture: Set CONFIG_BOOTPARAM_HOTPLUG_CPU0 to offline CPU 0
  rcutorture: Make scenario TREE04 enable lazy call_rcu()
  torture: Permit kvm-again.sh --duration to default to previous run
  torture: Enable clocksource watchdog with "tsc=watchdog"
  rcuscale: Move shutdown from wait_event() to wait_event_idle()
  refscale: Move shutdown from wait_event() to wait_event_idle()

Yue Hu (1):
  rcutorture: Eliminate variable n_rcu_torture_boost_rterror

Zqiang (1):
  rcutorture: Create nocb kthreads only when testing rcu in
    CONFIG_RCU_NOCB_CPU=y kernels

 kernel/rcu/rcuscale.c                         |  7 ++-
 kernel/rcu/rcutorture.c                       | 49 +++++++++++++++----
 kernel/rcu/refscale.c                         |  2 +-
 tools/rcu/extract-stall.sh                    | 26 +++++++---
 .../selftests/rcutorture/bin/kvm-again.sh     |  2 +-
 .../selftests/rcutorture/bin/torture.sh       |  6 +--
 .../selftests/rcutorture/configs/rcu/TREE01   |  1 +
 .../selftests/rcutorture/configs/rcu/TREE04   |  1 +
 8 files changed, 69 insertions(+), 25 deletions(-)
 mode change 100644 => 100755 tools/rcu/extract-stall.sh

-- 
2.38.1

[PATCH rcu v2 01/10] rcutorture: Add test_nmis module parameter

[Boqun Feng]

From: "Paul E. McKenney" <paulmck@kernel.org>

This commit adds a test_nmis module parameter to generate the
specified number of NMI stack backtraces 15 seconds apart.  This module
parameter can be used to test NMI delivery and accompanying diagnostics.
Note that this parameter is ignored when rcutorture is a module rather
than built into the kernel.  This could be changed with the addition of
an EXPORT_SYMBOL_GPL().

[ paulmck: Apply kernel test robot feedback. ]

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
 kernel/rcu/rcutorture.c | 32 ++++++++++++++++++++++++++++++--
 1 file changed, 30 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 8e6c023212cb..480bba142e3a 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -119,6 +119,7 @@ torture_param(int, stutter, 5, "Number of seconds to run/halt test");
 torture_param(int, test_boost, 1, "Test RCU prio boost: 0=no, 1=maybe, 2=yes.");
 torture_param(int, test_boost_duration, 4, "Duration of each boost test, seconds.");
 torture_param(int, test_boost_interval, 7, "Interval between boost tests, seconds.");
+torture_param(int, test_nmis, 0, "End-test NMI tests, 0 to disable.");
 torture_param(bool, test_no_idle_hz, true, "Test support for tickless idle CPUs");
 torture_param(int, verbose, 1, "Enable verbose debugging printk()s");
 
@@ -2358,7 +2359,8 @@ rcu_torture_print_module_parms(struct rcu_torture_ops *cur_ops, const char *tag)
 		 "n_barrier_cbs=%d "
 		 "onoff_interval=%d onoff_holdoff=%d "
 		 "read_exit_delay=%d read_exit_burst=%d "
-		 "nocbs_nthreads=%d nocbs_toggle=%d\n",
+		 "nocbs_nthreads=%d nocbs_toggle=%d "
+		 "test_nmis=%d\n",
 		 torture_type, tag, nrealreaders, nfakewriters,
 		 stat_interval, verbose, test_no_idle_hz, shuffle_interval,
 		 stutter, irqreader, fqs_duration, fqs_holdoff, fqs_stutter,
@@ -2369,7 +2371,8 @@ rcu_torture_print_module_parms(struct rcu_torture_ops *cur_ops, const char *tag)
 		 n_barrier_cbs,
 		 onoff_interval, onoff_holdoff,
 		 read_exit_delay, read_exit_burst,
-		 nocbs_nthreads, nocbs_toggle);
+		 nocbs_nthreads, nocbs_toggle,
+		 test_nmis);
 }
 
 static int rcutorture_booster_cleanup(unsigned int cpu)
@@ -3273,6 +3276,29 @@ static void rcu_torture_read_exit_cleanup(void)
 	torture_stop_kthread(rcutorture_read_exit, read_exit_task);
 }
 
+static void rcutorture_test_nmis(int n)
+{
+#if IS_BUILTIN(CONFIG_RCU_TORTURE_TEST)
+	int cpu;
+	int dumpcpu;
+	int i;
+
+	for (i = 0; i < n; i++) {
+		preempt_disable();
+		cpu = smp_processor_id();
+		dumpcpu = cpu + 1;
+		if (dumpcpu >= nr_cpu_ids)
+			dumpcpu = 0;
+		pr_alert("%s: CPU %d invoking dump_cpu_task(%d)\n", __func__, cpu, dumpcpu);
+		dump_cpu_task(dumpcpu);
+		preempt_enable();
+		schedule_timeout_uninterruptible(15 * HZ);
+	}
+#else // #if IS_BUILTIN(CONFIG_RCU_TORTURE_TEST)
+	WARN_ONCE(n, "Non-zero rcutorture.test_nmis=%d permitted only when rcutorture is built in.\n", test_nmis);
+#endif // #else // #if IS_BUILTIN(CONFIG_RCU_TORTURE_TEST)
+}
+
 static enum cpuhp_state rcutor_hp;
 
 static void
@@ -3297,6 +3323,8 @@ rcu_torture_cleanup(void)
 		return;
 	}
 
+	rcutorture_test_nmis(test_nmis);
+
 	if (cur_ops->gp_kthread_dbg)
 		cur_ops->gp_kthread_dbg();
 	rcu_torture_read_exit_cleanup();
-- 
2.38.1

[PATCH rcu v2 02/10] rcutorture: Set CONFIG_BOOTPARAM_HOTPLUG_CPU0 to offline CPU 0

[Boqun Feng]

From: "Paul E. McKenney" <paulmck@kernel.org>

There is now a BOOTPARAM_HOTPLUG_CPU0 Kconfig option that allows CPU 0
to be offlined on x86 systems.  This commit therefore sets this option in
the TREE01 rcutorture scenario in order to regularly test this capability.

Reported-by: "Zhang, Qiang1" <qiang1.zhang@intel.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
 tools/testing/selftests/rcutorture/configs/rcu/TREE01 | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/testing/selftests/rcutorture/configs/rcu/TREE01 b/tools/testing/selftests/rcutorture/configs/rcu/TREE01
index 8ae41d5f81a3..04831ef1f9b5 100644
--- a/tools/testing/selftests/rcutorture/configs/rcu/TREE01
+++ b/tools/testing/selftests/rcutorture/configs/rcu/TREE01
@@ -15,3 +15,4 @@ CONFIG_DEBUG_LOCK_ALLOC=n
 CONFIG_RCU_BOOST=n
 CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
 CONFIG_RCU_EXPERT=y
+CONFIG_BOOTPARAM_HOTPLUG_CPU0=y
-- 
2.38.1

[PATCH rcu v2 03/10] rcutorture: Make scenario TREE04 enable lazy call_rcu()

[Boqun Feng]

From: "Paul E. McKenney" <paulmck@kernel.org>

This commit enables the RCU_LAZY Kconfig option in scenario TREE04 in
order to provide some ongoing testing of this configuration.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
 tools/testing/selftests/rcutorture/configs/rcu/TREE04 | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/testing/selftests/rcutorture/configs/rcu/TREE04 b/tools/testing/selftests/rcutorture/configs/rcu/TREE04
index ae395981b5e5..dc4985064b3a 100644
--- a/tools/testing/selftests/rcutorture/configs/rcu/TREE04
+++ b/tools/testing/selftests/rcutorture/configs/rcu/TREE04
@@ -15,3 +15,4 @@ CONFIG_DEBUG_LOCK_ALLOC=n
 CONFIG_DEBUG_OBJECTS_RCU_HEAD=n
 CONFIG_RCU_EXPERT=y
 CONFIG_RCU_EQS_DEBUG=y
+CONFIG_RCU_LAZY=y
-- 
2.38.1

[PATCH rcu v2 04/10] tools: rcu: Add usage function and check for argument

[Boqun Feng]

From: Bhaskar Chowdhury <unixbhaskar@gmail.com>

This commit converts extract-stall.sh script's header comment to a
usage() function, and adds an argument check.  While in the area, make
this script be executable.

[ paulmck: Strength argument check, remove extraneous comment. ]

Signed-off-by: Bhaskar Chowdhury <unixbhaskar@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
 tools/rcu/extract-stall.sh | 26 ++++++++++++++++++++------
 1 file changed, 20 insertions(+), 6 deletions(-)
 mode change 100644 => 100755 tools/rcu/extract-stall.sh

diff --git a/tools/rcu/extract-stall.sh b/tools/rcu/extract-stall.sh
old mode 100644
new mode 100755
index e565697c9f90..08a39ad44320
--- a/tools/rcu/extract-stall.sh
+++ b/tools/rcu/extract-stall.sh
@@ -1,11 +1,25 @@
 #!/bin/sh
 # SPDX-License-Identifier: GPL-2.0+
-#
-# Extract any RCU CPU stall warnings present in specified file.
-# Filter out clocksource lines.  Note that preceding-lines excludes the
-# initial line of the stall warning but trailing-lines includes it.
-#
-# Usage: extract-stall.sh dmesg-file [ preceding-lines [ trailing-lines ] ]
+
+usage() {
+	echo Extract any RCU CPU stall warnings present in specified file.
+	echo Filter out clocksource lines.  Note that preceding-lines excludes the
+	echo initial line of the stall warning but trailing-lines includes it.
+	echo
+	echo Usage: $(basename $0) dmesg-file [ preceding-lines [ trailing-lines ] ]
+	echo
+	echo Error: $1
+}
+
+# Terminate the script, if the argument is missing
+
+if test -f "$1" && test -r "$1"
+then
+	:
+else
+	usage "Console log file \"$1\" missing or unreadable."
+	exit 1
+fi
 
 echo $1
 preceding_lines="${2-3}"
-- 
2.38.1

[PATCH rcu v2 05/10] torture: Permit kvm-again.sh --duration to default to previous run

[Boqun Feng]

From: "Paul E. McKenney" <paulmck@kernel.org>

Currently, invoking kvm-again.sh without a --duration argument results
in a bash error message.  This commit therefore adds quotes around the
$dur argument to kvm-transform.sh to allow a default duration to be
taken from the earlier run.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
 tools/testing/selftests/rcutorture/bin/kvm-again.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/rcutorture/bin/kvm-again.sh b/tools/testing/selftests/rcutorture/bin/kvm-again.sh
index 8a968fbda02c..88ca4e368489 100755
--- a/tools/testing/selftests/rcutorture/bin/kvm-again.sh
+++ b/tools/testing/selftests/rcutorture/bin/kvm-again.sh
@@ -193,7 +193,7 @@ do
 	qemu_cmd_dir="`dirname "$i"`"
 	kernel_dir="`echo $qemu_cmd_dir | sed -e 's/\.[0-9]\+$//'`"
 	jitter_dir="`dirname "$kernel_dir"`"
-	kvm-transform.sh "$kernel_dir/bzImage" "$qemu_cmd_dir/console.log" "$jitter_dir" $dur "$bootargs" < $T/qemu-cmd > $i
+	kvm-transform.sh "$kernel_dir/bzImage" "$qemu_cmd_dir/console.log" "$jitter_dir" "$dur" "$bootargs" < $T/qemu-cmd > $i
 	if test -n "$arg_remote"
 	then
 		echo "# TORTURE_KCONFIG_GDB_ARG=''" >> $i
-- 
2.38.1

[PATCH rcu v2 06/10] rcutorture: Eliminate variable n_rcu_torture_boost_rterror

[Boqun Feng]

From: Yue Hu <huyue2@coolpad.com>

After commit 8b700983de82 ("sched: Remove sched_set_*() return value"),
this variable is not used anymore. So eliminate it entirely.

Signed-off-by: Yue Hu <huyue2@coolpad.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
 kernel/rcu/rcutorture.c | 11 +++--------
 1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 480bba142e3a..c0b2fd687bbb 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -180,7 +180,6 @@ static atomic_t n_rcu_torture_mbchk_tries;
 static atomic_t n_rcu_torture_error;
 static long n_rcu_torture_barrier_error;
 static long n_rcu_torture_boost_ktrerror;
-static long n_rcu_torture_boost_rterror;
 static long n_rcu_torture_boost_failure;
 static long n_rcu_torture_boosts;
 static atomic_long_t n_rcu_torture_timers;
@@ -2195,12 +2194,11 @@ rcu_torture_stats_print(void)
 		atomic_read(&n_rcu_torture_alloc),
 		atomic_read(&n_rcu_torture_alloc_fail),
 		atomic_read(&n_rcu_torture_free));
-	pr_cont("rtmbe: %d rtmbkf: %d/%d rtbe: %ld rtbke: %ld rtbre: %ld ",
+	pr_cont("rtmbe: %d rtmbkf: %d/%d rtbe: %ld rtbke: %ld ",
 		atomic_read(&n_rcu_torture_mberror),
 		atomic_read(&n_rcu_torture_mbchk_fail), atomic_read(&n_rcu_torture_mbchk_tries),
 		n_rcu_torture_barrier_error,
-		n_rcu_torture_boost_ktrerror,
-		n_rcu_torture_boost_rterror);
+		n_rcu_torture_boost_ktrerror);
 	pr_cont("rtbf: %ld rtb: %ld nt: %ld ",
 		n_rcu_torture_boost_failure,
 		n_rcu_torture_boosts,
@@ -2218,15 +2216,13 @@ rcu_torture_stats_print(void)
 	if (atomic_read(&n_rcu_torture_mberror) ||
 	    atomic_read(&n_rcu_torture_mbchk_fail) ||
 	    n_rcu_torture_barrier_error || n_rcu_torture_boost_ktrerror ||
-	    n_rcu_torture_boost_rterror || n_rcu_torture_boost_failure ||
-	    i > 1) {
+	    n_rcu_torture_boost_failure || i > 1) {
 		pr_cont("%s", "!!! ");
 		atomic_inc(&n_rcu_torture_error);
 		WARN_ON_ONCE(atomic_read(&n_rcu_torture_mberror));
 		WARN_ON_ONCE(atomic_read(&n_rcu_torture_mbchk_fail));
 		WARN_ON_ONCE(n_rcu_torture_barrier_error);  // rcu_barrier()
 		WARN_ON_ONCE(n_rcu_torture_boost_ktrerror); // no boost kthread
-		WARN_ON_ONCE(n_rcu_torture_boost_rterror); // can't set RT prio
 		WARN_ON_ONCE(n_rcu_torture_boost_failure); // boost failed (TIMER_SOFTIRQ RT prio?)
 		WARN_ON_ONCE(i > 1); // Too-short grace period
 	}
@@ -3568,7 +3564,6 @@ rcu_torture_init(void)
 	atomic_set(&n_rcu_torture_error, 0);
 	n_rcu_torture_barrier_error = 0;
 	n_rcu_torture_boost_ktrerror = 0;
-	n_rcu_torture_boost_rterror = 0;
 	n_rcu_torture_boost_failure = 0;
 	n_rcu_torture_boosts = 0;
 	for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++)
-- 
2.38.1

[PATCH rcu v2 07/10] torture: Enable clocksource watchdog with "tsc=watchdog"

[Boqun Feng]

From: "Paul E. McKenney" <paulmck@kernel.org>

This commit tests the "tsc=watchdog" kernel boot parameter when running
the clocksourcewd torture tests.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
 tools/testing/selftests/rcutorture/bin/torture.sh | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/rcutorture/bin/torture.sh b/tools/testing/selftests/rcutorture/bin/torture.sh
index 130d0de4c3bb..5a2ae2264403 100755
--- a/tools/testing/selftests/rcutorture/bin/torture.sh
+++ b/tools/testing/selftests/rcutorture/bin/torture.sh
@@ -497,16 +497,16 @@ fi
 
 if test "$do_clocksourcewd" = "yes"
 then
-	torture_bootargs="rcupdate.rcu_cpu_stall_suppress_at_boot=1 torture.disable_onoff_at_boot rcupdate.rcu_task_stall_timeout=30000"
+	torture_bootargs="rcupdate.rcu_cpu_stall_suppress_at_boot=1 torture.disable_onoff_at_boot rcupdate.rcu_task_stall_timeout=30000 tsc=watchdog"
 	torture_set "clocksourcewd-1" tools/testing/selftests/rcutorture/bin/kvm.sh --allcpus --duration 45s --configs TREE03 --kconfig "CONFIG_TEST_CLOCKSOURCE_WATCHDOG=y" --trust-make
 
-	torture_bootargs="rcupdate.rcu_cpu_stall_suppress_at_boot=1 torture.disable_onoff_at_boot rcupdate.rcu_task_stall_timeout=30000 clocksource.max_cswd_read_retries=1"
+	torture_bootargs="rcupdate.rcu_cpu_stall_suppress_at_boot=1 torture.disable_onoff_at_boot rcupdate.rcu_task_stall_timeout=30000 clocksource.max_cswd_read_retries=1 tsc=watchdog"
 	torture_set "clocksourcewd-2" tools/testing/selftests/rcutorture/bin/kvm.sh --allcpus --duration 45s --configs TREE03 --kconfig "CONFIG_TEST_CLOCKSOURCE_WATCHDOG=y" --trust-make
 
 	# In case our work is already done...
 	if test "$do_rcutorture" != "yes"
 	then
-		torture_bootargs="rcupdate.rcu_cpu_stall_suppress_at_boot=1 torture.disable_onoff_at_boot rcupdate.rcu_task_stall_timeout=30000"
+		torture_bootargs="rcupdate.rcu_cpu_stall_suppress_at_boot=1 torture.disable_onoff_at_boot rcupdate.rcu_task_stall_timeout=30000 tsc=watchdog"
 		torture_set "clocksourcewd-3" tools/testing/selftests/rcutorture/bin/kvm.sh --allcpus --duration 45s --configs TREE03 --trust-make
 	fi
 fi
-- 
2.38.1

[PATCH rcu v2 08/10] rcutorture: Create nocb kthreads only when testing rcu in CONFIG_RCU_NOCB_CPU=y kernels

[Boqun Feng]

From: Zqiang <qiang1.zhang@intel.com>

Given a non-zero rcutorture.nocbs_nthreads module parameter, the specified
number of nocb kthreads will be created, regardless of whether or not
the RCU implementation under test is capable of offloading callbacks.
Please note that even vanilla RCU is incapable of offloading in kernels
built with CONFIG_RCU_NOCB_CPU=n.  And when the RCU implementation is
incapable of offloading callbacks, there is no point in creating those
kthreads.

This commit therefore checks the cur_ops.torture_type module parameter and
CONFIG_RCU_NOCB_CPU Kconfig option in order to avoid creating unnecessary
nocb tasks.

Signed-off-by: Zqiang <qiang1.zhang@intel.com>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
[ boqun: Fix checkpatch warning ]
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
 kernel/rcu/rcutorture.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index c0b2fd687bbb..e046d2c6fe10 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -3525,6 +3525,12 @@ rcu_torture_init(void)
 		pr_alert("rcu-torture: ->fqs NULL and non-zero fqs_duration, fqs disabled.\n");
 		fqs_duration = 0;
 	}
+	if (nocbs_nthreads != 0 && (cur_ops != &rcu_ops ||
+				    !IS_ENABLED(CONFIG_RCU_NOCB_CPU))) {
+		pr_alert("rcu-torture types: %s and CONFIG_RCU_NOCB_CPU=%d, nocb toggle disabled.\n",
+			 cur_ops->name, IS_ENABLED(CONFIG_RCU_NOCB_CPU));
+		nocbs_nthreads = 0;
+	}
 	if (cur_ops->init)
 		cur_ops->init();
 
-- 
2.38.1

[PATCH rcu v2 09/10] rcuscale: Move shutdown from wait_event() to wait_event_idle()

[Boqun Feng]

From: "Paul E. McKenney" <paulmck@kernel.org>

The rcu_scale_shutdown() and kfree_scale_shutdown() kthreads/functions
use wait_event() to wait for the rcuscale test to complete.  However,
each updater thread in such a test waits for at least 100 grace periods.
If each grace period takes more than 1.2 seconds, which is long, but
not insanely so, this can trigger the hung-task timeout.

This commit therefore replaces those wait_event() calls with calls to
wait_event_idle(), which do not trigger the hung-task timeout.

Reported-by: kernel test robot <yujie.liu@intel.com>
Reported-by: Liam Howlett <liam.howlett@oracle.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Tested-by: Yujie Liu <yujie.liu@intel.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
 kernel/rcu/rcuscale.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/kernel/rcu/rcuscale.c b/kernel/rcu/rcuscale.c
index 91fb5905a008..4120f94030c3 100644
--- a/kernel/rcu/rcuscale.c
+++ b/kernel/rcu/rcuscale.c
@@ -631,8 +631,7 @@ static int compute_real(int n)
 static int
 rcu_scale_shutdown(void *arg)
 {
-	wait_event(shutdown_wq,
-		   atomic_read(&n_rcu_scale_writer_finished) >= nrealwriters);
+	wait_event_idle(shutdown_wq, atomic_read(&n_rcu_scale_writer_finished) >= nrealwriters);
 	smp_mb(); /* Wake before output. */
 	rcu_scale_cleanup();
 	kernel_power_off();
@@ -771,8 +770,8 @@ kfree_scale_cleanup(void)
 static int
 kfree_scale_shutdown(void *arg)
 {
-	wait_event(shutdown_wq,
-		   atomic_read(&n_kfree_scale_thread_ended) >= kfree_nrealthreads);
+	wait_event_idle(shutdown_wq,
+			atomic_read(&n_kfree_scale_thread_ended) >= kfree_nrealthreads);
 
 	smp_mb(); /* Wake before output. */
 
-- 
2.38.1

[PATCH rcu v2 10/10] refscale: Move shutdown from wait_event() to wait_event_idle()

[Boqun Feng]

From: "Paul E. McKenney" <paulmck@kernel.org>

The ref_scale_shutdown() kthread/function uses wait_event() to wait for
the refscale test to complete.  However, although the read-side tests
are normally extremely fast, there is no law against specifying a very
large value for the refscale.loops module parameter or against having
a slow read-side primitive.  Either way, this might well trigger the
hung-task timeout.

This commit therefore replaces those wait_event() calls with calls to
wait_event_idle(), which do not trigger the hung-task timeout.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
 kernel/rcu/refscale.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/refscale.c b/kernel/rcu/refscale.c
index afa3e1a2f690..1970ce5f22d4 100644
--- a/kernel/rcu/refscale.c
+++ b/kernel/rcu/refscale.c
@@ -1031,7 +1031,7 @@ ref_scale_cleanup(void)
 static int
 ref_scale_shutdown(void *arg)
 {
-	wait_event(shutdown_wq, shutdown_start);
+	wait_event_idle(shutdown_wq, shutdown_start);
 
 	smp_mb(); // Wake before output.
 	ref_scale_cleanup();
-- 
2.38.1