[PATCH 08/11] rcutorture: Add a stall_only module parameter

["Paul E. McKenney" <paulmck@kernel.org>]

This commit adds a stall_only module parameter that shuts off all
rcutorture kthreads other than the RCU CPU stall-warning test kthreads.
The purpose of this is to test production applictions' reactions to
CPU stalls, and with minimal additional overhead.  Or you can omit the
stall-warning tests as well and get a heavy no-op, your choice!

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 .../admin-guide/kernel-parameters.txt          |  9 +++++++++
 kernel/rcu/rcutorture.c                        | 18 ++++++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index b942149720c9bf..40d2831add4a21 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -6211,6 +6211,15 @@ Kernel parameters
 			and stall_gp_kthread are specified, the
 			kthread is starved first, then the CPU.
 
+	rcutorture.stall_only= [KNL]
+			Shut off all rcutorture kthreads other than the
+			RCU CPU stall-warning test kthreads.  The purpose
+			of this is to test production applictions'
+			reactions to CPU stalls, and with minimal
+			additional overhead.  Or you can omit the
+			stall-warning tests as well and get a heavy
+			no-op, your choice!
+
 	rcutorture.stat_interval= [KNL]
 			Time (s) between statistics printk()s.
 
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index a6a8b9ba342d02..a0d27756141846 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -140,6 +140,7 @@ torture_param(int, stall_cpu_irqsoff, 0, "Disable interrupts while stalling.");
 torture_param(int, stall_cpu_block, 0, "Sleep while stalling.");
 torture_param(int, stall_cpu_repeat, 0, "Number of additional stalls after the first one.");
 torture_param(int, stall_gp_kthread, 0, "Grace-period kthread stall duration (s).");
+torture_param(bool, stall_only, 0, "Suppress all non-CPU-stall kthreads.");
 torture_param(int, stat_interval, 60, "Number of seconds between stats printk()s");
 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.");
@@ -4649,6 +4650,23 @@ rcu_torture_init(void)
 		cur_ops = NULL;
 		goto unwind;
 	}
+	if (stall_only) {
+		pr_alert("rcu-torture: stall_only specified, suppressing all else.\n");
+		fqs_stutter = 0;
+		fwd_progress = 0;
+		n_barrier_cbs = 0;
+		nfakewriters = 0;
+		nocbs_nthreads = 0;
+		nreaders = 0;
+		n_up_down = 0;
+		nwriters = 0;
+		onoff_interval = 0;
+		preempt_duration = 0;
+		read_exit_burst = 0;
+		shuffle_interval = 0;
+		stutter = 0;
+		test_boost = 0;
+	}
 	if (cur_ops->fqs == NULL && fqs_duration != 0) {
 		pr_alert("rcu-torture: ->fqs NULL and non-zero fqs_duration, fqs disabled.\n");
 		fqs_duration = 0;
-- 
2.40.1