[PATCH rcu 1/8] rcutorture: Add test_nmis module parameter

[Boqun Feng <boqun.feng@xxxxxxxxx>]

From: "Paul E. McKenney" <paulmck@xxxxxxxxxx>

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@xxxxxxxxxx>
Signed-off-by: Boqun Feng <boqun.feng@xxxxxxxxx>
---
 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();
-- 
2.39.2