rv: Add sample hybrid monitor stall

Add a sample monitor to showcase hybrid/timed automata.
The stall monitor identifies tasks stalled for longer than a threshold
and reacts when that happens.

Reviewed-by: Nam Cao <namcao@linutronix.de>
Link: https://lore.kernel.org/r/20260330111010.153663-7-gmonaco@redhat.com
Signed-off-by: Gabriele Monaco <gmonaco@redhat.com>

7 files changed, 266 insertions, 0 deletions

diff --git a/kernel/trace/rv/Kconfig b/kernel/trace/rv/Kconfig
index 4ad392dfc57f..720fbe4935f8 100644
--- a/kernel/trace/rv/Kconfig
+++ b/kernel/trace/rv/Kconfig
@@ -78,6 +78,7 @@ source "kernel/trace/rv/monitors/pagefault/Kconfig"
 source "kernel/trace/rv/monitors/sleep/Kconfig"
 # Add new rtapp monitors here
 
+source "kernel/trace/rv/monitors/stall/Kconfig"
 # Add new monitors here
 
 config RV_REACTORS
diff --git a/kernel/trace/rv/Makefile b/kernel/trace/rv/Makefile
index 750e4ad6fa0f..51c95e2d2da6 100644
--- a/kernel/trace/rv/Makefile
+++ b/kernel/trace/rv/Makefile
@@ -17,6 +17,7 @@ obj-$(CONFIG_RV_MON_STS) += monitors/sts/sts.o
 obj-$(CONFIG_RV_MON_NRP) += monitors/nrp/nrp.o
 obj-$(CONFIG_RV_MON_SSSW) += monitors/sssw/sssw.o
 obj-$(CONFIG_RV_MON_OPID) += monitors/opid/opid.o
+obj-$(CONFIG_RV_MON_STALL) += monitors/stall/stall.o
 # Add new monitors here
 obj-$(CONFIG_RV_REACTORS) += rv_reactors.o
 obj-$(CONFIG_RV_REACT_PRINTK) += reactor_printk.o
diff --git a/kernel/trace/rv/monitors/stall/Kconfig b/kernel/trace/rv/monitors/stall/Kconfig
new file mode 100644
index 000000000000..6f846b642544
--- /dev/null
+++ b/kernel/trace/rv/monitors/stall/Kconfig
@@ -0,0 +1,13 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+config RV_MON_STALL
+	depends on RV
+	select HA_MON_EVENTS_ID
+	bool "stall monitor"
+	help
+	  Enable the stall sample monitor that illustrates the usage of hybrid
+	  automata monitors. It can be used to identify tasks stalled for
+	  longer than a threshold.
+
+	  For further information, see:
+	    Documentation/trace/rv/monitor_stall.rst
diff --git a/kernel/trace/rv/monitors/stall/stall.c b/kernel/trace/rv/monitors/stall/stall.c
new file mode 100644
index 000000000000..9ccfda6b0e73
--- /dev/null
+++ b/kernel/trace/rv/monitors/stall/stall.c
@@ -0,0 +1,150 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/ftrace.h>
+#include <linux/tracepoint.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/rv.h>
+#include <rv/instrumentation.h>
+
+#define MODULE_NAME "stall"
+
+#include <trace/events/sched.h>
+#include <rv_trace.h>
+
+#define RV_MON_TYPE RV_MON_PER_TASK
+#define HA_TIMER_TYPE HA_TIMER_WHEEL
+#include "stall.h"
+#include <rv/ha_monitor.h>
+
+static u64 threshold_jiffies = 1000;
+module_param(threshold_jiffies, ullong, 0644);
+
+static u64 ha_get_env(struct ha_monitor *ha_mon, enum envs_stall env, u64 time_ns)
+{
+	if (env == clk_stall)
+		return ha_get_clk_jiffy(ha_mon, env);
+	return ENV_INVALID_VALUE;
+}
+
+static void ha_reset_env(struct ha_monitor *ha_mon, enum envs_stall env, u64 time_ns)
+{
+	if (env == clk_stall)
+		ha_reset_clk_jiffy(ha_mon, env);
+}
+
+static inline bool ha_verify_invariants(struct ha_monitor *ha_mon,
+					enum states curr_state, enum events event,
+					enum states next_state, u64 time_ns)
+{
+	if (curr_state == enqueued_stall)
+		return ha_check_invariant_jiffy(ha_mon, clk_stall, time_ns);
+	return true;
+}
+
+static inline bool ha_verify_guards(struct ha_monitor *ha_mon,
+				    enum states curr_state, enum events event,
+				    enum states next_state, u64 time_ns)
+{
+	bool res = true;
+
+	if (curr_state == dequeued_stall && event == sched_wakeup_stall)
+		ha_reset_env(ha_mon, clk_stall, time_ns);
+	else if (curr_state == running_stall && event == sched_switch_preempt_stall)
+		ha_reset_env(ha_mon, clk_stall, time_ns);
+	return res;
+}
+
+static inline void ha_setup_invariants(struct ha_monitor *ha_mon,
+				       enum states curr_state, enum events event,
+				       enum states next_state, u64 time_ns)
+{
+	if (next_state == curr_state)
+		return;
+	if (next_state == enqueued_stall)
+		ha_start_timer_jiffy(ha_mon, clk_stall, threshold_jiffies, time_ns);
+	else if (curr_state == enqueued_stall)
+		ha_cancel_timer(ha_mon);
+}
+
+static bool ha_verify_constraint(struct ha_monitor *ha_mon,
+				 enum states curr_state, enum events event,
+				 enum states next_state, u64 time_ns)
+{
+	if (!ha_verify_invariants(ha_mon, curr_state, event, next_state, time_ns))
+		return false;
+
+	if (!ha_verify_guards(ha_mon, curr_state, event, next_state, time_ns))
+		return false;
+
+	ha_setup_invariants(ha_mon, curr_state, event, next_state, time_ns);
+
+	return true;
+}
+
+static void handle_sched_switch(void *data, bool preempt,
+				struct task_struct *prev,
+				struct task_struct *next,
+				unsigned int prev_state)
+{
+	if (!preempt && prev_state != TASK_RUNNING)
+		da_handle_start_event(prev, sched_switch_wait_stall);
+	else
+		da_handle_event(prev, sched_switch_preempt_stall);
+	da_handle_event(next, sched_switch_in_stall);
+}
+
+static void handle_sched_wakeup(void *data, struct task_struct *p)
+{
+	da_handle_event(p, sched_wakeup_stall);
+}
+
+static int enable_stall(void)
+{
+	int retval;
+
+	retval = da_monitor_init();
+	if (retval)
+		return retval;
+
+	rv_attach_trace_probe("stall", sched_switch, handle_sched_switch);
+	rv_attach_trace_probe("stall", sched_wakeup, handle_sched_wakeup);
+
+	return 0;
+}
+
+static void disable_stall(void)
+{
+	rv_this.enabled = 0;
+
+	rv_detach_trace_probe("stall", sched_switch, handle_sched_switch);
+	rv_detach_trace_probe("stall", sched_wakeup, handle_sched_wakeup);
+
+	da_monitor_destroy();
+}
+
+static struct rv_monitor rv_this = {
+	.name = "stall",
+	.description = "identify tasks stalled for longer than a threshold.",
+	.enable = enable_stall,
+	.disable = disable_stall,
+	.reset = da_monitor_reset_all,
+	.enabled = 0,
+};
+
+static int __init register_stall(void)
+{
+	return rv_register_monitor(&rv_this, NULL);
+}
+
+static void __exit unregister_stall(void)
+{
+	rv_unregister_monitor(&rv_this);
+}
+
+module_init(register_stall);
+module_exit(unregister_stall);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Gabriele Monaco <gmonaco@redhat.com>");
+MODULE_DESCRIPTION("stall: identify tasks stalled for longer than a threshold.");
diff --git a/kernel/trace/rv/monitors/stall/stall.h b/kernel/trace/rv/monitors/stall/stall.h
new file mode 100644
index 000000000000..638520cb1082
--- /dev/null
+++ b/kernel/trace/rv/monitors/stall/stall.h
@@ -0,0 +1,81 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Automatically generated C representation of stall automaton
+ * For further information about this format, see kernel documentation:
+ *   Documentation/trace/rv/deterministic_automata.rst
+ */
+
+#define MONITOR_NAME stall
+
+enum states_stall {
+	dequeued_stall,
+	enqueued_stall,
+	running_stall,
+	state_max_stall,
+};
+
+#define INVALID_STATE state_max_stall
+
+enum events_stall {
+	sched_switch_in_stall,
+	sched_switch_preempt_stall,
+	sched_switch_wait_stall,
+	sched_wakeup_stall,
+	event_max_stall,
+};
+
+enum envs_stall {
+	clk_stall,
+	env_max_stall,
+	env_max_stored_stall = env_max_stall,
+};
+
+_Static_assert(env_max_stored_stall <= MAX_HA_ENV_LEN, "Not enough slots");
+
+struct automaton_stall {
+	char *state_names[state_max_stall];
+	char *event_names[event_max_stall];
+	char *env_names[env_max_stall];
+	unsigned char function[state_max_stall][event_max_stall];
+	unsigned char initial_state;
+	bool final_states[state_max_stall];
+};
+
+static const struct automaton_stall automaton_stall = {
+	.state_names = {
+		"dequeued",
+		"enqueued",
+		"running",
+	},
+	.event_names = {
+		"sched_switch_in",
+		"sched_switch_preempt",
+		"sched_switch_wait",
+		"sched_wakeup",
+	},
+	.env_names = {
+		"clk",
+	},
+	.function = {
+		{
+			INVALID_STATE,
+			INVALID_STATE,
+			INVALID_STATE,
+			enqueued_stall,
+		},
+		{
+			running_stall,
+			INVALID_STATE,
+			INVALID_STATE,
+			enqueued_stall,
+		},
+		{
+			running_stall,
+			enqueued_stall,
+			dequeued_stall,
+			running_stall,
+		},
+	},
+	.initial_state = dequeued_stall,
+	.final_states = { 1, 0, 0 },
+};
diff --git a/kernel/trace/rv/monitors/stall/stall_trace.h b/kernel/trace/rv/monitors/stall/stall_trace.h
new file mode 100644
index 000000000000..6a7cc1b1d040
--- /dev/null
+++ b/kernel/trace/rv/monitors/stall/stall_trace.h
@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+/*
+ * Snippet to be included in rv_trace.h
+ */
+
+#ifdef CONFIG_RV_MON_STALL
+DEFINE_EVENT(event_da_monitor_id, event_stall,
+	     TP_PROTO(int id, char *state, char *event, char *next_state, bool final_state),
+	     TP_ARGS(id, state, event, next_state, final_state));
+
+DEFINE_EVENT(error_da_monitor_id, error_stall,
+	     TP_PROTO(int id, char *state, char *event),
+	     TP_ARGS(id, state, event));
+
+DEFINE_EVENT(error_env_da_monitor_id, error_env_stall,
+	     TP_PROTO(int id, char *state, char *event, char *env),
+	     TP_ARGS(id, state, event, env));
+#endif /* CONFIG_RV_MON_STALL */
diff --git a/kernel/trace/rv/rv_trace.h b/kernel/trace/rv/rv_trace.h
index 7c598967bc0e..1661f8fe4a88 100644
--- a/kernel/trace/rv/rv_trace.h
+++ b/kernel/trace/rv/rv_trace.h
@@ -187,6 +187,7 @@ DECLARE_EVENT_CLASS(error_env_da_monitor_id,
 		__get_str(env))
 );
 
+#include <monitors/stall/stall_trace.h>
 // Add new monitors based on CONFIG_HA_MON_EVENTS_ID here
 
 #endif