rv: Add option for nested monitors and include sched

Monitors describing complex systems, such as the scheduler, can easily
grow to the point where they are just hard to understand because of the
many possible state transitions.
Often it is possible to break such descriptions into smaller monitors,
sharing some or all events. Enabling those smaller monitors concurrently
is, in fact, testing the system as if we had one single larger monitor.
Splitting models into multiple specification is not only easier to
understand, but gives some more clues when we see errors.

Add the possibility to create container monitors, whose only purpose is
to host other nested monitors. Enabling a container monitor enables all
nested ones, but it's still possible to enable nested monitors
independently.
Add the sched monitor as first container, for now empty.

Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Link: https://lore.kernel.org/20250305140406.350227-3-gmonaco@redhat.com
Signed-off-by: Gabriele Monaco <gmonaco@redhat.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

1 files changed, 131 insertions, 23 deletions

diff --git a/kernel/trace/rv/rv.c b/kernel/trace/rv/rv.c
index 8657fc8806e7..50344aa9f7f9 100644
--- a/kernel/trace/rv/rv.c
+++ b/kernel/trace/rv/rv.c
@@ -162,7 +162,7 @@ struct dentry *get_monitors_root(void)
 /*
  * Interface for the monitor register.
  */
-static LIST_HEAD(rv_monitors_list);
+LIST_HEAD(rv_monitors_list);
 
 static int task_monitor_count;
 static bool task_monitor_slots[RV_PER_TASK_MONITORS];
@@ -207,6 +207,30 @@ void rv_put_task_monitor_slot(int slot)
 }
 
 /*
+ * Monitors with a parent are nested,
+ * Monitors without a parent could be standalone or containers.
+ */
+bool rv_is_nested_monitor(struct rv_monitor_def *mdef)
+{
+	return mdef->parent != NULL;
+}
+
+/*
+ * We set our list to have nested monitors listed after their parent
+ * if a monitor has a child element its a container.
+ * Containers can be also identified based on their function pointers:
+ * as they are not real monitors they do not need function definitions
+ * for enable()/disable(). Use this condition to find empty containers.
+ * Keep both conditions in case we have some non-compliant containers.
+ */
+bool rv_is_container_monitor(struct rv_monitor_def *mdef)
+{
+	struct rv_monitor_def *next = list_next_entry(mdef, list);
+
+	return next->parent == mdef->monitor || !mdef->monitor->enable;
+}
+
+/*
  * This section collects the monitor/ files and folders.
  */
 static ssize_t monitor_enable_read_data(struct file *filp, char __user *user_buf, size_t count,
@@ -229,7 +253,8 @@ static int __rv_disable_monitor(struct rv_monitor_def *mdef, bool sync)
 
 	if (mdef->monitor->enabled) {
 		mdef->monitor->enabled = 0;
-		mdef->monitor->disable();
+		if (mdef->monitor->disable)
+			mdef->monitor->disable();
 
 		/*
 		 * Wait for the execution of all events to finish.
@@ -243,6 +268,60 @@ static int __rv_disable_monitor(struct rv_monitor_def *mdef, bool sync)
 	return 0;
 }
 
+static void rv_disable_single(struct rv_monitor_def *mdef)
+{
+	__rv_disable_monitor(mdef, true);
+}
+
+static int rv_enable_single(struct rv_monitor_def *mdef)
+{
+	int retval;
+
+	lockdep_assert_held(&rv_interface_lock);
+
+	if (mdef->monitor->enabled)
+		return 0;
+
+	retval = mdef->monitor->enable();
+
+	if (!retval)
+		mdef->monitor->enabled = 1;
+
+	return retval;
+}
+
+static void rv_disable_container(struct rv_monitor_def *mdef)
+{
+	struct rv_monitor_def *p = mdef;
+	int enabled = 0;
+
+	list_for_each_entry_continue(p, &rv_monitors_list, list) {
+		if (p->parent != mdef->monitor)
+			break;
+		enabled += __rv_disable_monitor(p, false);
+	}
+	if (enabled)
+		tracepoint_synchronize_unregister();
+	mdef->monitor->enabled = 0;
+}
+
+static int rv_enable_container(struct rv_monitor_def *mdef)
+{
+	struct rv_monitor_def *p = mdef;
+	int retval = 0;
+
+	list_for_each_entry_continue(p, &rv_monitors_list, list) {
+		if (retval || p->parent != mdef->monitor)
+			break;
+		retval = rv_enable_single(p);
+	}
+	if (retval)
+		rv_disable_container(mdef);
+	else
+		mdef->monitor->enabled = 1;
+	return retval;
+}
+
 /**
  * rv_disable_monitor - disable a given runtime monitor
  * @mdef: Pointer to the monitor definition structure.
@@ -251,7 +330,11 @@ static int __rv_disable_monitor(struct rv_monitor_def *mdef, bool sync)
  */
 int rv_disable_monitor(struct rv_monitor_def *mdef)
 {
-	__rv_disable_monitor(mdef, true);
+	if (rv_is_container_monitor(mdef))
+		rv_disable_container(mdef);
+	else
+		rv_disable_single(mdef);
+
 	return 0;
 }
 
@@ -265,15 +348,10 @@ int rv_enable_monitor(struct rv_monitor_def *mdef)
 {
 	int retval;
 
-	lockdep_assert_held(&rv_interface_lock);
-
-	if (mdef->monitor->enabled)
-		return 0;
-
-	retval = mdef->monitor->enable();
-
-	if (!retval)
-		mdef->monitor->enabled = 1;
+	if (rv_is_container_monitor(mdef))
+		retval = rv_enable_container(mdef);
+	else
+		retval = rv_enable_single(mdef);
 
 	return retval;
 }
@@ -336,9 +414,9 @@ static const struct file_operations interface_desc_fops = {
  * the monitor dir, where the specific options of the monitor
  * are exposed.
  */
-static int create_monitor_dir(struct rv_monitor_def *mdef)
+static int create_monitor_dir(struct rv_monitor_def *mdef, struct rv_monitor_def *parent)
 {
-	struct dentry *root = get_monitors_root();
+	struct dentry *root = parent ? parent->root_d : get_monitors_root();
 	const char *name = mdef->monitor->name;
 	struct dentry *tmp;
 	int retval;
@@ -377,7 +455,11 @@ static int monitors_show(struct seq_file *m, void *p)
 {
 	struct rv_monitor_def *mon_def = p;
 
-	seq_printf(m, "%s\n", mon_def->monitor->name);
+	if (mon_def->parent)
+		seq_printf(m, "%s:%s\n", mon_def->parent->name,
+			   mon_def->monitor->name);
+	else
+		seq_printf(m, "%s\n", mon_def->monitor->name);
 	return 0;
 }
 
@@ -514,7 +596,7 @@ static ssize_t enabled_monitors_write(struct file *filp, const char __user *user
 	struct rv_monitor_def *mdef;
 	int retval = -EINVAL;
 	bool enable = true;
-	char *ptr;
+	char *ptr, *tmp;
 	int len;
 
 	if (count < 1 || count > MAX_RV_MONITOR_NAME_SIZE + 1)
@@ -541,6 +623,11 @@ static ssize_t enabled_monitors_write(struct file *filp, const char __user *user
 
 	retval = -EINVAL;
 
+	/* we support 1 nesting level, trim the parent */
+	tmp = strstr(ptr, ":");
+	if (tmp)
+		ptr = tmp+1;
+
 	list_for_each_entry(mdef, &rv_monitors_list, list) {
 		if (strcmp(ptr, mdef->monitor->name) != 0)
 			continue;
@@ -613,7 +700,7 @@ static void reset_all_monitors(void)
 	struct rv_monitor_def *mdef;
 
 	list_for_each_entry(mdef, &rv_monitors_list, list) {
-		if (mdef->monitor->enabled)
+		if (mdef->monitor->enabled && mdef->monitor->reset)
 			mdef->monitor->reset();
 	}
 }
@@ -685,18 +772,19 @@ static void destroy_monitor_dir(struct rv_monitor_def *mdef)
 /**
  * rv_register_monitor - register a rv monitor.
  * @monitor:    The rv_monitor to be registered.
+ * @parent:     The parent of the monitor to be registered, NULL if not nested.
  *
  * Returns 0 if successful, error otherwise.
  */
-int rv_register_monitor(struct rv_monitor *monitor)
+int rv_register_monitor(struct rv_monitor *monitor, struct rv_monitor *parent)
 {
-	struct rv_monitor_def *r;
+	struct rv_monitor_def *r, *p = NULL;
 	int retval = 0;
 
 	if (strlen(monitor->name) >= MAX_RV_MONITOR_NAME_SIZE) {
 		pr_info("Monitor %s has a name longer than %d\n", monitor->name,
 			MAX_RV_MONITOR_NAME_SIZE);
-		return -1;
+		return -EINVAL;
 	}
 
 	mutex_lock(&rv_interface_lock);
@@ -704,11 +792,26 @@ int rv_register_monitor(struct rv_monitor *monitor)
 	list_for_each_entry(r, &rv_monitors_list, list) {
 		if (strcmp(monitor->name, r->monitor->name) == 0) {
 			pr_info("Monitor %s is already registered\n", monitor->name);
-			retval = -1;
+			retval = -EEXIST;
 			goto out_unlock;
 		}
 	}
 
+	if (parent) {
+		list_for_each_entry(r, &rv_monitors_list, list) {
+			if (strcmp(parent->name, r->monitor->name) == 0) {
+				p = r;
+				break;
+			}
+		}
+	}
+
+	if (p && rv_is_nested_monitor(p)) {
+		pr_info("Parent monitor %s is already nested, cannot nest further\n",
+			parent->name);
+		return -EINVAL;
+	}
+
 	r = kzalloc(sizeof(struct rv_monitor_def), GFP_KERNEL);
 	if (!r) {
 		retval = -ENOMEM;
@@ -716,14 +819,19 @@ int rv_register_monitor(struct rv_monitor *monitor)
 	}
 
 	r->monitor = monitor;
+	r->parent = parent;
 
-	retval = create_monitor_dir(r);
+	retval = create_monitor_dir(r, p);
 	if (retval) {
 		kfree(r);
 		goto out_unlock;
 	}
 
-	list_add_tail(&r->list, &rv_monitors_list);
+	/* keep children close to the parent for easier visualisation */
+	if (p)
+		list_add(&r->list, &p->list);
+	else
+		list_add_tail(&r->list, &rv_monitors_list);
 
 out_unlock:
 	mutex_unlock(&rv_interface_lock);