patches/0024-tracing-Add-variable-reference-handling-to-hist-trig.patch

From: Tom Zanussi <tom.zanussi@linux.intel.com>
Date: Tue, 5 Sep 2017 16:57:36 -0500
Subject: [PATCH 24/40] tracing: Add variable reference handling to hist
 triggers

Add the necessary infrastructure to allow the variables defined on one
event to be referenced in another.  This allows variables set by a
previous event to be referenced and used in expressions combining the
variable values saved by that previous event and the event fields of
the current event.  For example, here's how a latency can be
calculated and saved into yet another variable named 'wakeup_lat':

    # echo 'hist:keys=pid,prio:ts0=common_timestamp ...
    # echo 'hist:keys=next_pid:wakeup_lat=common_timestamp-$ts0 ...

In the first event, the event's timetamp is saved into the variable
ts0.  In the next line, ts0 is subtracted from the second event's
timestamp to produce the latency.

Further users of variable references will be described in subsequent
patches, such as for instance how the 'wakeup_lat' variable above can
be displayed in a latency histogram.

Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 kernel/trace/trace.c                |    2 
 kernel/trace/trace.h                |    3 
 kernel/trace/trace_events_hist.c    |  606 ++++++++++++++++++++++++++++++++----
 kernel/trace/trace_events_trigger.c |    6 
 4 files changed, 561 insertions(+), 56 deletions(-)

--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -7380,6 +7380,7 @@ static int instance_mkdir(const char *na
 
 	INIT_LIST_HEAD(&tr->systems);
 	INIT_LIST_HEAD(&tr->events);
+	INIT_LIST_HEAD(&tr->hist_vars);
 
 	if (allocate_trace_buffers(tr, trace_buf_size) < 0)
 		goto out_free_tr;
@@ -8112,6 +8113,7 @@ ssize_t trace_parse_run_command(struct f
 
 	INIT_LIST_HEAD(&global_trace.systems);
 	INIT_LIST_HEAD(&global_trace.events);
+	INIT_LIST_HEAD(&global_trace.hist_vars);
 	list_add(&global_trace.list, &ftrace_trace_arrays);
 
 	apply_trace_boot_options();
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -266,6 +266,7 @@ struct trace_array {
 	int			function_enabled;
 #endif
 	int			time_stamp_abs_ref;
+	struct list_head	hist_vars;
 };
 
 enum {
@@ -1442,6 +1443,8 @@ extern void pause_named_trigger(struct e
 extern void unpause_named_trigger(struct event_trigger_data *data);
 extern void set_named_trigger_data(struct event_trigger_data *data,
 				   struct event_trigger_data *named_data);
+extern struct event_trigger_data *
+get_named_trigger_data(struct event_trigger_data *data);
 extern int register_event_command(struct event_command *cmd);
 extern int unregister_event_command(struct event_command *cmd);
 extern int register_trigger_hist_enable_disable_cmds(void);
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -60,6 +60,9 @@ struct hist_field {
 	struct hist_var			var;
 	enum field_op_id		operator;
 	char				*name;
+	unsigned int			var_idx;
+	unsigned int			var_ref_idx;
+	bool                            read_once;
 };
 
 static u64 hist_field_none(struct hist_field *field,
@@ -215,6 +218,7 @@ enum hist_field_flags {
 	HIST_FIELD_FL_VAR		= 4096,
 	HIST_FIELD_FL_VAR_ONLY		= 8192,
 	HIST_FIELD_FL_EXPR		= 16384,
+	HIST_FIELD_FL_VAR_REF		= 32768,
 };
 
 struct var_defs {
@@ -255,6 +259,8 @@ struct hist_trigger_data {
 	struct tracing_map		*map;
 	bool				enable_timestamps;
 	bool				remove;
+	struct hist_field               *var_refs[TRACING_MAP_VARS_MAX];
+	unsigned int			n_var_refs;
 };
 
 static u64 hist_field_timestamp(struct hist_field *hist_field,
@@ -273,10 +279,344 @@ static u64 hist_field_timestamp(struct h
 	return ts;
 }
 
+struct hist_var_data {
+	struct list_head list;
+	struct hist_trigger_data *hist_data;
+};
+
+static struct hist_field *check_var_ref(struct hist_field *hist_field,
+					struct hist_trigger_data *var_data,
+					unsigned int var_idx)
+{
+	struct hist_field *found = NULL;
+
+	if (hist_field && hist_field->flags & HIST_FIELD_FL_VAR_REF) {
+		if (hist_field->var.idx == var_idx &&
+		    hist_field->var.hist_data == var_data) {
+			found = hist_field;
+		}
+	}
+
+	return found;
+}
+
+static struct hist_field *find_var_ref(struct hist_trigger_data *hist_data,
+				       struct hist_trigger_data *var_data,
+				       unsigned int var_idx)
+{
+	struct hist_field *hist_field, *found = NULL;
+	unsigned int i, j;
+
+	for_each_hist_field(i, hist_data) {
+		hist_field = hist_data->fields[i];
+		found = check_var_ref(hist_field, var_data, var_idx);
+		if (found)
+			return found;
+
+		for (j = 0; j < HIST_FIELD_OPERANDS_MAX; j++) {
+			struct hist_field *operand;
+
+			operand = hist_field->operands[j];
+			found = check_var_ref(operand, var_data, var_idx);
+			if (found)
+				return found;
+		}
+	}
+
+	return found;
+}
+
+static struct hist_field *find_any_var_ref(struct hist_trigger_data *hist_data,
+					   unsigned int var_idx)
+{
+	struct trace_array *tr = hist_data->event_file->tr;
+	struct hist_field *found = NULL;
+	struct hist_var_data *var_data;
+
+	list_for_each_entry(var_data, &tr->hist_vars, list) {
+		found = find_var_ref(var_data->hist_data, hist_data, var_idx);
+		if (found)
+			break;
+	}
+
+	return found;
+}
+
+static bool check_var_refs(struct hist_trigger_data *hist_data)
+{
+	struct hist_field *field;
+	bool found = false;
+	int i;
+
+	for_each_hist_field(i, hist_data) {
+		field = hist_data->fields[i];
+		if (field && field->flags & HIST_FIELD_FL_VAR) {
+			if (find_any_var_ref(hist_data, field->var.idx)) {
+				found = true;
+				break;
+			}
+		}
+	}
+
+	return found;
+}
+
+static struct hist_var_data *find_hist_vars(struct hist_trigger_data *hist_data)
+{
+	struct trace_array *tr = hist_data->event_file->tr;
+	struct hist_var_data *var_data, *found = NULL;
+
+	list_for_each_entry(var_data, &tr->hist_vars, list) {
+		if (var_data->hist_data == hist_data) {
+			found = var_data;
+			break;
+		}
+	}
+
+	return found;
+}
+
+static bool has_hist_vars(struct hist_trigger_data *hist_data)
+{
+	struct hist_field *hist_field;
+	int i, j;
+
+	for_each_hist_field(i, hist_data) {
+		hist_field = hist_data->fields[i];
+		if (hist_field &&
+		    (hist_field->flags & HIST_FIELD_FL_VAR ||
+		     hist_field->flags & HIST_FIELD_FL_VAR_REF))
+			return true;
+
+		for (j = 0; j < HIST_FIELD_OPERANDS_MAX; j++) {
+			struct hist_field *operand;
+
+			operand = hist_field->operands[j];
+			if (operand &&
+			    (operand->flags & HIST_FIELD_FL_VAR ||
+			     operand->flags & HIST_FIELD_FL_VAR_REF))
+				return true;
+		}
+	}
+
+	return false;
+}
+
+static int save_hist_vars(struct hist_trigger_data *hist_data)
+{
+	struct trace_array *tr = hist_data->event_file->tr;
+	struct hist_var_data *var_data;
+
+	var_data = find_hist_vars(hist_data);
+	if (var_data)
+		return 0;
+
+	if (trace_array_get(tr) < 0)
+		return -ENODEV;
+
+	var_data = kzalloc(sizeof(*var_data), GFP_KERNEL);
+	if (!var_data) {
+		trace_array_put(tr);
+		return -ENOMEM;
+	}
+
+	var_data->hist_data = hist_data;
+	list_add(&var_data->list, &tr->hist_vars);
+
+	return 0;
+}
+
+static void remove_hist_vars(struct hist_trigger_data *hist_data)
+{
+	struct trace_array *tr = hist_data->event_file->tr;
+	struct hist_var_data *var_data;
+
+	var_data = find_hist_vars(hist_data);
+	if (!var_data)
+		return;
+
+	if (WARN_ON(check_var_refs(hist_data)))
+		return;
+
+	list_del(&var_data->list);
+
+	kfree(var_data);
+
+	trace_array_put(tr);
+}
+
+static struct hist_field *find_var_field(struct hist_trigger_data *hist_data,
+					 const char *var_name)
+{
+	struct hist_field *hist_field, *found = NULL;
+	int i;
+
+	for_each_hist_field(i, hist_data) {
+		hist_field = hist_data->fields[i];
+		if (hist_field && hist_field->flags & HIST_FIELD_FL_VAR &&
+		    strcmp(hist_field->var.name, var_name) == 0) {
+			found = hist_field;
+			break;
+		}
+	}
+
+	return found;
+}
+
+static struct hist_field *find_var(struct trace_event_file *file,
+				   const char *var_name)
+{
+	struct hist_trigger_data *hist_data;
+	struct event_trigger_data *test;
+	struct hist_field *hist_field;
+
+	list_for_each_entry_rcu(test, &file->triggers, list) {
+		if (test->cmd_ops->trigger_type == ETT_EVENT_HIST) {
+			hist_data = test->private_data;
+			hist_field = find_var_field(hist_data, var_name);
+			if (hist_field)
+				return hist_field;
+		}
+	}
+
+	return NULL;
+}
+
+static struct trace_event_file *find_var_file(struct trace_array *tr,
+					      const char *system,
+					      const char *event_name,
+					      const char *var_name)
+{
+	struct hist_trigger_data *var_hist_data;
+	struct hist_var_data *var_data;
+	struct trace_event_call *call;
+	struct trace_event_file *file;
+	const char *name;
+
+	list_for_each_entry(var_data, &tr->hist_vars, list) {
+		var_hist_data = var_data->hist_data;
+		file = var_hist_data->event_file;
+		call = file->event_call;
+		name = trace_event_name(call);
+
+		if (!system || !event_name) {
+			if (find_var(file, var_name))
+				return file;
+			continue;
+		}
+
+		if (strcmp(event_name, name) != 0)
+			continue;
+		if (strcmp(system, call->class->system) != 0)
+			continue;
+
+		return file;
+	}
+
+	return NULL;
+}
+
+static struct hist_field *find_file_var(struct trace_event_file *file,
+					const char *var_name)
+{
+	struct hist_trigger_data *test_data;
+	struct event_trigger_data *test;
+	struct hist_field *hist_field;
+
+	list_for_each_entry_rcu(test, &file->triggers, list) {
+		if (test->cmd_ops->trigger_type == ETT_EVENT_HIST) {
+			test_data = test->private_data;
+			hist_field = find_var_field(test_data, var_name);
+			if (hist_field)
+				return hist_field;
+		}
+	}
+
+	return NULL;
+}
+
+static struct hist_field *find_event_var(struct trace_array *tr,
+					 const char *system,
+					 const char *event_name,
+					 const char *var_name)
+{
+	struct hist_field *hist_field = NULL;
+	struct trace_event_file *file;
+
+	file = find_var_file(tr, system, event_name, var_name);
+	if (!file)
+		return NULL;
+
+	hist_field = find_file_var(file, var_name);
+
+	return hist_field;
+}
+
 struct hist_elt_data {
 	char *comm;
+	u64 *var_ref_vals;
 };
 
+static u64 hist_field_var_ref(struct hist_field *hist_field,
+			      struct tracing_map_elt *elt,
+			      struct ring_buffer_event *rbe,
+			      void *event)
+{
+	struct hist_elt_data *elt_data;
+	u64 var_val = 0;
+
+	elt_data = elt->private_data;
+	var_val = elt_data->var_ref_vals[hist_field->var_ref_idx];
+
+	return var_val;
+}
+
+static bool resolve_var_refs(struct hist_trigger_data *hist_data, void *key,
+			     u64 *var_ref_vals, bool self)
+{
+	struct hist_trigger_data *var_data;
+	struct tracing_map_elt *var_elt;
+	struct hist_field *hist_field;
+	unsigned int i, var_idx;
+	bool resolved = true;
+	u64 var_val = 0;
+
+	for (i = 0; i < hist_data->n_var_refs; i++) {
+		hist_field = hist_data->var_refs[i];
+		var_idx = hist_field->var.idx;
+		var_data = hist_field->var.hist_data;
+
+		if (var_data == NULL) {
+			resolved = false;
+			break;
+		}
+
+		if ((self && var_data != hist_data) ||
+		    (!self && var_data == hist_data))
+			continue;
+
+		var_elt = tracing_map_lookup(var_data->map, key);
+		if (!var_elt) {
+			resolved = false;
+			break;
+		}
+
+		if (!tracing_map_var_set(var_elt, var_idx)) {
+			resolved = false;
+			break;
+		}
+
+		if (self || !hist_field->read_once)
+			var_val = tracing_map_read_var(var_elt, var_idx);
+		else
+			var_val = tracing_map_read_var_once(var_elt, var_idx);
+
+		var_ref_vals[i] = var_val;
+	}
+
+	return resolved;
+}
+
 static const char *hist_field_name(struct hist_field *field,
 				   unsigned int level)
 {
@@ -291,7 +631,8 @@ static const char *hist_field_name(struc
 		field_name = hist_field_name(field->operands[0], ++level);
 	else if (field->flags & HIST_FIELD_FL_TIMESTAMP)
 		field_name = "$common_timestamp";
-	else if (field->flags & HIST_FIELD_FL_EXPR)
+	else if (field->flags & HIST_FIELD_FL_EXPR ||
+		 field->flags & HIST_FIELD_FL_VAR_REF)
 		field_name = field->name;
 
 	if (field_name == NULL)
@@ -574,6 +915,8 @@ static char *expr_str(struct hist_field
 		return expr;
 	}
 
+	if (field->operands[0]->flags & HIST_FIELD_FL_VAR_REF)
+		strcat(expr, "$");
 	strcat(expr, hist_field_name(field->operands[0], 0));
 	if (field->operands[0]->flags) {
 		const char *flags_str = get_hist_field_flags(field->operands[0]);
@@ -596,6 +939,8 @@ static char *expr_str(struct hist_field
 		return NULL;
 	}
 
+	if (field->operands[1]->flags & HIST_FIELD_FL_VAR_REF)
+		strcat(expr, "$");
 	strcat(expr, hist_field_name(field->operands[1], 0));
 	if (field->operands[1]->flags) {
 		const char *flags_str = get_hist_field_flags(field->operands[1]);
@@ -675,6 +1020,11 @@ static struct hist_field *create_hist_fi
 	if (flags & HIST_FIELD_FL_EXPR)
 		goto out; /* caller will populate */
 
+	if (flags & HIST_FIELD_FL_VAR_REF) {
+		hist_field->fn = hist_field_var_ref;
+		goto out;
+	}
+
 	if (flags & HIST_FIELD_FL_HITCOUNT) {
 		hist_field->fn = hist_field_counter;
 		hist_field->size = sizeof(u64);
@@ -768,6 +1118,51 @@ static void destroy_hist_fields(struct h
 	}
 }
 
+static int init_var_ref(struct hist_field *ref_field,
+			struct hist_field *var_field)
+{
+	ref_field->var.idx = var_field->var.idx;
+	ref_field->var.hist_data = var_field->hist_data;
+	ref_field->size = var_field->size;
+	ref_field->is_signed = var_field->is_signed;
+
+	ref_field->name = kstrdup(var_field->var.name, GFP_KERNEL);
+	if (!ref_field->name)
+		return -ENOMEM;
+
+	ref_field->type = kstrdup(var_field->type, GFP_KERNEL);
+	if (!ref_field->type) {
+		kfree(ref_field->name);
+		return -ENOMEM;
+	}
+
+	return 0;
+}
+
+static struct hist_field *create_var_ref(struct hist_field *var_field)
+{
+	unsigned long flags = HIST_FIELD_FL_VAR_REF;
+	struct hist_field *ref_field;
+
+	ref_field = create_hist_field(var_field->hist_data, NULL, flags, NULL);
+	if (ref_field) {
+		if (init_var_ref(ref_field, var_field)) {
+			destroy_hist_field(ref_field, 0);
+			return NULL;
+		}
+	}
+
+	return ref_field;
+}
+
+static bool is_var_ref(char *var_name)
+{
+	if (!var_name || strlen(var_name) < 2 || var_name[0] != '$')
+		return false;
+
+	return true;
+}
+
 static char *field_name_from_var(struct hist_trigger_data *hist_data,
 				 char *var_name)
 {
@@ -779,7 +1174,7 @@ static char *field_name_from_var(struct
 
 		if (strcmp(var_name, name) == 0) {
 			field = hist_data->attrs->var_defs.expr[i];
-			if (contains_operator(field))
+			if (contains_operator(field) || is_var_ref(field))
 				continue;
 			return field;
 		}
@@ -791,11 +1186,32 @@ static char *field_name_from_var(struct
 static char *local_field_var_ref(struct hist_trigger_data *hist_data,
 				 char *var_name)
 {
+	if (!is_var_ref(var_name))
+		return NULL;
+
 	var_name++;
 
 	return field_name_from_var(hist_data, var_name);
 }
 
+static struct hist_field *parse_var_ref(struct trace_array *tr,
+					char *system, char *event_name,
+					char *var_name)
+{
+	struct hist_field *var_field = NULL, *ref_field = NULL;
+
+	if (!is_var_ref(var_name))
+		return NULL;
+
+	var_name++;
+
+	var_field = find_event_var(tr, system, event_name, var_name);
+	if (var_field)
+		ref_field = create_var_ref(var_field);
+
+	return ref_field;
+}
+
 static struct ftrace_event_field *
 parse_field(struct hist_trigger_data *hist_data, struct trace_event_file *file,
 	    char *field_str, unsigned long *flags)
@@ -852,13 +1268,31 @@ struct hist_field *parse_atom(struct his
 			      struct trace_event_file *file, char *str,
 			      unsigned long *flags, char *var_name)
 {
-	char *s;
+	char *s, *ref_system = NULL, *ref_event = NULL, *ref_var = str;
+	struct trace_array *tr = hist_data->event_file->tr;
 	struct ftrace_event_field *field = NULL;
 	struct hist_field *hist_field = NULL;
 	int ret = 0;
 
-	s = local_field_var_ref(hist_data, str);
-	if (s)
+	s = strchr(str, '.');
+	if (s) {
+		s = strchr(++s, '.');
+		if (s) {
+			ref_system = strsep(&str, ".");
+			ref_event = strsep(&str, ".");
+			ref_var = str;
+		}
+	}
+
+	s = local_field_var_ref(hist_data, ref_var);
+	if (!s) {
+		hist_field = parse_var_ref(tr, ref_system, ref_event, ref_var);
+		if (hist_field) {
+			hist_data->var_refs[hist_data->n_var_refs] = hist_field;
+			hist_field->var_ref_idx = hist_data->n_var_refs++;
+			return hist_field;
+		}
+	} else
 		str = s;
 
 	field = parse_field(hist_data, file, str, flags);
@@ -1029,6 +1463,9 @@ static struct hist_field *parse_expr(str
 		goto free;
 	}
 
+	operand1->read_once = true;
+	operand2->read_once = true;
+
 	expr->operands[0] = operand1;
 	expr->operands[1] = operand2;
 	expr->operator = field_op;
@@ -1075,43 +1512,6 @@ static int create_hitcount_val(struct hi
 	return 0;
 }
 
-static struct hist_field *find_var_field(struct hist_trigger_data *hist_data,
-					 const char *var_name)
-{
-	struct hist_field *hist_field, *found = NULL;
-	int i;
-
-	for_each_hist_field(i, hist_data) {
-		hist_field = hist_data->fields[i];
-		if (hist_field && hist_field->flags & HIST_FIELD_FL_VAR &&
-		    strcmp(hist_field->var.name, var_name) == 0) {
-			found = hist_field;
-			break;
-		}
-	}
-
-	return found;
-}
-
-static struct hist_field *find_var(struct trace_event_file *file,
-				   const char *var_name)
-{
-	struct hist_trigger_data *hist_data;
-	struct event_trigger_data *test;
-	struct hist_field *hist_field;
-
-	list_for_each_entry_rcu(test, &file->triggers, list) {
-		if (test->cmd_ops->trigger_type == ETT_EVENT_HIST) {
-			hist_data = test->private_data;
-			hist_field = find_var_field(hist_data, var_name);
-			if (hist_field)
-				return hist_field;
-		}
-	}
-
-	return NULL;
-}
-
 static int __create_val_field(struct hist_trigger_data *hist_data,
 			      unsigned int val_idx,
 			      struct trace_event_file *file,
@@ -1245,6 +1645,12 @@ static int create_key_field(struct hist_
 			goto out;
 		}
 
+		if (hist_field->flags & HIST_FIELD_FL_VAR_REF) {
+			destroy_hist_field(hist_field, 0);
+			ret = -EINVAL;
+			goto out;
+		}
+
 		key_size = hist_field->size;
 	}
 
@@ -1580,6 +1986,7 @@ create_hist_data(unsigned int map_bits,
 
 	hist_data->attrs = attrs;
 	hist_data->remove = remove;
+	hist_data->event_file = file;
 
 	ret = create_hist_fields(hist_data, file);
 	if (ret)
@@ -1602,12 +2009,6 @@ create_hist_data(unsigned int map_bits,
 	ret = create_tracing_map_fields(hist_data);
 	if (ret)
 		goto free;
-
-	ret = tracing_map_init(hist_data->map);
-	if (ret)
-		goto free;
-
-	hist_data->event_file = file;
  out:
 	return hist_data;
  free:
@@ -1622,12 +2023,17 @@ create_hist_data(unsigned int map_bits,
 
 static void hist_trigger_elt_update(struct hist_trigger_data *hist_data,
 				    struct tracing_map_elt *elt, void *rec,
-				    struct ring_buffer_event *rbe)
+				    struct ring_buffer_event *rbe,
+				    u64 *var_ref_vals)
 {
+	struct hist_elt_data *elt_data;
 	struct hist_field *hist_field;
 	unsigned int i, var_idx;
 	u64 hist_val;
 
+	elt_data = elt->private_data;
+	elt_data->var_ref_vals = var_ref_vals;
+
 	for_each_hist_val_field(i, hist_data) {
 		hist_field = hist_data->fields[i];
 		hist_val = hist_field->fn(hist_field, elt, rbe, rec);
@@ -1680,6 +2086,7 @@ static void event_hist_trigger(struct ev
 	struct hist_trigger_data *hist_data = data->private_data;
 	bool use_compound_key = (hist_data->n_keys > 1);
 	unsigned long entries[HIST_STACKTRACE_DEPTH];
+	u64 var_ref_vals[TRACING_MAP_VARS_MAX];
 	char compound_key[HIST_KEY_SIZE_MAX];
 	struct tracing_map_elt *elt = NULL;
 	struct stack_trace stacktrace;
@@ -1719,9 +2126,15 @@ static void event_hist_trigger(struct ev
 	if (use_compound_key)
 		key = compound_key;
 
+	if (hist_data->n_var_refs &&
+	    !resolve_var_refs(hist_data, key, var_ref_vals, false))
+		return;
+
 	elt = tracing_map_insert(hist_data->map, key);
-	if (elt)
-		hist_trigger_elt_update(hist_data, elt, rec, rbe);
+	if (!elt)
+		return;
+
+	hist_trigger_elt_update(hist_data, elt, rec, rbe, var_ref_vals);
 }
 
 static void hist_trigger_stacktrace_print(struct seq_file *m,
@@ -1824,7 +2237,8 @@ hist_trigger_entry_print(struct seq_file
 		field_name = hist_field_name(hist_data->fields[i], 0);
 
 		if (hist_data->fields[i]->flags & HIST_FIELD_FL_VAR ||
-		    hist_data->fields[i]->flags & HIST_FIELD_FL_EXPR)
+		    hist_data->fields[i]->flags & HIST_FIELD_FL_EXPR ||
+		    hist_data->fields[i]->flags & HIST_FIELD_FL_VAR_REF)
 			continue;
 
 		if (hist_data->fields[i]->flags & HIST_FIELD_FL_HEX) {
@@ -2074,7 +2488,11 @@ static void event_hist_trigger_free(stru
 	if (!data->ref) {
 		if (data->name)
 			del_named_trigger(data);
+
 		trigger_data_free(data);
+
+		remove_hist_vars(hist_data);
+
 		destroy_hist_data(hist_data);
 	}
 }
@@ -2288,23 +2706,55 @@ static int hist_register_trigger(char *g
 			goto out;
 	}
 
-	list_add_rcu(&data->list, &file->triggers);
 	ret++;
 
-	update_cond_flag(file);
-
 	if (hist_data->enable_timestamps)
 		tracing_set_time_stamp_abs(file->tr, true);
+ out:
+	return ret;
+}
+
+static int hist_trigger_enable(struct event_trigger_data *data,
+			       struct trace_event_file *file)
+{
+	int ret = 0;
+
+	list_add_rcu(&data->list, &file->triggers);
+
+	update_cond_flag(file);
 
 	if (trace_event_trigger_enable_disable(file, 1) < 0) {
 		list_del_rcu(&data->list);
 		update_cond_flag(file);
 		ret--;
 	}
- out:
+
 	return ret;
 }
 
+static bool hist_trigger_check_refs(struct event_trigger_data *data,
+				    struct trace_event_file *file)
+{
+	struct hist_trigger_data *hist_data = data->private_data;
+	struct event_trigger_data *test, *named_data = NULL;
+
+	if (hist_data->attrs->name)
+		named_data = find_named_trigger(hist_data->attrs->name);
+
+	list_for_each_entry_rcu(test, &file->triggers, list) {
+		if (test->cmd_ops->trigger_type == ETT_EVENT_HIST) {
+			if (!hist_trigger_match(data, test, named_data, false))
+				continue;
+			hist_data = test->private_data;
+			if (check_var_refs(hist_data))
+				return true;
+			break;
+		}
+	}
+
+	return false;
+}
+
 static void hist_unregister_trigger(char *glob, struct event_trigger_ops *ops,
 				    struct event_trigger_data *data,
 				    struct trace_event_file *file)
@@ -2335,10 +2785,30 @@ static void hist_unregister_trigger(char
 		tracing_set_time_stamp_abs(file->tr, false);
 }
 
+static bool hist_file_check_refs(struct trace_event_file *file)
+{
+	struct hist_trigger_data *hist_data;
+	struct event_trigger_data *test;
+
+	list_for_each_entry_rcu(test, &file->triggers, list) {
+		if (test->cmd_ops->trigger_type == ETT_EVENT_HIST) {
+			hist_data = test->private_data;
+			if (check_var_refs(hist_data))
+				return true;
+			break;
+		}
+	}
+
+	return false;
+}
+
 static void hist_unreg_all(struct trace_event_file *file)
 {
 	struct event_trigger_data *test, *n;
 
+	if (hist_file_check_refs(file))
+		return;
+
 	list_for_each_entry_safe(test, n, &file->triggers, list) {
 		if (test->cmd_ops->trigger_type == ETT_EVENT_HIST) {
 			list_del_rcu(&test->list);
@@ -2411,6 +2881,11 @@ static int event_hist_trigger_func(struc
 	}
 
 	if (remove) {
+		if (hist_trigger_check_refs(trigger_data, file)) {
+			ret = -EBUSY;
+			goto out_free;
+		}
+
 		cmd_ops->unreg(glob+1, trigger_ops, trigger_data, file);
 		ret = 0;
 		goto out_free;
@@ -2428,14 +2903,33 @@ static int event_hist_trigger_func(struc
 		goto out_free;
 	} else if (ret < 0)
 		goto out_free;
+
+	if (get_named_trigger_data(trigger_data))
+		goto enable;
+
+	if (has_hist_vars(hist_data))
+		save_hist_vars(hist_data);
+
+	ret = tracing_map_init(hist_data->map);
+	if (ret)
+		goto out_unreg;
+enable:
+	ret = hist_trigger_enable(trigger_data, file);
+	if (ret)
+		goto out_unreg;
+
 	/* Just return zero, not the number of registered triggers */
 	ret = 0;
  out:
 	return ret;
+ out_unreg:
+	cmd_ops->unreg(glob+1, trigger_ops, trigger_data, file);
  out_free:
 	if (cmd_ops->set_filter)
 		cmd_ops->set_filter(NULL, trigger_data, NULL);
 
+	remove_hist_vars(hist_data);
+
 	kfree(trigger_data);
 
 	destroy_hist_data(hist_data);
--- a/kernel/trace/trace_events_trigger.c
+++ b/kernel/trace/trace_events_trigger.c
@@ -909,6 +909,12 @@ void set_named_trigger_data(struct event
 	data->named_data = named_data;
 }
 
+struct event_trigger_data *
+get_named_trigger_data(struct event_trigger_data *data)
+{
+	return data->named_data;
+}
+
 static void
 traceon_trigger(struct event_trigger_data *data, void *rec,
 		struct ring_buffer_event *event)