Message-Id: <8411497118160688b13fcf500596f6094d2eabcd.1498510759.git.tom.zanussi@linux.intel.com>
Date:   Mon, 26 Jun 2017 17:49:24 -0500
From:   Tom Zanussi <tom.zanussi@...ux.intel.com>
To:     rostedt@...dmis.org
Cc:     tglx@...utronix.de, mhiramat@...nel.org, namhyung@...nel.org,
        vedang.patel@...el.com, linux-kernel@...r.kernel.org,
        linux-rt-users@...r.kernel.org,
        Tom Zanussi <tom.zanussi@...ux.intel.com>
Subject: [PATCH 23/32] tracing: Add 'onmatch' hist trigger action support

Add an 'onmatch(matching.event).<synthetic_event_name>(param list)'
hist trigger action which is invoked with the set of variables or
event fields named in the 'param list'.  The result is the generation
of a synthetic event that consists of the values contained in those
variables and/or fields at the time the invoking event was hit.

As an example the below defines a simple synthetic event using a
variable defined on the sched_wakeup_new event, and shows the event
definition with unresolved fields, since the sched_wakeup_new event
with the testpid variable hasn't been defined yet:

    # echo 'wakeup_new_test pid_t pid; int prio' >> \
      /sys/kernel/debug/tracing/synthetic_events

    # cat /sys/kernel/debug/tracing/synthetic_events
      wakeup_new_test pid_t pid; int prio

The following hist trigger both defines a testpid variable and
specifies an onmatch() trace action that uses that variable along with
a non-variable field to generate a wakeup_new_test synthetic event
whenever a sched_wakeup_new event occurs, which because of the 'if
comm == "cyclictest"' filter only happens when the executable is
cyclictest:

    # echo 'hist:keys=testpid=pid:\
      onmatch(sched.sched_wakeup_new).wakeup_new_test($testpid, prio) \
        if comm=="cyclictest"' >> \
      /sys/kernel/debug/tracing/events/sched/sched_wakeup_new/trigger

Creating and displaying a histogram based on those events is now just
a matter of using the fields and new synthetic event in the
tracing/events/synthetic directory, as usual:

    # echo 'hist:keys=pid,prio:sort=pid,prio' >> \
      /sys/kernel/debug/tracing/events/synthetic/wakeup_new_test/trigger

Signed-off-by: Tom Zanussi <tom.zanussi@...ux.intel.com>
---
 kernel/trace/trace_events_hist.c | 955 ++++++++++++++++++++++++++++++++++++++-
 1 file changed, 940 insertions(+), 15 deletions(-)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index e11b3a3..b1f859c 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -59,6 +59,7 @@ struct hist_field {
 	unsigned int			size;
 	unsigned int			offset;
 	unsigned int                    is_signed;
+	const char			*type;
 	struct hist_field		*operands[HIST_FIELD_OPERANDS_MAX];
 	struct hist_trigger_data	*hist_data;
 	struct hist_var			var;
@@ -243,6 +244,16 @@ struct hist_trigger_attrs {
 	unsigned int	n_actions;
 };
 
+struct field_var {
+	struct hist_field	*var;
+	struct hist_field	*val;
+};
+
+struct field_var_hist {
+	struct hist_trigger_data	*hist_data;
+	char				*cmd;
+};
+
 struct hist_trigger_data {
 	struct hist_field               *fields[HIST_FIELDS_MAX];
 	unsigned int			n_vals;
@@ -263,6 +274,14 @@ struct hist_trigger_data {
 
 	struct action_data		*actions[HIST_ACTIONS_MAX];
 	unsigned int			n_actions;
+
+	struct hist_field		*synth_var_refs[SYNTH_FIELDS_MAX];
+	unsigned int			n_synth_var_refs;
+	struct field_var		*field_vars[SYNTH_FIELDS_MAX];
+	unsigned int			n_field_vars;
+	unsigned int			n_field_var_str;
+	struct field_var_hist		*field_var_hists[SYNTH_FIELDS_MAX];
+	unsigned int			n_field_var_hists;
 };
 
 struct synth_field {
@@ -291,7 +310,14 @@ typedef void (*action_fn_t) (struct hist_trigger_data *hist_data,
 
 struct action_data {
 	action_fn_t		fn;
+	unsigned int		n_params;
+	char			*params[SYNTH_FIELDS_MAX];
+
 	unsigned int		var_ref_idx;
+	char			*match_event;
+	char			*match_event_system;
+	char			*synth_event_name;
+	struct synth_event	*synth_event;
 };
 
 static LIST_HEAD(synth_event_list);
@@ -802,6 +828,50 @@ static struct synth_event *alloc_synth_event(char *event_name, int n_fields,
 	return event;
 }
 
+static void action_trace(struct hist_trigger_data *hist_data,
+			 struct tracing_map_elt *elt, void *rec,
+			 struct ring_buffer_event *rbe,
+			 struct action_data *data, u64 *var_ref_vals)
+{
+	struct synth_event *event = data->synth_event;
+
+	trace_synth(event, var_ref_vals, data->var_ref_idx);
+}
+
+static bool check_hist_action_refs(struct hist_trigger_data *hist_data,
+				   struct synth_event *event)
+{
+	unsigned int i;
+
+	for (i = 0; i < hist_data->n_actions; i++) {
+		struct action_data *data = hist_data->actions[i];
+
+		if (data->fn == action_trace && data->synth_event == event)
+			return true;
+	}
+
+	return false;
+}
+
+static LIST_HEAD(hist_action_list);
+static LIST_HEAD(hist_var_list);
+
+struct hist_var_data {
+	struct list_head list;
+	struct hist_trigger_data *hist_data;
+};
+
+static bool check_synth_action_refs(struct synth_event *event)
+{
+	struct hist_var_data *var_data;
+
+	list_for_each_entry(var_data, &hist_action_list, list)
+		if (check_hist_action_refs(var_data->hist_data, event))
+			return true;
+
+	return false;
+}
+
 static int create_synth_event(int argc, char **argv)
 {
 	struct synth_field *fields[SYNTH_FIELDS_MAX];
@@ -832,15 +902,17 @@ static int create_synth_event(int argc, char **argv)
 	event = find_synth_event(name);
 	if (event) {
 		if (delete_event) {
+			if (check_synth_action_refs(event)) {
+				ret = -EBUSY;
+				goto out;
+			}
 			remove_synth_event(event);
 			goto err;
 		} else
 			ret = -EEXIST;
 		goto out;
-	} else if (delete_event) {
-		ret = -EINVAL;
+	} else if (delete_event)
 		goto out;
-	}
 
 	if (argc < 2) {
 		ret = -EINVAL;
@@ -891,11 +963,18 @@ static int release_all_synth_events(void)
 
 	mutex_lock(&synth_event_mutex);
 
+	list_for_each_entry(event, &synth_event_list, list) {
+		if (check_synth_action_refs(event)) {
+			ret = -EBUSY;
+			goto out;
+		}
+	}
+
 	list_for_each_entry_safe(event, e, &synth_event_list, list) {
 		remove_synth_event(event);
 		free_synth_event(event);
 	}
-
+ out:
 	mutex_unlock(&synth_event_mutex);
 
 	return ret;
@@ -992,13 +1071,6 @@ static u64 hist_field_timestamp(struct hist_field *hist_field,
 	return ts;
 }
 
-static LIST_HEAD(hist_var_list);
-
-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)
@@ -1248,6 +1320,7 @@ static struct hist_field *find_event_var(const char *system,
 struct hist_elt_data {
 	char *comm;
 	u64 *var_ref_vals;
+	char *field_var_str[SYNTH_FIELDS_MAX];
 };
 
 static u64 hist_field_var_ref(struct hist_field *hist_field,
@@ -1415,11 +1488,21 @@ static void destroy_hist_trigger_attrs(struct hist_trigger_attrs *attrs)
 
 static int parse_action(char *str, struct hist_trigger_attrs *attrs)
 {
-	int ret = 0;
+	int ret = -EINVAL;
 
 	if (attrs->n_actions >= HIST_ACTIONS_MAX)
 		return ret;
 
+	if ((strncmp(str, "onmatch(", strlen("onmatch(")) == 0)) {
+		attrs->action_str[attrs->n_actions] = kstrdup(str, GFP_KERNEL);
+		if (!attrs->action_str[attrs->n_actions]) {
+			ret = -ENOMEM;
+			return ret;
+		}
+		attrs->n_actions++;
+		ret = 0;
+	}
+
 	return ret;
 }
 
@@ -1525,7 +1608,14 @@ static inline void save_comm(char *comm, struct task_struct *task)
 
 static void hist_trigger_elt_data_free(struct tracing_map_elt *elt)
 {
+	struct hist_trigger_data *hist_data = elt->map->private_data;
 	struct hist_elt_data *private_data = elt->private_data;
+	unsigned int i, n_str;
+
+	n_str = hist_data->n_field_var_str;
+
+	for (i = 0; i < n_str; i++)
+		kfree(private_data->field_var_str[i]);
 
 	kfree(private_data->comm);
 	kfree(private_data);
@@ -1537,7 +1627,7 @@ static int hist_trigger_elt_data_alloc(struct tracing_map_elt *elt)
 	unsigned int size = TASK_COMM_LEN + 1;
 	struct hist_elt_data *elt_data;
 	struct hist_field *key_field;
-	unsigned int i;
+	unsigned int i, n_str;
 
 	elt->private_data = elt_data = kzalloc(sizeof(*elt_data), GFP_KERNEL);
 	if (!elt_data)
@@ -1557,6 +1647,16 @@ static int hist_trigger_elt_data_alloc(struct tracing_map_elt *elt)
 		}
 	}
 
+	n_str = hist_data->n_field_var_str;
+
+	for (i = 0; i < n_str; i++) {
+		elt_data->field_var_str[i] = kzalloc(size, GFP_KERNEL);
+		if (!elt_data->field_var_str[i]) {
+			hist_trigger_elt_data_free(elt);
+			return -ENOMEM;
+		}
+	}
+
 	return 0;
 }
 
@@ -1674,6 +1774,7 @@ static void destroy_hist_field(struct hist_field *hist_field,
 
 	kfree(hist_field->var.name);
 	kfree(hist_field->name);
+	kfree(hist_field->type);
 
 	kfree(hist_field);
 }
@@ -1704,6 +1805,10 @@ static struct hist_field *create_hist_field(struct hist_trigger_data *hist_data,
 
 	if (flags & HIST_FIELD_FL_HITCOUNT) {
 		hist_field->fn = hist_field_counter;
+		hist_field->size = sizeof(u64);
+		hist_field->type = kstrdup("u64", GFP_KERNEL);
+		if (!hist_field->type)
+			goto free;
 		goto out;
 	}
 
@@ -1717,12 +1822,18 @@ static struct hist_field *create_hist_field(struct hist_trigger_data *hist_data,
 		hist_field->fn = hist_field_log2;
 		hist_field->operands[0] = create_hist_field(hist_data, field, fl, NULL);
 		hist_field->size = hist_field->operands[0]->size;
+		hist_field->type = kstrdup(hist_field->operands[0]->type, GFP_KERNEL);
+		if (!hist_field->type)
+			goto free;
 		goto out;
 	}
 
 	if (flags & HIST_FIELD_FL_TIMESTAMP) {
 		hist_field->fn = hist_field_timestamp;
 		hist_field->size = sizeof(u64);
+		hist_field->type = kstrdup("u64", GFP_KERNEL);
+		if (!hist_field->type)
+			goto free;
 		goto out;
 	}
 
@@ -1731,6 +1842,10 @@ static struct hist_field *create_hist_field(struct hist_trigger_data *hist_data,
 
 	if (is_string_field(field)) {
 		flags |= HIST_FIELD_FL_STRING;
+		hist_field->size = MAX_FILTER_STR_VAL;
+		hist_field->type = kstrdup(field->type, GFP_KERNEL);
+		if (!hist_field->type)
+			goto free;
 
 		if (field->filter_type == FILTER_STATIC_STRING)
 			hist_field->fn = hist_field_string;
@@ -1739,6 +1854,12 @@ static struct hist_field *create_hist_field(struct hist_trigger_data *hist_data,
 		else
 			hist_field->fn = hist_field_pstring;
 	} else {
+		hist_field->size = field->size;
+		hist_field->is_signed = field->is_signed;
+		hist_field->type = kstrdup(field->type, GFP_KERNEL);
+		if (!hist_field->type)
+			goto free;
+
 		hist_field->fn = select_value_fn(field->size,
 						 field->is_signed);
 		if (!hist_field->fn) {
@@ -1786,7 +1907,10 @@ static struct hist_field *create_var_ref(struct hist_field *var_field)
 		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) {
+		ref_field->type = kstrdup(var_field->type, GFP_KERNEL);
+		if (!ref_field->name || !ref_field->type) {
+			kfree(ref_field->name);
+			kfree(ref_field->type);
 			destroy_hist_field(ref_field, 0);
 			return NULL;
 		}
@@ -1970,6 +2094,11 @@ static struct hist_field *parse_unary(struct hist_trigger_data *hist_data,
 	expr->operands[0] = operand1;
 	expr->operator = FIELD_OP_UNARY_MINUS;
 	expr->name = expr_str(expr, 0);
+	expr->type = kstrdup(operand1->type, GFP_KERNEL);
+	if (!expr->type) {
+		ret = -ENOMEM;
+		goto free;
+	}
 
 	return expr;
  free:
@@ -2053,6 +2182,11 @@ static struct hist_field *parse_expr(struct hist_trigger_data *hist_data,
 	expr->operands[1] = operand2;
 	expr->operator = field_op;
 	expr->name = expr_str(expr, 0);
+	expr->type = kstrdup(operand1->type, GFP_KERNEL);
+	if (!expr->type) {
+		ret = -ENOMEM;
+		goto free;
+	}
 
 	switch (field_op) {
 	case FIELD_OP_MINUS:
@@ -2074,6 +2208,718 @@ static struct hist_field *parse_expr(struct hist_trigger_data *hist_data,
 	return ERR_PTR(ret);
 }
 
+static struct hist_var_data *find_actions(struct hist_trigger_data *hist_data)
+{
+	struct hist_var_data *var_data, *found = NULL;
+
+	list_for_each_entry(var_data, &hist_action_list, list) {
+		if (var_data->hist_data == hist_data) {
+			found = var_data;
+			break;
+		}
+	}
+
+	return found;
+}
+
+static int save_hist_actions(struct hist_trigger_data *hist_data)
+{
+	struct hist_var_data *var_data;
+
+	var_data = find_actions(hist_data);
+	if (var_data)
+		return 0;
+
+	var_data = kzalloc(sizeof(*var_data), GFP_KERNEL);
+	if (!var_data)
+		return -ENOMEM;
+
+	var_data->hist_data = hist_data;
+	list_add(&var_data->list, &hist_action_list);
+
+	return 0;
+}
+
+static void remove_hist_actions(struct hist_trigger_data *hist_data)
+{
+	struct hist_var_data *var_data;
+
+	var_data = find_actions(hist_data);
+	if (!var_data)
+		return;
+
+	list_del(&var_data->list);
+
+	kfree(var_data);
+}
+
+static char *find_trigger_filter(struct hist_trigger_data *hist_data,
+				 struct trace_event_file *file)
+{
+	struct event_trigger_data *test;
+
+	list_for_each_entry_rcu(test, &file->triggers, list) {
+		if (test->cmd_ops->trigger_type == ETT_EVENT_HIST) {
+			if (test->private_data == hist_data)
+				return test->filter_str;
+		}
+	}
+
+	return NULL;
+}
+
+static struct event_command trigger_hist_cmd;
+static int event_hist_trigger_func(struct event_command *cmd_ops,
+				   struct trace_event_file *file,
+				   char *glob, char *cmd, char *param);
+
+static bool compatible_keys(struct hist_trigger_data *target_hist_data,
+			    struct hist_trigger_data *hist_data,
+			    unsigned int n_keys)
+{
+	struct hist_field *target_hist_field, *hist_field;
+	unsigned int n, i, j;
+
+	if (hist_data->n_fields - hist_data->n_vals != n_keys)
+		return false;
+
+	i = hist_data->n_vals;
+	j = target_hist_data->n_vals;
+
+	for (n = 0; n < n_keys; n++) {
+		hist_field = hist_data->fields[i + n];
+		target_hist_field = hist_data->fields[j + n];
+
+		if (strcmp(hist_field->type, target_hist_field->type) != 0)
+			return false;
+		if (hist_field->size != target_hist_field->size)
+			return false;
+		if (hist_field->is_signed != target_hist_field->is_signed)
+			return false;
+	}
+
+	return true;
+}
+
+static struct hist_trigger_data *
+find_compatible_hist(struct hist_trigger_data *target_hist_data,
+		     struct trace_event_file *file)
+{
+	struct hist_trigger_data *hist_data;
+	struct event_trigger_data *test;
+	unsigned int n_keys;
+
+	n_keys = target_hist_data->n_fields - target_hist_data->n_vals;
+
+	list_for_each_entry_rcu(test, &file->triggers, list) {
+		if (test->cmd_ops->trigger_type == ETT_EVENT_HIST) {
+			hist_data = test->private_data;
+
+			if (compatible_keys(target_hist_data, hist_data, n_keys))
+				return hist_data;
+		}
+	}
+
+	return NULL;
+}
+
+static struct trace_event_file *event_file(char *system, char *event_name)
+{
+	struct trace_event_file *file;
+	struct trace_array *tr;
+
+	tr = top_trace_array();
+	if (!tr)
+		return ERR_PTR(-ENODEV);
+
+	file = find_event_file(tr, system, event_name);
+	if (!file)
+		return ERR_PTR(-EINVAL);
+
+	return file;
+}
+
+static struct hist_field *
+create_field_var_hist(struct hist_trigger_data *target_hist_data,
+		      char *system, char *event_name, char *field_name)
+{
+	struct hist_field *event_var = ERR_PTR(-EINVAL);
+	struct hist_trigger_data *hist_data;
+	unsigned int i, n, first = true;
+	struct field_var_hist *var_hist;
+	struct trace_event_file *file;
+	struct hist_field *key_field;
+	struct trace_array *tr;
+	char *saved_filter;
+	char *cmd;
+	int ret;
+
+	if (target_hist_data->n_field_var_hists >= SYNTH_FIELDS_MAX)
+		return ERR_PTR(-EINVAL);
+
+	tr = top_trace_array();
+	if (!tr)
+		return ERR_PTR(-ENODEV);
+
+	file = event_file(system, event_name);
+	if (IS_ERR(file)) {
+		ret = PTR_ERR(file);
+		return ERR_PTR(ret);
+	}
+
+	hist_data = find_compatible_hist(target_hist_data, file);
+	if (!hist_data)
+		return ERR_PTR(-EINVAL);
+
+	var_hist = kzalloc(sizeof(*var_hist), GFP_KERNEL);
+	if (!var_hist)
+		return ERR_PTR(-ENOMEM);
+
+	cmd = kzalloc(MAX_FILTER_STR_VAL, GFP_KERNEL);
+	if (!cmd) {
+		kfree(var_hist);
+		return ERR_PTR(-ENOMEM);
+	}
+
+	strcat(cmd, "keys=");
+
+	for_each_hist_key_field(i, hist_data) {
+		key_field = hist_data->fields[i];
+		if (!first)
+			strcat(cmd, ",");
+		strcat(cmd, key_field->field->name);
+		first = false;
+	}
+
+	strcat(cmd, ":synthetic_");
+	strcat(cmd, field_name);
+	strcat(cmd, "=");
+	strcat(cmd, field_name);
+
+	saved_filter = find_trigger_filter(hist_data, file);
+	if (saved_filter) {
+		strcat(cmd, " if ");
+		strcat(cmd, saved_filter);
+	}
+
+	var_hist->cmd = kstrdup(cmd, GFP_KERNEL);
+	if (!var_hist->cmd) {
+		kfree(cmd);
+		kfree(var_hist);
+		return ERR_PTR(-ENOMEM);
+	}
+
+	var_hist->hist_data = hist_data;
+
+	ret = event_hist_trigger_func(&trigger_hist_cmd, file,
+				      "", "hist", cmd);
+	if (ret) {
+		kfree(cmd);
+		kfree(var_hist->cmd);
+		kfree(var_hist);
+		return ERR_PTR(ret);
+	}
+
+	strcpy(cmd, "synthetic_");
+	strcat(cmd, field_name);
+
+	event_var = find_event_var(system, event_name, cmd);
+	if (!event_var) {
+		kfree(cmd);
+		kfree(var_hist->cmd);
+		kfree(var_hist);
+		return ERR_PTR(-EINVAL);
+	}
+
+	n = target_hist_data->n_field_var_hists;
+	target_hist_data->field_var_hists[n] = var_hist;
+	target_hist_data->n_field_var_hists++;
+
+	return event_var;
+}
+
+static struct hist_field *
+find_target_event_var(struct hist_trigger_data *hist_data,
+		      char *system, char *event_name, char *var_name)
+{
+	struct trace_event_file *file = hist_data->event_file;
+	struct hist_field *hist_field = NULL;
+
+	if (system) {
+		struct trace_event_call *call;
+
+		if (!event_name)
+			return NULL;
+
+		call = file->event_call;
+
+		if (strcmp(system, call->class->system) != 0)
+			return NULL;
+
+		if (strcmp(event_name, trace_event_name(call)) != 0)
+			return NULL;
+	}
+
+	hist_field = find_var_field(hist_data, var_name);
+
+	return hist_field;
+}
+
+static inline void __update_field_vars(struct tracing_map_elt *elt,
+				       struct ring_buffer_event *rbe,
+				       void *rec,
+				       struct field_var **field_vars,
+				       unsigned int n_field_vars,
+				       unsigned int field_var_str_start)
+{
+	struct hist_elt_data *elt_data = elt->private_data;
+	unsigned int i, j, var_idx;
+	u64 var_val;
+
+	for (i = 0, j = field_var_str_start; i < n_field_vars; i++) {
+		struct field_var *field_var = field_vars[i];
+		struct hist_field *var = field_var->var;
+		struct hist_field *val = field_var->val;
+
+		var_val = val->fn(val, elt, rbe, rec);
+		var_idx = var->var.idx;
+
+		if (val->flags & HIST_FIELD_FL_STRING) {
+			char *str = elt_data->field_var_str[j++];
+
+			memcpy(str, (char *)(uintptr_t)var_val,
+			       TASK_COMM_LEN + 1);
+			var_val = (u64)(uintptr_t)str;
+		}
+		tracing_map_set_var(elt, var_idx, var_val);
+	}
+}
+
+static void update_field_vars(struct hist_trigger_data *hist_data,
+			      struct tracing_map_elt *elt,
+			      struct ring_buffer_event *rbe,
+			      void *rec)
+{
+	__update_field_vars(elt, rbe, rec, hist_data->field_vars,
+			    hist_data->n_field_vars, 0);
+}
+
+static struct hist_field *create_var(struct hist_trigger_data *hist_data,
+				     struct trace_event_file *file,
+				     char *name, int size, const char *type)
+{
+	struct hist_field *var;
+	int idx;
+
+	if (find_var(file, name) && !hist_data->remove) {
+		var = ERR_PTR(-EINVAL);
+		goto out;
+	}
+
+	var = kzalloc(sizeof(struct hist_field), GFP_KERNEL);
+	if (!var) {
+		var = ERR_PTR(-ENOMEM);
+		goto out;
+	}
+
+	idx = tracing_map_add_var(hist_data->map);
+	if (idx < 0) {
+		kfree(var);
+		var = ERR_PTR(-EINVAL);
+		goto out;
+	}
+
+	var->flags = HIST_FIELD_FL_VAR;
+	var->var.idx = idx;
+	var->var.hist_data = var->hist_data = hist_data;
+	var->size = size;
+	var->var.name = kstrdup(name, GFP_KERNEL);
+	var->type = kstrdup(type, GFP_KERNEL);
+	if (!var->var.name || !var->type) {
+		kfree(var->var.name);
+		kfree(var->type);
+		kfree(var);
+		var = ERR_PTR(-ENOMEM);
+	}
+ out:
+	return var;
+}
+
+static struct field_var *create_field_var(struct hist_trigger_data *hist_data,
+					  struct trace_event_file *file,
+					  char *field_name)
+{
+	struct hist_field *val = NULL, *var = NULL;
+	unsigned long flags = HIST_FIELD_FL_VAR;
+	struct field_var *field_var;
+	int ret = 0;
+
+	if (hist_data->n_field_vars >= SYNTH_FIELDS_MAX) {
+		ret = -EINVAL;
+		goto err;
+	}
+
+	val = parse_atom(hist_data, file, field_name, &flags, NULL);
+	if (IS_ERR(val)) {
+		ret = PTR_ERR(val);
+		goto err;
+	}
+
+	var = create_var(hist_data, file, field_name, val->size, val->type);
+	if (IS_ERR(var)) {
+		kfree(val);
+		ret = PTR_ERR(var);
+		goto err;
+	}
+
+	field_var = kzalloc(sizeof(struct field_var), GFP_KERNEL);
+	if (!field_var) {
+		kfree(val);
+		kfree(var);
+		ret =  -ENOMEM;
+		goto err;
+	}
+
+	field_var->var = var;
+	field_var->val = val;
+ out:
+	return field_var;
+ err:
+	field_var = ERR_PTR(ret);
+	goto out;
+}
+
+static struct field_var *
+create_target_field_var(struct hist_trigger_data *hist_data,
+			char *system, char *event_name, char *var_name)
+{
+	struct trace_event_file *file = hist_data->event_file;
+
+	if (system) {
+		struct trace_event_call *call;
+
+		if (!event_name)
+			return NULL;
+
+		call = file->event_call;
+
+		if (strcmp(system, call->class->system) != 0)
+			return NULL;
+
+		if (strcmp(event_name, trace_event_name(call)) != 0)
+			return NULL;
+	}
+
+	return create_field_var(hist_data, file, var_name);
+}
+
+static void onmatch_destroy(struct action_data *data)
+{
+	unsigned int i;
+
+	kfree(data->match_event);
+	kfree(data->match_event_system);
+	kfree(data->synth_event_name);
+
+	for (i = 0; i < data->n_params; i++)
+		kfree(data->params[i]);
+
+	kfree(data);
+}
+
+static void destroy_field_var(struct field_var *field_var)
+{
+	if (!field_var)
+		return;
+
+	destroy_hist_field(field_var->var, 0);
+	destroy_hist_field(field_var->val, 0);
+
+	kfree(field_var);
+}
+
+static void destroy_field_vars(struct hist_trigger_data *hist_data)
+{
+	unsigned int i;
+
+	for (i = 0; i < hist_data->n_field_vars; i++)
+		destroy_field_var(hist_data->field_vars[i]);
+}
+
+static void save_field_var(struct hist_trigger_data *hist_data,
+			   struct field_var *field_var)
+{
+	hist_data->field_vars[hist_data->n_field_vars++] = field_var;
+
+	if (field_var->val->flags & HIST_FIELD_FL_STRING)
+		hist_data->n_field_var_str++;
+}
+
+static void destroy_synth_var_refs(struct hist_trigger_data *hist_data)
+{
+	unsigned int i;
+
+	for (i = 0; i < hist_data->n_synth_var_refs; i++)
+		destroy_hist_field(hist_data->synth_var_refs[i], 0);
+}
+
+static void save_synth_var_ref(struct hist_trigger_data *hist_data,
+			 struct hist_field *var_ref)
+{
+	hist_data->synth_var_refs[hist_data->n_synth_var_refs++] = var_ref;
+
+	hist_data->var_refs[hist_data->n_var_refs] = var_ref;
+	var_ref->var_ref_idx = hist_data->n_var_refs++;
+}
+
+static int check_synth_field(struct synth_event *event,
+			     struct hist_field *hist_field,
+			     unsigned int field_pos)
+{
+	struct synth_field *field;
+
+	if (field_pos >= event->n_fields)
+		return -EINVAL;
+
+	field = event->fields[field_pos];
+
+	if (strcmp(field->type, hist_field->type) != 0)
+		return -EINVAL;
+
+	return 0;
+}
+
+static int parse_action_params(char *params, struct action_data *data)
+{
+	char *param, *saved_param;
+	int ret = 0;
+
+	while (params) {
+		if (data->n_params >= SYNTH_FIELDS_MAX)
+			goto out;
+
+		param = strsep(&params, ",");
+		if (!param)
+			goto out;
+
+		param = strstrip(param);
+		if (strlen(param) < 2) {
+			ret = -EINVAL;
+			goto out;
+		}
+
+		saved_param = kstrdup(param, GFP_KERNEL);
+		if (!saved_param) {
+			ret = -ENOMEM;
+			goto out;
+		}
+
+		data->params[data->n_params++] = saved_param;
+	}
+ out:
+	return ret;
+}
+
+static struct hist_field *
+onmatch_find_var(struct hist_trigger_data *hist_data, struct action_data *data,
+		 char *system, char *event, char *var)
+{
+	struct hist_field *hist_field;
+
+	var++; /* skip '$' */
+
+	hist_field = find_target_event_var(hist_data, system, event, var);
+	if (!hist_field) {
+		if (!system) {
+			system = data->match_event_system;
+			event = data->match_event;
+		}
+
+		hist_field = find_event_var(system, event, var);
+	}
+
+	return hist_field;
+}
+
+static struct hist_field *
+onmatch_create_field_var(struct hist_trigger_data *hist_data,
+			 struct action_data *data, char *system,
+			 char *event, char *var)
+{
+	struct hist_field *hist_field = NULL;
+	struct field_var *field_var;
+
+	field_var = create_target_field_var(hist_data, system, event, var);
+	if (IS_ERR(field_var))
+		goto out;
+
+	if (field_var) {
+		save_field_var(hist_data, field_var);
+		hist_field = field_var->var;
+	} else {
+		if (!system) {
+			system = data->match_event_system;
+			event = data->match_event;
+		}
+
+		hist_field = create_field_var_hist(hist_data, system, event, var);
+		if (IS_ERR(hist_field))
+			goto free;
+	}
+ out:
+	return hist_field;
+ free:
+	destroy_field_var(field_var);
+	hist_field = NULL;
+	goto out;
+}
+
+static int onmatch_create(struct hist_trigger_data *hist_data,
+			  struct trace_event_file *file,
+			  struct action_data *data)
+{
+	char *event_name, *param, *system = NULL;
+	struct hist_field *hist_field, *var_ref;
+	unsigned int i, var_ref_idx;
+	unsigned int field_pos = 0;
+	struct synth_event *event;
+	int ret = 0;
+
+	mutex_lock(&synth_event_mutex);
+
+	event = find_synth_event(data->synth_event_name);
+	if (!event) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	var_ref_idx = hist_data->n_var_refs;
+
+	for (i = 0; i < data->n_params; i++) {
+		char *p;
+
+		p = param = kstrdup(data->params[i], GFP_KERNEL);
+		if (!param)
+			goto out;
+
+		system = strsep(&param, ".");
+		if (!param) {
+			param = (char *)system;
+			system = event_name = NULL;
+		} else {
+			event_name = strsep(&param, ".");
+			if (!param) {
+				kfree(p);
+				ret = -EINVAL;
+				goto out;
+			}
+		}
+
+		if (param[0] == '$')
+			hist_field = onmatch_find_var(hist_data, data, system,
+						      event_name, param);
+		else
+			hist_field = onmatch_create_field_var(hist_data, data,
+							      system,
+							      event_name,
+							      param);
+
+		if (!hist_field) {
+			kfree(p);
+			ret = -EINVAL;
+			goto out;
+		}
+
+		if (check_synth_field(event, hist_field, field_pos) == 0) {
+			var_ref = create_var_ref(hist_field);
+			if (!var_ref) {
+				kfree(p);
+				ret = -ENOMEM;
+				goto out;
+			}
+
+			save_synth_var_ref(hist_data, var_ref);
+			field_pos++;
+			kfree(p);
+			continue;
+		}
+
+		kfree(p);
+		ret = -EINVAL;
+		goto out;
+	}
+
+	if (field_pos != event->n_fields) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	data->fn = action_trace;
+	data->synth_event = event;
+	data->var_ref_idx = var_ref_idx;
+	hist_data->actions[hist_data->n_actions++] = data;
+	save_hist_actions(hist_data);
+ out:
+	mutex_unlock(&synth_event_mutex);
+
+	return ret;
+}
+
+static struct action_data *onmatch_parse(char *str)
+{
+	char *match_event, *match_event_system;
+	char *synth_event_name, *params;
+	struct action_data *data;
+	int ret = -EINVAL;
+
+	data = kzalloc(sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return ERR_PTR(-ENOMEM);
+
+	match_event = strsep(&str, ")");
+	if (!match_event || !str)
+		goto free;
+
+	match_event_system = strsep(&match_event, ".");
+	if (!match_event)
+		goto free;
+
+	if (IS_ERR(event_file(match_event_system, match_event)))
+		goto free;
+
+	data->match_event = kstrdup(match_event, GFP_KERNEL);
+	data->match_event_system = kstrdup(match_event_system, GFP_KERNEL);
+
+	strsep(&str, ".");
+	if (!str)
+		goto free;
+
+	synth_event_name = strsep(&str, "(");
+	if (!synth_event_name || !str)
+		goto free;
+	data->synth_event_name = kstrdup(synth_event_name, GFP_KERNEL);
+
+	params = strsep(&str, ")");
+	if (!params || !str || (str && strlen(str)))
+		goto free;
+
+	ret = parse_action_params(params, data);
+	if (ret)
+		goto free;
+
+	if (!data->match_event_system || !data->match_event ||
+	    !data->synth_event_name) {
+		ret = -ENOMEM;
+		goto free;
+	}
+ out:
+	return data;
+ free:
+	onmatch_destroy(data);
+	data = ERR_PTR(ret);
+	goto out;
+}
+
 static int create_hitcount_val(struct hist_trigger_data *hist_data)
 {
 	hist_data->fields[HITCOUNT_IDX] =
@@ -2465,19 +3311,37 @@ static void destroy_actions(struct hist_trigger_data *hist_data)
 	for (i = 0; i < hist_data->n_actions; i++) {
 		struct action_data *data = hist_data->actions[i];
 
-		kfree(data);
+		if (data->fn == action_trace)
+			onmatch_destroy(data);
+		else
+			kfree(data);
 	}
 }
 
 static int create_actions(struct hist_trigger_data *hist_data,
 			  struct trace_event_file *file)
 {
+	struct action_data *data;
 	unsigned int i;
 	int ret = 0;
 	char *str;
 
 	for (i = 0; i < hist_data->attrs->n_actions; i++) {
 		str = hist_data->attrs->action_str[i];
+
+		if (strncmp(str, "onmatch(", strlen("onmatch(")) == 0) {
+			char *action_str = str + strlen("onmatch(");
+
+			data = onmatch_parse(action_str);
+			if (IS_ERR(data))
+				return PTR_ERR(data);
+
+			ret = onmatch_create(hist_data, file, data);
+			if (ret) {
+				onmatch_destroy(data);
+				return ret;
+			}
+		}
 	}
 
 	return ret;
@@ -2494,6 +3358,26 @@ static void print_actions(struct seq_file *m,
 	}
 }
 
+static void print_onmatch_spec(struct seq_file *m,
+			       struct hist_trigger_data *hist_data,
+			       struct action_data *data)
+{
+	unsigned int i;
+
+	seq_printf(m, ":onmatch(%s.%s).", data->match_event_system,
+		   data->match_event);
+
+	seq_printf(m, "%s(", data->synth_event->name);
+
+	for (i = 0; i < data->n_params; i++) {
+		if (i)
+			seq_puts(m, ",");
+		seq_printf(m, "%s", data->params[i]);
+	}
+
+	seq_puts(m, ")");
+}
+
 static void print_actions_spec(struct seq_file *m,
 			       struct hist_trigger_data *hist_data)
 {
@@ -2501,6 +3385,19 @@ static void print_actions_spec(struct seq_file *m,
 
 	for (i = 0; i < hist_data->n_actions; i++) {
 		struct action_data *data = hist_data->actions[i];
+
+		if (data->fn == action_trace)
+			print_onmatch_spec(m, hist_data, data);
+	}
+}
+
+static void destroy_field_var_hists(struct hist_trigger_data *hist_data)
+{
+	unsigned int i;
+
+	for (i = 0; i < hist_data->n_field_var_hists; i++) {
+		kfree(hist_data->field_var_hists[i]->cmd);
+		kfree(hist_data->field_var_hists[i]);
 	}
 }
 
@@ -2514,6 +3411,9 @@ static void destroy_hist_data(struct hist_trigger_data *hist_data)
 	tracing_map_destroy(hist_data->map);
 
 	destroy_actions(hist_data);
+	destroy_field_vars(hist_data);
+	destroy_field_var_hists(hist_data);
+	destroy_synth_var_refs(hist_data);
 
 	kfree(hist_data);
 }
@@ -2648,6 +3548,8 @@ static void hist_trigger_elt_update(struct hist_trigger_data *hist_data,
 			tracing_map_set_var(elt, var_idx, hist_val);
 		}
 	}
+
+	update_field_vars(hist_data, elt, rbe, rec);
 }
 
 static inline void add_to_key(char *compound_key, void *key,
@@ -2861,6 +3763,8 @@ static void hist_trigger_stacktrace_print(struct seq_file *m,
 		}
 	}
 
+	print_actions(m, hist_data, elt);
+
 	seq_puts(m, "\n");
 }
 
@@ -3128,6 +4032,8 @@ static void event_hist_trigger_free(struct event_trigger_ops *ops,
 
 		remove_hist_vars(hist_data);
 
+		remove_hist_actions(hist_data);
+
 		destroy_hist_data(hist_data);
 	}
 }
@@ -3390,6 +4296,21 @@ static bool hist_trigger_check_refs(struct event_trigger_data *data,
 	return false;
 }
 
+static void unregister_field_var_hists(struct hist_trigger_data *hist_data)
+{
+	struct trace_event_file *file;
+	unsigned int i;
+	char *cmd;
+	int ret;
+
+	for (i = 0; i < hist_data->n_field_var_hists; i++) {
+		file = hist_data->field_var_hists[i]->hist_data->event_file;
+		cmd = hist_data->field_var_hists[i]->cmd;
+		ret = event_hist_trigger_func(&trigger_hist_cmd, file,
+					      "!hist", "hist", cmd);
+	}
+}
+
 static void hist_unregister_trigger(char *glob, struct event_trigger_ops *ops,
 				    struct event_trigger_data *data,
 				    struct trace_event_file *file)
@@ -3405,6 +4326,7 @@ static void hist_unregister_trigger(char *glob, struct event_trigger_ops *ops,
 		if (test->cmd_ops->trigger_type == ETT_EVENT_HIST) {
 			if (!hist_trigger_match(data, test, named_data, false))
 				continue;
+			unregister_field_var_hists(test->private_data);
 			unregistered = true;
 			list_del_rcu(&test->list);
 			trace_event_trigger_enable_disable(file, 0);
@@ -3448,6 +4370,7 @@ static void hist_unreg_all(struct trace_event_file *file)
 
 	list_for_each_entry_safe(test, n, &file->triggers, list) {
 		if (test->cmd_ops->trigger_type == ETT_EVENT_HIST) {
+			unregister_field_var_hists(test->private_data);
 			list_del_rcu(&test->list);
 			trace_event_trigger_enable_disable(file, 0);
 			update_cond_flag(file);
@@ -3571,6 +4494,8 @@ static int event_hist_trigger_func(struct event_command *cmd_ops,
 
 	remove_hist_vars(hist_data);
 
+	remove_hist_actions(hist_data);
+
 	kfree(trigger_data);
 	destroy_hist_data(hist_data);
 
-- 
1.9.3

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