tracing/filters: improve subsystem filter

Currently a subsystem filter should be applicable to all events
under the subsystem, and if it failed, all the event filters
will be cleared. Those behaviors make subsys filter much less
useful:

  # echo 'vec == 1' > irq/softirq_entry/filter
  # echo 'irq == 5' > irq/filter
  bash: echo: write error: Invalid argument
  # cat irq/softirq_entry/filter
  none

I'd expect it set the filter for irq_handler_entry/exit, and
not touch softirq_entry/exit.

The basic idea is, try to see if the filter can be applied
to which events, and then just apply to the those events:

  # echo 'vec == 1' > softirq_entry/filter
  # echo 'irq == 5' > filter
  # cat irq_handler_entry/filter
  irq == 5
  # cat softirq_entry/filter
  vec == 1

Changelog for v2:
- do some cleanups to address Frederic's comments.

Inspired-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <4A63D485.7030703@cn.fujitsu.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

include/linux/ftrace_event.h

@@ -101,6 +101,8 @@ void trace_current_buffer_discard_commit(struct ring_buffer_event *event);
 
 void tracing_record_cmdline(struct task_struct *tsk);
 
+struct event_filter;
+
 struct ftrace_event_call {
 	struct list_head	list;
 	char			*name;
@@ -116,7 +118,7 @@ struct ftrace_event_call {
 	int			(*define_fields)(void);
 	struct list_head	fields;
 	int			filter_active;
-	void			*filter;
+	struct event_filter	*filter;
 	void			*mod;
 
 #ifdef CONFIG_EVENT_PROFILE

kernel/trace/trace.h

@@ -750,13 +750,14 @@ struct event_filter {
 	int			n_preds;
 	struct filter_pred	**preds;
 	char			*filter_string;
+	bool			no_reset;
 };
 
 struct event_subsystem {
 	struct list_head	list;
 	const char		*name;
 	struct dentry		*entry;
-	void			*filter;
+	struct event_filter	*filter;
 	int			nr_events;
 };
 

kernel/trace/trace_events_filter.c

@@ -420,7 +420,14 @@ int init_preds(struct ftrace_event_call *call)
 }
 EXPORT_SYMBOL_GPL(init_preds);
 
-static void filter_free_subsystem_preds(struct event_subsystem *system)
+enum {
+	FILTER_DISABLE_ALL,
+	FILTER_INIT_NO_RESET,
+	FILTER_SKIP_NO_RESET,
+};
+
+static void filter_free_subsystem_preds(struct event_subsystem *system,
+					int flag)
 {
 	struct ftrace_event_call *call;
 
@@ -428,6 +435,14 @@ static void filter_free_subsystem_preds(struct event_subsystem *system)
 		if (!call->define_fields)
 			continue;
 
+		if (flag == FILTER_INIT_NO_RESET) {
+			call->filter->no_reset = false;
+			continue;
+		}
+
+		if (flag == FILTER_SKIP_NO_RESET && call->filter->no_reset)
+			continue;
+
 		if (!strcmp(call->system, system->name)) {
 			filter_disable_preds(call);
 			remove_filter_string(call->filter);
@@ -529,7 +544,8 @@ static filter_pred_fn_t select_comparison_fn(int op, int field_size,
 
 static int filter_add_pred(struct filter_parse_state *ps,
 			   struct ftrace_event_call *call,
-			   struct filter_pred *pred)
+			   struct filter_pred *pred,
+			   bool dry_run)
 {
 	struct ftrace_event_field *field;
 	filter_pred_fn_t fn;
@@ -541,10 +557,12 @@ static int filter_add_pred(struct filter_parse_state *ps,
 
 	if (pred->op == OP_AND) {
 		pred->pop_n = 2;
-		return filter_add_pred_fn(ps, call, pred, filter_pred_and);
+		fn = filter_pred_and;
+		goto add_pred_fn;
 	} else if (pred->op == OP_OR) {
 		pred->pop_n = 2;
-		return filter_add_pred_fn(ps, call, pred, filter_pred_or);
+		fn = filter_pred_or;
+		goto add_pred_fn;
 	}
 
 	field = find_event_field(call, pred->field_name);
@@ -567,9 +585,6 @@ static int filter_add_pred(struct filter_parse_state *ps,
 		else
 			fn = filter_pred_strloc;
 		pred->str_len = field->size;
-		if (pred->op == OP_NE)
-			pred->not = 1;
-		return filter_add_pred_fn(ps, call, pred, fn);
 	} else {
 		if (field->is_signed)
 			ret = strict_strtoll(pred->str_val, 0, &val);
@@ -580,27 +595,33 @@ static int filter_add_pred(struct filter_parse_state *ps,
 			return -EINVAL;
 		}
 		pred->val = val;
-	}
 
-	fn = select_comparison_fn(pred->op, field->size, field->is_signed);
-	if (!fn) {
-		parse_error(ps, FILT_ERR_INVALID_OP, 0);
-		return -EINVAL;
+		fn = select_comparison_fn(pred->op, field->size,
+					  field->is_signed);
+		if (!fn) {
+			parse_error(ps, FILT_ERR_INVALID_OP, 0);
+			return -EINVAL;
+		}
 	}
 
 	if (pred->op == OP_NE)
 		pred->not = 1;
 
-	return filter_add_pred_fn(ps, call, pred, fn);
+add_pred_fn:
+	if (!dry_run)
+		return filter_add_pred_fn(ps, call, pred, fn);
+	return 0;
 }
 
 static int filter_add_subsystem_pred(struct filter_parse_state *ps,
 				     struct event_subsystem *system,
 				     struct filter_pred *pred,
-				     char *filter_string)
+				     char *filter_string,
+				     bool dry_run)
 {
 	struct ftrace_event_call *call;
 	int err = 0;
+	bool fail = true;
 
 	list_for_each_entry(call, &ftrace_events, list) {
 
@@ -610,16 +631,24 @@ static int filter_add_subsystem_pred(struct filter_parse_state *ps,
 		if (strcmp(call->system, system->name))
 			continue;
 
-		err = filter_add_pred(ps, call, pred);
-		if (err) {
-			filter_free_subsystem_preds(system);
-			parse_error(ps, FILT_ERR_BAD_SUBSYS_FILTER, 0);
-			goto out;
-		}
-		replace_filter_string(call->filter, filter_string);
+		if (call->filter->no_reset)
+			continue;
+
+		err = filter_add_pred(ps, call, pred, dry_run);
+		if (err)
+			call->filter->no_reset = true;
+		else
+			fail = false;
+
+		if (!dry_run)
+			replace_filter_string(call->filter, filter_string);
 	}
-out:
-	return err;
+
+	if (fail) {
+		parse_error(ps, FILT_ERR_BAD_SUBSYS_FILTER, 0);
+		return err;
+	}
+	return 0;
 }
 
 static void parse_init(struct filter_parse_state *ps,
@@ -978,12 +1007,14 @@ static int check_preds(struct filter_parse_state *ps)
 static int replace_preds(struct event_subsystem *system,
 			 struct ftrace_event_call *call,
 			 struct filter_parse_state *ps,
-			 char *filter_string)
+			 char *filter_string,
+			 bool dry_run)
 {
 	char *operand1 = NULL, *operand2 = NULL;
 	struct filter_pred *pred;
 	struct postfix_elt *elt;
 	int err;
+	int n_preds = 0;
 
 	err = check_preds(ps);
 	if (err)
@@ -1002,19 +1033,14 @@ static int replace_preds(struct event_subsystem *system,
 			continue;
 		}
 
+		if (n_preds++ == MAX_FILTER_PRED) {
+			parse_error(ps, FILT_ERR_TOO_MANY_PREDS, 0);
+			return -ENOSPC;
+		}
+
 		if (elt->op == OP_AND || elt->op == OP_OR) {
 			pred = create_logical_pred(elt->op);
-			if (call)
-				err = filter_add_pred(ps, call, pred);
-			else
-				err = filter_add_subsystem_pred(ps, system,
-							pred, filter_string);
-			filter_free_pred(pred);
-			if (err)
-				return err;
-
-			operand1 = operand2 = NULL;
-			continue;
+			goto add_pred;
 		}
 
 		if (!operand1 || !operand2) {
@@ -1023,11 +1049,12 @@ static int replace_preds(struct event_subsystem *system,
 		}
 
 		pred = create_pred(elt->op, operand1, operand2);
+add_pred:
 		if (call)
-			err = filter_add_pred(ps, call, pred);
+			err = filter_add_pred(ps, call, pred, false);
 		else
 			err = filter_add_subsystem_pred(ps, system, pred,
-							filter_string);
+						filter_string, dry_run);
 		filter_free_pred(pred);
 		if (err)
 			return err;
@@ -1068,7 +1095,7 @@ int apply_event_filter(struct ftrace_event_call *call, char *filter_string)
 		goto out;
 	}
 
-	err = replace_preds(NULL, call, ps, filter_string);
+	err = replace_preds(NULL, call, ps, filter_string, false);
 	if (err)
 		append_filter_err(ps, call->filter);
 
@@ -1092,7 +1119,7 @@ int apply_subsystem_event_filter(struct event_subsystem *system,
 	mutex_lock(&event_mutex);
 
 	if (!strcmp(strstrip(filter_string), "0")) {
-		filter_free_subsystem_preds(system);
+		filter_free_subsystem_preds(system, FILTER_DISABLE_ALL);
 		remove_filter_string(system->filter);
 		mutex_unlock(&event_mutex);
 		return 0;
@@ -1103,7 +1130,6 @@ int apply_subsystem_event_filter(struct event_subsystem *system,
 	if (!ps)
 		goto out_unlock;
 
-	filter_free_subsystem_preds(system);
 	replace_filter_string(system->filter, filter_string);
 
 	parse_init(ps, filter_ops, filter_string);
@@ -1113,9 +1139,23 @@ int apply_subsystem_event_filter(struct event_subsystem *system,
 		goto out;
 	}
 
-	err = replace_preds(system, NULL, ps, filter_string);
-	if (err)
+	filter_free_subsystem_preds(system, FILTER_INIT_NO_RESET);
+
+	/* try to see the filter can be applied to which events */
+	err = replace_preds(system, NULL, ps, filter_string, true);
+	if (err) {
 		append_filter_err(ps, system->filter);
+		goto out;
+	}
+
+	filter_free_subsystem_preds(system, FILTER_SKIP_NO_RESET);
+
+	/* really apply the filter to the events */
+	err = replace_preds(system, NULL, ps, filter_string, false);
+	if (err) {
+		append_filter_err(ps, system->filter);
+		filter_free_subsystem_preds(system, 2);
+	}
 
 out:
 	filter_opstack_clear(ps);