linux-kernel - Re: Unresolved reference for histogram variable

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Message-ID: <20200116165658.4e8d15fb@gandalf.local.home>
Date:   Thu, 16 Jan 2020 16:56:58 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Tom Zanussi <zanussi@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: Re: Unresolved reference for histogram variable

On Thu, 16 Jan 2020 15:42:16 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> in parse_expr():
> 
> 	operand1->read_once = true;
> 	operand2->read_once = true;
> 
> Why is that?
> 
> This means that any variable used in an expression can not be use later
> on.
> 
> Or should the variable be detected that it is used multiple times in
> the expression, and have the parser detect this, and just reuse the
> same variable multiple times?

This patch seems to fix the problem, and lets us reuse the same
variable multiple times.

-- Steve

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 117a1202a6b9..b7f944735a4a 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -116,6 +116,7 @@ struct hist_field {
 	struct ftrace_event_field	*field;
 	unsigned long			flags;
 	hist_field_fn_t			fn;
+	unsigned int			ref;
 	unsigned int			size;
 	unsigned int			offset;
 	unsigned int                    is_signed;
@@ -2432,8 +2433,16 @@ static int contains_operator(char *str)
 	return field_op;
 }
 
+static void get_hist_field(struct hist_field *hist_field)
+{
+	hist_field->ref++;
+}
+
 static void __destroy_hist_field(struct hist_field *hist_field)
 {
+	if (--hist_field->ref > 1)
+		return;
+
 	kfree(hist_field->var.name);
 	kfree(hist_field->name);
 	kfree(hist_field->type);
@@ -2475,6 +2484,8 @@ static struct hist_field *create_hist_field(struct hist_trigger_data *hist_data,
 	if (!hist_field)
 		return NULL;
 
+	hist_field->ref = 1;
+
 	hist_field->hist_data = hist_data;
 
 	if (flags & HIST_FIELD_FL_EXPR || flags & HIST_FIELD_FL_ALIAS)
@@ -2670,6 +2681,19 @@ static struct hist_field *create_var_ref(struct hist_trigger_data *hist_data,
 {
 	unsigned long flags = HIST_FIELD_FL_VAR_REF;
 	struct hist_field *ref_field;
+	int i;
+
+	for (i = 0; i < hist_data->n_var_refs; i++) {
+		ref_field = hist_data->var_refs[i];
+		/* Maybe this is overkill? */
+		if (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) {
+			get_hist_field(ref_field);
+			return ref_field;
+		}
+	}
 
 	ref_field = create_hist_field(var_field->hist_data, NULL, flags, NULL);
 	if (ref_field) {