[PATCH 6.18.y 1/4] tracing: Fix fully-qualified variable reference printing in histograms

[Sasha Levin <sashal@kernel.org>]

From: Tom Zanussi <zanussi@kernel.org>

[ Upstream commit 9236eebd138aa2753f7b30fc6cee7b7202841247 ]

The syntax for fully-qualified variable references in histograms is
subsys.event.$var, which is parsed correctly, but not displayed correctly
when printing a histogram spec. The current code puts the $ reference at
the beginning of the fully-qualified variable name i.e. $subsys.event.var,
which is incorrect.

Before:

trigger info: hist:keys=next_comm:vals=hitcount:wakeup_lat=common_timestamp.usecs-$sched.sched_wakeup.ts0: ...

After:

trigger info: hist:keys=next_comm:vals=hitcount:wakeup_lat=common_timestamp.usecs-sched.sched_wakeup.$ts0: ...

Link: https://patch.msgid.link/5dee9a86d062a4dd68c2214f3d90ac93811e1951.1776112478.git.zanussi@kernel.org
Signed-off-by: Tom Zanussi <zanussi@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Stable-dep-of: a0777b9e5315 ("tracing: Fix NULL dereference when copying keys for a field variable")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/trace/trace_events_hist.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 20d23a08b5b8b..dab2b3dc176b9 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -1355,9 +1355,12 @@ static const char *hist_field_name(struct hist_field *field,
 		 field->flags & HIST_FIELD_FL_VAR_REF) {
 		if (field->system) {
 			static char full_name[MAX_FILTER_STR_VAL];
+			static char *fmt;
 			int len;
 
-			len = snprintf(full_name, sizeof(full_name), "%s.%s.%s",
+			fmt = field->flags & HIST_FIELD_FL_VAR_REF ? "%s.%s.$%s" : "%s.%s.%s";
+
+			len = snprintf(full_name, sizeof(full_name), fmt,
 				       field->system, field->event_name,
 				       field->name);
 			if (len < sizeof(full_name))
@@ -1734,9 +1737,10 @@ static const char *get_hist_field_flags(struct hist_field *hist_field)
 
 static void expr_field_str(struct hist_field *field, char *expr)
 {
-	if (field->flags & HIST_FIELD_FL_VAR_REF)
-		strcat(expr, "$");
-	else if (field->flags & HIST_FIELD_FL_CONST) {
+	if (field->flags & HIST_FIELD_FL_VAR_REF) {
+		if (!field->system)
+			strcat(expr, "$");
+	} else if (field->flags & HIST_FIELD_FL_CONST) {
 		char str[HIST_CONST_DIGITS_MAX];
 
 		snprintf(str, HIST_CONST_DIGITS_MAX, "%llu", field->constant);
@@ -6167,7 +6171,8 @@ static void hist_field_print(struct seq_file *m, struct hist_field *hist_field)
 	else if (field_name) {
 		if (hist_field->flags & HIST_FIELD_FL_VAR_REF ||
 		    hist_field->flags & HIST_FIELD_FL_ALIAS)
-			seq_putc(m, '$');
+			if (!hist_field->system)
+				seq_putc(m, '$');
 		seq_printf(m, "%s", field_name);
 	} else if (hist_field->flags & HIST_FIELD_FL_TIMESTAMP)
 		seq_puts(m, "common_timestamp");
-- 
2.53.0