[PATCH v6] tracing: Preserve repeated boot-time tracing parameters

[Wesley Atwell <atwellwea@gmail.com>]

Some tracing boot parameters already accept delimited value lists, but
their __setup() handlers keep only the last instance seen at boot.
Make repeated instances append to the same boot-time buffer in the
format each parser already consumes.

Use a shared trace_append_boot_param() helper for the ftrace filters,
trace_options, and kprobe_event boot parameters. trace_trigger=
still tokenizes a temporary parse buffer in place, but now copies each
parsed event/trigger pair into boot-time storage so repeated instances
do not overwrite earlier ones.

This also lets Bootconfig array values work naturally when they expand
to repeated param=value entries.

Before this change, only the last instance from each repeated
parameter survived boot.

Signed-off-by: Wesley Atwell <atwellwea@gmail.com>
---
Changes since v5: https://lore.kernel.org/all/20260328201842.1782806-1-atwellwea@gmail.com/
- add the separator accounting comment in trace_append_boot_param()
- keep the existing trace_trigger= temporary buffer and copy each
  parsed event/trigger pair into boot-time storage instead of tracking
  a running offset inside that buffer

 kernel/trace/ftrace.c       | 12 ++++++++----
 kernel/trace/trace.c        | 30 +++++++++++++++++++++++++++++-
 kernel/trace/trace.h        |  2 ++
 kernel/trace/trace_events.c | 24 +++++++++++++++++++++---
 kernel/trace/trace_kprobe.c |  3 ++-
 5 files changed, 62 insertions(+), 9 deletions(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 413310912609..8bd3dd1d549c 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -6841,7 +6841,8 @@ bool ftrace_filter_param __initdata;
 static int __init set_ftrace_notrace(char *str)
 {
 	ftrace_filter_param = true;
-	strscpy(ftrace_notrace_buf, str, FTRACE_FILTER_SIZE);
+	trace_append_boot_param(ftrace_notrace_buf, str, ',',
+				FTRACE_FILTER_SIZE);
 	return 1;
 }
 __setup("ftrace_notrace=", set_ftrace_notrace);
@@ -6849,7 +6850,8 @@ __setup("ftrace_notrace=", set_ftrace_notrace);
 static int __init set_ftrace_filter(char *str)
 {
 	ftrace_filter_param = true;
-	strscpy(ftrace_filter_buf, str, FTRACE_FILTER_SIZE);
+	trace_append_boot_param(ftrace_filter_buf, str, ',',
+				FTRACE_FILTER_SIZE);
 	return 1;
 }
 __setup("ftrace_filter=", set_ftrace_filter);
@@ -6861,14 +6863,16 @@ static int ftrace_graph_set_hash(struct ftrace_hash *hash, char *buffer);
 
 static int __init set_graph_function(char *str)
 {
-	strscpy(ftrace_graph_buf, str, FTRACE_FILTER_SIZE);
+	trace_append_boot_param(ftrace_graph_buf, str, ',',
+				FTRACE_FILTER_SIZE);
 	return 1;
 }
 __setup("ftrace_graph_filter=", set_graph_function);
 
 static int __init set_graph_notrace_function(char *str)
 {
-	strscpy(ftrace_graph_notrace_buf, str, FTRACE_FILTER_SIZE);
+	trace_append_boot_param(ftrace_graph_notrace_buf, str, ',',
+				FTRACE_FILTER_SIZE);
 	return 1;
 }
 __setup("ftrace_graph_notrace=", set_graph_notrace_function);
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index a626211ceb9a..2fbfcb506b24 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -228,6 +228,33 @@ static int boot_instance_index;
 static char boot_snapshot_info[COMMAND_LINE_SIZE] __initdata;
 static int boot_snapshot_index;
 
+/*
+ * Repeated boot parameters, including Bootconfig array expansions, need
+ * to stay in the delimiter form that the existing parser consumes.
+ */
+void __init trace_append_boot_param(char *buf, const char *str, char sep,
+				    int size)
+{
+	int len, needed, str_len;
+
+	if (!*str)
+		return;
+
+	len = strlen(buf);
+	str_len = strlen(str);
+	needed = len + str_len + 1;
+	/* For continuation, account for the separator. */
+	if (len)
+		needed++;
+	if (needed > size)
+		return;
+
+	if (len)
+		buf[len++] = sep;
+
+	strscpy(buf + len, str, size - len);
+}
+
 static int __init set_cmdline_ftrace(char *str)
 {
 	strscpy(bootup_tracer_buf, str, MAX_TRACER_SIZE);
@@ -329,7 +356,8 @@ static char trace_boot_options_buf[MAX_TRACER_SIZE] __initdata;
 
 static int __init set_trace_boot_options(char *str)
 {
-	strscpy(trace_boot_options_buf, str, MAX_TRACER_SIZE);
+	trace_append_boot_param(trace_boot_options_buf, str, ',',
+				MAX_TRACER_SIZE);
 	return 1;
 }
 __setup("trace_options=", set_trace_boot_options);
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index b8f3804586a0..237a0417de1c 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -863,6 +863,8 @@ extern int DYN_FTRACE_TEST_NAME(void);
 extern int DYN_FTRACE_TEST_NAME2(void);
 
 extern void trace_set_ring_buffer_expanded(struct trace_array *tr);
+void __init trace_append_boot_param(char *buf, const char *str,
+				    char sep, int size);
 extern bool tracing_selftest_disabled;
 
 #ifdef CONFIG_FTRACE_STARTUP_TEST
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 249d1cba72c0..1c4a4a46169e 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -17,6 +17,7 @@
 #include <linux/kthread.h>
 #include <linux/tracefs.h>
 #include <linux/uaccess.h>
+#include <linux/memblock.h>
 #include <linux/module.h>
 #include <linux/ctype.h>
 #include <linux/sort.h>
@@ -3674,7 +3675,7 @@ trace_create_new_event(struct trace_event_call *call,
 #define MAX_BOOT_TRIGGERS 32
 
 static struct boot_triggers {
-	const char		*event;
+	char			*event;
 	char			*trigger;
 } bootup_triggers[MAX_BOOT_TRIGGERS];
 
@@ -3683,6 +3684,7 @@ static int nr_boot_triggers;
 
 static __init int setup_trace_triggers(char *str)
 {
+	char *event;
 	char *trigger;
 	char *buf;
 	int i;
@@ -3692,14 +3694,30 @@ static __init int setup_trace_triggers(char *str)
 	disable_tracing_selftest("running event triggers");
 
 	buf = bootup_trigger_buf;
-	for (i = 0; i < MAX_BOOT_TRIGGERS; i++) {
+	for (i = nr_boot_triggers; i < MAX_BOOT_TRIGGERS; i++) {
 		trigger = strsep(&buf, ",");
 		if (!trigger)
 			break;
-		bootup_triggers[i].event = strsep(&trigger, ".");
+		event = strsep(&trigger, ".");
 		bootup_triggers[i].trigger = trigger;
 		if (!bootup_triggers[i].trigger)
 			break;
+
+		/*
+		 * Keep each parsed trigger outside the temporary setup
+		 * buffer so repeated trace_trigger= entries do not
+		 * overwrite earlier ones.
+		 */
+		bootup_triggers[i].event =
+			memblock_alloc_or_panic(strlen(event) + 1,
+						SMP_CACHE_BYTES);
+		strscpy(bootup_triggers[i].event, event,
+			strlen(event) + 1);
+		bootup_triggers[i].trigger =
+			memblock_alloc_or_panic(strlen(trigger) + 1,
+						SMP_CACHE_BYTES);
+		strscpy(bootup_triggers[i].trigger, trigger,
+			strlen(trigger) + 1);
 	}
 
 	nr_boot_triggers = i;
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index a5dbb72528e0..e9f1c55aea64 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -31,7 +31,8 @@ static char kprobe_boot_events_buf[COMMAND_LINE_SIZE] __initdata;
 
 static int __init set_kprobe_boot_events(char *str)
 {
-	strscpy(kprobe_boot_events_buf, str, COMMAND_LINE_SIZE);
+	trace_append_boot_param(kprobe_boot_events_buf, str, ';',
+				COMMAND_LINE_SIZE);
 	disable_tracing_selftest("running kprobe events");
 
 	return 1;
-- 
2.43.0