[PATCH v2] tracing: kprobe-event: Return directly when trace kprobes is empty

[sunliming@linux.dev]

From: sunliming <sunliming@kylinos.cn>

In enable_boot_kprobe_events(), it returns directly when trace kprobes is
empty, thereby reducing the function's execution time. This function may
otherwise wait for the event_mutex lock for tens of milliseconds on certain
machines, which is unnecessary when trace kprobes is empty.

Signed-off-by: sunliming <sunliming@kylinos.cn>
---
v2:
- wrap the the null check for the dyn_event_list with macro trace_kprobe_list_empty
---
 kernel/trace/trace_kprobe.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 9953506370a5..95f2c42603d5 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -82,6 +82,7 @@ static struct trace_kprobe *to_trace_kprobe(struct dyn_event *ev)
 #define for_each_trace_kprobe(pos, dpos)	\
 	for_each_dyn_event(dpos)		\
 		if (is_trace_kprobe(dpos) && (pos = to_trace_kprobe(dpos)))
+#define trace_kprobe_list_empty() list_empty(&dyn_event_list)
 
 static nokprobe_inline bool trace_kprobe_is_return(struct trace_kprobe *tk)
 {
@@ -1982,6 +1983,9 @@ static __init void enable_boot_kprobe_events(void)
 	struct trace_kprobe *tk;
 	struct dyn_event *pos;
 
+	if (trace_kprobe_list_empty())
+		return;
+
 	guard(mutex)(&event_mutex);
 	for_each_trace_kprobe(tk, pos) {
 		list_for_each_entry(file, &tr->events, list)
-- 
2.25.1