tracing: Rename eval_map_wq and allow other parts of tracing use it

The eval_map_work_func() function, though queued in eval_map_wq,
holds the trace_event_sem read-write lock for a long time during
kernel boot. This causes blocking issues for other functions.

Rename eval_map_wq to trace_init_wq and make it global, thereby
allowing other parts of tracing to schedule work on this queue
asynchronously and avoiding blockage of the main boot thread.

Link: https://patch.msgid.link/20260204015344.162818-1-tianyaxiong@kylinos.cn
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Yaxiong Tian <tianyaxiong@kylinos.cn>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Author: Yaxiong Tian

kernel/trace/trace.c

@@ -10785,7 +10785,7 @@ int tracing_init_dentry(void)
 extern struct trace_eval_map *__start_ftrace_eval_maps[];
 extern struct trace_eval_map *__stop_ftrace_eval_maps[];
 
-static struct workqueue_struct *eval_map_wq __initdata;
+struct workqueue_struct *trace_init_wq __initdata;
 static struct work_struct eval_map_work __initdata;
 static struct work_struct tracerfs_init_work __initdata;
 
@@ -10801,15 +10801,15 @@ static int __init trace_eval_init(void)
 {
 	INIT_WORK(&eval_map_work, eval_map_work_func);
 
-	eval_map_wq = alloc_workqueue("eval_map_wq", WQ_UNBOUND, 0);
-	if (!eval_map_wq) {
-		pr_err("Unable to allocate eval_map_wq\n");
+	trace_init_wq = alloc_workqueue("trace_init_wq", WQ_UNBOUND, 0);
+	if (!trace_init_wq) {
+		pr_err("Unable to allocate trace_init_wq\n");
 		/* Do work here */
 		eval_map_work_func(&eval_map_work);
 		return -ENOMEM;
 	}
 
-	queue_work(eval_map_wq, &eval_map_work);
+	queue_work(trace_init_wq, &eval_map_work);
 	return 0;
 }
 
@@ -10818,8 +10818,8 @@ subsys_initcall(trace_eval_init);
 static int __init trace_eval_sync(void)
 {
 	/* Make sure the eval map updates are finished */
-	if (eval_map_wq)
-		destroy_workqueue(eval_map_wq);
+	if (trace_init_wq)
+		destroy_workqueue(trace_init_wq);
 	return 0;
 }
 
@@ -10980,9 +10980,9 @@ static __init int tracer_init_tracefs(void)
 	if (ret)
 		return 0;
 
-	if (eval_map_wq) {
+	if (trace_init_wq) {
 		INIT_WORK(&tracerfs_init_work, tracer_init_tracefs_work_func);
-		queue_work(eval_map_wq, &tracerfs_init_work);
+		queue_work(trace_init_wq, &tracerfs_init_work);
 	} else {
 		tracer_init_tracefs_work_func(NULL);
 	}

kernel/trace/trace.h

@@ -769,6 +769,7 @@ extern cpumask_var_t __read_mostly tracing_buffer_mask;
 extern unsigned long nsecs_to_usecs(unsigned long nsecs);
 
 extern unsigned long tracing_thresh;
+extern struct workqueue_struct *trace_init_wq __initdata;
 
 /* PID filtering */