tracing/boot, kprobe, synth: Initialize boot-time tracing earlier

Initialize boot-time tracing in core_initcall_sync instead of
fs_initcall, and initialize required tracers (kprobes and synth)
in core_initcall. This will allow the boot-time tracing to trace
__init code from the beginning of postcore_initcall stage.

Link: https://lkml.kernel.org/r/159974155727.478751.7486926132902849578.stgit@devnote2Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/trace_boot.c

@@ -340,5 +340,8 @@ static int __init trace_boot_init(void)
 
 	return 0;
 }
-
-fs_initcall(trace_boot_init);
+/*
+ * Start tracing at the end of core-initcall, so that it starts tracing
+ * from the beginning of postcore_initcall.
+ */
+core_initcall_sync(trace_boot_init);

kernel/trace/trace_events_synth.c

@@ -1754,17 +1754,26 @@ static const struct file_operations synth_events_fops = {
 	.release        = seq_release,
 };
 
-static __init int trace_events_synth_init(void)
+/*
+ * Register dynevent at core_initcall. This allows kernel to setup kprobe
+ * events in postcore_initcall without tracefs.
+ */
+static __init int trace_events_synth_init_early(void)
 {
-	struct dentry *entry = NULL;
 	int err = 0;
 
 	err = dyn_event_register(&synth_event_ops);
-	if (err) {
+	if (err)
 		pr_warn("Could not register synth_event_ops\n");
-		return err;
-	}
 
+	return err;
+}
+core_initcall(trace_events_synth_init_early);
+
+static __init int trace_events_synth_init(void)
+{
+	struct dentry *entry = NULL;
+	int err = 0;
 	err = tracing_init_dentry();
 	if (err)
 		goto err;

kernel/trace/trace_kprobe.c

@@ -1897,8 +1897,8 @@ static __init void setup_boot_kprobe_events(void)
 }
 
 /*
- * Register dynevent at subsys_initcall. This allows kernel to setup kprobe
- * events in fs_initcall without tracefs.
+ * Register dynevent at core_initcall. This allows kernel to setup kprobe
+ * events in postcore_initcall without tracefs.
  */
 static __init int init_kprobe_trace_early(void)
 {
@@ -1913,7 +1913,7 @@ static __init int init_kprobe_trace_early(void)
 
 	return 0;
 }
-subsys_initcall(init_kprobe_trace_early);
+core_initcall(init_kprobe_trace_early);
 
 /* Make a tracefs interface for controlling probe points */
 static __init int init_kprobe_trace(void)