linux-kernel - [PATCH 5/6] tracing/boot,kprobe,synth: Initialize boot-time tracing earlier

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Date:   Thu, 10 Sep 2020 21:39:17 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>,
        Jonathan Corbet <corbet@....net>
Cc:     mhiramat@...nel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, Randy Dunlap <rdunlap@...radead.org>,
        Ingo Molnar <mingo@...nel.org>
Subject: [PATCH 5/6] 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.

Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
---
 kernel/trace/trace_boot.c         |    7 +++++--
 kernel/trace/trace_events_synth.c |   22 ++++++++++++++++------
 kernel/trace/trace_kprobe.c       |    6 +++---
 3 files changed, 24 insertions(+), 11 deletions(-)

diff --git a/kernel/trace/trace_boot.c b/kernel/trace/trace_boot.c
index d52d441a17e8..754e3cf2df3a 100644
--- a/kernel/trace/trace_boot.c
+++ b/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);
diff --git a/kernel/trace/trace_events_synth.c b/kernel/trace/trace_events_synth.c
index c6cca0d1d584..6eb77d95fd64 100644
--- a/kernel/trace/trace_events_synth.c
+++ b/kernel/trace/trace_events_synth.c
@@ -1754,17 +1754,27 @@ 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;
-	struct dentry *d_tracer;
 	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;
+	struct dentry *d_tracer;
+	int err = 0;
 
 	d_tracer = tracing_init_dentry();
 	if (IS_ERR(d_tracer)) {
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index e33690a12255..a6a08199e79f 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -1896,8 +1896,8 @@ 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)
 {
@@ -1912,7 +1912,7 @@ 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)