[PATCH 4.14 27/62] tracing: Make sure trace_printk() can output as soon as it can be used

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Steven Rostedt (Google) <rostedt@goodmis.org>

commit 3bb06eb6e9acf7c4a3e1b5bc87aed398ff8e2253 upstream.

Currently trace_printk() can be used as soon as early_trace_init() is
called from start_kernel(). But if a crash happens, and
"ftrace_dump_on_oops" is set on the kernel command line, all you get will
be:

  [    0.456075]   <idle>-0         0dN.2. 347519us : Unknown type 6
  [    0.456075]   <idle>-0         0dN.2. 353141us : Unknown type 6
  [    0.456075]   <idle>-0         0dN.2. 358684us : Unknown type 6

This is because the trace_printk() event (type 6) hasn't been registered
yet. That gets done via an early_initcall(), which may be early, but not
early enough.

Instead of registering the trace_printk() event (and other ftrace events,
which are not trace events) via an early_initcall(), have them registered at
the same time that trace_printk() can be used. This way, if there is a
crash before early_initcall(), then the trace_printk()s will actually be
useful.

Link: https://lkml.kernel.org/r/20230104161412.019f6c55@gandalf.local.home

Cc: stable@vger.kernel.org
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Fixes: e725c731e3bb1 ("tracing: Split tracing initialization into two for early initialization")
Reported-by: "Joel Fernandes (Google)" <joel@joelfernandes.org>
Tested-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 kernel/trace/trace.c        |    2 ++
 kernel/trace/trace.h        |    1 +
 kernel/trace/trace_output.c |    3 +--
 3 files changed, 4 insertions(+), 2 deletions(-)

--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -8487,6 +8487,8 @@ void __init early_trace_init(void)
 			static_key_enable(&tracepoint_printk_key.key);
 	}
 	tracer_alloc_buffers();
+
+	init_events();
 }
 
 void __init trace_init(void)
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -1531,6 +1531,7 @@ trace_find_event_field(struct trace_even
 extern void trace_event_enable_cmd_record(bool enable);
 extern void trace_event_enable_tgid_record(bool enable);
 
+extern int init_events(void);
 extern int event_trace_add_tracer(struct dentry *parent, struct trace_array *tr);
 extern int event_trace_del_tracer(struct trace_array *tr);
 
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -1394,7 +1394,7 @@ static struct trace_event *events[] __in
 	NULL
 };
 
-__init static int init_events(void)
+__init int init_events(void)
 {
 	struct trace_event *event;
 	int i, ret;
@@ -1412,4 +1412,3 @@ __init static int init_events(void)
 
 	return 0;
 }
-early_initcall(init_events);