tracing: Make sure trace_printk() can output as soon as it can be used

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>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index c7c92b0eed04819b34c15c2edf83ab51fecdcf87..f06d48be5a9696f64b5067a3230c8f5ad7355bd6 100644 (file)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -9680,6 +9680,8 @@ void __init early_trace_init(void)
                        static_key_enable(&tracepoint_printk_key.key);
        }
        tracer_alloc_buffers();
+
+       init_events();
 }
 
 void __init trace_init(void)

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 8d67f7f44840048ab875ef8e3eebb4acebe1c987..37f616bf5fa93b5af703c013494016e4550e6f84 100644 (file)
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -1673,6 +1673,7 @@ extern void trace_event_enable_cmd_record(bool enable);
 extern void trace_event_enable_tgid_record(bool enable);
 
 extern int event_trace_init(void);
+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);
 extern void __trace_early_add_events(struct trace_array *tr);

diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index 000e9dc224c61376643cf9c400fb01f7ce39631d..b3ee8d9b6b62aeb54f9fb4474acfb58da1772327 100644 (file)
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -1378,7 +1378,7 @@ static struct trace_event *events[] __initdata = {
        NULL
 };
 
-__init static int init_events(void)
+__init int init_events(void)
 {
        struct trace_event *event;
        int i, ret;
@@ -1396,4 +1396,3 @@ __init static int init_events(void)
 
        return 0;
 }
-early_initcall(init_events);