[for-linus][PATCH 02/11] tracing: Make sure trace_printk() can output as soon as it can be used

Steven Rostedt
2023-01-25T16:20:16Z

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

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>
---
kernel/trace/trace.c | 2 ++
kernel/trace/trace.h | 1 +
kernel/trace/trace_output.c | 3 +--
3 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index a555a861b978..78ed5f1baa8c 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -10295,6 +10295,8 @@ 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 e46a49269be2..4eb6d6b97a9f 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -1490,6 +1490,7 @@ 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 57a13b61f186..bd475a00f96d 100644
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -1535,7 +1535,7 @@ 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;
@@ -1548,4 +1548,3 @@ __init static int init_events(void)

return 0;
}
-early_initcall(init_events);
--
2.39.0