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);