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);