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: 546b9546f5307 ("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 1090b240411045cdd4b55ac24b198ddc95ad236b..8b87f1f74e325d8a4d2d3efb1f3882dc27d73fe7 100644 (file)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -9317,6 +9317,8 @@ 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 1d514a1a31554e09cbee7f7281d1dc0f1371da39..f2ff39353e037feedc0d515a0e65a88678718290 100644 (file)
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -1590,6 +1590,7 @@ 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);
 

diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index a0a45901dc027c774c8825ec59c5b749f4494c14..b194dd1c8420fb51c23197987a460123b104193d 100644 (file)
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -1366,7 +1366,7 @@ 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;
@@ -1384,4 +1384,3 @@ __init static int init_events(void)
 
        return 0;
 }
-early_initcall(init_events);