Re: [PATCH] tracing: Make sure trace_printk() can output as soon as it can be used
From: Joel Fernandes <hidden>
Date: 2023-01-05 01:06:25
Also in:
lkml
On Wed, Jan 04, 2023 at 04:14:12PM -0500, Steven Rostedt wrote:
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.
Cc: stable@vger.kernel.org
Reported-by: "Joel Fernandes (Google)" <redacted>
Fixes: e725c731e3bb1 ("tracing: Split tracing initialization into two for early initialization")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>Tested-by: Joel Fernandes (Google) <redacted> thanks, - Joel
quoted hunk ↗ jump to hunk
--- 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 d3005279165d..80de338f1277 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c@@ -10196,6 +10196,8 @@ 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 900e75d96c84..11c4918ff202 100644 --- a/kernel/trace/trace.h +++ b/kernel/trace/trace.h@@ -1504,6 +1504,7 @@ 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 67f47ea27921..5cd4fb656306 100644 --- a/kernel/trace/trace_output.c +++ b/kernel/trace/trace_output.c@@ -1568,7 +1568,7 @@ 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;@@ -1581,4 +1581,3 @@ __init static int init_events(void) return 0; } -early_initcall(init_events);-- 2.35.1