From: Joel Fernandes <joel@joelfernandes.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
Linux Trace Kernel <linux-trace-kernel@vger.kernel.org>,
Masami Hiramatsu <mhiramat@kernel.org>
Subject: Re: [PATCH] tracing: Make sure trace_printk() can output as soon as it can be used
Date: Thu, 5 Jan 2023 01:06:18 +0000 [thread overview]
Message-ID: <Y7YiiogG7xbOjrNE@google.com> (raw)
In-Reply-To: <20230104161412.019f6c55@gandalf.local.home>
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)" <joel@joelfernandes.org>
> 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) <joel@joelfernandes.org>
thanks,
- Joel
> ---
> 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
>
prev parent reply other threads:[~2023-01-05 1:06 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-04 21:14 [PATCH] tracing: Make sure trace_printk() can output as soon as it can be used Steven Rostedt
2023-01-05 1:06 ` Joel Fernandes [this message]
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