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[34.150.221.228]) by smtp.gmail.com with ESMTPSA id o6-20020ac872c6000000b003a57a317c17sm21131484qtp.74.2023.01.04.17.06.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 04 Jan 2023 17:06:18 -0800 (PST) Date: Thu, 5 Jan 2023 01:06:18 +0000 From: Joel Fernandes To: Steven Rostedt Cc: LKML , Linux Trace Kernel , Masami Hiramatsu Subject: Re: [PATCH] tracing: Make sure trace_printk() can output as soon as it can be used Message-ID: References: <20230104161412.019f6c55@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230104161412.019f6c55@gandalf.local.home> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 04, 2023 at 04:14:12PM -0500, Steven Rostedt wrote: > From: "Steven Rostedt (Google)" > > 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] -0 0dN.2. 347519us : Unknown type 6 > [ 0.456075] -0 0dN.2. 353141us : Unknown type 6 > [ 0.456075] -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)" > Fixes: e725c731e3bb1 ("tracing: Split tracing initialization into two for early initialization") > Signed-off-by: Steven Rostedt (Google) Tested-by: Joel Fernandes (Google) 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 >