This is a note to let you know that I've just added the patch titled
tracing: Make sure trace_printk() can output as soon as it can be used
to the 4.19-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
tracing-make-sure-trace_printk-can-output-as-soon-as-it-can-be-used.patch
and it can be found in the queue-4.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 3bb06eb6e9acf7c4a3e1b5bc87aed398ff8e2253 Mon Sep 17 00:00:00 2001
From: "Steven Rostedt (Google)" <rostedt@xxxxxxxxxxx>
Date: Wed, 4 Jan 2023 16:14:12 -0500
Subject: tracing: Make sure trace_printk() can output as soon as it can be used
From: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
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@xxxxxxxxxxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx
Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Fixes: e725c731e3bb1 ("tracing: Split tracing initialization into two for early initialization")
Reported-by: "Joel Fernandes (Google)" <joel@xxxxxxxxxxxxxxxxx>
Tested-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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
@@ -8674,6 +8674,8 @@ 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
@@ -1530,6 +1530,7 @@ extern void trace_event_enable_cmd_recor
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);
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -1395,7 +1395,7 @@ 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;
@@ -1413,4 +1413,3 @@ __init static int init_events(void)
return 0;
}
-early_initcall(init_events);
Patches currently in stable-queue which might be from rostedt@xxxxxxxxxxx are
queue-4.19/trace_events_hist-add-check-for-return-value-of-create_hist_field.patch
queue-4.19/tracing-make-sure-trace_printk-can-output-as-soon-as-it-can-be-used.patch
