[RFC PATCH 1/2] tracing: Move enabling tracepoints to just after mm_init()

[Steven Rostedt <rostedt@goodmis.org>]

Enabling tracepoints at boot up can be very useful. The tracepoint
can be initialized right after memory has been. There's no need to
wait for the early_initcall() to be called. That's too late for some
things that can use tracepoints for debugging. Move the logic to
enable tracepoints out of the initcalls and into init/main.c to
right after mm_init().

This also allows trace_printk() to be used early too.

Link: http://lkml.kernel.org/r/alpine.DEB.2.11.1412121539300.16494@nanos

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 include/linux/ftrace.h        |  6 ++++++
 init/main.c                   |  3 +++
 kernel/trace/trace.c          |  8 +++++++-
 kernel/trace/trace.h          | 13 +++++++++++++
 kernel/trace/trace_events.c   | 10 ++++++++--
 kernel/trace/trace_syscalls.c |  3 +--
 6 files changed, 38 insertions(+), 5 deletions(-)

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index ed501953f0b2..0fc3e720d4fd 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -39,6 +39,12 @@
 # define FTRACE_FORCE_LIST_FUNC 0
 #endif
 
+/* Main tracing buffer and events set up */
+#ifdef CONFIG_TRACING
+void trace_init(void);
+#else
+static inline trace_init(void) { }
+#endif
 
 struct module;
 struct ftrace_hash;
diff --git a/init/main.c b/init/main.c
index 800a0daede7e..060e60b6aa59 100644
--- a/init/main.c
+++ b/init/main.c
@@ -561,6 +561,9 @@ asmlinkage __visible void __init start_kernel(void)
 	trap_init();
 	mm_init();
 
+	/* trace_printk() and trace points may be used after this */
+	trace_init();
+
 	/*
 	 * Set up the scheduler prior starting any interrupts (such as the
 	 * timer interrupt). Full topology setup happens at smp_init()
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 4ceb2546c7ef..ec3ca694665f 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -6876,6 +6876,13 @@ out:
 	return ret;
 }
 
+void __init trace_init(void)
+{
+	tracer_alloc_buffers();
+	init_ftrace_syscalls();
+	trace_event_init();	
+}
+
 __init static int clear_boot_tracer(void)
 {
 	/*
@@ -6895,6 +6902,5 @@ __init static int clear_boot_tracer(void)
 	return 0;
 }
 
-early_initcall(tracer_alloc_buffers);
 fs_initcall(tracer_init_debugfs);
 late_initcall(clear_boot_tracer);
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 3255dfb054a0..c138c149d6ef 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -1301,4 +1301,17 @@ int perf_ftrace_event_register(struct ftrace_event_call *call,
 #define perf_ftrace_event_register NULL
 #endif
 
+#ifdef CONFIG_FTRACE_SYSCALLS
+void init_ftrace_syscalls(void);
+#else
+static inline void init_ftrace_syscalls(void) { }
+#endif
+
+#ifdef CONFIG_EVENT_TRACING
+void trace_event_init(void);
+#else
+static inline void __init trace_event_init(void) { }
+#endif
+
+
 #endif /* _LINUX_KERNEL_TRACE_H */
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index f9d0cbe014b7..fd9deb0e03f0 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -2477,8 +2477,14 @@ static __init int event_trace_init(void)
 #endif
 	return 0;
 }
-early_initcall(event_trace_memsetup);
-core_initcall(event_trace_enable);
+
+void __init trace_event_init(void)
+{
+	event_trace_memsetup();
+	init_ftrace_syscalls();
+	event_trace_enable();
+}
+
 fs_initcall(event_trace_init);
 
 #ifdef CONFIG_FTRACE_STARTUP_TEST
diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
index a72f3d8d813e..542219ea33ed 100644
--- a/kernel/trace/trace_syscalls.c
+++ b/kernel/trace/trace_syscalls.c
@@ -514,7 +514,7 @@ unsigned long __init __weak arch_syscall_addr(int nr)
 	return (unsigned long)sys_call_table[nr];
 }
 
-static int __init init_ftrace_syscalls(void)
+void __init init_ftrace_syscalls(void)
 {
 	struct syscall_metadata *meta;
 	unsigned long addr;
@@ -539,7 +539,6 @@ static int __init init_ftrace_syscalls(void)
 
 	return 0;
 }
-early_initcall(init_ftrace_syscalls);
 
 #ifdef CONFIG_PERF_EVENTS
 
-- 
1.8.1.4