tracing/fastboot: use sched switch tracer from boot tracer

Impact: enhance boot trace output with scheduling events

Use the sched_switch tracer from the boot tracer.

We also can trace schedule events inside the initcalls.
Sched tracing is disabled after the initcall has finished and
then reenabled before the next one is started.
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/trace/trace.c

@@ -3251,6 +3251,8 @@ __init static int tracer_alloc_buffers(void)
 
 	register_tracer(&nop_trace);
 #ifdef CONFIG_BOOT_TRACER
+	/* We don't want to launch sched_switch tracer yet */
+	global_trace.ctrl = 0;
 	register_tracer(&boot_tracer);
 	current_trace = &boot_tracer;
 	current_trace->init(&global_trace);

kernel/trace/trace.h

@@ -49,6 +49,7 @@ struct ftrace_entry {
 	unsigned long		parent_ip;
 };
 extern struct tracer boot_tracer;
+extern struct tracer sched_switch_trace; /* Used by the boot tracer */
 
 /*
  * Context switch trace entry - which task (and prio) we switched from/to:

kernel/trace/trace_boot.c

@@ -27,10 +27,14 @@ void start_boot_trace(void)
 
 void enable_boot_trace(void)
 {
+	if (pre_initcalls_finished)
+		tracing_start_cmdline_record();
 }
 
 void disable_boot_trace(void)
 {
+	if (pre_initcalls_finished)
+		tracing_stop_cmdline_record();
 }
 
 void reset_boot_trace(struct trace_array *tr)
@@ -45,6 +49,8 @@ static void boot_trace_init(struct trace_array *tr)
 
 	for_each_cpu_mask(cpu, cpu_possible_map)
 		tracing_reset(tr, cpu);
+
+	sched_switch_trace.init(tr);
 }
 
 static void boot_trace_ctrl_update(struct trace_array *tr)

kernel/trace/trace_sched_switch.c

@@ -127,6 +127,7 @@ static void tracing_start_sched_switch(void)
 	long ref;
 
 	mutex_lock(&tracepoint_mutex);
+	tracer_enabled = 1;
 	ref = atomic_inc_return(&sched_ref);
 	if (ref == 1)
 		tracing_sched_register();
@@ -138,6 +139,7 @@ static void tracing_stop_sched_switch(void)
 	long ref;
 
 	mutex_lock(&tracepoint_mutex);
+	tracer_enabled = 0;
 	ref = atomic_dec_and_test(&sched_ref);
 	if (ref)
 		tracing_sched_unregister();
@@ -158,12 +160,10 @@ static void start_sched_trace(struct trace_array *tr)
 {
 	sched_switch_reset(tr);
 	tracing_start_cmdline_record();
-	tracer_enabled = 1;
 }
 
 static void stop_sched_trace(struct trace_array *tr)
 {
-	tracer_enabled = 0;
 	tracing_stop_cmdline_record();
 }
 
@@ -190,7 +190,7 @@ static void sched_switch_trace_ctrl_update(struct trace_array *tr)
 		stop_sched_trace(tr);
 }
 
-static struct tracer sched_switch_trace __read_mostly =
+struct tracer sched_switch_trace __read_mostly =
 {
 	.name		= "sched_switch",
 	.init		= sched_switch_trace_init,