ftrace: fix comm on function trace output

In cleaning up of the sched_switch code, the function trace recording
of task comms was removed. This patch adds back the recording of comms
for function trace. The output of ftrace now has the task comm instead
of <...>.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

kernel/trace/trace.c

@@ -620,7 +620,12 @@ static unsigned map_cmdline_to_pid[SAVED_CMDLINES];
 static char saved_cmdlines[SAVED_CMDLINES][TASK_COMM_LEN];
 static int cmdline_idx;
 static DEFINE_SPINLOCK(trace_cmdline_lock);
-atomic_t trace_record_cmdline_disabled;
+
+/* trace in all context switches */
+atomic_t trace_record_cmdline_enabled __read_mostly;
+
+/* temporary disable recording */
+atomic_t trace_record_cmdline_disabled __read_mostly;
 
 static void trace_init_cmdlines(void)
 {

kernel/trace/trace.h

@@ -216,6 +216,8 @@ extern unsigned long nsecs_to_usecs(unsigned long nsecs);
 extern unsigned long tracing_max_latency;
 extern unsigned long tracing_thresh;
 
+extern atomic_t trace_record_cmdline_enabled;
+
 void update_max_tr(struct trace_array *tr, struct task_struct *tsk, int cpu);
 void update_max_tr_single(struct trace_array *tr,
 			  struct task_struct *tsk, int cpu);

kernel/trace/trace_functions.c

@@ -29,12 +29,14 @@ static void function_reset(struct trace_array *tr)
 static void start_function_trace(struct trace_array *tr)
 {
 	function_reset(tr);
+	atomic_inc(&trace_record_cmdline_enabled);
 	tracing_start_function_trace();
 }
 
 static void stop_function_trace(struct trace_array *tr)
 {
 	tracing_stop_function_trace();
+	atomic_dec(&trace_record_cmdline_enabled);
 }
 
 static void function_trace_init(struct trace_array *tr)

kernel/trace/trace_sched_switch.c

@@ -29,8 +29,6 @@ ctx_switch_func(void *__rq, struct task_struct *prev, struct task_struct *next)
 	if (!tracer_enabled)
 		return;
 
-	tracing_record_cmdline(prev);
-
 	local_irq_save(flags);
 	cpu = raw_smp_processor_id();
 	data = tr->data[cpu];
@@ -73,6 +71,9 @@ void
 ftrace_ctx_switch(void *__rq, struct task_struct *prev,
 		  struct task_struct *next)
 {
+	if (unlikely(atomic_read(&trace_record_cmdline_enabled)))
+		tracing_record_cmdline(prev);
+
 	/*
 	 * If tracer_switch_func only points to the local
 	 * switch func, it still needs the ptr passed to it.
@@ -134,11 +135,13 @@ static void sched_switch_reset(struct trace_array *tr)
 static void start_sched_trace(struct trace_array *tr)
 {
 	sched_switch_reset(tr);
+	atomic_inc(&trace_record_cmdline_enabled);
 	tracer_enabled = 1;
 }
 
 static void stop_sched_trace(struct trace_array *tr)
 {
+	atomic_dec(&trace_record_cmdline_enabled);
 	tracer_enabled = 0;
 }