tracing/function-return-tracer: clean up task start/exit callbacks

Impact: cleanup

Eliminate #ifdefs in core code by using empty inline functions.
Signed-off-by: NIngo Molnar <mingo@elte.hu>

include/linux/ftrace.h

@@ -335,6 +335,9 @@ extern void unregister_ftrace_return(void);
 
 extern void ftrace_retfunc_init_task(struct task_struct *t);
 extern void ftrace_retfunc_exit_task(struct task_struct *t);
+#else
+static inline void ftrace_retfunc_init_task(struct task_struct *t) { }
+static inline void ftrace_retfunc_exit_task(struct task_struct *t) { }
 #endif
 
 #endif /* _LINUX_FTRACE_H */

kernel/exit.c

@@ -1128,9 +1128,7 @@ NORET_TYPE void do_exit(long code)
 	preempt_disable();
 	/* causes final put_task_struct in finish_task_switch(). */
 	tsk->state = TASK_DEAD;
-#ifdef CONFIG_FUNCTION_RET_TRACER
 	ftrace_retfunc_exit_task(tsk);
-#endif
 	schedule();
 	BUG();
 	/* Avoid "noreturn function does return".  */

kernel/fork.c

@@ -1270,9 +1270,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 	total_forks++;
 	spin_unlock(&current->sighand->siglock);
 	write_unlock_irq(&tasklist_lock);
-#ifdef CONFIG_FUNCTION_RET_TRACER
 	ftrace_retfunc_init_task(p);
-#endif
 	proc_fork_connector(p);
 	cgroup_post_fork(p);
 	return p;

kernel/sched.c

@@ -5901,9 +5901,7 @@ void __cpuinit init_idle(struct task_struct *idle, int cpu)
 	 * The idle tasks have their own, simple scheduling class:
 	 */
 	idle->sched_class = &idle_sched_class;
-#ifdef CONFIG_FUNCTION_RET_TRACER
 	ftrace_retfunc_init_task(idle);
-#endif
 }
 
 /*