First confirm that you have root privilege.

Second check the config of kernel that you have the configs on:

CONFIG_FTRACE=yCONFIG_FUNCTION_GRAPH_TRACER=yCONFIG_EVENT_TRACING=y

CONFIG_FUNCTION_TRACERCONFIG_STACK_TRACERCONFIG_DYNAMIC_FTRACE

Last you confirm you have your debugfs/tracefs mounted, by: 

mount -t debugfs nodev /sys/kernel/debug/

Then go into the sys entry tracing and you will find the friendly README.

List some triggers: 

options/funcgraph-irqs, tracing_on, max_graph_depth, set_graph_function, set_ftrace_filter, set_ftrace_pid, current_tracer.

stack_trace can probe runtime kernel address of functions.