Note, the proc sysctl ftrace_enable is a big on/off switch for the function tracer. By default it is enabled (when function tracing is enabled in the kernel). If it is disabled, all function tracing is disabled. This includes not only the function tracers for ftrace, but also for any other uses (perf, kprobes, stack tracing, profiling, etc). It cannot be disabled if there is a callback with FTRACE_OPS_FL_PERMANENT set registered.
Please disable this with care.
This can be disable (and enabled) with::
sysctl kernel.ftrace_enabled=0 sysctl kernel.ftrace_enabled=1
or
echo 0 > /proc/sys/kernel/ftrace_enabled echo 1 > /proc/sys/kernel/ftrace_enabled