tracing/kprobes: Support soft-mode disabling

Support soft-mode disabling on kprobe-based dynamic events.
Soft-disabling is just ignoring recording if the soft disabled
flag is set.

Link: http://lkml.kernel.org/r/20130509054454.30398.7237.stgit@mhiramat-M0-7522

Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Tom Zanussi <tom.zanussi@intel.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/trace_kprobe.c

@@ -845,6 +845,9 @@ __kprobe_trace_func(struct trace_probe *tp, struct pt_regs *regs,
 
 	WARN_ON(call != ftrace_file->event_call);
 
+	if (test_bit(FTRACE_EVENT_FL_SOFT_DISABLED_BIT, &ftrace_file->flags))
+		return;
+
 	local_save_flags(irq_flags);
 	pc = preempt_count();
 
@@ -893,6 +896,9 @@ __kretprobe_trace_func(struct trace_probe *tp, struct kretprobe_instance *ri,
 
 	WARN_ON(call != ftrace_file->event_call);
 
+	if (test_bit(FTRACE_EVENT_FL_SOFT_DISABLED_BIT, &ftrace_file->flags))
+		return;
+
 	local_save_flags(irq_flags);
 	pc = preempt_count();