tracing/ftrace: Allow for instances to trigger their own stacktrace probes

Have the stacktrace function trigger probe trigger stack traces within the
instance that they were added to in the set_ftrace_filter.

 ># cd /sys/kernel/debug/tracing
 ># mkdir instances/foo
 ># cd instances/foo
 ># echo schedule:stacktrace:1 > set_ftrace_filter
 ># cat trace
 # tracer: nop
 #
 # entries-in-buffer/entries-written: 1/1   #P:4
 #
 #                              _-----=> irqs-off
 #                             / _----=> need-resched
 #                            | / _---=> hardirq/softirq
 #                            || / _--=> preempt-depth
 #                            ||| /     delay
 #           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
 #              | |       |   ||||       |         |
           <idle>-0     [001] .N.2   202.585010: <stack trace>
  =>
  => schedule
  => schedule_preempt_disabled
  => do_idle
  => cpu_startup_entry
  => start_secondary
  => verify_cpu
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/trace_functions.c

@@ -375,12 +375,23 @@ ftrace_traceoff(unsigned long ip, unsigned long parent_ip,
  */
 #define STACK_SKIP 4
 
+static __always_inline void trace_stack(struct trace_array *tr)
+{
+	unsigned long flags;
+	int pc;
+
+	local_save_flags(flags);
+	pc = preempt_count();
+
+	__trace_stack(tr, flags, STACK_SKIP, pc);
+}
+
 static void
 ftrace_stacktrace(unsigned long ip, unsigned long parent_ip,
 		  struct trace_array *tr, struct ftrace_probe_ops *ops,
 		  void *data)
 {
-	trace_dump_stack(STACK_SKIP);
+	trace_stack(tr);
 }
 
 static void
@@ -398,7 +409,7 @@ ftrace_stacktrace_count(unsigned long ip, unsigned long parent_ip,
 
 	/* unlimited? */
 	if (!mapper) {
-		trace_dump_stack(STACK_SKIP);
+		trace_stack(tr);
 		return;
 	}
 
@@ -417,7 +428,7 @@ ftrace_stacktrace_count(unsigned long ip, unsigned long parent_ip,
 		new_count = old_count - 1;
 		new_count = cmpxchg(count, old_count, new_count);
 		if (new_count == old_count)
-			trace_dump_stack(STACK_SKIP);
+			trace_stack(tr);
 
 		if (!tracing_is_on())
 			return;