tracing: Create set_event_notrace_pid to not trace tasks

There's currently a way to select a task that should only have its events
traced, but there's no way to select a task not to have itsevents traced.
Add a set_event_notrace_pid file that acts the same as set_event_pid (and is
also affected by event-fork), but the task pids in this file will not be
traced even if they are listed in the set_event_pid file. This makes it easy
for tools like trace-cmd to "hide" itself from beint traced by events when
it is recording other tasks.
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/ftrace.c

@@ -6987,11 +6987,6 @@ void ftrace_pid_follow_fork(struct trace_array *tr, bool enable)
 	}
 }
 
-enum {
-	TRACE_PIDS		= BIT(0),
-	TRACE_NO_PIDS		= BIT(1),
-};
-
 static void clear_ftrace_pids(struct trace_array *tr, int type)
 {
 	struct trace_pid_list *pid_list;
@@ -7004,13 +6999,11 @@ static void clear_ftrace_pids(struct trace_array *tr, int type)
 						lockdep_is_held(&ftrace_lock));
 
 	/* Make sure there's something to do */
-	if (!(((type & TRACE_PIDS) && pid_list) ||
-	      ((type & TRACE_NO_PIDS) && no_pid_list)))
+	if (!pid_type_enabled(type, pid_list, no_pid_list))
 		return;
 
 	/* See if the pids still need to be checked after this */
-	if (!((!(type & TRACE_PIDS) && pid_list) ||
-	      (!(type & TRACE_NO_PIDS) && no_pid_list))) {
+	if (!still_need_pid_events(type, pid_list, no_pid_list)) {
 		unregister_trace_sched_switch(ftrace_filter_pid_sched_switch_probe, tr);
 		for_each_possible_cpu(cpu)
 			per_cpu_ptr(tr->array_buffer.data, cpu)->ftrace_ignore_pid = FTRACE_PID_TRACE;

kernel/trace/trace.h

@@ -207,6 +207,30 @@ struct trace_pid_list {
 	unsigned long			*pids;
 };
 
+enum {
+	TRACE_PIDS		= BIT(0),
+	TRACE_NO_PIDS		= BIT(1),
+};
+
+static inline bool pid_type_enabled(int type, struct trace_pid_list *pid_list,
+				    struct trace_pid_list *no_pid_list)
+{
+	/* Return true if the pid list in type has pids */
+	return ((type & TRACE_PIDS) && pid_list) ||
+		((type & TRACE_NO_PIDS) && no_pid_list);
+}
+
+static inline bool still_need_pid_events(int type, struct trace_pid_list *pid_list,
+					 struct trace_pid_list *no_pid_list)
+{
+	/*
+	 * Turning off what is in @type, return true if the "other"
+	 * pid list, still has pids in it.
+	 */
+	return (!(type & TRACE_PIDS) && pid_list) ||
+		(!(type & TRACE_NO_PIDS) && no_pid_list);
+}
+
 typedef bool (*cond_update_fn_t)(struct trace_array *tr, void *cond_data);
 
 /**
@@ -285,6 +309,7 @@ struct trace_array {
 #endif
 #endif
 	struct trace_pid_list	__rcu *filtered_pids;
+	struct trace_pid_list	__rcu *filtered_no_pids;
 	/*
 	 * max_lock is used to protect the swapping of buffers
 	 * when taking a max snapshot. The buffers themselves are