context_tracking: User/kernel broundary cross trace events

This can be useful to track all kernel/user round trips.
And it's also helpful to debug the context tracking subsystem.

Signed-off-by: Frederic Weisbecker <[e-mail]>
Cc: Steven Rostedt <[e-mail]>
Cc: Paul E. McKenney <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Borislav Petkov <[e-mail]>
Cc: Li Zhong <[e-mail]>
Cc: Mike Galbraith <[e-mail]>
Cc: Kevin Hilman <[e-mail]>

include/trace/events/context_tracking.h

···
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM context_tracking
+
+#if !defined(_TRACE_CONTEXT_TRACKING_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_CONTEXT_TRACKING_H
+
+#include <linux/tracepoint.h>
+
+DECLARE_EVENT_CLASS(context_tracking_user,
+
+	TP_PROTO(int dummy),
+
+	TP_ARGS(dummy),
+
+	TP_STRUCT__entry(
+		__field( int,	dummy	)
+	),
+
+	TP_fast_assign(
+		__entry->dummy		= dummy;
+	),
+
+	TP_printk("%s", "")
+);
+
+/**
+ * user_enter - called when the kernel resumes to userspace
+ * @dummy:	dummy arg to make trace event macro happy
+ *
+ * This event occurs when the kernel resumes to userspace  after
+ * an exception or a syscall.
+ */
+DEFINE_EVENT(context_tracking_user, user_enter,
+
+	TP_PROTO(int dummy),
+
+	TP_ARGS(dummy)
+);
+
+/**
+ * user_exit - called when userspace enters the kernel
+ * @dummy:	dummy arg to make trace event macro happy
+ *
+ * This event occurs when userspace enters the kernel through
+ * an exception or a syscall.
+ */
+DEFINE_EVENT(context_tracking_user, user_exit,
+
+	TP_PROTO(int dummy),
+
+	TP_ARGS(dummy)
+);
+
+
+#endif /*  _TRACE_CONTEXT_TRACKING_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>

kernel/context_tracking.c

···
 #include <linux/hardirq.h>
 #include <linux/export.h>
 
+#define CREATE_TRACE_POINTS
+#include <trace/events/context_tracking.h>
+
 struct static_key context_tracking_enabled = STATIC_KEY_INIT_FALSE;
 EXPORT_SYMBOL_GPL(context_tracking_enabled);
 
···
 	local_irq_save(flags);
 	if ( __this_cpu_read(context_tracking.state) != IN_USER) {
 		if (__this_cpu_read(context_tracking.active)) {
+			trace_user_enter(0);
 			/*
 			 * At this stage, only low level arch entry code remains and
 			 * then we'll run in userspace. We can assume there won't be
···
 			 */
 			rcu_user_exit();
 			vtime_user_exit(current);
+			trace_user_exit(0);
 		}
 		__this_cpu_write(context_tracking.state, IN_KERNEL);
 	}