notifiers: add tracepoints to the notifiers infrastructure

Currently there is no way to show the callback names for registered,
unregistered or executed notifiers. This is very useful for debug
purposes, hence add this functionality here in the form of notifiers'
tracepoints, one per operation.

[[email protected]: coding-style cleanups]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Guilherme G. Piccoli <[email protected]>
Cc: Arjan van de Ven <[email protected]>
Cc: Michael Kelley <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Xiaoming Ni <[email protected]>
Cc: Baoquan He <[email protected]>
Cc: Cong Wang <[email protected]>
Cc: Dmitry Osipenko <[email protected]>
Cc: Guilherme G. Piccoli <[email protected]>
Cc: Guilherme G. Piccoli <[email protected]>
Cc: Petr Mladek <[email protected]>
Cc: Rafael J. Wysocki <[email protected]>
Cc: Sebastian Andrzej Siewior <[email protected]>
Cc: Valentin Schneider <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

include/trace/events/notifier.h

@@ -0,0 +1,69 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM notifier
+
+#if !defined(_TRACE_NOTIFIERS_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_NOTIFIERS_H
+
+#include <linux/tracepoint.h>
+
+DECLARE_EVENT_CLASS(notifier_info,
+
+	TP_PROTO(void *cb),
+
+	TP_ARGS(cb),
+
+	TP_STRUCT__entry(
+		__field(void *, cb)
+	),
+
+	TP_fast_assign(
+		__entry->cb = cb;
+	),
+
+	TP_printk("%ps", __entry->cb)
+);
+
+/*
+ * notifier_register - called upon notifier callback registration
+ *
+ * @cb:		callback pointer
+ *
+ */
+DEFINE_EVENT(notifier_info, notifier_register,
+
+	TP_PROTO(void *cb),
+
+	TP_ARGS(cb)
+);
+
+/*
+ * notifier_unregister - called upon notifier callback unregistration
+ *
+ * @cb:		callback pointer
+ *
+ */
+DEFINE_EVENT(notifier_info, notifier_unregister,
+
+	TP_PROTO(void *cb),
+
+	TP_ARGS(cb)
+);
+
+/*
+ * notifier_run - called upon notifier callback execution
+ *
+ * @cb:		callback pointer
+ *
+ */
+DEFINE_EVENT(notifier_info, notifier_run,
+
+	TP_PROTO(void *cb),
+
+	TP_ARGS(cb)
+);
+
+#endif /* _TRACE_NOTIFIERS_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>

kernel/notifier.c

@@ -7,6 +7,9 @@
 #include <linux/vmalloc.h>
 #include <linux/reboot.h>
 
+#define CREATE_TRACE_POINTS
+#include <trace/events/notifier.h>
+
 /*
  *	Notifier list for kernel code which wants to be called
  *	at shutdown. This is used to stop any idling DMA operations
@@ -37,6 +40,7 @@ static int notifier_chain_register(struct notifier_block **nl,
 	}
 	n->next = *nl;
 	rcu_assign_pointer(*nl, n);
+	trace_notifier_register((void *)n->notifier_call);
 	return 0;
 }
 
@@ -46,6 +50,7 @@ static int notifier_chain_unregister(struct notifier_block **nl,
 	while ((*nl) != NULL) {
 		if ((*nl) == n) {
 			rcu_assign_pointer(*nl, n->next);
+			trace_notifier_unregister((void *)n->notifier_call);
 			return 0;
 		}
 		nl = &((*nl)->next);
@@ -84,6 +89,7 @@ static int notifier_call_chain(struct notifier_block **nl,
 			continue;
 		}
 #endif
+		trace_notifier_run((void *)nb->notifier_call);
 		ret = nb->notifier_call(nb, val, v);
 
 		if (nr_calls)