From f4708a82dc45fbf08bd3c68fc3eb32397e9121a1 Mon Sep 17 00:00:00 2001
From: "Guilherme G. Piccoli" <gpiccoli@igalia.com>
Date: Tue, 14 Mar 2023 17:00:58 -0300
Subject: [PATCH] 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.

[akpm@linux-foundation.org: coding-style cleanups]
Link: https://lkml.kernel.org/r/20230314200058.1326909-1-gpiccoli@igalia.com
Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Michael Kelley <mikelley@microsoft.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Xiaoming Ni <nixiaoming@huawei.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Cc: Guilherme G. Piccoli <gpiccoli@igalia.com>
Cc: Guilherme G. Piccoli <kernel@gpiccoli.net>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
 include/trace/events/notifier.h | 69 +++++++++++++++++++++++++++++++++
 kernel/notifier.c               |  6 +++
 2 files changed, 75 insertions(+)
 create mode 100644 include/trace/events/notifier.h

diff --git a/include/trace/events/notifier.h b/include/trace/events/notifier.h
new file mode 100644
index 000000000000..26b298a31950
--- /dev/null
+++ b/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>
diff --git a/kernel/notifier.c b/kernel/notifier.c
index d353e4b5402d..b3ce28f39eb6 100644
--- a/kernel/notifier.c
+++ b/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)