[PATCH 13/28] hazptr: Add waiter-enqueue tracepoint

[Kunwu Chan <kunwu.chan@gmail.com>]

Production tracepoint fired when hazptr_synchronize() enqueues a
waiter onto the scan kthread's pending list.  Downstream users
include hazptrtorture's staged hot-address scenario, which uses
it to confirm enqueue before running its controls.

Signed-off-by: Kunwu Chan <kunwu.chan@gmail.com>
---
 include/trace/events/hazptr.h | 29 +++++++++++++++++++++++++++++
 kernel/hazptr.c               |  5 +++++
 2 files changed, 34 insertions(+)
 create mode 100644 include/trace/events/hazptr.h

diff --git a/include/trace/events/hazptr.h b/include/trace/events/hazptr.h
new file mode 100644
index 000000000000..1eed4c9fd682
--- /dev/null
+++ b/include/trace/events/hazptr.h
@@ -0,0 +1,29 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM hazptr
+
+#if !defined(_TRACE_HAZPTR_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_HAZPTR_H
+
+#include <linux/tracepoint.h>
+
+TRACE_EVENT(hazptr_waiter_enqueue,
+
+	TP_PROTO(void *addr),
+
+	TP_ARGS(addr),
+
+	TP_STRUCT__entry(
+		__field(void *, addr)
+	),
+
+	TP_fast_assign(
+		__entry->addr = addr;
+	),
+
+	TP_printk("addr=%p", __entry->addr)
+);
+
+#endif /* _TRACE_HAZPTR_H */
+
+#include <trace/define_trace.h>
diff --git a/kernel/hazptr.c b/kernel/hazptr.c
index 4784df78be4e..16f6e2acaf87 100644
--- a/kernel/hazptr.c
+++ b/kernel/hazptr.c
@@ -19,6 +19,10 @@
 #include <linux/bitops.h>
 #include <linux/bitmap.h>
 
+#define CREATE_TRACE_POINTS
+#include <trace/events/hazptr.h>
+EXPORT_TRACEPOINT_SYMBOL_GPL(hazptr_waiter_enqueue);
+
 #define HAZPTR_WILDCARD	((void *) 1UL)
 
 static DEFINE_MUTEX(hazptr_phase_lock);	/* Protect the list phase flip. */
@@ -411,6 +415,7 @@ static void hazptr_synchronize_queued(void *addr)
 
 	mutex_lock(&hazptr_scan.lock);
 	list_add_tail(&waiter.node, &hazptr_scan.pending);
+	trace_hazptr_waiter_enqueue(addr);
 	if (!READ_ONCE(hazptr_scan.wakeup)) {
 		WRITE_ONCE(hazptr_scan.wakeup, true);
 		swake_up_one(&hazptr_scan.wq);
-- 
2.43.0