[PATCH v2 2/2] net: add trace events for net_device refcnt

[Tony Lu]

The net_device refcnt leak is hard to trace and debug for now. We need
the ability to know when and who manipulated the refcnt.

Adding the trace events for net_device pcpu_refcnt and also tracepoints
in dev_put()/dev_hold(), provides the history of net_device refcnt inc
and desc. With trace logs analysis, paring the put and hold history, we
can find out who leaked.

Signed-off-by: Dust Li <dust.li@xxxxxxxxxxxxxxxxx>
Signed-off-by: Tony Lu <tonylu@xxxxxxxxxxxxxxxxx>
---
 include/trace/events/net.h | 41 ++++++++++++++++++++++++++++++++++++++
 net/core/dev.c             |  4 ++++
 2 files changed, 45 insertions(+)

diff --git a/include/trace/events/net.h b/include/trace/events/net.h
index 3b28843652d2..3bf6dd738882 100644
--- a/include/trace/events/net.h
+++ b/include/trace/events/net.h
@@ -326,6 +326,47 @@ DEFINE_EVENT(net_dev_rx_exit_template, netif_receive_skb_list_exit,
 	TP_ARGS(ret)
 );
 
+DECLARE_EVENT_CLASS(net_dev_refcnt_template,
+
+	TP_PROTO(struct net_device *dev, void *location),
+
+	TP_ARGS(dev, location),
+
+	TP_STRUCT__entry(
+		__string(	name,		dev->name	)
+		__field(	int,		refcnt		)
+		__field(	void *,		location	)
+	),
+
+	TP_fast_assign(
+		int i, refcnt = 0;
+
+		for_each_possible_cpu(i)
+			refcnt += *per_cpu_ptr(dev->pcpu_refcnt, i);
+
+		__assign_str(name, dev->name);
+		__entry->refcnt = refcnt;
+		__entry->location = location;
+	),
+
+	TP_printk("dev=%s refcnt=%d location=%p",
+		__get_str(name), __entry->refcnt, __entry->location)
+);
+
+DEFINE_EVENT(net_dev_refcnt_template, net_dev_put,
+
+	TP_PROTO(struct net_device *dev, void *location),
+
+	TP_ARGS(dev, location)
+);
+
+DEFINE_EVENT(net_dev_refcnt_template, net_dev_hold,
+
+	TP_PROTO(struct net_device *dev, void *location),
+
+	TP_ARGS(dev, location)
+);
+
 #endif /* _TRACE_NET_H */
 
 /* This part must be outside protection */
diff --git a/net/core/dev.c b/net/core/dev.c
index 620fb3d6718a..163870a09984 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1302,6 +1302,8 @@ EXPORT_SYMBOL(netdev_notify_peers);
  */
 void dev_put(struct net_device *dev)
 {
+	trace_net_dev_put(dev, __builtin_return_address(0));
+
 	this_cpu_dec(*dev->pcpu_refcnt);
 }
 EXPORT_SYMBOL(dev_put);
@@ -1314,6 +1316,8 @@ EXPORT_SYMBOL(dev_put);
  */
 void dev_hold(struct net_device *dev)
 {
+	trace_net_dev_hold(dev, __builtin_return_address(0));
+
 	this_cpu_inc(*dev->pcpu_refcnt);
 }
 EXPORT_SYMBOL(dev_hold);
-- 
2.24.0