[PATCH v1 net-next 02/12] af_unix: Set drop reason in unix_release_sock().

[Kuniyuki Iwashima <kuniyu@amazon.com>]

unix_release_sock() is called when the last refcnt of struct file
is released.

Let's define a new drop reason SKB_DROP_REASON_SOCKET_CLOSE and
set it for kfree_skb() in unix_release_sock().

  # echo 1 > /sys/kernel/tracing/events/skb/kfree_skb/enable

  # python3
  >>> from socket import *
  >>> s1, s2 = socketpair(AF_UNIX)
  >>> s1.send(b'hello world')
  >>> s2.close()

  # cat /sys/kernel/tracing/trace_pipe
  ...
     python3-280 ... kfree_skb: ... protocol=0 location=unix_release_sock+0x260/0x420 reason: SOCKET_CLOSE

To be precise, unix_release_sock() is also called for a new child
socket in unix_stream_connect() when something fails, but the new
sk does not have skb in the recv queue then and no event is logged.

Note that only tcp_inbound_ao_hash() uses a similar drop reason,
SKB_DROP_REASON_TCP_CLOSE, and this can be generalised later.

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
---
 include/net/dropreason-core.h | 3 +++
 net/unix/af_unix.c            | 4 ++--
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/include/net/dropreason-core.h b/include/net/dropreason-core.h
index efeae9f0f956..8823de6539d1 100644
--- a/include/net/dropreason-core.h
+++ b/include/net/dropreason-core.h
@@ -6,6 +6,7 @@
 #define DEFINE_DROP_REASON(FN, FNe)	\
 	FN(NOT_SPECIFIED)		\
 	FN(NO_SOCKET)			\
+	FN(SOCKET_CLOSE)		\
 	FN(SOCKET_FILTER)		\
 	FN(SOCKET_RCVBUFF)		\
 	FN(PKT_TOO_SMALL)		\
@@ -137,6 +138,8 @@ enum skb_drop_reason {
 	 * 3) no valid child socket during 3WHS process
 	 */
 	SKB_DROP_REASON_NO_SOCKET,
+	/** @SKB_DROP_REASON_SOCKET_CLOSE: socket is close()d */
+	SKB_DROP_REASON_SOCKET_CLOSE,
 	/** @SKB_DROP_REASON_SOCKET_FILTER: dropped by socket filter */
 	SKB_DROP_REASON_SOCKET_FILTER,
 	/** @SKB_DROP_REASON_SOCKET_RCVBUFF: socket receive buff is full */
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 8f2b605ce5b3..a05d25cc5545 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -715,8 +715,8 @@ static void unix_release_sock(struct sock *sk, int embrion)
 		if (state == TCP_LISTEN)
 			unix_release_sock(skb->sk, 1);
 
-		/* passed fds are erased in the kfree_skb hook	      */
-		kfree_skb(skb);
+		/* passed fds are erased in the kfree_skb hook */
+		kfree_skb_reason(skb, SKB_DROP_REASON_SOCKET_CLOSE);
 	}
 
 	if (path.dentry)
-- 
2.39.5 (Apple Git-154)