netdev - [PATCH v1 net-next 1/7] af_unix: Don't hold unix_state_lock() in __unix_dgram

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Message-ID: <20250702223606.1054680-2-kuniyu@google.com>
Date: Wed,  2 Jul 2025 22:35:13 +0000
From: Kuniyuki Iwashima <kuniyu@...gle.com>
To: "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Cc: Simon Horman <horms@...nel.org>, Kuniyuki Iwashima <kuniyu@...gle.com>, 
	Kuniyuki Iwashima <kuni1840@...il.com>, netdev@...r.kernel.org
Subject: [PATCH v1 net-next 1/7] af_unix: Don't hold unix_state_lock() in __unix_dgram_recvmsg().

When __skb_try_recv_datagram() returns NULL in __unix_dgram_recvmsg(),
we hold unix_state_lock() unconditionally.

This is because SOCK_SEQPACKET sk needs to return EOF in case its peer
has been close()d concurrently.

This behaviour totally depends on the timing of the peer's close() and
reading sk->sk_shutdown, and taking the lock does not play a role.

Let's drop the lock from __unix_dgram_recvmsg() and use READ_ONCE().

Signed-off-by: Kuniyuki Iwashima <kuniyu@...gle.com>
---
 net/unix/af_unix.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 564c970d97ff..1fa232ff4a2e 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -2528,12 +2528,10 @@ int __unix_dgram_recvmsg(struct sock *sk, struct msghdr *msg, size_t size,
 					      &err, &timeo, last));
 
 	if (!skb) { /* implies iolock unlocked */
-		unix_state_lock(sk);
 		/* Signal EOF on disconnected non-blocking SEQPACKET socket. */
 		if (sk->sk_type == SOCK_SEQPACKET && err == -EAGAIN &&
-		    (sk->sk_shutdown & RCV_SHUTDOWN))
+		    (READ_ONCE(sk->sk_shutdown) & RCV_SHUTDOWN))
 			err = 0;
-		unix_state_unlock(sk);
 		goto out;
 	}
 
-- 
2.50.0.727.gbf7dc18ff4-goog