[PATCH net-next 1/3] net: qrtr: do not take the sock lock on blocking recv

[Chunkai Deng]

qrtr_recvmsg() takes lock_sock() before skb_recv_datagram() and keeps it
while waiting for a datagram. Any other call on the same socket, such as
sendmsg(), bind() or ioctl(), blocks until a packet arrives.

Take the lock only once a datagram has been dequeued. The receive queue
has its own lock and the enqueue path never takes the socket lock. The
lock is still needed around the copy and skb_free_datagram(), since
TIOCINQ peeks the queue under lock_sock() only.

Testing SOCK_ZAPPED without the lock means a recv() racing with bind()
may return -EADDRNOTAVAIL for a port that was just published. There is
no ordering between the two calls anyway.

Signed-off-by: Chunkai Deng <chunkai.deng@xxxxxxxxxxxxxxxx>
---
 net/qrtr/af_qrtr.c | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/net/qrtr/af_qrtr.c b/net/qrtr/af_qrtr.c
index d02ef9a74c3ca..2d7339338e460 100644
--- a/net/qrtr/af_qrtr.c
+++ b/net/qrtr/af_qrtr.c
@@ -1034,18 +1034,14 @@ static int qrtr_recvmsg(struct socket *sock, struct msghdr *msg,
 	struct qrtr_cb *cb;
 	int copied, rc;
 
-	lock_sock(sk);
-
-	if (sock_flag(sk, SOCK_ZAPPED)) {
-		release_sock(sk);
+	if (sock_flag(sk, SOCK_ZAPPED))
 		return -EADDRNOTAVAIL;
-	}
 
 	skb = skb_recv_datagram(sk, flags, &rc);
-	if (!skb) {
-		release_sock(sk);
+	if (!skb)
 		return rc;
-	}
+
+	lock_sock(sk);
 	cb = (struct qrtr_cb *)skb->cb;
 
 	copied = skb->len;

-- 
2.43.0