[RFC PATCH v8 19/19] af_vsock: serialize writes to shared socket

[Arseny Krasnov]

This add logic, that serializes write access to single socket
by multiple threads. It is implemented be adding field with TID
of current writer. When writer tries to send something, it checks
that field is -1(free), else it sleep in the same way as waiting
for free space at peers' side.

This implementation is PoC and not related to SEQPACKET close, so
i've placed it after whole patchset.

Signed-off-by: Arseny Krasnov <arseny.krasnov@xxxxxxxxxxxxx>
---
 include/net/af_vsock.h   |  1 +
 net/vmw_vsock/af_vsock.c | 10 +++++++++-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
index 53d3f33dbdbf..786df80b9fc3 100644
--- a/include/net/af_vsock.h
+++ b/include/net/af_vsock.h
@@ -69,6 +69,7 @@ struct vsock_sock {
 	u64 buffer_size;
 	u64 buffer_min_size;
 	u64 buffer_max_size;
+	pid_t tid_owner;
 
 	/* Private to transport. */
 	void *trans;
diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
index 54bee7e643f4..d00f8c07a9d3 100644
--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c
@@ -1765,7 +1765,9 @@ static int vsock_connectible_sendmsg(struct socket *sock, struct msghdr *msg,
 		ssize_t written;
 
 		add_wait_queue(sk_sleep(sk), &wait);
-		while (vsock_stream_has_space(vsk) == 0 &&
+		while ((vsock_stream_has_space(vsk) == 0 ||
+			(vsk->tid_owner != current->pid &&
+			 vsk->tid_owner != -1)) &&
 		       sk->sk_err == 0 &&
 		       !(sk->sk_shutdown & SEND_SHUTDOWN) &&
 		       !(vsk->peer_shutdown & RCV_SHUTDOWN)) {
@@ -1796,6 +1798,8 @@ static int vsock_connectible_sendmsg(struct socket *sock, struct msghdr *msg,
 				goto out_err;
 			}
 		}
+
+		vsk->tid_owner = current->pid;
 		remove_wait_queue(sk_sleep(sk), &wait);
 
 		/* These checks occur both as part of and after the loop
@@ -1852,7 +1856,10 @@ static int vsock_connectible_sendmsg(struct socket *sock, struct msghdr *msg,
 			err = total_written;
 	}
 out:
+	vsk->tid_owner = -1;
 	release_sock(sk);
+	sk->sk_write_space(sk);
+
 	return err;
 }
 
@@ -2199,6 +2206,7 @@ static int vsock_create(struct net *net, struct socket *sock,
 		return -ENOMEM;
 
 	vsk = vsock_sk(sk);
+	vsk->tid_owner = -1;
 
 	if (sock->type == SOCK_DGRAM) {
 		ret = vsock_assign_transport(vsk, NULL);
-- 
2.25.1