Re: [RFC PATCH dlm/next 2/4] dlm: use SHUT_RDWR for SCTP shutdown

[Heming Zhao <heming.zhao@suse.com>]

On 4/30/25 04:29, Alexander Aring wrote:
> Currently SCTP shutdown() call gets stuck because there is no incoming
> EOF indicator on its socket. On the peer side the EOF indicator as
> recvmsg() returns 0 will be triggered as mechanism to flush the socket
> queue on the receive side. In SCTP recvmsg() function sctp_recvmsg() we
> can see that only if sk_shutdown has the bit RCV_SHUTDOWN set SCTP will
> recvmsg() will return EOF. The RCV_SHUTDOWN bit will only be set when
> shutdown with SHUT_RD is called. We use now SHUT_RDWR to also get a EOF
> indicator from recvmsg() call on the shutdown() initiator.
> 
> SCTP does not support half closed sockets and the semantic of SHUT_WR is
> different here, it seems that calling SHUT_WR on sctp sockets keeps the
> socket open to have the possibility to do some specific SCTP operations on
> it that we don't do here.
> 
> There exists still a difference in the limitations of TCP vs SCTP in
> case if we are required to have a half closed socket functionality. This
> was tried to archieve with DLM protocol changes in the past and
> hopefully we really don't require half closed socket functionality.
> 
> Signed-off-by: Alexander Aring <aahringo@redhat.com>

Tested-by: Heming zhao <heming.zhao@suse.com>
Reviewed-by: Heming zhao <heming.zhao@suse.com>

> ---
>   fs/dlm/lowcomms.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/dlm/lowcomms.c b/fs/dlm/lowcomms.c
> index 50c42b368c83..e4373bce1bc2 100644
> --- a/fs/dlm/lowcomms.c
> +++ b/fs/dlm/lowcomms.c
> @@ -160,6 +160,7 @@ struct dlm_proto_ops {
>   	bool try_new_addr;
>   	const char *name;
>   	int proto;
> +	int how;
>   
>   	void (*sockopts)(struct socket *sock);
>   	int (*bind)(struct socket *sock);
> @@ -810,7 +811,7 @@ static void shutdown_connection(struct connection *con, bool and_other)
>   		return;
>   	}
>   
> -	ret = kernel_sock_shutdown(con->sock, SHUT_WR);
> +	ret = kernel_sock_shutdown(con->sock, dlm_proto_ops->how);
>   	up_read(&con->sock_lock);
>   	if (ret) {
>   		log_print("Connection %p failed to shutdown: %d will force close",
> @@ -1858,6 +1859,7 @@ static int dlm_tcp_listen_bind(struct socket *sock)
>   static const struct dlm_proto_ops dlm_tcp_ops = {
>   	.name = "TCP",
>   	.proto = IPPROTO_TCP,
> +	.how = SHUT_WR,
>   	.sockopts = dlm_tcp_sockopts,
>   	.bind = dlm_tcp_bind,
>   	.listen_validate = dlm_tcp_listen_validate,
> @@ -1896,6 +1898,7 @@ static void dlm_sctp_sockopts(struct socket *sock)
>   static const struct dlm_proto_ops dlm_sctp_ops = {
>   	.name = "SCTP",
>   	.proto = IPPROTO_SCTP,
> +	.how = SHUT_RDWR,
>   	.try_new_addr = true,
>   	.sockopts = dlm_sctp_sockopts,
>   	.bind = dlm_sctp_bind,