On Wed, May 2, 2018 at 5:06 PM, Michal Kubecek <mkubecek@xxxxxxx> wrote: > Hello, > > while investigating a bug, we noticed that DLM tries to connect an SCTP > socket in non-blocking mode using > > result = sock->ops->connect(sock, (struct sockaddr *)&daddr, addr_len, > O_NONBLOCK); > > which does not work. The reason is that inet_dgram_connect() cannot pass > its flags argument to sctp_connect() so that __sctp_connect() which does > the actual waiting resorts to checking sk->sk_socket->file->f_flags > instead. As the socket used by DLM is a kernel socket with no associated > file, it ends up blocking. > > TCP doesn't suffer from this problem as for TCP, the waiting is done in > inet_stream_connect() which has the flags argument. I also checked other > proto::connect handlers and sctp_connect() seems to be the only one with > this kind of problem. > > This could be worked around in DLM and further experiments indicate > current DLM code wouldn't actually handle the non-blocking connect > properly. But I still feel ignoring the flags argument is rather a trap > that should be fixed. It is a bug, https://bugzilla.redhat.com/show_bug.cgi?id=1251530 We have the fix which also includes some cleanup, and needs to do more testing. > > I have prepared a series adding flags argument to proto::connect and > using it in sctp_connect() and __sctp_connect(). But I'm not sure if > it's not too big hammer to address issue only affecting one handler. > So my question is: would such generic approach be preferred or should we, > rather make SCTP work the way TCP does, i.e. move the waiting from, > proto::connect() to proto_ops::connect()? This would require introducing > inet_seqpacket_connect() as inet_dgram_connect() is primarily intended > for use with UDP.) We don't fix it in the generic proto::connect, which will afftect many other places. We're replacing only sctp's proto_ops::connect with sctp_connect and leave its proto::connect as NULL, so that it can get this flags param without touching the generic struct and code. -- To unsubscribe from this list: send the line "unsubscribe linux-sctp" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
