Date: Sun, 03 Jul 2011 18:00:09 +0300 From: Mikolaj Golub <trociny@freebsd.org> To: freebsd-net@freebsd.org Cc: Kostik Belousov <kib@FreeBSD.org>, Pawel Jakub Dawidek <pjd@FreeBSD.org>, Andre Oppermann <andre@FreeBSD.org> Subject: soreceive_stream: issues with O_NONBLOCK Message-ID: <867h7zxvd2.fsf@kopusha.home.net>
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Hi, Trying soreceive_stream I found that many applications (like firefox, pidgin, gnus) might hang in soreceive_stream/sbwait. It was shown up that the issue was with O_NONBLOCK connections -- they blocked in recv() when should not have been. This can be checked with this simple test: http://people.freebsd.org/~trociny/test_nonblock.c In soreceive_stream we have the following code that looks wrong: 1968 /* Socket buffer is empty and we shall not block. */ 1969 if (sb->sb_cc == 0 && 1970 ((sb->sb_flags & SS_NBIO) || (flags & (MSG_DONTWAIT|MSG_NBIO)))) { 1971 error = EAGAIN; 1972 goto out; 1973 } It should check so->so_state agains SS_NBIO, not sb->sb_flags. But just changing this is not enough. This check is called too early -- before checking that socket state is not SBS_CANTRCVMORE. As a result, if the peer closes the connection recv() returns EAGAIN instead of 0. See this example: http://people.freebsd.org/~trociny/test_close.c So I moved the "nonblock" check below SBS_CANTRCVMORE check and ended up with this patch: http://people.freebsd.org/~trociny/uipc_socket.c.soreceive_stream.patch It works for me fine. Also, this part looks wrong: 1958 /* We will never ever get anything unless we are connected. */ 1959 if (!(so->so_state & (SS_ISCONNECTED|SS_ISDISCONNECTED))) { 1960 /* When disconnecting there may be still some data left. */ 1961 if (sb->sb_cc > 0) 1962 goto deliver; 1963 if (!(so->so_state & SS_ISDISCONNECTED)) 1964 error = ENOTCONN; 1965 goto out; 1966 } Why we check in 1959 that state is not SS_ISDISCONNECTED? If it is valid then the check at 1963 is useless becase it will be always true. Shouldn't it be something like below? if (!(so->so_state & (SS_ISCONNECTED|SS_ISCONNECTING))) { /* When disconnecting there may be still some data left. */ if (sb->sb_cc > 0) goto deliver; error = ENOTCONN; goto out; } (I don't see why we souldn't set ENOTCONN if the state is SS_ISDISCONNECTED). And the last :-). Currently, to try soreceive_stream one need to rebuild kernel with TCP_SORECEIVE_STREAM and then set tunable net.inet.tcp.soreceive_stream. Why do we need TCP_SORECEIVE_STREAM option? Wouldn't tunable be enough? It would simplify trying soreceive_stream by users and we might have more testing/feedback. -- Mikolaj Golub
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