Re: BUG in TCP for multithreaded apps

Alan Cox (alan@lxorguk.ukuu.org.uk)
Thu, 9 Dec 1999 13:23:59 +0000 (GMT)

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In reply to: David Malone: "TCP alwayskeepalive option."

> appears with multithreaded applications. If a thread is doing a select() on
> a file descriptor which is a socket in LISTEN state, and another thread is
> closing the file descriptor, then select() does not return (with EBADF set).

When you close a handle the final close only takes affect when everyone has
stopped using the handle. That is after the select returns

> My guess is that in tcp_close() for the special case state == TCP_LISTEN,
> there is no call to sk->state_change(sk) before it is marked as dead.

More likely it is that the poll() function for a listening socket does not
wake on closed. In fact this appears to be the problem.

If you edit net/ipv4/tcp.c:tcp_close() and move the

sk->shutdown = SHUTDOWN_MSK

above the
if (sk->state == LISTEN)

Then I think it will work. Let me know

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In reply to: David Malone: "TCP alwayskeepalive option."