On Fri, Sep 5, 2014 at 12:40 PM, Chris Perl <chris.perl@xxxxxxxxx> wrote:
> When attempting to establish a local ephemeral endpoint for a TCP or UDP
> socket, do not explicitly call bind, instead let it happen implicilty when the
> socket is first used.
>
> The main motivating factor for this change is when TCP runs out of unique
> ephemeral ports (i.e. cannot find any ephemeral ports which are not a part of
> *any* TCP connection). In this situation if you explicitly call bind, then the
> call will fail with EADDRINUSE. However, if you allow the allocation of an
> ephemeral port to happen implicitly as part of connect (or other functions),
> then ephemeral ports can be reused, so long as the combination of (local_ip,
> local_port, remote_ip, remote_port) is unique for TCP sockets on the system.
>
> This doesn't matter for UDP sockets, but it seemed easiest to treat TCP and UDP
> sockets the same.
>
> This can allow mount.nfs(8) to continue to function successfully, even in the
> face of misbehaving applications which are creating a large number of TCP
> connections.
>
> Signed-off-by: Chris Perl <chris.perl@xxxxxxxxx>
> ---
> net/sunrpc/xprtsock.c | 20 ++++++++++++++++++--
> 1 file changed, 18 insertions(+), 2 deletions(-)
>
> diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
> index 43cd89e..7ed47b4 100644
> --- a/net/sunrpc/xprtsock.c
> +++ b/net/sunrpc/xprtsock.c
> @@ -1746,13 +1746,29 @@ static int xs_bind(struct sock_xprt *transport, struct socket *sock)
> unsigned short port = xs_get_srcport(transport);
> unsigned short last;
>
> + /*
> + * If we are asking for any ephemeral port (i.e. port == 0 &&
> + * transport->xprt.resvport == 0), don't bind. Let the local
> + * port selection happen implicitly when the socket is used
> + * (for example at connect time).
> + *
> + * This ensures that we can continue to establish TCP
> + * connections even when all local ephemeral ports are already
> + * a part of some TCP connection. This makes no difference
> + * for UDP sockets, but also doens't harm them.
> + *
> + * If we're asking for any reserved port (i.e. port == 0 &&
> + * transport->xprt.resvport == 1) xs_get_srcport above will
> + * ensure that port is non-zero and we will bind as needed.
> + */
> + if (port == 0)
> + return 0;
> +
> memcpy(&myaddr, &transport->srcaddr, transport->xprt.addrlen);
> do {
> rpc_set_port((struct sockaddr *)&myaddr, port);
> err = kernel_bind(sock, (struct sockaddr *)&myaddr,
> transport->xprt.addrlen);
> - if (port == 0)
> - break;
> if (err == 0) {
> transport->srcport = port;
> break;
> --
> 1.8.3.1
>
This change looks harmless to me, but since we've lived with the
current situation for several years, I'm not prepared to consider it a
must-fix for 3.17 quite yet. If it's OK with you, I'll therefore queue
it for 3.18.
--
Trond Myklebust
Linux NFS client maintainer, PrimaryData
trond.myklebust@xxxxxxxxxxxxxxx
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