Re: PROBLEM: Linux kernel 2.6.31 IPv4 TCP fails to open huge amount of outgoing connections (unable to bind ... )

[Eric Dumazet <eric.dumazet@gmail.com>]

Le mercredi 21 avril 2010 à 13:58 +0400, Evgeniy Polyakov a écrit :
> On Wed, Apr 21, 2010 at 11:02:15AM +0200, Eric Dumazet (eric.dumazet@gmail.com) wrote:
> > Le mercredi 21 avril 2010 à 12:25 +0400, Evgeniy Polyakov a écrit :
> > 
> > > I believe this is a useful patch, but it addresses a different issue.
> > > This path should not fire up when we bind to single address.
> > 
> > Well, the real problem is that following sequence can happen :
> > 
> > socket(PF_INET, SOCK_STREAM, IPPROTO_IP) = 5
> > setsockopt(5, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
> > bind(5, {sa_family=AF_INET, sin_port=htons(0), sin_addr=inet_addr("127.0.0.2")}, 16) = 0
> > getsockname(5, {sa_family=AF_INET, sin_port=htons(34000), sin_addr=inet_addr("127.0.0.2")}, [16]) = 0
> > socket(PF_INET, SOCK_STREAM, IPPROTO_IP) = 6
> > setsockopt(6, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
> > bind(6, {sa_family=AF_INET, sin_port=htons(0), sin_addr=inet_addr("127.0.0.2")}, 16) = 0
> > getsockname(6, {sa_family=AF_INET, sin_port=htons(34002), sin_addr=inet_addr("127.0.0.2")}, [16]) = 0
> > socket(PF_INET, SOCK_STREAM, IPPROTO_IP) = 7
> > setsockopt(7, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
> > bind(7, {sa_family=AF_INET, sin_port=htons(0), sin_addr=inet_addr("127.0.0.2")}, 16) = 0
> > getsockname(7, {sa_family=AF_INET, sin_port=htons(34001), sin_addr=inet_addr("127.0.0.2")}, [16]) = 0
> > socket(PF_INET, SOCK_STREAM, IPPROTO_IP) = 8
> > setsockopt(8, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
> > bind(8, {sa_family=AF_INET, sin_port=htons(0), sin_addr=inet_addr("127.0.0.2")}, 16) = 0
> > getsockname(8, {sa_family=AF_INET, sin_port=htons(34002), sin_addr=inet_addr("127.0.0.2")}, [16]) = 0
> > socket(PF_INET, SOCK_STREAM, IPPROTO_IP) = 9
> > setsockopt(9, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
> > bind(9, {sa_family=AF_INET, sin_port=htons(0), sin_addr=inet_addr("127.0.0.2")}, 16) = 0
> > getsockname(9, {sa_family=AF_INET, sin_port=htons(34000), sin_addr=inet_addr("127.0.0.2")}, [16]) = 0
> > socket(PF_INET, SOCK_STREAM, IPPROTO_IP) = 10
> > setsockopt(10, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
> > bind(10, {sa_family=AF_INET, sin_port=htons(0), sin_addr=inet_addr("127.0.0.2")}, 16) = 0
> > getsockname(10, {sa_family=AF_INET, sin_port=htons(34002), sin_addr=inet_addr("127.0.0.2")}, [16]) = 0
> > socket(PF_INET, SOCK_STREAM, IPPROTO_IP) = 11
> > setsockopt(11, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
> > bind(11, {sa_family=AF_INET, sin_port=htons(0), sin_addr=inet_addr("127.0.0.2")}, 16) = 0
> > getsockname(11, {sa_family=AF_INET, sin_port=htons(34001), sin_addr=inet_addr("127.0.0.2")}, [16]) = 0
> > 
> > 
> > Note ports are given several times for different sockets.
> > 
> > So several sockets are 'bound' to same IP:port values
> 
> That's kind of weird, since address is the same. I'm curious why bind
> conflict does not resolve that. Likely because socket is not yet
> connected.
> 
> > At connect() time, we refuse and say address is not available.
> 
> Yup. But isn't it a different problem from what Gaspar observed?
> Netcat connects after bind so it should not be an issue here.
> 

Well, just replace the "#if 0" in program, and i'll connect, and
reproduce same problem

conflict only checks :

                        if (!reuse || !sk2->sk_reuse ||
                            sk2->sk_state == TCP_LISTEN) {
                                const __be32 sk2_rcv_saddr =
inet_rcv_saddr(sk2);
                                if (!sk2_rcv_saddr || !sk_rcv_saddr ||
                                    sk2_rcv_saddr == sk_rcv_saddr)
                                        break;
                        }


ie it wont re-allocate a port only if a listener uses this port.

If sk2 is connected or close, it doesnt matter, and port can be reused.