Run segfaulting_server with 'rustc segfaulting_server.rs && export RUST_LOG=extra::net_tcp=debug && ./segfaulting_server', then run the client. The server will segfault after the 3rd client request. If you comment out lines 43 & 44, everything works great.

segfaulting_server.rs

extern mod extra;

use std::{int,io,result,task};
use extra::{net,net_tcp,uv};

fn server(outer_ch: Chan<Chan<~str>>) {
    let (accept_port, accept_chan) = stream();
    let (finish_port, finish_chan) = stream();

    let addr = extra::net_ip::v4::parse_addr("127.0.0.1");
    let port = 8080;

    do spawn {
        let backlog = 128;
        let iotask = &uv::global_loop::get();

        do net::tcp::listen(addr, port, backlog, iotask, |_| {}) |conn, kill_ch| {
            let (res_po, res_ch) = stream::<Option<net_tcp::TcpErrData>>();
            accept_chan.send((conn, res_ch));
            match res_po.recv() {
                Some(err_data) => kill_ch.send(Some(err_data)),
                None => ()
            }
        };
        finish_chan.send(());
    }

    do spawn {
        loop {
            let (conn, res_ch) = accept_port.recv();
            do spawn {
                let accept_result = net::tcp::accept(conn);
                match accept_result {
                    Err(accept_error) => {
                        res_ch.send(Some(accept_error));
                    },
                    Ok(sock) => {
                        res_ch.send(None);
                        let buf = net::tcp::socket_buf(sock);
                        let line = buf.read_line();
                        io::println(fmt!("From client: %s", line));
                        buf.write_str("pong\n");
                        //Comment these next 2 lines out and everything's great.
                        let (inner_po, inner_ch) = stream();
                        outer_ch.send(inner_ch);
                    }
                }
            }
        }
    }

    finish_port.recv();
}


fn main() {
    let (outer_po, outer_ch) = stream::<Chan<~str>>();
    do task::spawn_with(outer_ch) |ch| { server(ch); }
}

segfaulting_server_client.rs

extern mod extra;

use std::{int,io,result};
use extra::{net,net_tcp,uv};

fn main() {
    let addr = extra::net_ip::v4::parse_addr("127.0.0.1");
    let port = 8080;

    let mut counter = 0;

    loop {
        let iotask = &uv::global_loop::get();
        let connect_result = net_tcp::connect(copy addr, port, iotask);
        assert!(connect_result.is_ok());
        let sock = result::unwrap(connect_result);
        let buf = net_tcp::socket_buf(sock);
        buf.write_str(fmt!("ping %i\n", counter));
        let line = buf.read_line();
        io::println(fmt!("From server: %s", line));
        counter += 1;
        unsafe { std::libc::sleep(1); }
    }
}

segfaulting_server_output

$ rustc server.rs && export RUST_LOG=extra::net_tcp=debug && ./server
server.rs:3:10: 3:13 warning: unused import [-W unused-imports (default)]
server.rs:3 use std::{int,io,result,task};
                      ^~~
server.rs:3:17: 3:23 warning: unused import [-W unused-imports (default)]
server.rs:3 use std::{int,io,result,task};
                             ^~~~~~
server.rs:46:29: 46:37 warning: unused variable: `inner_po` [-W unused-variable (default)]
server.rs:46                         let (inner_po, inner_ch) = stream();
                                          ^~~~~~~~
server.rs:59:9: 59:17 warning: unused variable: `outer_po` [-W unused-variable (default)]
server.rs:59     let (outer_po, outer_ch) = stream::<Chan<~str>>();
                      ^~~~~~~~
warning: no debug symbols in executable (-arch x86_64)
rust: ~"addr: &{sin_family: 512, sin_port: 5632, sin_addr: 16777343, sin_zero: (0, 0, 0, 0, 0, 0, 0, 0)}"
rust: ~"\"in interact cb for tcp::accept\""
rust: ~"\"uv_tcp_init successful for client stream\""
rust: ~"successfully accepted client connection: stream 7f96d0d031f0, socket data 7f96d0d032f0"
rust: ~"ptrs: 7f96d0d032f0 7f96d0d032f0"
rust: ~"\"starting tcp::read\""
rust: ~"\"in tcp::read_start before interact loop\""
rust: ~"in tcp::read_start interact cb 140285725122848"
rust: ~"\"success doing uv_read_start\""
rust: ~"\"tcp::read before recv_timeout\""
rust: ~"\"tcp read on_alloc_cb!\""
rust: ~"tcp read on_alloc_cb h: 140285725127152 char_ptr: 140285728421376 sugsize: 65536"
rust: ~"entering on_tcp_read_cb stream: 7f96d0d031f0 nread: 7"
rust: ~"socket data is 7f96d0d032f0"
rust: ~"tcp on_read_cb nread: 7"
rust: ~"\"exiting on_tcp_read_cb\""
rust: ~"\"tcp::read after recv_timeout\""
rust: ~"\"tcp::read got data\""
rust: ~"\"in interact cb for tcp::read_stop\""
rust: ~"\"successfully called uv_read_stop\""
From client: ping 0
rust: ~"in interact cb for tcp::write 140285725122848"
rust: ~"\"uv_write() invoked successfully\""
rust: ~"\"successful write complete\""
rust: ~"interact dtor for tcp_socket stream 140285725127152 loop 140285725122848"
rust: ~"\"tcp_socket_dtor_close_cb exiting..\""
rust: ~"\"exiting dtor for tcp_socket\""
rust: ~"\"in interact cb for tcp::accept\""
rust: ~"\"uv_tcp_init successful for client stream\""
rust: ~"successfully accepted client connection: stream 7f96d0e00db0, socket data 7f96d0e00eb0"
rust: ~"ptrs: 7f96d0e00eb0 7f96d0e00eb0"
rust: ~"\"starting tcp::read\""
rust: ~"\"in tcp::read_start before interact loop\""
rust: ~"in tcp::read_start interact cb 140285725122848"
rust: ~"\"success doing uv_read_start\""
rust: ~"\"tcp read on_alloc_cb!\""
rust: ~"\"tcp::read before recv_timeout\""
rust: ~"tcp read on_alloc_cb h: 140285726166448 char_ptr: 140285736871424 sugsize: 65536"
rust: ~"entering on_tcp_read_cb stream: 7f96d0e00db0 nread: 7"
rust: ~"socket data is 7f96d0e00eb0"
rust: ~"tcp on_read_cb nread: 7"
rust: ~"\"exiting on_tcp_read_cb\""
rust: ~"\"tcp::read after recv_timeout\""
rust: ~"\"tcp::read got data\""
rust: ~"\"in interact cb for tcp::read_stop\""
rust: ~"\"successfully called uv_read_stop\""
From client: ping 1
rust: ~"in interact cb for tcp::write 140285725122848"
rust: ~"\"uv_write() invoked successfully\""
rust: ~"\"successful write complete\""
rust: task failed at 'option::unwrap none', /Users/jason/src/rust/src/libstd/option.rs:268
rust: ~"interact dtor for tcp_socket stream 140285726166448 loop 140285725122848"
rust: ~"\"tcp_socket_dtor_close_cb exiting..\""
rust: ~"\"exiting dtor for tcp_socket\""
rust: domain main @0x7f96d1812410 root task failed
rust: task failed at 'killed', /Users/jason/src/rust/src/libstd/pipes.rs:286
rust: task failed at 'killed', /Users/jason/src/rust/src/libstd/pipes.rs:286
rust: task failed at 'killed', /Users/jason/src/rust/src/libstd/pipes.rs:286
rust: task failed at 'killed', /Users/jason/src/rust/src/libstd/pipes.rs:286
rust: task failed at 'killed', /Users/jason/src/rust/src/libstd/pipes.rs:286
Segmentation fault: 11

backtrace from gdb:

Program received signal EXC_BAD_ACCESS, Could not access memory.
Reason: KERN_INVALID_ADDRESS at address: 0x0000000000000000
[Switching to process 4515 thread 0x1703]
0x0000000000000000 in ?? ()
(gdb) bt
#0 0x0000000000000000 in ?? ()
#1 0x000000010098bcf2 in uv__io_poll () at rust_task.cpp:1327
#2 0x000000010097dac8 in uv_run () at rust_task.cpp:1327
#3 0x00000001005a0ba1 in rust_uv_run__c_stack_shim ()
#4 0x000000010097cd51 in __morestack () at rust_task.cpp:1327
#5 0x000000010096d5de in rust_task::call_on_c_stack (this=0x100c02120, args=0x1, fn_ptr=0x1) at rust_task.h:484
#6 0x000000010096de0f in upcall_call_shim_on_c_stack (args=0x1051000c8, fn_ptr=0x1050fee30) at rust_upcall.cpp:70
#7 0x000000010064d7ee in uv_iotask::spawn_iotask::anon::expr_fn_21659 ()
#8 0x0000000100660722 in uv_global_loop::spawn_loop::anon::anon::anon::expr_fn_23194 ()
#9 0x00000001001c2590 in unstable::weak_task::weaken_task::_633e817ba3eab3b9::_07pre ()
#10 0x0000000100215c2b in __morestack ()

Previous frame inner to this frame (gdb could not unwind past this frame)