Repository: go
Issue: net: mass tcp dial timeout with the concurrency more than 10000
Labels: NeedsInvestigation

<!-- Please answer these questions before submitting your issue. Thanks! -->

### What version of Go are you using (`go version`)?

<pre>
$ go version
go version go1.12.1 linux/amd64

</pre>

### Does this issue reproduce with the latest release?
yes


### What operating system and processor architecture are you using (`go env`)?

<details><summary><code>go env</code> Output</summary><br><pre>
$ go env
GOARCH="amd64"
GOBIN="/home/zhoudazhuang/gobin/"
GOCACHE="/home/zhoudazhuang/.cache/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/zhoudazhuang/db11/jm/pro"
GOPROXY=""
GORACE=""
GOROOT="/home/zhoudazhuang/usr/local/go1.12.1/go"
GOTMPDIR=""
GOTOOLDIR="/home/zhoudazhuang/usr/local/go1.12.1/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build631445118=/tmp/go-build -gno-record-gcc-switches"
</pre></details>

### What did you do?
My tested code:
Server:
```
func main() {
	l, err := net.Listen("tcp", ":8888")
	if err != nil {
		log.Println("listen error:", err)
		return
	}

	for {
		c, err := l.Accept()
		if err != nil {
			log.Println("accept error:", err)
			break
		}
		go c.Close()
		// start a new goroutine to handle
		// the new connection.
		//log.Println("accept a new connection")
		//go handleConn(c)
	}
}
```
Client:
```
package main

import (
	"fmt"
	"github.com/jessevdk/go-flags"
	"net"
	"os"
	"sync"
	"time"
)

var args struct {
	Addr string `short:"a"  required:"yes" description:"服务端地址"`
	Concurrence int `short:"c"  required:"yes" description:"并发请求数"`
	Count int `short:"t" required:"yes" description:"测试次数"`
}

func main() {
	argParser := flags.NewNamedParser("tcp_test", flags.PassDoubleDash)
	argParser.AddGroup("Mock parameters", "", &args)
	_, err := argParser.Parse()
	if err != nil {
		fmt.Println(err)
		argParser.WriteHelp(os.Stdout)
		os.Exit(1)
	}
	fmt.Printf("测试参数: %+v\n",args)
	wg := sync.WaitGroup{}
	for j:=0; j<args.Count;j++ {
		for i:=0; i<args.Concurrence;i++{
			wg.Add(1)
			go func() {
				defer wg.Done()
				time.Sleep(time.Second*5)
				conn, err := net.DialTimeout("tcp", args.Addr, time.Second*3)
				if err != nil {
					fmt.Printf("dialog err: %+v i为%d:\n",err,j)
					return
				}
				time.Sleep(time.Millisecond*10)
				conn.Close()
			}()
		}
	}
	fmt.Println("start wait")
	wg.Wait()
	fmt.Println("ok")
}
```
The cmd:    ./Test -a 127.0.0.1:8888 -c 10000 -t 3
╰─># cat /proc/sys/net/ipv4/ip_local_port_range 
4096	65535
╰─># ulimit -a
core file size          (blocks, -c) 0
data seg size           (kbytes, -d) unlimited
scheduling priority             (-e) 0
file size               (blocks, -f) unlimited
pending signals                 (-i) 386849
max locked memory       (kbytes, -l) 64
max memory size         (kbytes, -m) unlimited
open files                      (-n) 10000000
pipe size            (512 bytes, -p) 8
POSIX message queues     (bytes, -q) 819200
real-time priority              (-r) 0
stack size              (kbytes, -s) 10240
cpu time               (seconds, -t) unlimited
max user processes              (-u) 1000000
virtual memory          (kbytes, -v) unlimited
file locks                      (-x) unlimited


╰─># free -h
             total       used       free     shared    buffers     cached
Mem:           94G        85G       9.3G       2.0M        54M        42G
-/+ buffers/cache:        42G        51G
Swap:           0B         0B         0B

╰─># lscpu
Architecture:          x86_64
CPU op-mode(s):        32-bit, 64-bit
Byte Order:            Little Endian
CPU(s):                32
On-line CPU(s) list:   0-31
Thread(s) per core:    2
Core(s) per socket:    8
Socket(s):             2
NUMA node(s):          2
Vendor ID:             GenuineIntel
CPU family:            6
Model:                 79
Model name:            Intel(R) Xeon(R) CPU E5-26xx v4
Stepping:              1
CPU MHz:               3192.606
BogoMIPS:              6385.21
Hypervisor vendor:     KVM
Virtualization type:   full
L1d cache:             32K
L1i cache:             32K
L2 cache:              4096K
NUMA node0 CPU(s):     0-15
NUMA node1 CPU(s):     16-31

<!--
If possible, provide a recipe for reproducing the error.
A complete runnable program is good.
A link on play.golang.org is best.
-->



### What did you expect to see?
no tcp dial timeout.


### What did you see instead?
dialog err: dial tcp 127.0.0.1:8888: i/o timeout i为3:
dialog err: dial tcp 127.0.0.1:8888: i/o timeout i为3:
dialog err: dial tcp 127.0.0.1:8888: i/o timeout i为3:
dialog err: dial tcp 127.0.0.1:8888: i/o timeout i为3: