found the goroutine leak in tikv client

[zier-one]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

func (s *serverOptionSuite) TestDDLPullerGoroutine(c *check.C) {
	go func() {
		err := http.ListenAndServe("localhost:8300", nil)
		log.Info("exit http server", zap.Error(err))
	}()

	_ = store.Register("tikv", tikv.Driver{})
	urlv, err := flags.NewURLsValue("http://127.0.0.1:2379")
	c.Assert(err, check.IsNil)

	tiPath := fmt.Sprintf("tikv://%s?disableGC=true", urlv.HostString())
	for {
		tiStore, err := store.New(tiPath)
		c.Assert(err, check.IsNil)
		time.Sleep(2 * time.Second)
		err = tiStore.Close()
		log.Info("one tick ", zap.Error(err))
		time.Sleep(2 * time.Second)
	}
}

run this code, and you can find the goroutine leak

2. What did you expect to see? (Required)

no goroutine leak

3. What did you see instead (Required)

goroutine leak

4. What is your TiDB version? (Required)

github.com/pingcap/tidb v1.1.0-beta.0.20200921080130-30cfb6af225c

[SunRunAway]

@leoppro would you like file a PR?

[cfzjywxk]

@tiancaiamao could help to take a look at this.

[cfzjywxk]

@MyonKeminta will help to verify if the leak still exist in master and the release branch.

[MyonKeminta]

The leak is found caused by not closing the etcd client in EtcdSafePointKV. The fix: #20808
It should exist in all release branches.

[ti-srebot]

Please edit this comment to complete the following information

Bug

Note: Make Sure that 'component', and 'severity' labels are added
Example for how to fill out the template: #20100

1. Root Cause Analysis (RCA) (optional)

The issue is caused by not closing the etcd client in EtcdSafePointKV after closing the tikvStore. Therefore every time open and close a tikv client, an etcd client will leak.

2. Symptom (optional)

goroutine leak after closing tikv client.

3. All Trigger Conditions (optional)

Closing a tikv client.

4. Workaround (optional)

-

5. Affected versions

[v2.0.0:v2.0.11], [v3.0.0:v3.0.19], [v3.1.0:v3.1.2], [v4.0.0:v4.0.8]

6. Fixed versions

v3.0.20, v4.0.9