mysqlctl: Improve handling of the lock file (#15404)

Signed-off-by: Dirkjan Bussink <[email protected]>

go/vt/mysqlctl/mysqld.go

@@ -460,6 +460,10 @@ func cleanupLockfile(socket string, ts string) error {
 		log.Errorf("%v: error parsing pid from lock file: %v", ts, err)
 		return err
 	}
+	if os.Getpid() == p {
+		log.Infof("%v: lock file at %s is ours, removing it", ts, lockPath)
+		return os.Remove(lockPath)
+	}
 	proc, err := os.FindProcess(p)
 	if err != nil {
 		log.Errorf("%v: error finding process: %v", ts, err)
@@ -469,7 +473,13 @@ func cleanupLockfile(socket string, ts string) error {
 	if err == nil {
 		// If the process still exists, it's not safe to
 		// remove the lock file, so we have to keep it around.
-		log.Errorf("%v: not removing socket lock file: %v with pid %v", ts, lockPath, p)
+		cmdline, err := os.ReadFile(fmt.Sprintf("/proc/%d/cmdline", p))
+		if err == nil {
+			name := string(bytes.ReplaceAll(cmdline, []byte{0}, []byte(" ")))
+			log.Errorf("%v: not removing socket lock file: %v with pid %v for %q", ts, lockPath, p, name)
+		} else {
+			log.Errorf("%v: not removing socket lock file: %v with pid %v (failed to read process name: %v)", ts, lockPath, p, err)
+		}
 		return fmt.Errorf("process %v is still running", p)
 	}
 	if !errors.Is(err, os.ErrProcessDone) {

go/vt/mysqlctl/mysqld_test.go

@@ -193,8 +193,14 @@ func TestCleanupLockfile(t *testing.T) {
 	assert.NoError(t, cleanupLockfile("mysql.sock", ts))
 	assert.NoFileExists(t, "mysql.sock.lock")
 
-	// If the lockfile exists, and the process is found, we don't clean it up.
+	// If the lockfile exists, and the process is found, but it's for ourselves,
+	// we clean it up.
 	os.WriteFile("mysql.sock.lock", []byte(strconv.Itoa(os.Getpid())), 0o600)
+	assert.NoError(t, cleanupLockfile("mysql.sock", ts))
+	assert.NoFileExists(t, "mysql.sock.lock")
+
+	// If the lockfile exists, and the process is found, we don't clean it up.
+	os.WriteFile("mysql.sock.lock", []byte(strconv.Itoa(os.Getppid())), 0o600)
 	assert.Error(t, cleanupLockfile("mysql.sock", ts))
 	assert.FileExists(t, "mysql.sock.lock")
 }