libgit2: remove deadlock

Some scenarios may lead to deadlocks, specially
in image automation controller.

Signed-off-by: Paulo Gomes <paulo.gomes@weave.works>

Author: Paulo Gomes

pkg/git/libgit2/managed/ssh.go

@@ -54,6 +54,7 @@ import (
 	"runtime"
 	"strings"
 	"sync"
+	"sync/atomic"
 	"time"
 
 	"golang.org/x/crypto/ssh"
@@ -80,10 +81,12 @@ func registerManagedSSH() error {
 }
 
 func sshSmartSubtransportFactory(remote *git2go.Remote, transport *git2go.Transport) (git2go.SmartSubtransport, error) {
+	var closed int32 = 0
 	return &sshSmartSubtransport{
-		transport: transport,
-		ctx:       context.Background(),
-		logger:    logr.Discard(),
+		transport:      transport,
+		ctx:            context.Background(),
+		logger:         logr.Discard(),
+		closedSessions: &closed,
 	}, nil
 }
 
@@ -109,6 +112,8 @@ type sshSmartSubtransport struct {
 	stdin      io.WriteCloser
 	stdout     io.Reader
 
+	closedSessions *int32
+
 	con connection
 }
 
@@ -117,7 +122,6 @@ type connection struct {
 	session       *ssh.Session
 	currentStream *sshSmartSubtransportStream
 	connected     bool
-	m             sync.RWMutex
 }
 
 func (t *sshSmartSubtransport) Action(transportOptionsURL string, action git2go.SmartServiceAction) (git2go.SmartSubtransportStream, error) {
@@ -208,13 +212,11 @@ func (t *sshSmartSubtransport) Action(transportOptionsURL string, action git2go.
 		return nil
 	}
 
-	t.con.m.RLock()
-	if t.con.connected == true {
+	if t.con.connected {
 		// The connection is no longer shared across actions, so ensures
 		// all has been released before starting a new connection.
 		_ = t.Close()
 	}
-	t.con.m.RUnlock()
 
 	err = t.createConn(addr, sshConfig)
 	if err != nil {
@@ -251,7 +253,6 @@ func (t *sshSmartSubtransport) Action(transportOptionsURL string, action git2go.
 					"recovered from libgit2 ssh smart subtransport panic")
 			}
 		}()
-
 		var cancel context.CancelFunc
 		ctx := t.ctx
 
@@ -261,19 +262,17 @@ func (t *sshSmartSubtransport) Action(transportOptionsURL string, action git2go.
 			defer cancel()
 		}
 
+		closedAlready := atomic.LoadInt32(t.closedSessions)
 		for {
 			select {
 			case <-ctx.Done():
 				t.Close()
 				return nil
 
 			default:
-				t.con.m.RLock()
-				if !t.con.connected {
-					t.con.m.RUnlock()
+				if atomic.LoadInt32(t.closedSessions) > closedAlready {
 					return nil
 				}
-				t.con.m.RUnlock()
 
 				_, err := io.Copy(w, reader)
 				if err != nil {
@@ -311,10 +310,8 @@ func (t *sshSmartSubtransport) createConn(addr string, sshConfig *ssh.ClientConf
 		return err
 	}
 
-	t.con.m.Lock()
 	t.con.connected = true
 	t.con.client = ssh.NewClient(c, chans, reqs)
-	t.con.m.Unlock()
 
 	return nil
 }
@@ -330,8 +327,6 @@ func (t *sshSmartSubtransport) createConn(addr string, sshConfig *ssh.ClientConf
 // SmartSubTransport (i.e. unreleased resources, staled connections).
 func (t *sshSmartSubtransport) Close() error {
 	t.logger.V(logger.TraceLevel).Info("sshSmartSubtransport.Close()")
-	t.con.m.Lock()
-	defer t.con.m.Unlock()
 
 	t.con.currentStream = nil
 	if t.con.client != nil && t.stdin != nil {
@@ -349,8 +344,10 @@ func (t *sshSmartSubtransport) Close() error {
 		_ = t.con.client.Close()
 		t.logger.V(logger.TraceLevel).Info("close client")
 	}
+	t.con.client = nil
 
 	t.con.connected = false
+	atomic.AddInt32(t.closedSessions, 1)
 
 	return nil
 }