quic: avoid deadlock on listener close

Avoid holding Listener.connsMu while blocking on a Conn's loop,
since the Conn can acquire the mutex while shutting down.

Fix Conn.waitReady to check conn readiness before checking
the Context doneness. This doesn't make a difference in the
current exported API, but this simplifies some tests and
will be useful once 0-RTT is implemented.

Refactor a bit of the testConn datagram handling to use a
testListener type, which helped expose the above deadlock
and will be useful for writing tests which don't involve
a Conn.

Change-Id: I064fca99ae9a165631fc0ff46eb334d25d7dd957
Reviewed-on: https://go-review.googlesource.com/c/net/+/529935
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Jonathan Amsterdam <jba@google.com>

internal/quic/conn_close.go

@@ -168,6 +168,13 @@ func (c *Conn) enterDraining(err error) {
 }
 
 func (c *Conn) waitReady(ctx context.Context) error {
+	select {
+	case <-c.lifetime.readyc:
+		return nil
+	case <-c.lifetime.drainingc:
+		return c.lifetime.finalErr
+	default:
+	}
 	select {
 	case <-c.lifetime.readyc:
 		return nil
@@ -215,7 +222,7 @@ func (c *Conn) Abort(err error) {
 	if err == nil {
 		err = localTransportError(errNo)
 	}
-	c.runOnLoop(func(now time.Time, c *Conn) {
+	c.sendMsg(func(now time.Time, c *Conn) {
 		c.abort(now, err)
 	})
 }
@@ -228,11 +235,18 @@ func (c *Conn) abort(now time.Time, err error) {
 	c.lifetime.localErr = err
 }
 
+// abortImmediately terminates a connection.
+// The connection does not send a CONNECTION_CLOSE, and skips the draining period.
+func (c *Conn) abortImmediately(now time.Time, err error) {
+	c.abort(now, err)
+	c.enterDraining(err)
+	c.exited = true
+}
+
 // exit fully terminates a connection immediately.
 func (c *Conn) exit() {
-	c.runOnLoop(func(now time.Time, c *Conn) {
+	c.sendMsg(func(now time.Time, c *Conn) {
 		c.enterDraining(errors.New("connection closed"))
 		c.exited = true
 	})
-	<-c.donec
 }

internal/quic/conn_test.go

@@ -13,9 +13,7 @@ import (
 	"errors"
 	"flag"
 	"fmt"
-	"io"
 	"math"
-	"net"
 	"net/netip"
 	"reflect"
 	"strings"
@@ -112,7 +110,7 @@ const maxTestKeyPhases = 3
 type testConn struct {
 	t              *testing.T
 	conn           *Conn
-	listener       *Listener
+	listener       *testListener
 	now            time.Time
 	timer          time.Time
 	timerLastFired time.Time
@@ -231,8 +229,8 @@ func newTestConn(t *testing.T, side connSide, opts ...any) *testConn {
 	tc.peerTLSConn.SetTransportParameters(marshalTransportParameters(peerProvidedParams))
 	tc.peerTLSConn.Start(context.Background())
 
-	tc.listener = newListener((*testConnUDPConn)(tc), config, (*testConnHooks)(tc))
-	conn, err := tc.listener.newConn(
+	tc.listener = newTestListener(t, config, (*testConnHooks)(tc))
+	conn, err := tc.listener.l.newConn(
 		tc.now,
 		side,
 		initialConnID,
@@ -335,7 +333,7 @@ func (tc *testConn) cleanup() {
 		return
 	}
 	tc.conn.exit()
-	tc.listener.Close(context.Background())
+	<-tc.conn.donec
 }
 
 func (tc *testConn) logDatagram(text string, d *testDatagram) {
@@ -388,6 +386,7 @@ func (tc *testConn) write(d *testDatagram) {
 	for len(buf) < d.paddedSize {
 		buf = append(buf, 0)
 	}
+	// TODO: This should use tc.listener.write.
 	tc.conn.sendMsg(&datagram{
 		b: buf,
 	})
@@ -457,11 +456,10 @@ func (tc *testConn) readDatagram() *testDatagram {
 	tc.wait()
 	tc.sentPackets = nil
 	tc.sentFrames = nil
-	if len(tc.sentDatagrams) == 0 {
+	buf := tc.listener.read()
+	if buf == nil {
 		return nil
 	}
-	buf := tc.sentDatagrams[0]
-	tc.sentDatagrams = tc.sentDatagrams[1:]
 	d := tc.parseTestDatagram(buf)
 	// Log the datagram before removing ignored frames.
 	// When things go wrong, it's useful to see all the frames.
@@ -982,31 +980,6 @@ func testPeerConnID(seq int64) []byte {
 	return []byte{0xbe, 0xee, 0xff, byte(seq)}
 }
 
-// testConnUDPConn implements UDPConn.
-type testConnUDPConn testConn
-
-func (tc *testConnUDPConn) Close() error {
-	close(tc.recvDatagram)
-	return nil
-}
-
-func (tc *testConnUDPConn) LocalAddr() net.Addr {
-	return net.UDPAddrFromAddrPort(netip.MustParseAddrPort("127.0.0.1:443"))
-}
-
-func (tc *testConnUDPConn) ReadMsgUDPAddrPort(b, control []byte) (n, controln, flags int, _ netip.AddrPort, _ error) {
-	for d := range tc.recvDatagram {
-		n = copy(b, d.b)
-		return n, 0, 0, d.addr, nil
-	}
-	return 0, 0, 0, netip.AddrPort{}, io.EOF
-}
-
-func (tc *testConnUDPConn) WriteToUDPAddrPort(b []byte, addr netip.AddrPort) (int, error) {
-	tc.sentDatagrams = append(tc.sentDatagrams, append([]byte(nil), b...))
-	return len(b), nil
-}
-
 // canceledContext returns a canceled Context.
 //
 // Functions which take a context preference progress over cancelation.

internal/quic/listener.go

@@ -104,7 +104,7 @@ func (l *Listener) Close(ctx context.Context) error {
 	if !l.closing {
 		l.closing = true
 		for c := range l.conns {
-			c.Close()
+			c.Abort(errors.New("listener closed"))
 		}
 		if len(l.conns) == 0 {
 			l.udpConn.Close()

internal/quic/listener_test.go

@@ -10,6 +10,8 @@ import (
 	"bytes"
 	"context"
 	"io"
+	"net"
+	"net/netip"
 	"testing"
 )
 
@@ -86,3 +88,76 @@ func newLocalListener(t *testing.T, side connSide, conf *Config) *Listener {
 	})
 	return l
 }
+
+type testListener struct {
+	t             *testing.T
+	l             *Listener
+	recvc         chan *datagram
+	idlec         chan struct{}
+	sentDatagrams [][]byte
+}
+
+func newTestListener(t *testing.T, config *Config, testHooks connTestHooks) *testListener {
+	tl := &testListener{
+		t:     t,
+		recvc: make(chan *datagram),
+		idlec: make(chan struct{}),
+	}
+	tl.l = newListener((*testListenerUDPConn)(tl), config, testHooks)
+	t.Cleanup(tl.cleanup)
+	return tl
+}
+
+func (tl *testListener) cleanup() {
+	tl.l.Close(canceledContext())
+}
+
+func (tl *testListener) wait() {
+	tl.idlec <- struct{}{}
+}
+
+func (tl *testListener) write(d *datagram) {
+	tl.recvc <- d
+	tl.wait()
+}
+
+func (tl *testListener) read() []byte {
+	tl.wait()
+	if len(tl.sentDatagrams) == 0 {
+		return nil
+	}
+	d := tl.sentDatagrams[0]
+	tl.sentDatagrams = tl.sentDatagrams[1:]
+	return d
+}
+
+// testListenerUDPConn implements UDPConn.
+type testListenerUDPConn testListener
+
+func (tl *testListenerUDPConn) Close() error {
+	close(tl.recvc)
+	return nil
+}
+
+func (tl *testListenerUDPConn) LocalAddr() net.Addr {
+	return net.UDPAddrFromAddrPort(netip.MustParseAddrPort("127.0.0.1:443"))
+}
+
+func (tl *testListenerUDPConn) ReadMsgUDPAddrPort(b, control []byte) (n, controln, flags int, _ netip.AddrPort, _ error) {
+	for {
+		select {
+		case d, ok := <-tl.recvc:
+			if !ok {
+				return 0, 0, 0, netip.AddrPort{}, io.EOF
+			}
+			n = copy(b, d.b)
+			return n, 0, 0, d.addr, nil
+		case <-tl.idlec:
+		}
+	}
+}
+
+func (tl *testListenerUDPConn) WriteToUDPAddrPort(b []byte, addr netip.AddrPort) (int, error) {
+	tl.sentDatagrams = append(tl.sentDatagrams, append([]byte(nil), b...))
+	return len(b), nil
+}