Make `stack.Route` thread safe

Currently we rely on the user to take the lock on the endpoint that owns the
route, in order to modify it safely. We can instead move
`Route.RemoteLinkAddress` under `Route`'s mutex, and allow non-locking and
thread-safe access to other fields of `Route`.

PiperOrigin-RevId: 345461586

1 files changed, 4 insertions, 33 deletions

diff --git a/pkg/tcpip/transport/udp/endpoint.go b/pkg/tcpip/transport/udp/endpoint.go
index 912d33da8..5043e7aa5 100644
--- a/pkg/tcpip/transport/udp/endpoint.go
+++ b/pkg/tcpip/transport/udp/endpoint.go
@@ -18,7 +18,6 @@ import (
 	"fmt"
 	"sync/atomic"
 
-	"gvisor.dev/gvisor/pkg/sleep"
 	"gvisor.dev/gvisor/pkg/sync"
 	"gvisor.dev/gvisor/pkg/tcpip"
 	"gvisor.dev/gvisor/pkg/tcpip/buffer"
@@ -457,36 +456,9 @@ func (e *endpoint) write(p tcpip.Payloader, opts tcpip.WriteOptions) (int64, <-c
 		}
 	}
 
-	var route *stack.Route
-	var resolve func(waker *sleep.Waker) (ch <-chan struct{}, err *tcpip.Error)
-	var dstPort uint16
-	if to == nil {
-		route = e.route
-		dstPort = e.dstPort
-		resolve = func(waker *sleep.Waker) (ch <-chan struct{}, err *tcpip.Error) {
-			// Promote lock to exclusive if using a shared route, given that it may
-			// need to change in Route.Resolve() call below.
-			e.mu.RUnlock()
-			e.mu.Lock()
-
-			// Recheck state after lock was re-acquired.
-			if e.EndpointState() != StateConnected {
-				err = tcpip.ErrInvalidEndpointState
-			}
-			if err == nil && route.IsResolutionRequired() {
-				ch, err = route.Resolve(waker)
-			}
-
-			e.mu.Unlock()
-			e.mu.RLock()
-
-			// Recheck state after lock was re-acquired.
-			if e.EndpointState() != StateConnected {
-				err = tcpip.ErrInvalidEndpointState
-			}
-			return ch, err
-		}
-	} else {
+	route := e.route
+	dstPort := e.dstPort
+	if to != nil {
 		// Reject destination address if it goes through a different
 		// NIC than the endpoint was bound to.
 		nicID := to.NIC
@@ -516,7 +488,6 @@ func (e *endpoint) write(p tcpip.Payloader, opts tcpip.WriteOptions) (int64, <-c
 
 		route = r
 		dstPort = dst.Port
-		resolve = route.Resolve
 	}
 
 	if !e.ops.GetBroadcast() && route.IsOutboundBroadcast() {
@@ -524,7 +495,7 @@ func (e *endpoint) write(p tcpip.Payloader, opts tcpip.WriteOptions) (int64, <-c
 	}
 
 	if route.IsResolutionRequired() {
-		if ch, err := resolve(nil); err != nil {
+		if ch, err := route.Resolve(nil); err != nil {
 			if err == tcpip.ErrWouldBlock {
 				return 0, ch, tcpip.ErrNoLinkAddress
 			}