Inline handleSynSegment

This function has only one caller.

Remove segment reference count manipulation since it is only used
synchronously.

PiperOrigin-RevId: 399525343

pkg/tcpip/transport/tcp/accept.go

@@ -444,77 +444,6 @@ func (e *endpoint) notifyAborted() {
 	e.waiterQueue.Notify(waiter.EventHUp | waiter.EventErr | waiter.ReadableEvents | waiter.WritableEvents)
 }
 
-// handleSynSegment is called in its own goroutine once the listening endpoint
-// receives a SYN segment. It is responsible for completing the handshake and
-// queueing the new endpoint for acceptance.
-//
-// A limited number of these goroutines are allowed before TCP starts using SYN
-// cookies to accept connections.
-//
-// +checklocks:e.mu
-func (e *endpoint) handleSynSegment(ctx *listenContext, s *segment, opts header.TCPSynOptions) tcpip.Error {
-	defer s.decRef()
-
-	h, err := ctx.startHandshake(s, opts, &waiter.Queue{}, e.owner)
-	if err != nil {
-		e.stack.Stats().TCP.FailedConnectionAttempts.Increment()
-		e.stats.FailedConnectionAttempts.Increment()
-		atomic.AddInt32(&e.synRcvdCount, -1)
-		return err
-	}
-
-	go func() {
-		// Note that startHandshake returns a locked endpoint. The
-		// force call here just makes it so.
-		if err := h.complete(); err != nil { // +checklocksforce
-			e.stack.Stats().TCP.FailedConnectionAttempts.Increment()
-			e.stats.FailedConnectionAttempts.Increment()
-			ctx.cleanupFailedHandshake(h)
-			atomic.AddInt32(&e.synRcvdCount, -1)
-			return
-		}
-		ctx.cleanupCompletedHandshake(h)
-		h.ep.startAcceptedLoop()
-		e.stack.Stats().TCP.PassiveConnectionOpenings.Increment()
-
-		// Deliver the endpoint to the accept queue.
-		e.mu.Lock()
-		e.pendingAccepted.Add(1)
-		e.mu.Unlock()
-		defer e.pendingAccepted.Done()
-
-		// Drop the lock before notifying to avoid deadlock in user-specified
-		// callbacks.
-		delivered := func() bool {
-			e.acceptMu.Lock()
-			defer e.acceptMu.Unlock()
-			for {
-				if e.accepted == (accepted{}) {
-					// If the listener has transitioned out of the listen state (accepted
-					// is the zero value), the new endpoint is reset instead.
-					return false
-				}
-				if e.accepted.acceptQueueIsFullLocked() {
-					e.acceptCond.Wait()
-					continue
-				}
-
-				e.accepted.endpoints.PushBack(h.ep)
-				atomic.AddInt32(&e.synRcvdCount, -1)
-				return true
-			}
-		}()
-
-		if delivered {
-			e.waiterQueue.Notify(waiter.ReadableEvents)
-		} else {
-			h.ep.notifyProtocolGoroutine(notifyReset)
-		}
-	}()
-
-	return nil
-}
-
 func (e *endpoint) synRcvdBacklogFull() bool {
 	e.acceptMu.Lock()
 	acceptedCap := e.accepted.cap
@@ -581,10 +510,69 @@ func (e *endpoint) handleListenSegment(ctx *listenContext, s *segment) tcpip.Err
 
 		opts := parseSynSegmentOptions(s)
 		if !alwaysUseSynCookies && !e.synRcvdBacklogFull() {
-			s.incRef()
 			atomic.AddInt32(&e.synRcvdCount, 1)
-			return e.handleSynSegment(ctx, s, opts)
+
+			h, err := ctx.startHandshake(s, opts, &waiter.Queue{}, e.owner)
+			if err != nil {
+				e.stack.Stats().TCP.FailedConnectionAttempts.Increment()
+				e.stats.FailedConnectionAttempts.Increment()
+				atomic.AddInt32(&e.synRcvdCount, -1)
+				return err
+			}
+
+			go func() {
+				// Note that startHandshake returns a locked endpoint. The force call
+				// here just makes it so.
+				if err := h.complete(); err != nil { // +checklocksforce
+					e.stack.Stats().TCP.FailedConnectionAttempts.Increment()
+					e.stats.FailedConnectionAttempts.Increment()
+					ctx.cleanupFailedHandshake(h)
+					atomic.AddInt32(&e.synRcvdCount, -1)
+					return
+				}
+				ctx.cleanupCompletedHandshake(h)
+				h.ep.startAcceptedLoop()
+				e.stack.Stats().TCP.PassiveConnectionOpenings.Increment()
+
+				// Deliver the endpoint to the accept queue.
+				e.mu.Lock()
+				e.pendingAccepted.Add(1)
+				e.mu.Unlock()
+				defer e.pendingAccepted.Done()
+
+				// Drop the lock before notifying to avoid deadlock in user-specified
+				// callbacks.
+				delivered := func() bool {
+					e.acceptMu.Lock()
+					defer e.acceptMu.Unlock()
+					for {
+						if e.accepted == (accepted{}) {
+							// If the listener has transitioned out of the listen state
+							// (accepted is the zero value), the new endpoint is reset
+							// instead.
+							return false
+						}
+						if e.accepted.acceptQueueIsFullLocked() {
+							e.acceptCond.Wait()
+							continue
+						}
+
+						e.accepted.endpoints.PushBack(h.ep)
+						atomic.AddInt32(&e.synRcvdCount, -1)
+						return true
+					}
+				}()
+
+				if delivered {
+					e.waiterQueue.Notify(waiter.ReadableEvents)
+				} else {
+					h.ep.notifyProtocolGoroutine(notifyReset)
+				}
+			}()
+
+			return nil
 		}
+
 		route, err := e.stack.FindRoute(s.nicID, s.dstAddr, s.srcAddr, s.netProto, false /* multicastLoop */)
 		if err != nil {
 			return err
@@ -789,9 +777,6 @@ func (e *endpoint) protocolListenLoop(rcvWnd seqnum.Size) {
 	ctx := newListenContext(e.stack, e.protocol, e, rcvWnd, v6Only, e.NetProto)
 
 	defer func() {
-		// Mark endpoint as closed. This will prevent goroutines running
-		// handleSynSegment() from attempting to queue new connections
-		// to the endpoint.
 		e.setEndpointState(StateClose)
 
 		// Close any endpoints in SYN-RCVD state.