From d55f3a6b5e9d3979f83788339842abc1a3857438 Mon Sep 17 00:00:00 2001
From: Tamir Duberstein <tamird@google.com>
Date: Tue, 25 May 2021 09:53:11 -0700
Subject: Use embedded mutex pattern

PiperOrigin-RevId: 375728461
---
 pkg/tcpip/stack/nud.go | 71 +++++++++++++++++++++++---------------------------
 1 file changed, 33 insertions(+), 38 deletions(-)

diff --git a/pkg/tcpip/stack/nud.go b/pkg/tcpip/stack/nud.go
index 5a94e9ac6..02f905351 100644
--- a/pkg/tcpip/stack/nud.go
+++ b/pkg/tcpip/stack/nud.go
@@ -323,26 +323,21 @@ type Rand interface {
 type NUDState struct {
 	rng Rand
 
-	// mu protects the fields below.
-	//
-	// It is necessary for NUDState to handle its own locking since neighbor
-	// entries may access the NUD state from within the goroutine spawned by
-	// time.AfterFunc(). This goroutine may run concurrently with the main
-	// process for controlling the neighbor cache and would otherwise introduce
-	// race conditions if NUDState was not locked properly.
-	mu sync.RWMutex
-
-	config NUDConfigurations
-
-	// reachableTime is the duration to wait for a REACHABLE entry to
-	// transition into STALE after inactivity. This value is calculated with
-	// the algorithm defined in RFC 4861 section 6.3.2.
-	reachableTime time.Duration
-
-	expiration            time.Time
-	prevBaseReachableTime time.Duration
-	prevMinRandomFactor   float32
-	prevMaxRandomFactor   float32
+	mu struct {
+		sync.RWMutex
+
+		config NUDConfigurations
+
+		// reachableTime is the duration to wait for a REACHABLE entry to
+		// transition into STALE after inactivity. This value is calculated with
+		// the algorithm defined in RFC 4861 section 6.3.2.
+		reachableTime time.Duration
+
+		expiration            time.Time
+		prevBaseReachableTime time.Duration
+		prevMinRandomFactor   float32
+		prevMaxRandomFactor   float32
+	}
 }
 
 // NewNUDState returns new NUDState using c as configuration and the specified
@@ -351,7 +346,7 @@ func NewNUDState(c NUDConfigurations, rng Rand) *NUDState {
 	s := &NUDState{
 		rng: rng,
 	}
-	s.config = c
+	s.mu.config = c
 	return s
 }
 
@@ -359,14 +354,14 @@ func NewNUDState(c NUDConfigurations, rng Rand) *NUDState {
 func (s *NUDState) Config() NUDConfigurations {
 	s.mu.RLock()
 	defer s.mu.RUnlock()
-	return s.config
+	return s.mu.config
 }
 
 // SetConfig replaces the existing NUD configurations with c.
 func (s *NUDState) SetConfig(c NUDConfigurations) {
 	s.mu.Lock()
 	defer s.mu.Unlock()
-	s.config = c
+	s.mu.config = c
 }
 
 // ReachableTime returns the duration to wait for a REACHABLE entry to
@@ -377,13 +372,13 @@ func (s *NUDState) ReachableTime() time.Duration {
 	s.mu.Lock()
 	defer s.mu.Unlock()
 
-	if time.Now().After(s.expiration) ||
-		s.config.BaseReachableTime != s.prevBaseReachableTime ||
-		s.config.MinRandomFactor != s.prevMinRandomFactor ||
-		s.config.MaxRandomFactor != s.prevMaxRandomFactor {
+	if time.Now().After(s.mu.expiration) ||
+		s.mu.config.BaseReachableTime != s.mu.prevBaseReachableTime ||
+		s.mu.config.MinRandomFactor != s.mu.prevMinRandomFactor ||
+		s.mu.config.MaxRandomFactor != s.mu.prevMaxRandomFactor {
 		s.recomputeReachableTimeLocked()
 	}
-	return s.reachableTime
+	return s.mu.reachableTime
 }
 
 // recomputeReachableTimeLocked forces a recalculation of ReachableTime using
@@ -408,23 +403,23 @@ func (s *NUDState) ReachableTime() time.Duration {
 //
 // s.mu MUST be locked for writing.
 func (s *NUDState) recomputeReachableTimeLocked() {
-	s.prevBaseReachableTime = s.config.BaseReachableTime
-	s.prevMinRandomFactor = s.config.MinRandomFactor
-	s.prevMaxRandomFactor = s.config.MaxRandomFactor
+	s.mu.prevBaseReachableTime = s.mu.config.BaseReachableTime
+	s.mu.prevMinRandomFactor = s.mu.config.MinRandomFactor
+	s.mu.prevMaxRandomFactor = s.mu.config.MaxRandomFactor
 
-	randomFactor := s.config.MinRandomFactor + s.rng.Float32()*(s.config.MaxRandomFactor-s.config.MinRandomFactor)
+	randomFactor := s.mu.config.MinRandomFactor + s.rng.Float32()*(s.mu.config.MaxRandomFactor-s.mu.config.MinRandomFactor)
 
 	// Check for overflow, given that minRandomFactor and maxRandomFactor are
 	// guaranteed to be positive numbers.
-	if float32(math.MaxInt64)/randomFactor < float32(s.config.BaseReachableTime) {
-		s.reachableTime = time.Duration(math.MaxInt64)
+	if math.MaxInt64/randomFactor < float32(s.mu.config.BaseReachableTime) {
+		s.mu.reachableTime = time.Duration(math.MaxInt64)
 	} else if randomFactor == 1 {
 		// Avoid loss of precision when a large base reachable time is used.
-		s.reachableTime = s.config.BaseReachableTime
+		s.mu.reachableTime = s.mu.config.BaseReachableTime
 	} else {
-		reachableTime := int64(float32(s.config.BaseReachableTime) * randomFactor)
-		s.reachableTime = time.Duration(reachableTime)
+		reachableTime := int64(float32(s.mu.config.BaseReachableTime) * randomFactor)
+		s.mu.reachableTime = time.Duration(reachableTime)
 	}
 
-	s.expiration = time.Now().Add(2 * time.Hour)
+	s.mu.expiration = time.Now().Add(2 * time.Hour)
 }
-- 
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