From 8febc348c8d7b4307e77972422d37bed5eb54b59 Mon Sep 17 00:00:00 2001
From: Felix Lange <fjl@twurst.com>
Date: Thu, 24 Jan 2019 12:48:34 +0100
Subject: [PATCH] light: fix disableCheckFreq locking

This change unbreaks the build and removes racy access to
disableCheckFreq. Even though the field is set while holding
the lock, it was read outside of the protected section.
---
 light/lightchain.go | 32 +++++++++++++-------------------
 1 file changed, 13 insertions(+), 19 deletions(-)

diff --git a/light/lightchain.go b/light/lightchain.go
index 47161c9ef7..3691f1304f 100644
--- a/light/lightchain.go
+++ b/light/lightchain.go
@@ -35,7 +35,7 @@ import (
 	"github.com/ethereum/go-ethereum/log"
 	"github.com/ethereum/go-ethereum/params"
 	"github.com/ethereum/go-ethereum/rlp"
-	"github.com/hashicorp/golang-lru"
+	lru "github.com/hashicorp/golang-lru"
 )
 
 var (
@@ -50,6 +50,7 @@ type LightChain struct {
 	hc            *core.HeaderChain
 	indexerConfig *IndexerConfig
 	chainDb       ethdb.Database
+	engine        consensus.Engine
 	odr           OdrBackend
 	chainFeed     event.Feed
 	chainSideFeed event.Feed
@@ -57,21 +58,18 @@ type LightChain struct {
 	scope         event.SubscriptionScope
 	genesisBlock  *types.Block
 
-	chainmu sync.RWMutex
-
 	bodyCache    *lru.Cache // Cache for the most recent block bodies
 	bodyRLPCache *lru.Cache // Cache for the most recent block bodies in RLP encoded format
 	blockCache   *lru.Cache // Cache for the most recent entire blocks
 
+	chainmu sync.RWMutex // protects header inserts
 	quit    chan struct{}
-	running int32 // running must be called automically
-	// procInterrupt must be atomically called
-	procInterrupt int32 // interrupt signaler for block processing
-	wg            sync.WaitGroup
+	wg      sync.WaitGroup
 
-	engine consensus.Engine
-
-	disableCheckFreq bool
+	// Atomic boolean switches:
+	running          int32 // whether LightChain is running or stopped
+	procInterrupt    int32 // interrupts chain insert
+	disableCheckFreq int32 // disables header verification
 }
 
 // NewLightChain returns a fully initialised light chain using information
@@ -356,7 +354,7 @@ func (self *LightChain) postChainEvents(events []interface{}) {
 // In the case of a light chain, InsertHeaderChain also creates and posts light
 // chain events when necessary.
 func (self *LightChain) InsertHeaderChain(chain []*types.Header, checkFreq int) (int, error) {
-	if self.disableCheckFreq {
+	if atomic.LoadInt32(&self.disableCheckFreq) == 1 {
 		checkFreq = 0
 	}
 	start := time.Now()
@@ -532,16 +530,12 @@ func (self *LightChain) SubscribeRemovedLogsEvent(ch chan<- core.RemovedLogsEven
 	return self.scope.Track(new(event.Feed).Subscribe(ch))
 }
 
-//DisableCheckFreq disables header validation. It needs for ULC
+// DisableCheckFreq disables header validation. This is used for ultralight mode.
 func (self *LightChain) DisableCheckFreq() {
-	self.mu.Lock()
-	defer self.mu.Unlock()
-	self.disableCheckFreq = true
+	atomic.StoreInt32(&self.disableCheckFreq, 1)
 }
 
-//EnableCheckFreq enables header validation
+// EnableCheckFreq enables header validation.
 func (self *LightChain) EnableCheckFreq() {
-	self.mu.Lock()
-	defer self.mu.Unlock()
-	self.disableCheckFreq = false
+	atomic.StoreInt32(&self.disableCheckFreq, 0)
 }