eth: fix data race accessing peer.td

eth/handler.go

@@ -356,7 +356,7 @@ func (pm *ProtocolManager) importBlock(p *peer, block *types.Block, td *big.Int)
 	p.blockHashes.Add(hash)
 	p.SetHead(hash)
 	if td != nil {
-		p.td = td
+		p.SetTd(td)
 	}
 	// Log the block's arrival
 	_, chainHead, _ := pm.chainman.Status()
@@ -369,7 +369,7 @@ func (pm *ProtocolManager) importBlock(p *peer, block *types.Block, td *big.Int)
 	})
 	// If the block's already known or its difficulty is lower than ours, drop
 	if pm.chainman.HasBlock(hash) {
-		p.td = pm.chainman.GetBlock(hash).Td // update the peer's TD to the real value
+		p.SetTd(pm.chainman.GetBlock(hash).Td) // update the peer's TD to the real value
 		return nil
 	}
 	if td != nil && pm.chainman.Td().Cmp(td) > 0 && new(big.Int).Add(block.Number(), big.NewInt(7)).Cmp(pm.chainman.CurrentBlock().Number()) < 0 {

eth/peer.go

@@ -41,10 +41,10 @@ type peer struct {
 	protv, netid int
 
 	id string
-	td *big.Int
 
 	head common.Hash
-	headLock sync.RWMutex
+	td   *big.Int
+	lock sync.RWMutex
 
 	genesis, ourHash common.Hash
 	ourTd            *big.Int
@@ -72,8 +72,8 @@ func newPeer(protv, netid int, genesis, head common.Hash, td *big.Int, p *p2p.Pe
 
 // Head retrieves a copy of the current head (most recent) hash of the peer.
 func (p *peer) Head() (hash common.Hash) {
-	p.headLock.RLock()
-	defer p.headLock.RUnlock()
+	p.lock.RLock()
+	defer p.lock.RUnlock()
 
 	copy(hash[:], p.head[:])
 	return hash
@@ -81,12 +81,28 @@ func (p *peer) Head() (hash common.Hash) {
 
 // SetHead updates the head (most recent) hash of the peer.
 func (p *peer) SetHead(hash common.Hash) {
-	p.headLock.Lock()
-	defer p.headLock.Unlock()
+	p.lock.Lock()
+	defer p.lock.Unlock()
 
 	copy(p.head[:], hash[:])
 }
 
+// Td retrieves the current total difficulty of a peer.
+func (p *peer) Td() *big.Int {
+	p.lock.RLock()
+	defer p.lock.RUnlock()
+
+	return new(big.Int).Set(p.td)
+}
+
+// SetTd updates the current total difficulty of a peer.
+func (p *peer) SetTd(td *big.Int) {
+	p.lock.Lock()
+	defer p.lock.Unlock()
+
+	p.td.Set(td)
+}
+
 // sendTransactions sends transactions to the peer and includes the hashes
 // in it's tx hash set for future reference. The tx hash will allow the
 // manager to check whether the peer has already received this particular
@@ -275,11 +291,14 @@ func (ps *peerSet) BestPeer() *peer {
 	ps.lock.RLock()
 	defer ps.lock.RUnlock()
 
-	var best *peer
+	var (
+		bestPeer *peer
+		bestTd   *big.Int
+	)
 	for _, p := range ps.peers {
-		if best == nil || p.td.Cmp(best.td) > 0 {
-			best = p
+		if td := p.Td(); bestPeer == nil || td.Cmp(bestTd) > 0 {
+			bestPeer, bestTd = p, td
 		}
 	}
-	return best
+	return bestPeer
 }

eth/sync.go

@@ -208,7 +208,7 @@ func (pm *ProtocolManager) synchronise(peer *peer) {
 		return
 	}
 	// Make sure the peer's TD is higher than our own. If not drop.
-	if peer.td.Cmp(pm.chainman.Td()) <= 0 {
+	if peer.Td().Cmp(pm.chainman.Td()) <= 0 {
 		return
 	}
 	// FIXME if we have the hash in our chain and the TD of the peer is