From 44147d057dd91d8b35dd6f4ed025bdb4baf225eb Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?P=C3=A9ter=20Szil=C3=A1gyi?= <peterke@gmail.com>
Date: Tue, 9 Jun 2015 14:27:44 +0300
Subject: [PATCH] eth: fix data race accessing peer.recentHash

---
 eth/handler.go |  6 +++---
 eth/peer.go    | 31 +++++++++++++++++++++++++------
 eth/sync.go    |  7 ++++---
 3 files changed, 32 insertions(+), 12 deletions(-)

diff --git a/eth/handler.go b/eth/handler.go
index 64f89b273d..847e7a0e8e 100644
--- a/eth/handler.go
+++ b/eth/handler.go
@@ -157,7 +157,7 @@ func (pm *ProtocolManager) handle(p *peer) error {
 	}
 	defer pm.removePeer(p.id)
 
-	if err := pm.downloader.RegisterPeer(p.id, p.recentHash, p.requestHashes, p.requestBlocks); err != nil {
+	if err := pm.downloader.RegisterPeer(p.id, p.Head(), p.requestHashes, p.requestBlocks); err != nil {
 		return err
 	}
 	// propagate existing transactions. new transactions appearing
@@ -303,7 +303,7 @@ func (self *ProtocolManager) handleMsg(p *peer) error {
 		// Mark the hashes as present at the remote node
 		for _, hash := range hashes {
 			p.blockHashes.Add(hash)
-			p.recentHash = hash
+			p.SetHead(hash)
 		}
 		// Schedule all the unknown hashes for retrieval
 		unknown := make([]common.Hash, 0, len(hashes))
@@ -354,7 +354,7 @@ func (pm *ProtocolManager) importBlock(p *peer, block *types.Block, td *big.Int)
 
 	// Mark the block as present at the remote node (don't duplicate already held data)
 	p.blockHashes.Add(hash)
-	p.recentHash = hash
+	p.SetHead(hash)
 	if td != nil {
 		p.td = td
 	}
diff --git a/eth/peer.go b/eth/peer.go
index cf2c58ec9f..5f50078911 100644
--- a/eth/peer.go
+++ b/eth/peer.go
@@ -40,9 +40,11 @@ type peer struct {
 
 	protv, netid int
 
-	recentHash common.Hash
-	id         string
-	td         *big.Int
+	id string
+	td *big.Int
+
+	head     common.Hash
+	headLock sync.RWMutex
 
 	genesis, ourHash common.Hash
 	ourTd            *big.Int
@@ -51,14 +53,14 @@ type peer struct {
 	blockHashes *set.Set
 }
 
-func newPeer(protv, netid int, genesis, recentHash common.Hash, td *big.Int, p *p2p.Peer, rw p2p.MsgReadWriter) *peer {
+func newPeer(protv, netid int, genesis, head common.Hash, td *big.Int, p *p2p.Peer, rw p2p.MsgReadWriter) *peer {
 	id := p.ID()
 
 	return &peer{
 		Peer:        p,
 		rw:          rw,
 		genesis:     genesis,
-		ourHash:     recentHash,
+		ourHash:     head,
 		ourTd:       td,
 		protv:       protv,
 		netid:       netid,
@@ -68,6 +70,23 @@ func newPeer(protv, netid int, genesis, recentHash common.Hash, td *big.Int, p *
 	}
 }
 
+// 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()
+
+	copy(hash[:], p.head[:])
+	return 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()
+
+	copy(p.head[:], hash[:])
+}
+
 // 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
@@ -160,7 +179,7 @@ func (p *peer) handleStatus() error {
 	// Set the total difficulty of the peer
 	p.td = status.TD
 	// set the best hash of the peer
-	p.recentHash = status.CurrentBlock
+	p.head = status.CurrentBlock
 
 	return <-errc
 }
diff --git a/eth/sync.go b/eth/sync.go
index dd7414da84..b3184364fb 100644
--- a/eth/sync.go
+++ b/eth/sync.go
@@ -214,14 +214,15 @@ func (pm *ProtocolManager) synchronise(peer *peer) {
 	// FIXME if we have the hash in our chain and the TD of the peer is
 	// much higher than ours, something is wrong with us or the peer.
 	// Check if the hash is on our own chain
-	if pm.chainman.HasBlock(peer.recentHash) {
+	head := peer.Head()
+	if pm.chainman.HasBlock(head) {
 		glog.V(logger.Debug).Infoln("Synchronisation canceled: head already known")
 		return
 	}
 	// Get the hashes from the peer (synchronously)
-	glog.V(logger.Detail).Infof("Attempting synchronisation: %v, 0x%x", peer.id, peer.recentHash)
+	glog.V(logger.Detail).Infof("Attempting synchronisation: %v, 0x%x", peer.id, head)
 
-	err := pm.downloader.Synchronise(peer.id, peer.recentHash)
+	err := pm.downloader.Synchronise(peer.id, head)
 	switch err {
 	case nil:
 		glog.V(logger.Detail).Infof("Synchronisation completed")