From eedd5ce1b60174439d66b12ba23974b42ec7b890 Mon Sep 17 00:00:00 2001
From: Wilmer Paulino <wilmer.paulino@gmail.com>
Date: Wed, 5 Jun 2019 16:12:18 -0700
Subject: [PATCH] chain: prevent deadlock while notifying RescanFinished for
 NeutrinoClient

---
 chain/neutrino.go | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/chain/neutrino.go b/chain/neutrino.go
index fb109b4..c87e89e 100644
--- a/chain/neutrino.go
+++ b/chain/neutrino.go
@@ -322,16 +322,17 @@ func (s *NeutrinoClient) Rescan(startHash *chainhash.Hash, addrs []btcutil.Addre
 	outPoints map[wire.OutPoint]btcutil.Address) error {
 
 	s.clientMtx.Lock()
-	defer s.clientMtx.Unlock()
 	if !s.started {
+		s.clientMtx.Unlock()
 		return fmt.Errorf("can't do a rescan when the chain client " +
 			"is not started")
 	}
 	if s.scanning {
 		// Restart the rescan by killing the existing rescan.
 		close(s.rescanQuit)
+		rescan := s.rescan
 		s.clientMtx.Unlock()
-		s.rescan.WaitForShutdown()
+		rescan.WaitForShutdown()
 		s.clientMtx.Lock()
 		s.rescan = nil
 		s.rescanErr = nil
@@ -342,6 +343,7 @@ func (s *NeutrinoClient) Rescan(startHash *chainhash.Hash, addrs []btcutil.Addre
 	s.lastProgressSent = false
 	s.lastFilteredBlockHeader = nil
 	s.isRescan = true
+	s.clientMtx.Unlock()
 
 	bestBlock, err := s.CS.BestBlock()
 	if err != nil {
@@ -357,7 +359,14 @@ func (s *NeutrinoClient) Rescan(startHash *chainhash.Hash, addrs []btcutil.Addre
 	// with state that indicates a "fresh" wallet, we'll send a
 	// notification indicating the rescan has "finished".
 	if header.BlockHash() == *startHash {
+		s.clientMtx.Lock()
 		s.finished = true
+		rescanQuit := s.rescanQuit
+		s.clientMtx.Unlock()
+
+		// Release the lock while dispatching the notification since
+		// it's possible for the notificationHandler to be waiting to
+		// acquire it before receiving the notification.
 		select {
 		case s.enqueueNotification <- &RescanFinished{
 			Hash:   startHash,
@@ -366,7 +375,7 @@ func (s *NeutrinoClient) Rescan(startHash *chainhash.Hash, addrs []btcutil.Addre
 		}:
 		case <-s.quit:
 			return nil
-		case <-s.rescanQuit:
+		case <-rescanQuit:
 			return nil
 		}
 	}
@@ -375,6 +384,7 @@ func (s *NeutrinoClient) Rescan(startHash *chainhash.Hash, addrs []btcutil.Addre
 	for op, addr := range outPoints {
 		addrScript, err := txscript.PayToAddrScript(addr)
 		if err != nil {
+			return err
 		}
 
 		inputsToWatch = append(inputsToWatch, neutrino.InputWithScript{
@@ -383,6 +393,7 @@ func (s *NeutrinoClient) Rescan(startHash *chainhash.Hash, addrs []btcutil.Addre
 		})
 	}
 
+	s.clientMtx.Lock()
 	newRescan := neutrino.NewRescan(
 		&neutrino.RescanChainSource{
 			ChainService: s.CS,
@@ -400,6 +411,7 @@ func (s *NeutrinoClient) Rescan(startHash *chainhash.Hash, addrs []btcutil.Addre
 	)
 	s.rescan = newRescan
 	s.rescanErr = s.rescan.Start()
+	s.clientMtx.Unlock()
 
 	return nil
 }