From 2eb55317476ce5325da0b1ad847a4571f6f6990a Mon Sep 17 00:00:00 2001
From: Matt Corallo <git@bluematt.me>
Date: Sun, 24 Dec 2017 11:59:02 -0500
Subject: [PATCH] Avoid cs_main in net_processing ActivateBestChain calls

---
 src/net_processing.cpp | 31 +++++++++++++++++++------------
 1 file changed, 19 insertions(+), 12 deletions(-)

diff --git a/src/net_processing.cpp b/src/net_processing.cpp
index a9d6fab39076b..20850a16067d7 100644
--- a/src/net_processing.cpp
+++ b/src/net_processing.cpp
@@ -1060,8 +1060,6 @@ static void RelayAddress(const CAddress& addr, bool fReachable, CConnman& connma
 
 void static ProcessGetBlockData(CNode* pfrom, const Consensus::Params& consensusParams, const CInv& inv, CConnman& connman, const std::atomic<bool>& interruptMsgProc)
 {
-    LOCK(cs_main);
-
     bool send = false;
     std::shared_ptr<const CBlock> a_recent_block;
     std::shared_ptr<const CBlockHeaderAndShortTxIDs> a_recent_compact_block;
@@ -1071,7 +1069,9 @@ void static ProcessGetBlockData(CNode* pfrom, const Consensus::Params& consensus
         a_recent_compact_block = most_recent_compact_block;
     }
 
+    bool need_activate_chain = false;
     {
+        LOCK(cs_main);
         BlockMap::iterator mi = mapBlockIndex.find(inv.hash);
         if (mi != mapBlockIndex.end())
         {
@@ -1082,11 +1082,16 @@ void static ProcessGetBlockData(CNode* pfrom, const Consensus::Params& consensus
                 // before ActivateBestChain but after AcceptBlock).
                 // In this case, we need to run ActivateBestChain prior to checking the relay
                 // conditions below.
-                CValidationState dummy;
-                ActivateBestChain(dummy, Params(), a_recent_block);
+                need_activate_chain = true;
             }
         }
+    } // release cs_main before calling ActivateBestChain
+    if (need_activate_chain) {
+        CValidationState dummy;
+        ActivateBestChain(dummy, Params(), a_recent_block);
     }
+
+    LOCK(cs_main);
     BlockMap::iterator mi = mapBlockIndex.find(inv.hash);
     if (mi != mapBlockIndex.end()) {
         send = BlockRequestAllowed(mi->second, consensusParams);
@@ -1181,6 +1186,8 @@ void static ProcessGetBlockData(CNode* pfrom, const Consensus::Params& consensus
 
 void static ProcessGetData(CNode* pfrom, const Consensus::Params& consensusParams, CConnman& connman, const std::atomic<bool>& interruptMsgProc)
 {
+    AssertLockNotHeld(cs_main);
+
     std::deque<CInv>::iterator it = pfrom->vRecvGetData.begin();
     std::vector<CInv> vNotFound;
     const CNetMsgMaker msgMaker(pfrom->GetSendVersion());
@@ -1362,15 +1369,15 @@ void static ProcessGetData(CNode* pfrom, const Consensus::Params& consensusParam
             // Track requests for our stuff.
             GetMainSignals().Inventory(inv.hash);
         }
+    } // release cs_main
 
-        if (it != pfrom->vRecvGetData.end()) {
-            const CInv &inv = *it;
-            it++;
-            if (inv.type == MSG_BLOCK || inv.type == MSG_FILTERED_BLOCK || inv.type == MSG_CMPCT_BLOCK) {
-                ProcessGetBlockData(pfrom, consensusParams, inv, connman, interruptMsgProc);
-            }
+    if (it != pfrom->vRecvGetData.end()) {
+        const CInv &inv = *it;
+        it++;
+        if (inv.type == MSG_BLOCK || inv.type == MSG_FILTERED_BLOCK || inv.type == MSG_CMPCT_BLOCK) {
+            ProcessGetBlockData(pfrom, consensusParams, inv, connman, interruptMsgProc);
         }
-    } // release cs_main
+    }
 
     pfrom->vRecvGetData.erase(pfrom->vRecvGetData.begin(), it);
 
@@ -1977,7 +1984,7 @@ bool static ProcessMessage(CNode* pfrom, const std::string& strCommand, CDataStr
             inv.type = MSG_BLOCK;
             inv.hash = req.blockhash;
             pfrom->vRecvGetData.push_back(inv);
-            ProcessGetData(pfrom, chainparams.GetConsensus(), connman, interruptMsgProc);
+            // The message processing loop will go around again (without pausing) and we'll respond then (without cs_main)
             return true;
         }