Avoid cs_main in net_processing ActivateBestChain calls

Author: TheBlueMatt

src/net_processing.cpp

@@ -1040,8 +1040,6 @@ 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;
@@ -1053,7 +1051,9 @@ void static ProcessGetBlockData(CNode* pfrom, const Consensus::Params& consensus
         fWitnessesPresentInARecentCompactBlock = fWitnessesPresentInMostRecentCompactBlock;
     }
 
+    bool need_activate_chain = false;
     {
+        LOCK(cs_main);
         BlockMap::iterator mi = mapBlockIndex.find(inv.hash);
         if (mi != mapBlockIndex.end())
         {
@@ -1064,11 +1064,16 @@ 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);
@@ -1177,6 +1182,8 @@ 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());
@@ -1216,15 +1223,15 @@ 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 || inv.type == MSG_WITNESS_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 || inv.type == MSG_WITNESS_BLOCK) {
+            ProcessGetBlockData(pfrom, consensusParams, inv, connman, interruptMsgProc);
         }
-    } // release cs_main
+    }
 
     pfrom->vRecvGetData.erase(pfrom->vRecvGetData.begin(), it);
 
@@ -2027,7 +2034,7 @@ bool static ProcessMessage(CNode* pfrom, const std::string& strCommand, CDataStr
             inv.type = State(pfrom->GetId())->fWantsCmpctWitness ? MSG_WITNESS_BLOCK : 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;
         }