Fix large reorgs

qa/pull-tester/run-bitcoind-for-test.sh.in

@@ -10,7 +10,7 @@ touch "$DATADIR/regtest/debug.log"
 tail -q -n 1 -F "$DATADIR/regtest/debug.log" | grep -m 1 -q "Done loading" &
 WAITER=$!
 PORT=`expr 10000 + $$ % 55536`
-"@abs_top_builddir@/src/bitcoind@EXEEXT@" -connect=0.0.0.0 -datadir="$DATADIR" -rpcuser=user -rpcpassword=pass -listen -keypool=3 -debug -debug=net -logtimestamps -port=$PORT -whitelist=127.0.0.1 -regtest -rpcport=`expr $PORT + 1` &
+"@abs_top_builddir@/src/bitcoind@EXEEXT@" -connect=0.0.0.0 -datadir="$DATADIR" -rpcuser=user -rpcpassword=pass -listen -keypool=3 -debug -debug=net -logtimestamps -checkmempool=0 -port=$PORT -whitelist=127.0.0.1 -regtest -rpcport=`expr $PORT + 1` &
 BITCOIND=$!
 
 #Install a watchdog.

src/main.cpp

@@ -385,10 +385,11 @@ void FindNextBlocksToDownload(NodeId nodeid, unsigned int count, std::vector<CBl
 
     std::vector<CBlockIndex*> vToFetch;
     CBlockIndex *pindexWalk = state->pindexLastCommonBlock;
-    // Never fetch further than the best block we know the peer has, or more than BLOCK_DOWNLOAD_WINDOW + 1 beyond our
-    // current tip. The +1 is so we can detect stalling, namely if we would be able to download that next block if the
-    // window were 1 larger.
-    int nMaxHeight = std::min<int>(state->pindexBestKnownBlock->nHeight, chainActive.Height() + BLOCK_DOWNLOAD_WINDOW + 1);
+    // Never fetch further than the best block we know the peer has, or more than BLOCK_DOWNLOAD_WINDOW + 1 beyond the last
+    // linked block we have in common with this peer. The +1 is so we can detect stalling, namely if we would be able to
+    // download that next block if the window were 1 larger.
+    int nWindowEnd = state->pindexLastCommonBlock->nHeight + BLOCK_DOWNLOAD_WINDOW;
+    int nMaxHeight = std::min<int>(state->pindexBestKnownBlock->nHeight, nWindowEnd + 1);
     NodeId waitingfor = -1;
     while (pindexWalk->nHeight < nMaxHeight) {
         // Read up to 128 (or more, if more blocks than that are needed) successors of pindexWalk (towards
@@ -411,7 +412,7 @@ void FindNextBlocksToDownload(NodeId nodeid, unsigned int count, std::vector<CBl
                     state->pindexLastCommonBlock = pindex;
             } else if (mapBlocksInFlight.count(pindex->GetBlockHash()) == 0) {
                 // The block is not already downloaded, and not yet in flight.
-                if (pindex->nHeight > chainActive.Height() + (int)BLOCK_DOWNLOAD_WINDOW) {
+                if (pindex->nHeight > nWindowEnd) {
                     // We reached the end of the window.
                     if (vBlocks.size() == 0 && waitingfor != nodeid) {
                         // We aren't able to fetch anything, but we would be if the download window was one larger.