Merge #13431: validation: count blocks correctly for check level < 3

f618ebc validation: count blocks correctly for check level < 3 (Karl-Johan Alm)

Pull request description:

  As noted in bitcoin/bitcoin#13428 (comment) there is a bug where if check level < 3, the resulting count for blocks is wrong, because `pindexState` is never updated.

  Post-commit `./bitcoin-cli verifychain 1 3`:
  ```

  2018-06-11T07:12:28Z Verifying last 3 blocks at level 1
  2018-06-11T07:12:28Z [0%]...[33%]...[66%]...[99%]...[DONE].
  2018-06-11T07:12:28Z No coin database inconsistencies in last 3 blocks (0 transactions)
  ```

  Pre-commit `./bitcoin-cli verifychain 1 3`:
  ```
  2018-06-11T07:13:34Z Verifying last 3 blocks at level 1
  2018-06-11T07:13:34Z [0%]...[33%]...[66%]...[99%]...[DONE].
  2018-06-11T07:13:34Z No coin database inconsistencies in last 0 blocks (0 transactions)
  ```

Tree-SHA512: 3d82ed26665162c9615fb0e6e91a46ed4d229a5e6797c6c420e6b0bf1be6e5e02401c6e9a93b7a5aec503a2650d8c20d1b45fe300a922379e4cef8ee26e18d96

Author: MarcoFalke

src/validation.cpp

@@ -3984,14 +3984,13 @@ bool CVerifyDB::VerifyDB(const CChainParams& chainparams, CCoinsView *coinsview,
     nCheckLevel = std::max(0, std::min(4, nCheckLevel));
     LogPrintf("Verifying last %i blocks at level %i\n", nCheckDepth, nCheckLevel);
     CCoinsViewCache coins(coinsview);
-    CBlockIndex* pindexState = chainActive.Tip();
+    CBlockIndex* pindex;
     CBlockIndex* pindexFailure = nullptr;
     int nGoodTransactions = 0;
     CValidationState state;
     int reportDone = 0;
     LogPrintf("[0%%]..."); /* Continued */
-    for (CBlockIndex* pindex = chainActive.Tip(); pindex && pindex->pprev; pindex = pindex->pprev)
-    {
+    for (pindex = chainActive.Tip(); pindex && pindex->pprev; pindex = pindex->pprev) {
         boost::this_thread::interruption_point();
         int percentageDone = std::max(1, std::min(99, (int)(((double)(chainActive.Height() - pindex->nHeight)) / (double)nCheckDepth * (nCheckLevel >= 4 ? 50 : 100))));
         if (reportDone < percentageDone/10) {
@@ -4025,13 +4024,12 @@ bool CVerifyDB::VerifyDB(const CChainParams& chainparams, CCoinsView *coinsview,
             }
         }
         // check level 3: check for inconsistencies during memory-only disconnect of tip blocks
-        if (nCheckLevel >= 3 && pindex == pindexState && (coins.DynamicMemoryUsage() + pcoinsTip->DynamicMemoryUsage()) <= nCoinCacheUsage) {
+        if (nCheckLevel >= 3 && (coins.DynamicMemoryUsage() + pcoinsTip->DynamicMemoryUsage()) <= nCoinCacheUsage) {
             assert(coins.GetBestBlock() == pindex->GetBlockHash());
             DisconnectResult res = g_chainstate.DisconnectBlock(block, pindex, coins);
             if (res == DISCONNECT_FAILED) {
                 return error("VerifyDB(): *** irrecoverable inconsistency in block data at %d, hash=%s", pindex->nHeight, pindex->GetBlockHash().ToString());
             }
-            pindexState = pindex->pprev;
             if (res == DISCONNECT_UNCLEAN) {
                 nGoodTransactions = 0;
                 pindexFailure = pindex;
@@ -4045,9 +4043,11 @@ bool CVerifyDB::VerifyDB(const CChainParams& chainparams, CCoinsView *coinsview,
     if (pindexFailure)
         return error("VerifyDB(): *** coin database inconsistencies found (last %i blocks, %i good transactions before that)\n", chainActive.Height() - pindexFailure->nHeight + 1, nGoodTransactions);
 
+    // store block count as we move pindex at check level >= 4
+    int block_count = chainActive.Height() - pindex->nHeight;
+
     // check level 4: try reconnecting blocks
     if (nCheckLevel >= 4) {
-        CBlockIndex *pindex = pindexState;
         while (pindex != chainActive.Tip()) {
             boost::this_thread::interruption_point();
             uiInterface.ShowProgress(_("Verifying blocks..."), std::max(1, std::min(99, 100 - (int)(((double)(chainActive.Height() - pindex->nHeight)) / (double)nCheckDepth * 50))), false);
@@ -4061,7 +4061,7 @@ bool CVerifyDB::VerifyDB(const CChainParams& chainparams, CCoinsView *coinsview,
     }
 
     LogPrintf("[DONE].\n");
-    LogPrintf("No coin database inconsistencies in last %i blocks (%i transactions)\n", chainActive.Height() - pindexState->nHeight, nGoodTransactions);
+    LogPrintf("No coin database inconsistencies in last %i blocks (%i transactions)\n", block_count, nGoodTransactions);
 
     return true;
 }