Merge #15552: 0.18: Granular invalidateblock and RewindBlockIndex

519b0bc5dc Make last disconnected block BLOCK_FAILED_VALID, even when aborted (Pieter Wuille)
8d220417cd Optimization: don't add txn back to mempool after 10 invalidates (Pieter Wuille)
9ce9c37004 Prevent callback overruns in InvalidateBlock and RewindBlockIndex (Pieter Wuille)
9bb32eb571 Release cs_main during InvalidateBlock iterations (Pieter Wuille)
9b1ff5c742 Call InvalidateBlock without cs_main held (Pieter Wuille)
241b2c74ac Make RewindBlockIndex interruptible (Pieter Wuille)
880ce7d46b Call RewindBlockIndex without cs_main held (Pieter Wuille)
436f7d735f Release cs_main during RewindBlockIndex operation (Pieter Wuille)
1d342875c2 Merge the disconnection and erasing loops in RewindBlockIndex (Pieter Wuille)
32b2696ab4 Move erasure of non-active blocks to a separate loop in RewindBlockIndex (Pieter Wuille)
9d6dcc52c6 Abstract EraseBlockData out of RewindBlockIndex (Pieter Wuille)

Pull request description:

  Same repo and branch like  "Granular invalidateblock and RewindBlockIndex #15402 ", can be merged as is.

  This saves us all the cherry-picks and review of the backport cherry-picks.

Tree-SHA512: 20c27c5f807c3d85e0072f9e2cdefad4ad7d329d6b26658a00844d5fcf0ed729059daf765e04e6382db2b5915117b15949cd4989d864917ab105c92e2e5e9986

src/init.cpp

@@ -1468,11 +1468,11 @@ bool AppInitMain(InitInterfaces& interfaces)
 
         uiInterface.InitMessage(_("Loading block index..."));
 
-        LOCK(cs_main);
-
         do {
             const int64_t load_block_index_start_time = GetTimeMillis();
+            bool is_coinsview_empty;
             try {
+                LOCK(cs_main);
                 UnloadBlockIndex();
                 pcoinsTip.reset();
                 pcoinsdbview.reset();
@@ -1544,7 +1544,7 @@ bool AppInitMain(InitInterfaces& interfaces)
                 // The on-disk coinsdb is now in a good state, create the cache
                 pcoinsTip.reset(new CCoinsViewCache(pcoinscatcher.get()));
 
-                bool is_coinsview_empty = fReset || fReindexChainState || pcoinsTip->GetBestBlock().IsNull();
+                is_coinsview_empty = fReset || fReindexChainState || pcoinsTip->GetBestBlock().IsNull();
                 if (!is_coinsview_empty) {
                     // LoadChainTip sets chainActive based on pcoinsTip's best block
                     if (!LoadChainTip(chainparams)) {
@@ -1553,18 +1553,25 @@ bool AppInitMain(InitInterfaces& interfaces)
                     }
                     assert(chainActive.Tip() != nullptr);
                 }
+            } catch (const std::exception& e) {
+                LogPrintf("%s\n", e.what());
+                strLoadError = _("Error opening block database");
+                break;
+            }
 
-                if (!fReset) {
-                    // Note that RewindBlockIndex MUST run even if we're about to -reindex-chainstate.
-                    // It both disconnects blocks based on chainActive, and drops block data in
-                    // mapBlockIndex based on lack of available witness data.
-                    uiInterface.InitMessage(_("Rewinding blocks..."));
-                    if (!RewindBlockIndex(chainparams)) {
-                        strLoadError = _("Unable to rewind the database to a pre-fork state. You will need to redownload the blockchain");
-                        break;
-                    }
+            if (!fReset) {
+                // Note that RewindBlockIndex MUST run even if we're about to -reindex-chainstate.
+                // It both disconnects blocks based on chainActive, and drops block data in
+                // mapBlockIndex based on lack of available witness data.
+                uiInterface.InitMessage(_("Rewinding blocks..."));
+                if (!RewindBlockIndex(chainparams)) {
+                    strLoadError = _("Unable to rewind the database to a pre-fork state. You will need to redownload the blockchain");
+                    break;
                 }
+            }
 
+            try {
+                LOCK(cs_main);
                 if (!is_coinsview_empty) {
                     uiInterface.InitMessage(_("Verifying blocks..."));
                     if (fHavePruned && gArgs.GetArg("-checkblocks", DEFAULT_CHECKBLOCKS) > MIN_BLOCKS_TO_KEEP) {

src/rpc/blockchain.cpp

@@ -1583,15 +1583,15 @@ static UniValue invalidateblock(const JSONRPCRequest& request)
     uint256 hash(ParseHashV(request.params[0], "blockhash"));
     CValidationState state;
 
+    CBlockIndex* pblockindex;
     {
         LOCK(cs_main);
-        CBlockIndex* pblockindex = LookupBlockIndex(hash);
+        pblockindex = LookupBlockIndex(hash);
         if (!pblockindex) {
             throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Block not found");
         }
-
-        InvalidateBlock(state, Params(), pblockindex);
     }
+    InvalidateBlock(state, Params(), pblockindex);
 
     if (state.IsValid()) {
         ActivateBestChain(state, Params());

src/validation.cpp

@@ -177,7 +177,7 @@ public:
 
     // Manual block validity manipulation:
     bool PreciousBlock(CValidationState& state, const CChainParams& params, CBlockIndex* pindex) LOCKS_EXCLUDED(cs_main);
-    bool InvalidateBlock(CValidationState& state, const CChainParams& chainparams, CBlockIndex* pindex) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
+    bool InvalidateBlock(CValidationState& state, const CChainParams& chainparams, CBlockIndex* pindex);
     void ResetBlockFailureFlags(CBlockIndex* pindex) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
 
     bool ReplayBlocks(const CChainParams& params, CCoinsView* view);
@@ -206,8 +206,10 @@ private:
     CBlockIndex* FindMostWorkChain() EXCLUSIVE_LOCKS_REQUIRED(cs_main);
     void ReceivedBlockTransactions(const CBlock& block, CBlockIndex* pindexNew, const CDiskBlockPos& pos, const Consensus::Params& consensusParams) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
 
-
     bool RollforwardBlock(const CBlockIndex* pindex, CCoinsViewCache& inputs, const CChainParams& params) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
+
+    //! Mark a block as not having block data
+    void EraseBlockData(CBlockIndex* index) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
 } g_chainstate;
 
 /**
@@ -2634,6 +2636,14 @@ static void NotifyHeaderTip() LOCKS_EXCLUDED(cs_main) {
     }
 }
 
+static void LimitValidationInterfaceQueue() {
+    AssertLockNotHeld(cs_main);
+
+    if (GetMainSignals().CallbacksPending() > 10) {
+        SyncWithValidationInterfaceQueue();
+    }
+}
+
 /**
  * Make the best chain active, in multiple steps. The result is either failure
  * or an activated best chain. pblock is either nullptr or a pointer to a block
@@ -2662,15 +2672,13 @@ bool CChainState::ActivateBestChain(CValidationState &state, const CChainParams&
     do {
         boost::this_thread::interruption_point();
 
-        if (GetMainSignals().CallbacksPending() > 10) {
-            // Block until the validation queue drains. This should largely
-            // never happen in normal operation, however may happen during
-            // reindex, causing memory blowup if we run too far ahead.
-            // Note that if a validationinterface callback ends up calling
-            // ActivateBestChain this may lead to a deadlock! We should
-            // probably have a DEBUG_LOCKORDER test for this in the future.
-            SyncWithValidationInterfaceQueue();
-        }
+        // Block until the validation queue drains. This should largely
+        // never happen in normal operation, however may happen during
+        // reindex, causing memory blowup if we run too far ahead.
+        // Note that if a validationinterface callback ends up calling
+        // ActivateBestChain this may lead to a deadlock! We should
+        // probably have a DEBUG_LOCKORDER test for this in the future.
+        LimitValidationInterfaceQueue();
 
         {
             LOCK(cs_main);
@@ -2781,64 +2789,85 @@ bool PreciousBlock(CValidationState& state, const CChainParams& params, CBlockIn
 
 bool CChainState::InvalidateBlock(CValidationState& state, const CChainParams& chainparams, CBlockIndex *pindex)
 {
-    AssertLockHeld(cs_main);
-
-    // We first disconnect backwards and then mark the blocks as invalid.
-    // This prevents a case where pruned nodes may fail to invalidateblock
-    // and be left unable to start as they have no tip candidates (as there
-    // are no blocks that meet the "have data and are not invalid per
-    // nStatus" criteria for inclusion in setBlockIndexCandidates).
-
+    CBlockIndex* to_mark_failed = pindex;
     bool pindex_was_in_chain = false;
-    CBlockIndex *invalid_walk_tip = chainActive.Tip();
+    int disconnected = 0;
 
-    DisconnectedBlockTransactions disconnectpool;
-    while (chainActive.Contains(pindex)) {
+    // Disconnect (descendants of) pindex, and mark them invalid.
+    while (true) {
+        if (ShutdownRequested()) break;
+
+        // Make sure the queue of validation callbacks doesn't grow unboundedly.
+        LimitValidationInterfaceQueue();
+
+        LOCK(cs_main);
+        if (!chainActive.Contains(pindex)) break;
         pindex_was_in_chain = true;
+        CBlockIndex *invalid_walk_tip = chainActive.Tip();
+
         // ActivateBestChain considers blocks already in chainActive
         // unconditionally valid already, so force disconnect away from it.
-        if (!DisconnectTip(state, chainparams, &disconnectpool)) {
-            // It's probably hopeless to try to make the mempool consistent
-            // here if DisconnectTip failed, but we can try.
-            UpdateMempoolForReorg(disconnectpool, false);
-            return false;
-        }
-    }
+        DisconnectedBlockTransactions disconnectpool;
+        bool ret = DisconnectTip(state, chainparams, &disconnectpool);
+        // DisconnectTip will add transactions to disconnectpool.
+        // Adjust the mempool to be consistent with the new tip, adding
+        // transactions back to the mempool if disconnecting was succesful,
+        // and we're not doing a very deep invalidation (in which case
+        // keeping the mempool up to date is probably futile anyway).
+        UpdateMempoolForReorg(disconnectpool, /* fAddToMempool = */ (++disconnected <= 10) && ret);
+        if (!ret) return false;
+        assert(invalid_walk_tip->pprev == chainActive.Tip());
 
-    // Now mark the blocks we just disconnected as descendants invalid
-    // (note this may not be all descendants).
-    while (pindex_was_in_chain && invalid_walk_tip != pindex) {
-        invalid_walk_tip->nStatus |= BLOCK_FAILED_CHILD;
+        // We immediately mark the disconnected blocks as invalid.
+        // This prevents a case where pruned nodes may fail to invalidateblock
+        // and be left unable to start as they have no tip candidates (as there
+        // are no blocks that meet the "have data and are not invalid per
+        // nStatus" criteria for inclusion in setBlockIndexCandidates).
+        invalid_walk_tip->nStatus |= BLOCK_FAILED_VALID;
         setDirtyBlockIndex.insert(invalid_walk_tip);
         setBlockIndexCandidates.erase(invalid_walk_tip);
-        invalid_walk_tip = invalid_walk_tip->pprev;
-    }
-
-    // Mark the block itself as invalid.
-    pindex->nStatus |= BLOCK_FAILED_VALID;
-    setDirtyBlockIndex.insert(pindex);
-    setBlockIndexCandidates.erase(pindex);
-    m_failed_blocks.insert(pindex);
-
-    // DisconnectTip will add transactions to disconnectpool; try to add these
-    // back to the mempool.
-    UpdateMempoolForReorg(disconnectpool, true);
-
-    // The resulting new best tip may not be in setBlockIndexCandidates anymore, so
-    // add it again.
-    BlockMap::iterator it = mapBlockIndex.begin();
-    while (it != mapBlockIndex.end()) {
-        if (it->second->IsValid(BLOCK_VALID_TRANSACTIONS) && it->second->HaveTxsDownloaded() && !setBlockIndexCandidates.value_comp()(it->second, chainActive.Tip())) {
-            setBlockIndexCandidates.insert(it->second);
+        setBlockIndexCandidates.insert(invalid_walk_tip->pprev);
+        if (invalid_walk_tip->pprev == to_mark_failed && (to_mark_failed->nStatus & BLOCK_FAILED_VALID)) {
+            // We only want to mark the last disconnected block as BLOCK_FAILED_VALID; its children
+            // need to be BLOCK_FAILED_CHILD instead.
+            to_mark_failed->nStatus = (to_mark_failed->nStatus ^ BLOCK_FAILED_VALID) | BLOCK_FAILED_CHILD;
+            setDirtyBlockIndex.insert(to_mark_failed);
         }
-        it++;
+
+        // Track the last disconnected block, so we can correct its BLOCK_FAILED_CHILD status in future
+        // iterations, or, if it's the last one, call InvalidChainFound on it.
+        to_mark_failed = invalid_walk_tip;
     }
 
-    InvalidChainFound(pindex);
+    {
+        LOCK(cs_main);
+        if (chainActive.Contains(to_mark_failed)) {
+            // If the to-be-marked invalid block is in the active chain, something is interfering and we can't proceed.
+            return false;
+        }
+
+        // Mark pindex (or the last disconnected block) as invalid, even when it never was in the main chain
+        to_mark_failed->nStatus |= BLOCK_FAILED_VALID;
+        setDirtyBlockIndex.insert(to_mark_failed);
+        setBlockIndexCandidates.erase(to_mark_failed);
+        m_failed_blocks.insert(to_mark_failed);
+
+        // The resulting new best tip may not be in setBlockIndexCandidates anymore, so
+        // add it again.
+        BlockMap::iterator it = mapBlockIndex.begin();
+        while (it != mapBlockIndex.end()) {
+            if (it->second->IsValid(BLOCK_VALID_TRANSACTIONS) && it->second->HaveTxsDownloaded() && !setBlockIndexCandidates.value_comp()(it->second, chainActive.Tip())) {
+                setBlockIndexCandidates.insert(it->second);
+            }
+            it++;
+        }
+
+        InvalidChainFound(to_mark_failed);
+    }
 
     // Only notify about a new block tip if the active chain was modified.
     if (pindex_was_in_chain) {
-        uiInterface.NotifyBlockTip(IsInitialBlockDownload(), pindex->pprev);
+        uiInterface.NotifyBlockTip(IsInitialBlockDownload(), to_mark_failed->pprev);
     }
     return true;
 }
@@ -4162,38 +4191,114 @@ bool ReplayBlocks(const CChainParams& params, CCoinsView* view) {
     return g_chainstate.ReplayBlocks(params, view);
 }
 
+//! Helper for CChainState::RewindBlockIndex
+void CChainState::EraseBlockData(CBlockIndex* index)
+{
+    AssertLockHeld(cs_main);
+    assert(!chainActive.Contains(index)); // Make sure this block isn't active
+
+    // Reduce validity
+    index->nStatus = std::min<unsigned int>(index->nStatus & BLOCK_VALID_MASK, BLOCK_VALID_TREE) | (index->nStatus & ~BLOCK_VALID_MASK);
+    // Remove have-data flags.
+    index->nStatus &= ~(BLOCK_HAVE_DATA | BLOCK_HAVE_UNDO);
+    // Remove storage location.
+    index->nFile = 0;
+    index->nDataPos = 0;
+    index->nUndoPos = 0;
+    // Remove various other things
+    index->nTx = 0;
+    index->nChainTx = 0;
+    index->nSequenceId = 0;
+    // Make sure it gets written.
+    setDirtyBlockIndex.insert(index);
+    // Update indexes
+    setBlockIndexCandidates.erase(index);
+    std::pair<std::multimap<CBlockIndex*, CBlockIndex*>::iterator, std::multimap<CBlockIndex*, CBlockIndex*>::iterator> ret = mapBlocksUnlinked.equal_range(index->pprev);
+    while (ret.first != ret.second) {
+        if (ret.first->second == index) {
+            mapBlocksUnlinked.erase(ret.first++);
+        } else {
+            ++ret.first;
+        }
+    }
+    // Mark parent as eligible for main chain again
+    if (index->pprev && index->pprev->IsValid(BLOCK_VALID_TRANSACTIONS) && index->pprev->HaveTxsDownloaded()) {
+        setBlockIndexCandidates.insert(index->pprev);
+    }
+}
+
 bool CChainState::RewindBlockIndex(const CChainParams& params)
 {
-    LOCK(cs_main);
-
     // Note that during -reindex-chainstate we are called with an empty chainActive!
 
-    int nHeight = 1;
-    while (nHeight <= chainActive.Height()) {
-        // Although SCRIPT_VERIFY_WITNESS is now generally enforced on all
-        // blocks in ConnectBlock, we don't need to go back and
-        // re-download/re-verify blocks from before segwit actually activated.
-        if (IsWitnessEnabled(chainActive[nHeight - 1], params.GetConsensus()) && !(chainActive[nHeight]->nStatus & BLOCK_OPT_WITNESS)) {
-            break;
+    // First erase all post-segwit blocks without witness not in the main chain,
+    // as this can we done without costly DisconnectTip calls. Active
+    // blocks will be dealt with below (releasing cs_main in between).
+    {
+        LOCK(cs_main);
+        for (const auto& entry : mapBlockIndex) {
+            if (IsWitnessEnabled(entry.second->pprev, params.GetConsensus()) && !(entry.second->nStatus & BLOCK_OPT_WITNESS) && !chainActive.Contains(entry.second)) {
+                EraseBlockData(entry.second);
+            }
         }
-        nHeight++;
     }
 
+    // Find what height we need to reorganize to.
+    CBlockIndex *tip;
+    int nHeight = 1;
+    {
+        LOCK(cs_main);
+        while (nHeight <= chainActive.Height()) {
+            // Although SCRIPT_VERIFY_WITNESS is now generally enforced on all
+            // blocks in ConnectBlock, we don't need to go back and
+            // re-download/re-verify blocks from before segwit actually activated.
+            if (IsWitnessEnabled(chainActive[nHeight - 1], params.GetConsensus()) && !(chainActive[nHeight]->nStatus & BLOCK_OPT_WITNESS)) {
+                break;
+            }
+            nHeight++;
+        }
+
+        tip = chainActive.Tip();
+    }
     // nHeight is now the height of the first insufficiently-validated block, or tipheight + 1
+
     CValidationState state;
-    CBlockIndex* pindex = chainActive.Tip();
-    while (chainActive.Height() >= nHeight) {
-        if (fPruneMode && !(chainActive.Tip()->nStatus & BLOCK_HAVE_DATA)) {
-            // If pruning, don't try rewinding past the HAVE_DATA point;
-            // since older blocks can't be served anyway, there's
-            // no need to walk further, and trying to DisconnectTip()
-            // will fail (and require a needless reindex/redownload
-            // of the blockchain).
-            break;
-        }
-        if (!DisconnectTip(state, params, nullptr)) {
-            return error("RewindBlockIndex: unable to disconnect block at height %i (%s)", pindex->nHeight, FormatStateMessage(state));
+    // Loop until the tip is below nHeight, or we reach a pruned block.
+    while (!ShutdownRequested()) {
+        {
+            LOCK(cs_main);
+            // Make sure nothing changed from under us (this won't happen because RewindBlockIndex runs before importing/network are active)
+            assert(tip == chainActive.Tip());
+            if (tip == nullptr || tip->nHeight < nHeight) break;
+            if (fPruneMode && !(tip->nStatus & BLOCK_HAVE_DATA)) {
+                // If pruning, don't try rewinding past the HAVE_DATA point;
+                // since older blocks can't be served anyway, there's
+                // no need to walk further, and trying to DisconnectTip()
+                // will fail (and require a needless reindex/redownload
+                // of the blockchain).
+                break;
+            }
+
+            // Disconnect block
+            if (!DisconnectTip(state, params, nullptr)) {
+                return error("RewindBlockIndex: unable to disconnect block at height %i (%s)", tip->nHeight, FormatStateMessage(state));
+            }
+
+            // Reduce validity flag and have-data flags.
+            // We do this after actual disconnecting, otherwise we'll end up writing the lack of data
+            // to disk before writing the chainstate, resulting in a failure to continue if interrupted.
+            // Note: If we encounter an insufficiently validated block that
+            // is on chainActive, it must be because we are a pruning node, and
+            // this block or some successor doesn't HAVE_DATA, so we were unable to
+            // rewind all the way.  Blocks remaining on chainActive at this point
+            // must not have their validity reduced.
+            EraseBlockData(tip);
+
+            tip = tip->pprev;
         }
+        // Make sure the queue of validation callbacks doesn't grow unboundedly.
+        LimitValidationInterfaceQueue();
+
         // Occasionally flush state to disk.
         if (!FlushStateToDisk(params, state, FlushStateMode::PERIODIC)) {
             LogPrintf("RewindBlockIndex: unable to flush state to disk (%s)\n", FormatStateMessage(state));
@@ -4201,55 +4306,17 @@ bool CChainState::RewindBlockIndex(const CChainParams& params)
         }
     }
 
-    // Reduce validity flag and have-data flags.
-    // We do this after actual disconnecting, otherwise we'll end up writing the lack of data
-    // to disk before writing the chainstate, resulting in a failure to continue if interrupted.
-    for (const auto& entry : mapBlockIndex) {
-        CBlockIndex* pindexIter = entry.second;
+    {
+        LOCK(cs_main);
+        if (chainActive.Tip() != nullptr) {
+            // We can't prune block index candidates based on our tip if we have
+            // no tip due to chainActive being empty!
+            PruneBlockIndexCandidates();
 
-        // Note: If we encounter an insufficiently validated block that
-        // is on chainActive, it must be because we are a pruning node, and
-        // this block or some successor doesn't HAVE_DATA, so we were unable to
-        // rewind all the way.  Blocks remaining on chainActive at this point
-        // must not have their validity reduced.
-        if (IsWitnessEnabled(pindexIter->pprev, params.GetConsensus()) && !(pindexIter->nStatus & BLOCK_OPT_WITNESS) && !chainActive.Contains(pindexIter)) {
-            // Reduce validity
-            pindexIter->nStatus = std::min<unsigned int>(pindexIter->nStatus & BLOCK_VALID_MASK, BLOCK_VALID_TREE) | (pindexIter->nStatus & ~BLOCK_VALID_MASK);
-            // Remove have-data flags.
-            pindexIter->nStatus &= ~(BLOCK_HAVE_DATA | BLOCK_HAVE_UNDO);
-            // Remove storage location.
-            pindexIter->nFile = 0;
-            pindexIter->nDataPos = 0;
-            pindexIter->nUndoPos = 0;
-            // Remove various other things
-            pindexIter->nTx = 0;
-            pindexIter->nChainTx = 0;
-            pindexIter->nSequenceId = 0;
-            // Make sure it gets written.
-            setDirtyBlockIndex.insert(pindexIter);
-            // Update indexes
-            setBlockIndexCandidates.erase(pindexIter);
-            std::pair<std::multimap<CBlockIndex*, CBlockIndex*>::iterator, std::multimap<CBlockIndex*, CBlockIndex*>::iterator> ret = mapBlocksUnlinked.equal_range(pindexIter->pprev);
-            while (ret.first != ret.second) {
-                if (ret.first->second == pindexIter) {
-                    mapBlocksUnlinked.erase(ret.first++);
-                } else {
-                    ++ret.first;
-                }
-            }
-        } else if (pindexIter->IsValid(BLOCK_VALID_TRANSACTIONS) && pindexIter->HaveTxsDownloaded()) {
-            setBlockIndexCandidates.insert(pindexIter);
+            CheckBlockIndex(params.GetConsensus());
         }
     }
 
-    if (chainActive.Tip() != nullptr) {
-        // We can't prune block index candidates based on our tip if we have
-        // no tip due to chainActive being empty!
-        PruneBlockIndexCandidates();
-
-        CheckBlockIndex(params.GetConsensus());
-    }
-
     return true;
 }
 

src/validation.h

@@ -448,7 +448,7 @@ CBlockIndex* FindForkInGlobalIndex(const CChain& chain, const CBlockLocator& loc
 bool PreciousBlock(CValidationState& state, const CChainParams& params, CBlockIndex *pindex) LOCKS_EXCLUDED(cs_main);
 
 /** Mark a block as invalid. */
-bool InvalidateBlock(CValidationState& state, const CChainParams& chainparams, CBlockIndex* pindex) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
+bool InvalidateBlock(CValidationState& state, const CChainParams& chainparams, CBlockIndex* pindex);
 
 /** Remove invalidity status from a block and its descendants. */
 void ResetBlockFailureFlags(CBlockIndex* pindex) EXCLUSIVE_LOCKS_REQUIRED(cs_main);