Merge #15402: Granular invalidateblock and RewindBlockIndex

519b0bc5dc5155b6f7e2362c2105552bb7618ad0 Make last disconnected block BLOCK_FAILED_VALID, even when aborted (Pieter Wuille)
8d220417cd7bc34464e28a4861a885193ec091c2 Optimization: don't add txn back to mempool after 10 invalidates (Pieter Wuille)
9ce9c37004440d6a329874dbf66b51666d497dcb Prevent callback overruns in InvalidateBlock and RewindBlockIndex (Pieter Wuille)
9bb32eb571a846b66ed3bac493f55cee11a3a1b9 Release cs_main during InvalidateBlock iterations (Pieter Wuille)
9b1ff5c742dec0a6e0d6aab29b0bb771ad6d8135 Call InvalidateBlock without cs_main held (Pieter Wuille)
241b2c74ac8c4c3000e778554da1271e3f293e5d Make RewindBlockIndex interruptible (Pieter Wuille)
880ce7d46b51835c00d77a366ec28f54a05239df Call RewindBlockIndex without cs_main held (Pieter Wuille)
436f7d735f1c37e77d42ff59d4cbb1bd76d5fcfb Release cs_main during RewindBlockIndex operation (Pieter Wuille)
1d342875c21b5d0a17cf4d176063bb14b35b657e Merge the disconnection and erasing loops in RewindBlockIndex (Pieter Wuille)
32b2696ab4b079db736074b57bbc24deaee0b3d9 Move erasure of non-active blocks to a separate loop in RewindBlockIndex (Pieter Wuille)
9d6dcc52c6cb0cdcda220fddccaabb0ffd40068d Abstract EraseBlockData out of RewindBlockIndex (Pieter Wuille)

Pull request description:

  This PR makes a number of improvements to the InvalidateBlock (`invalidateblock` RPC) and RewindBlockIndex functions, primarily around breaking up their long-term cs_main holding. In addition:
  * They're made safely interruptible (`bitcoind` can be shutdown, and no progress in either will be lost, though if incomplete, `invalidateblock` won't continue after restart and will need to be called again)
  * The validation queue is prevented from overflowing (meaning `invalidateblock` on a very old block will not drive bitcoind OOM) (see #14289).
  * `invalidateblock` won't bother to move transactions back into the mempool after 10 blocks (optimization).

  This is not an optimal solution, as we're relying on the scheduler call sites to make sure the scheduler doesn't overflow. Ideally, the scheduler would guarantee this directly, but that needs a few further changes (moving the signal emissions out of cs_main) to prevent deadlocks.

  I have manually tested the `invalidateblock` changes (including interrupting, and running with -checkblockindex and -checkmempool), but haven't tried the rewinding (which is probably becoming increasingly unnecessary, as very few pre-0.13.1 nodes remain that would care to upgrade).

Tree-SHA512: 692e42758bd3d3efc2eb701984a8cb5db25fbeee32e7575df0183a00d0c2c30fdf72ce64c7625c32ad8c8bdc56313da72a7471658faeb0d39eefe39c4b8b8474

4 files changed, 211 insertions, 137 deletions

diff --git a/src/init.cpp b/src/init.cpp
index ee9a451d0b..0898d0ff25 100644
--- a/src/init.cpp
+++ b/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) {
diff --git a/src/rpc/blockchain.cpp b/src/rpc/blockchain.cpp
index 72fec2eaa5..1827aec637 100644
--- a/src/rpc/blockchain.cpp
+++ b/src/rpc/blockchain.cpp
@@ -1579,15 +1579,15 @@ 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());
diff --git a/src/validation.cpp b/src/validation.cpp
index 358992b74d..a9b5bcf4a4 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -178,7 +178,7 @@ 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);
@@ -207,8 +207,10 @@ private:
     CBlockIndex* FindMostWorkChain() EXCLUSIVE_LOCKS_REQUIRED(cs_main);
     void ReceivedBlockTransactions(const CBlock& block, CBlockIndex* pindexNew, const FlatFilePos& 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;
 
 /**
@@ -2626,6 +2628,14 @@ 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
@@ -2654,15 +2664,13 @@ 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);
@@ -2773,64 +2781,85 @@ bool PreciousBlock(CValidationState& state, const CChainParams& params, CBlockIn
 
 bool CChainState::InvalidateBlock(CValidationState& state, const CChainParams& chainparams, CBlockIndex *pindex)
 {
-    AssertLockHeld(cs_main);
+    CBlockIndex* to_mark_failed = pindex;
+    bool pindex_was_in_chain = false;
+    int disconnected = 0;
 
-    // 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).
+    // Disconnect (descendants of) pindex, and mark them invalid.
+    while (true) {
+        if (ShutdownRequested()) break;
 
-    bool pindex_was_in_chain = false;
-    CBlockIndex *invalid_walk_tip = chainActive.Tip();
+        // Make sure the queue of validation callbacks doesn't grow unboundedly.
+        LimitValidationInterfaceQueue();
 
-    DisconnectedBlockTransactions disconnectpool;
-    while (chainActive.Contains(pindex)) {
+        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;
-        }
-    }
-
-    // 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;
+        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());
+
+        // 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;
-    }
+        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);
+        }
 
-    // Mark the block itself as invalid.
-    pindex->nStatus |= BLOCK_FAILED_VALID;
-    setDirtyBlockIndex.insert(pindex);
-    setBlockIndexCandidates.erase(pindex);
-    m_failed_blocks.insert(pindex);
+        // 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;
+    }
 
-    // DisconnectTip will add transactions to disconnectpool; try to add these
-    // back to the mempool.
-    UpdateMempoolForReorg(disconnectpool, true);
+    {
+        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;
+        }
 
-    // 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);
+        // 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++;
         }
-        it++;
-    }
 
-    InvalidChainFound(pindex);
+        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;
 }
@@ -4113,38 +4142,114 @@ bool ReplayBlocks(const CChainParams& params, CCoinsView* view) {
     return g_chainstate.ReplayBlocks(params, view);
 }
 
-bool CChainState::RewindBlockIndex(const CChainParams& params)
+//! Helper for CChainState::RewindBlockIndex
+void CChainState::EraseBlockData(CBlockIndex* index)
 {
-    LOCK(cs_main);
+    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)
+{
     // 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));
@@ -4152,53 +4257,15 @@ 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;
-
-        // 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);
-        }
-    }
-
-    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();
+    {
+        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();
 
-        CheckBlockIndex(params.GetConsensus());
+            CheckBlockIndex(params.GetConsensus());
+        }
     }
 
     return true;
diff --git a/src/validation.h b/src/validation.h
index 4ef82ee2c7..0acca013b5 100644
--- a/src/validation.h
+++ b/src/validation.h
@@ -443,7 +443,7 @@ 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);