From 9bb32eb571a846b66ed3bac493f55cee11a3a1b9 Mon Sep 17 00:00:00 2001
From: Pieter Wuille <pieter.wuille@gmail.com>
Date: Wed, 13 Feb 2019 16:37:30 -0800
Subject: [PATCH] Release cs_main during InvalidateBlock iterations

---
 src/validation.cpp | 94 +++++++++++++++++++++++++---------------------
 1 file changed, 52 insertions(+), 42 deletions(-)

diff --git a/src/validation.cpp b/src/validation.cpp
index dd4436c9c..8f7e9fba6 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -2789,64 +2789,74 @@ bool PreciousBlock(CValidationState& state, const CChainParams& params, CBlockIn
 
 bool CChainState::InvalidateBlock(CValidationState& state, const CChainParams& chainparams, CBlockIndex *pindex)
 {
-    LOCK(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();
 
-    DisconnectedBlockTransactions disconnectpool;
-    while (chainActive.Contains(pindex)) {
+    // Disconnect (descendants of) pindex, and mark them invalid.
+    while (true) {
+        if (ShutdownRequested()) break;
+
+        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.
+        UpdateMempoolForReorg(disconnectpool, /* fAddToMempool = */ 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) {
+        // 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_CHILD;
         setDirtyBlockIndex.insert(invalid_walk_tip);
         setBlockIndexCandidates.erase(invalid_walk_tip);
-        invalid_walk_tip = invalid_walk_tip->pprev;
+        setBlockIndexCandidates.insert(invalid_walk_tip->pprev);
+
+        // If we abort invalidation after this iteration, make sure
+        // the last disconnected block gets marked failed (rather than
+        // just child of failed)
+        to_mark_failed = invalid_walk_tip;
     }
 
-    // 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);
+    {
+        // Mark pindex (or the last disconnected block) as invalid, regardless of whether it was in the main chain or not.
+        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;
         }
-        it++;
-    }
 
-    InvalidChainFound(pindex);
+        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;
 }