Have testBlockValidity hold cs_main instead of caller

The goal of interfaces is to eventually run in their own process,
so we can't use EXCLUSIVE_LOCKS_REQUIRED in their declaration.

However TestBlockValidaty will crash (in its call to ConnectBlock)
if the tip changes from under the proposed block.

Have the testBlockValidity implementation  hold the lock instead,
and non-fatally check for this condition.

3 files changed, 10 insertions, 7 deletions

diff --git a/src/interfaces/mining.h b/src/interfaces/mining.h
index bc98448833..7d71a01450 100644
--- a/src/interfaces/mining.h
+++ b/src/interfaces/mining.h
@@ -67,7 +67,7 @@ public:
      * @param[in] block the block to validate
      * @param[in] check_merkle_root call CheckMerkleRoot()
      * @param[out] state details of why a block failed to validate
-     * @returns false if any of the checks fail
+     * @returns false if it does not build on the current tip, or any of the checks fail
      */
     virtual bool testBlockValidity(const CBlock& block, bool check_merkle_root, BlockValidationState& state) = 0;
 
diff --git a/src/node/interfaces.cpp b/src/node/interfaces.cpp
index 5e87bf234a..fa151407fa 100644
--- a/src/node/interfaces.cpp
+++ b/src/node/interfaces.cpp
@@ -872,8 +872,15 @@ public:
 
     bool testBlockValidity(const CBlock& block, bool check_merkle_root, BlockValidationState& state) override
     {
-        LOCK(::cs_main);
-        return TestBlockValidity(state, chainman().GetParams(), chainman().ActiveChainstate(), block, chainman().ActiveChain().Tip(), /*fCheckPOW=*/false, check_merkle_root);
+        LOCK(cs_main);
+        CBlockIndex* tip{chainman().ActiveChain().Tip()};
+        // Fail if the tip updated before the lock was taken
+        if (block.hashPrevBlock != tip->GetBlockHash()) {
+            state.Error("Block does not connect to current chain tip.");
+            return false;
+        }
+
+        return TestBlockValidity(state, chainman().GetParams(), chainman().ActiveChainstate(), block, tip, /*fCheckPOW=*/false, check_merkle_root);
     }
 
     std::unique_ptr<CBlockTemplate> createNewBlock(const CScript& script_pub_key, bool use_mempool) override
diff --git a/src/rpc/mining.cpp b/src/rpc/mining.cpp
index d9fd82d708..7e420dcd9b 100644
--- a/src/rpc/mining.cpp
+++ b/src/rpc/mining.cpp
@@ -371,8 +371,6 @@ static RPCHelpMan generateblock()
 
     ChainstateManager& chainman = EnsureChainman(node);
     {
-        LOCK(cs_main);
-
         std::unique_ptr<CBlockTemplate> blocktemplate{miner.createNewBlock(coinbase_script, /*use_mempool=*/false)};
         if (!blocktemplate) {
             throw JSONRPCError(RPC_INTERNAL_ERROR, "Couldn't create new block");
@@ -387,8 +385,6 @@ static RPCHelpMan generateblock()
     RegenerateCommitments(block, chainman);
 
     {
-        LOCK(cs_main);
-
         BlockValidationState state;
         if (!miner.testBlockValidity(block, /*check_merkle_root=*/false, state)) {
             throw JSONRPCError(RPC_VERIFY_ERROR, strprintf("testBlockValidity failed: %s", state.ToString()));