Merge #14193: validation: Add missing mempool locks

fa2b083c3f [test] Add test to check mempool consistency in case of reorgs (MarcoFalke)
fabeb1f613 validation: Add missing mempool locks (MarcoFalke)
fa0c9dbf91 txpool: Make nTransactionsUpdated atomic (MarcoFalke)

Pull request description:

  Take the mempool read lock during reorgs, so that we don't accidentally read an inconsistent mempool.

ACKs for top commit:
  laanwj:
    code review ACK fa2b083c3f
  ryanofsky:
    utACK fa2b083c3f [EDIT: was ~e284e422e75189794e24fe482819d8b1407857c3~, from bad copy and paste]. Changes since last review: rebase after #15976, adding vTxHashes lock annotation, adding new commit dropping mempool lock for nTransactionsUpdated and making it atomic to avoid deadlock between mempool lock and g_best_block_mutex

Tree-SHA512: cfe7777993589087753e000e3736d79d320dca412383fb77b56bef8946a04049722bf888c11b6f722adf677165185c7e58b4a269f7c5fa25e84dda375f6c8a7d

src/rpc/mining.cpp

@@ -469,7 +469,7 @@ static UniValue getblocktemplate(const JSONRPCRequest& request)
             nTransactionsUpdatedLastLP = nTransactionsUpdatedLast;
         }
 
-        // Release the wallet and main lock while waiting
+        // Release lock while waiting
         LEAVE_CRITICAL_SECTION(cs_main);
         {
             checktxtime = std::chrono::steady_clock::now() + std::chrono::minutes(1);
@@ -480,6 +480,7 @@ static UniValue getblocktemplate(const JSONRPCRequest& request)
                 if (g_best_block_cv.wait_until(lock, checktxtime) == std::cv_status::timeout)
                 {
                     // Timeout: Check transactions for update
+                    // without holding ::mempool.cs to avoid deadlocks
                     if (mempool.GetTransactionsUpdated() != nTransactionsUpdatedLastLP)
                         break;
                     checktxtime += std::chrono::seconds(10);