Merge bitcoin#12368: Hold mempool.cs for the duration of ATMP.

02fc886 Add braces to meet code style on line-after-the-one-changed. (Matt Corallo)
85aa839 Hold mempool.cs for the duration of ATMP. (Matt Corallo)

Pull request description:

  This resolves an issue where getrawmempool() can race mempool
  notification signals. Intuitively we use mempool.cs as a "read
  lock" on the mempool with cs_main being the write lock, so holding
  the read lock intermittently while doing write operations is
  somewhat strange.

  This also avoids the introduction of cs_main in getrawmempool()
  which reviewers objected to in the previous fix in bitcoin#12273

Tree-SHA512: 29464b9ca3890010ae13b7dc1c53487cc2bc9c3cf3d32a14cb09c8aa33848f57959d8991ea096beebcfb72f062e4e1962f104aefe4252c7db87633bbfe4ab317

src/validation.cpp

@@ -543,8 +543,10 @@ static bool AcceptToMemoryPoolWorker(const CChainParams& chainparams, CTxMemPool
     const CTransaction& tx = *ptx;
     const uint256 hash = tx.GetHash();
     AssertLockHeld(cs_main);
-    if (pfMissingInputs)
+    LOCK(pool.cs); // mempool "read lock" (held through GetMainSignals().TransactionAddedToMempool())
+    if (pfMissingInputs) {
         *pfMissingInputs = false;
+    }
 
     if (!CheckTransaction(tx, state))
         return false; // state filled in by CheckTransaction
@@ -590,8 +592,6 @@ static bool AcceptToMemoryPoolWorker(const CChainParams& chainparams, CTxMemPool
     }
 
     // Check for conflicts with in-memory transactions
-    {
-    LOCK(pool.cs); // protect pool.mapNextTx
     for (const CTxIn &txin : tx.vin)
     {
         auto itConflicting = pool.mapNextTx.find(txin.prevout);
@@ -603,15 +603,12 @@ static bool AcceptToMemoryPoolWorker(const CChainParams& chainparams, CTxMemPool
             return state.Invalid(false, REJECT_DUPLICATE, "txn-mempool-conflict");
         }
     }
-    }
 
     {
         CCoinsView dummy;
         CCoinsViewCache view(&dummy);
 
         LockPoints lp;
-        {
-        LOCK(pool.cs);
         CCoinsViewMemPool viewMemPool(pcoinsTip.get(), pool);
         view.SetBackend(viewMemPool);
 
@@ -650,8 +647,6 @@ static bool AcceptToMemoryPoolWorker(const CChainParams& chainparams, CTxMemPool
         if (!CheckSequenceLocks(tx, STANDARD_LOCKTIME_VERIFY_FLAGS, &lp))
             return state.DoS(0, false, REJECT_NONSTANDARD, "non-BIP68-final");
 
-        } // end LOCK(pool.cs)
-
         CAmount nFees = 0;
         if (!Consensus::CheckTxInputs(tx, state, view, GetSpendHeight(view), nFees)) {
             return error("%s: Consensus::CheckTxInputs: %s, %s", __func__, tx.GetHash().ToString(), FormatStateMessage(state));