[validation] make CheckSequenceLocks context-free

Allow CheckSequenceLocks to use heights and coins from any CoinsView and
CBlockIndex provided. This means that CheckSequenceLocks() doesn't need
to hold the mempool lock or cs_main. The caller is responsible for
ensuring the CoinsView and CBlockIndex are consistent before passing
them in. The typical usage is still to create a CCoinsViewMemPool from
the mempool and grab the CBlockIndex from the chainstate tip.

1 files changed, 6 insertions, 13 deletions

diff --git a/src/validation.cpp b/src/validation.cpp
index 4f9b8687b7..ac02cc0515 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -245,18 +245,13 @@ bool TestLockPointValidity(CChain& active_chain, const LockPoints* lp)
     return true;
 }
 
-bool CheckSequenceLocks(CChainState& active_chainstate,
-                        const CTxMemPool& pool,
+bool CheckSequenceLocks(CBlockIndex* tip,
+                        const CCoinsView& coins_view,
                         const CTransaction& tx,
                         int flags,
                         LockPoints* lp,
                         bool useExistingLockPoints)
 {
-    AssertLockHeld(cs_main);
-    AssertLockHeld(pool.cs);
-    assert(std::addressof(::ChainstateActive()) == std::addressof(active_chainstate));
-
-    CBlockIndex* tip = active_chainstate.m_chain.Tip();
     assert(tip != nullptr);
 
     CBlockIndex index;
@@ -276,14 +271,12 @@ bool CheckSequenceLocks(CChainState& active_chainstate,
         lockPair.second = lp->time;
     }
     else {
-        // CoinsTip() contains the UTXO set for active_chainstate.m_chain.Tip()
-        CCoinsViewMemPool viewMemPool(&active_chainstate.CoinsTip(), pool);
         std::vector<int> prevheights;
         prevheights.resize(tx.vin.size());
         for (size_t txinIndex = 0; txinIndex < tx.vin.size(); txinIndex++) {
             const CTxIn& txin = tx.vin[txinIndex];
             Coin coin;
-            if (!viewMemPool.GetCoin(txin.prevout, coin)) {
+            if (!coins_view.GetCoin(txin.prevout, coin)) {
                 return error("%s: Missing input", __func__);
             }
             if (coin.nHeight == MEMPOOL_HEIGHT) {
@@ -686,10 +679,10 @@ bool MemPoolAccept::PreChecks(ATMPArgs& args, Workspace& ws)
     // Only accept BIP68 sequence locked transactions that can be mined in the next
     // block; we don't want our mempool filled up with transactions that can't
     // be mined yet.
-    // Must keep pool.cs for this unless we change CheckSequenceLocks to take a
-    // CoinsViewCache instead of create its own
+    // Pass in m_view which has all of the relevant inputs cached. Note that, since m_view's
+    // backend was removed, it no longer pulls coins from the mempool.
     assert(std::addressof(::ChainstateActive()) == std::addressof(m_active_chainstate));
-    if (!CheckSequenceLocks(m_active_chainstate, m_pool, tx, STANDARD_LOCKTIME_VERIFY_FLAGS, &lp))
+    if (!CheckSequenceLocks(m_active_chainstate.m_chain.Tip(), m_view, tx, STANDARD_LOCKTIME_VERIFY_FLAGS, &lp))
         return state.Invalid(TxValidationResult::TX_PREMATURE_SPEND, "non-BIP68-final");
 
     assert(std::addressof(g_chainman.m_blockman) == std::addressof(m_active_chainstate.m_blockman));