update recent_rejects filters on ActiveTipChange

Resetting m_recent_rejects once per block is more efficient than
comparing hashRecentRejectsChainTip with the chain tip every time we
call AlreadyHaveTx. We keep hashRecentRejectsChainTip for now to assert
that updates happen correctly; it is removed in the next commit.

src/net_processing.cpp

@@ -489,6 +489,8 @@ class PeerManagerImpl final : public PeerManager
                     CTxMemPool& pool, node::Warnings& warnings, Options opts);
 
     /** Overridden from CValidationInterface. */
+    void ActiveTipChange(const CBlockIndex* new_tip, bool) override
+        EXCLUSIVE_LOCKS_REQUIRED(!m_recent_confirmed_transactions_mutex, !m_tx_download_mutex);
     void BlockConnected(ChainstateRole role, const std::shared_ptr<const CBlock>& pblock, const CBlockIndex* pindexConnected) override
         EXCLUSIVE_LOCKS_REQUIRED(!m_recent_confirmed_transactions_mutex, !m_tx_download_mutex);
     void BlockDisconnected(const std::shared_ptr<const CBlock> &block, const CBlockIndex* pindex) override
@@ -2074,6 +2076,22 @@ void PeerManagerImpl::StartScheduledTasks(CScheduler& scheduler)
     scheduler.scheduleFromNow([&] { ReattemptInitialBroadcast(scheduler); }, delta);
 }
 
+void PeerManagerImpl::ActiveTipChange(const CBlockIndex* new_tip, bool is_ibd)
+{
+    AssertLockNotHeld(m_mempool.cs);
+    AssertLockNotHeld(m_tx_download_mutex);
+
+    if (!is_ibd) {
+        LOCK(m_tx_download_mutex);
+        // If the chain tip has changed, previously rejected transactions might now be valid, e.g. due
+        // to a timelock. Reset the rejection filters to give those transactions another chance if we
+        // see them again.
+        m_recent_rejects.reset();
+        m_recent_rejects_reconsiderable.reset();
+        hashRecentRejectsChainTip = new_tip->GetBlockHash();
+    }
+}
+
 /**
  * Evict orphan txn pool entries based on a newly connected
  * block, remember the recently confirmed transactions, and delete tracked
@@ -2277,7 +2295,11 @@ bool PeerManagerImpl::AlreadyHaveTx(const GenTxid& gtxid, bool include_reconside
     AssertLockHeld(::cs_main);
     AssertLockHeld(m_tx_download_mutex);
 
-    if (m_chainman.ActiveChain().Tip()->GetBlockHash() != hashRecentRejectsChainTip) {
+    // Since recent_rejects is updated whenever the tip changes, and hashRecentRejectsChainTip is
+    // not set until the first time it is called outside of IBD, hashRecentRejectsChainTip should
+    // always be up to date with the current chain tip.
+    if (!Assume(hashRecentRejectsChainTip == uint256::ZERO ||
+                hashRecentRejectsChainTip == m_chainman.ActiveChain().Tip()->GetBlockHash())) {
         // If the chain tip has changed previously rejected transactions
         // might be now valid, e.g. due to a nLockTime'd tx becoming valid,
         // or a double-spend. Reset the rejects filter and give those