f duh - just update under the lock

Author: TheBlueMatt

lightning/src/chain/chainmonitor.rs

@@ -262,19 +262,18 @@ where C::Target: chain::Filter,
 		FN: Fn(&ChannelMonitor<ChannelSigner>, &TransactionData) -> Vec<TransactionOutputs>
 	{
 		let mut dependent_txdata = Vec::new();
-		if let Some(height) = best_height {
-			// Sadly AtomicUsize::fetch_max wasn't stabilized until 1.45, so until then we have to
-			// manually CAS.
-			let mut old_height = self.highest_chain_height.load(Ordering::Relaxed);
-			let new_height = height as usize;
-			while new_height > old_height && self.highest_chain_height
-				.compare_exchange(old_height, new_height, Ordering::AcqRel, Ordering::Relaxed).is_err()
-			{
-				old_height = self.highest_chain_height.load(Ordering::Acquire);
-			}
-		}
 		{
 			let monitor_states = self.monitors.write().unwrap();
+			if let Some(height) = best_height {
+				// If the best block height is being updated, update highest_chain_height under the
+				// monitors write lock.
+				let old_height = self.highest_chain_height.load(Ordering::Acquire);
+				let new_height = height as usize;
+				if new_height > old_height {
+					self.highest_chain_height.store(new_height, Ordering::Release);
+				}
+			}
+
 			for (funding_outpoint, monitor_state) in monitor_states.iter() {
 				let monitor = &monitor_state.monitor;
 				let mut txn_outputs;