Fix for Issue 4762

prdoc/pr_4803.prdoc

@@ -0,0 +1,13 @@
+# Schema: Polkadot SDK PRDoc Schema (prdoc) v1.0.0
+# See doc at https://raw.githubusercontent.com/paritytech/polkadot-sdk/master/prdoc/schema_user.json
+
+title: Fix for issue #4762
+
+doc:
+  - audience: Runtime Dev
+    description: |
+      When the status of the queue is on_initialize, throw a defensive message and return weight of 0, 
+      however when status is on_idle, do not throw a defensive message, only return weight of 0
+
+crates:
+  - name: MQ pallet

substrate/frame/message-queue/src/lib.rs

@@ -649,7 +649,7 @@ pub mod pallet {
 	impl<T: Config> Hooks<BlockNumberFor<T>> for Pallet<T> {
 		fn on_initialize(_n: BlockNumberFor<T>) -> Weight {
 			if let Some(weight_limit) = T::ServiceWeight::get() {
-				Self::service_queues(weight_limit)
+				Self::service_queues(weight_limit, ServiceQueuesContext::OnInitialize)
 			} else {
 				Weight::zero()
 			}
@@ -658,7 +658,7 @@ pub mod pallet {
 		fn on_idle(_n: BlockNumberFor<T>, remaining_weight: Weight) -> Weight {
 			if let Some(weight_limit) = T::IdleMaxServiceWeight::get() {
 				// Make use of the remaining weight to process enqueued messages.
-				Self::service_queues(weight_limit.min(remaining_weight))
+				Self::service_queues(weight_limit.min(remaining_weight), ServiceQueuesContext::OnIdle)
 			} else {
 				Weight::zero()
 			}
@@ -777,6 +777,16 @@ enum MessageExecutionStatus {
 	StackLimitReached,
 }
 
+/// The context to pass to service_queues through on_idle and on_initialize hooks
+/// We don't want to throw the defensive message if called from on_idle hook
+#[derive(PartialEq)]
+enum ServiceQueuesContext {
+	/// Context of on_idle hook
+	OnIdle,
+	/// Context of on_initialize hook
+	OnInitialize,
+}
+
 impl<T: Config> Pallet<T> {
 	/// Knit `origin` into the ready ring right at the end.
 	///
@@ -1579,13 +1589,12 @@ impl<T: Get<O>, O: Into<u32>> Get<u32> for IntoU32<T, O> {
 impl<T: Config> ServiceQueues for Pallet<T> {
 	type OverweightMessageAddress = (MessageOriginOf<T>, PageIndex, T::Size);
 
-	fn service_queues(weight_limit: Weight) -> Weight {
+	fn service_queues(weight_limit: Weight, context: ServiceQueuesContext) -> Weight {
 		let mut weight = WeightMeter::with_limit(weight_limit);
 
 		// Get the maximum weight that processing a single message may take:
 		let max_weight = Self::max_message_weight(weight_limit).unwrap_or_else(|| {
-			defensive!("Not enough weight to service a single message.");
-			Weight::zero()
+			check_queue_context(context);
 		});
 
 		match with_service_mutex(|| {
@@ -1654,6 +1663,16 @@ impl<T: Config> ServiceQueues for Pallet<T> {
 			},
 		)
 	}
+
+	// Check the message queue context for on_idle and on_initialize status
+	// throw defensive message in `on_initialize` status
+	// don't throw defensive message in `on_idle` status
+	fn check_queue_context(context: ServiceQueuesContext) -> Weight {
+		if matches(context, ServiceQueuesContext::OnInitialize) {
+			defensive!("Not enough weight to service a single message.");
+		}
+		Weight::zero()
+	}
 }
 
 impl<T: Config> EnqueueMessage<MessageOriginOf<T>> for Pallet<T> {