IoUringAssmEngine: Acquire spinlock in stall timeout branch

stimBuffApis/livoxGen1/ioUringAssemblyEngine.cpp

@@ -418,6 +418,23 @@ public:
 		// Check if timer was cancelled (ignore if operation_aborted)
 		if (error == boost::asio::error::operation_aborted) { return; }
 
+		/**	EXPLANATION:
+		 * This lock acquisition here will also cover the call to
+		 * assembleFrameReq3 below. Because of that, it means that the
+		 * requirement that the lock be held while accessing
+		 * the metadata that's destroyed in stop() is satisfied.
+		 *
+		 * In theory though, we shouldn't need to hold the lock into
+		 * assembleFrameReq3 below because that function doesn't really access
+		 * any state that's destroyed in stop()? But I'm not sure, and we have
+		 * indeed seen a SEGFAULT even in the current code with locking, so
+		 * I'm going to hold the lock here for now.
+		 */
+		SpinLock::Guard lock(context->engine.isAssemblingLock);
+
+		if (!context->engine.isAssembling)
+			{ return; }
+
 		// Set timer fired flag
 		context->timerFired.store(true);
 		context->assembleFrameReq3(context);