runtime: make channels work in interrupts

src/runtime/gc_conservative.go

@@ -29,6 +29,8 @@ package runtime
 // Moss.
 
 import (
+	"internal/task"
+	"runtime/interrupt"
 	"unsafe"
 )
 
@@ -292,10 +294,36 @@ func GC() {
 	}
 
 	// Mark phase: mark all reachable objects, recursively.
-	markGlobals()
 	markStack()
+	markGlobals()
+
+	// Channel operations in interrupts may move task pointers around while we are marking.
+	// Therefore we need to scan the runqueue seperately.
+	var markedTaskQueue task.Queue
+runqueueScan:
+	for !runqueue.Empty() {
+		// Pop the next task off of the runqueue.
+		t := runqueue.Pop()
+
+		// Mark the task if it has not already been marked.
+		markRoot(uintptr(unsafe.Pointer(&runqueue)), uintptr(unsafe.Pointer(t)))
+
+		// Push the task onto our temporary queue.
+		markedTaskQueue.Push(t)
+	}
+
 	finishMark()
 
+	// Restore the runqueue.
+	i := interrupt.Disable()
+	if !runqueue.Empty() {
+		// Something new came in while finishing the mark.
+		interrupt.Restore(i)
+		goto runqueueScan
+	}
+	runqueue = markedTaskQueue
+	interrupt.Restore(i)
+
 	// Sweep phase: free all non-marked objects and unmark marked objects for
 	// the next collection cycle.
 	sweep()