safely scan the runqueue on the list scheduler

Author: niaow

src/runtime/gc_list.go

@@ -2,6 +2,12 @@
 
 package runtime
 
+import (
+	"internal/task"
+	"runtime/interrupt"
+	"unsafe"
+)
+
 // This memory manager is partially inspired by the memory allocator included in avr-libc.
 // Unlike avr-libc malloc, this memory manager stores an allocation list instead of a free list.
 // This gives an overhead of 2 pointers/allocation (up from avr-libc's 1 pointer-width/allocation).
@@ -10,8 +16,6 @@ package runtime
 // This allocator has an effective allocation complexity of O(n) and worst-case GC complexity of O(n^2).
 // Due to architectural quirks, as well as tiny heaps, this should almost always be faster than the standard conservative collector on AVR.
 
-import "unsafe"
-
 // isInHeap checks if an address is inside the heap.
 func isInHeap(addr uintptr) bool {
 	return addr >= heapStart && addr < heapEnd
@@ -77,6 +81,23 @@ func GC() {
 	// Mark phase: mark all reachable objects, recursively.
 	markGlobals()
 	markStack()
+	var markedTaskQueue task.Queue
+runqueueScan:
+	if baremetal && hasScheduler {
+		// Channel operations in interrupts may move task pointers around while we are marking.
+		// Therefore we need to scan the runqueue seperately.
+		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)
+		}
+	}
+
 	var keep *allocNode
 	for scanList != nil {
 		// Pop a node off of the scan list.
@@ -102,6 +123,18 @@ func GC() {
 		}
 	}
 
+	if baremetal && hasScheduler {
+		// 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: replace the heap.
 	allocList = keep
 }