wip: improve error handling for OOM

Use gc_abort_mark_alive() helper in case of OOM.  In addition to
freeing the stack, we need to ensure that no object has the alive bit
set on it.  This also adding missing error handling in the case that
propagate_alive_bits() fails.

Author: nascheme

Python/gc_free_threading.c

@@ -484,12 +484,37 @@ mark_alive_stack_push(PyObject *op, _PyObjectStack *stack)
     // alive so we don't traverse it a second time.
     gc_set_alive(op);
     if (_PyObjectStack_Push(stack, op) < 0) {
-        _PyObjectStack_Clear(stack);
         return -1;
     }
     return 0;
 }
 
+static bool
+gc_clear_alive_bits(const mi_heap_t *heap, const mi_heap_area_t *area,
+                    void *block, size_t block_size, void *args)
+{
+    PyObject *op = op_from_block(block, args, false);
+    if (op == NULL) {
+        return true;
+    }
+    if (gc_is_alive(op)) {
+        gc_clear_alive(op);
+    }
+    return true;
+}
+
+static void
+gc_abort_mark_alive(PyInterpreterState *interp,
+                    struct collection_state *state,
+                    _PyObjectStack *stack)
+{
+    // We failed to allocate memory for "stack" while doing the "mark
+    // alive" phase.  In that case, free the object stack and make sure
+    // that no objects have the alive bit set.
+    _PyObjectStack_Clear(stack);
+    gc_visit_heaps(interp, &gc_clear_alive_bits, &state->base);
+}
+
 #ifdef GC_MARK_ALIVE_STACKS
 static int
 gc_visit_stackref_mark_alive(_PyObjectStack *stack, _PyStackRef stackref)
@@ -901,6 +926,7 @@ mark_alive_from_roots(PyInterpreterState *interp,
 
     #define STACK_PUSH(op) \
         if (mark_alive_stack_push(op, &stack) < 0) { \
+            gc_abort_mark_alive(interp, state, &stack); \
             return -1; \
         }
     STACK_PUSH(interp->sysdict);
@@ -919,13 +945,17 @@ mark_alive_from_roots(PyInterpreterState *interp,
 #endif
 #ifdef GC_MARK_ALIVE_STACKS
     if (gc_visit_thread_stacks_mark_alive(interp, &stack) < 0) {
+        gc_abort_mark_alive(interp, state, &stack);
         return -1;
     }
 #endif
     #undef STACK_PUSH
 
     // Use tp_traverse to find everything reachable from roots.
-    propagate_alive_bits(&stack);
+    if (propagate_alive_bits(&stack) < 0) {
+        gc_abort_mark_alive(interp, state, &stack);
+        return -1;
+    }
 
     return 0;
 }