Ensure `vm_stack` is cleared after fork.

1 files changed, 26 insertions, 10 deletions

diff --git a/vm.c b/vm.c
index 1f09411d39..495d5ddcb6 100644
--- a/vm.c
+++ b/vm.c
@@ -2514,7 +2514,7 @@ rb_execution_context_mark(const rb_execution_context_t *ec)
 #endif
 
     /* mark VM stack */
-    if (ec->vm_stack && ec->cfp) {
+    if (ec->vm_stack) {
 	VALUE *p = ec->vm_stack;
 	VALUE *sp = ec->cfp->sp;
 	rb_control_frame_t *cfp = ec->cfp;
@@ -2685,20 +2685,36 @@ thread_alloc(VALUE klass)
     return obj;
 }
 
+inline void
+rb_ec_set_vm_stack(rb_execution_context_t *ec, VALUE *stack, size_t size)
+{
+    ec->vm_stack = stack;
+    ec->vm_stack_size = size;
+}
+
 void
 rb_ec_initialize_vm_stack(rb_execution_context_t *ec, VALUE *stack, size_t size)
 {
-  rb_ec_set_vm_stack(ec, stack, size);
+    rb_ec_set_vm_stack(ec, stack, size);
+
+    ec->cfp = (void *)(ec->vm_stack + ec->vm_stack_size);
 
-  ec->cfp = (void *)(ec->vm_stack + ec->vm_stack_size);
+    rb_vm_push_frame(ec,
+        NULL /* dummy iseq */,
+        VM_FRAME_MAGIC_DUMMY | VM_ENV_FLAG_LOCAL | VM_FRAME_FLAG_FINISH | VM_FRAME_FLAG_CFRAME /* dummy frame */,
+        Qnil /* dummy self */, VM_BLOCK_HANDLER_NONE /* dummy block ptr */,
+        0 /* dummy cref/me */,
+        0 /* dummy pc */, ec->vm_stack, 0, 0
+    );
+}
+
+void
+rb_ec_clear_vm_stack(rb_execution_context_t *ec)
+{
+    rb_ec_set_vm_stack(ec, NULL, 0);
 
-  rb_vm_push_frame(ec,
-      NULL /* dummy iseq */,
-      VM_FRAME_MAGIC_DUMMY | VM_ENV_FLAG_LOCAL | VM_FRAME_FLAG_FINISH | VM_FRAME_FLAG_CFRAME /* dummy frame */,
-      Qnil /* dummy self */, VM_BLOCK_HANDLER_NONE /* dummy block ptr */,
-      0 /* dummy cref/me */,
-      0 /* dummy pc */, ec->vm_stack, 0, 0
-  );
+    // Avoid dangling pointers:
+    ec->cfp = NULL;
 }
 
 static void