Prevent the stack from being marked twice

This commit prevents the stack from being marked twice: once via the
Fiber, and once via the Thread.  It introduces an assertion to assert
that the ec on the thread is the same as the ec on the Fiber being
marked via the thread.

3 files changed, 9 insertions, 2 deletions

diff --git a/cont.c b/cont.c
index 36f47d9ee6..590d6c250f 100644
--- a/cont.c
+++ b/cont.c
@@ -1194,6 +1194,12 @@ cont_init_mjit_cont(rb_context_t *cont)
     }
 }
 
+struct rb_execution_context_struct *
+rb_fiberptr_get_ec(struct rb_fiber_struct *fiber)
+{
+    return &fiber->cont.saved_ec;
+}
+
 static void
 cont_init(rb_context_t *cont, rb_thread_t *th)
 {
diff --git a/internal/cont.h b/internal/cont.h
index 5ab120e9ab..abffc97104 100644
--- a/internal/cont.h
+++ b/internal/cont.h
@@ -12,6 +12,7 @@
 
 struct rb_thread_struct;        /* in vm_core.h */
 struct rb_fiber_struct;         /* in cont.c */
+struct rb_execution_context_struct; /* in vm_core.c */
 
 /* cont.c */
 void rb_fiber_reset_root_local_storage(struct rb_thread_struct *);
@@ -20,5 +21,6 @@ void rb_fiber_init_mjit_cont(struct rb_fiber_struct *fiber);
 
 VALUE rb_fiberptr_self(struct rb_fiber_struct *fiber);
 unsigned int rb_fiberptr_blocking(struct rb_fiber_struct *fiber);
+struct rb_execution_context_struct * rb_fiberptr_get_ec(struct rb_fiber_struct *fiber);
 
 #endif /* INTERNAL_CONT_H */
diff --git a/vm.c b/vm.c
index c2dda3fdc4..4538c8b607 100644
--- a/vm.c
+++ b/vm.c
@@ -3138,8 +3138,7 @@ thread_mark(void *ptr)
     RUBY_MARK_UNLESS_NULL(th->top_wrapper);
     if (th->root_fiber) rb_fiber_mark_self(th->root_fiber);
 
-    /* Ensure EC stack objects are pinned */
-    rb_execution_context_mark(th->ec);
+    RUBY_ASSERT(th->ec == rb_fiberptr_get_ec(th->ec->fiber_ptr));
     RUBY_MARK_UNLESS_NULL(th->stat_insn_usage);
     RUBY_MARK_UNLESS_NULL(th->last_status);
     RUBY_MARK_UNLESS_NULL(th->locking_mutex);