Fix env debug assertion failure w/ Ractors+JITs

Previously when using a JIT and Ractors at the same time with debug
assertions turned on this could rarely fail with:

    vm_core.h:1448: Assertion Failed: VM_ENV_FLAGS:FIXNUM_P(flags)

When using Ractors, any time the VM lock is acquired, that may join a
barrier as another Ractor initiates GC. This could be made to happen
reliably by replacing the invalidation with a call to rb_gc().

This assertion failure happens because

    VM_STACK_ENV_WRITE(ep, 0, (VALUE)env);

Is setting VM_ENV_DATA_INDEX_FLAGS to the environment, which is not a
valid set of flags (it should be a fixnum). Although we update cfp->ep,
rb_execution_context_mark will also mark the PREV_EP, and until the
recursive calls to vm_make_env_each all finish the "next" ep may still
be pointing to the stack env we've just escaped.

I'm not completely sure why we need to store this on the stack - why is
setting cfp->ep not enough? I'm also not sure why
rb_execution_context_mark needs to mark the prev_ep.

0 files changed, 0 insertions, 0 deletions