clarify retagging onm fn enter

diff --git a/personal/_posts/2018-08-07-stacked-borrows.md b/personal/_posts/2018-08-07-stacked-borrows.md
index 54dd417c8aecb7aee373717ca1d1a21b8646f551..6469a1d8ed0f11164e3dad53219bf00fa91357c5 100644 (file)
--- a/personal/_posts/2018-08-07-stacked-borrows.md
+++ b/personal/_posts/2018-08-07-stacked-borrows.md
@@ -442,7 +442,7 @@ Now we can look at what happens for each operation.
   - Compute `new_bor` from `new_tag` and the type of the reference being created.
   - `reactivate(bor)`.
   - If this is a function argument coming in: `loc.borrows.push(FnBarrier(stack_height))`.
   - Compute `new_bor` from `new_tag` and the type of the reference being created.
   - `reactivate(bor)`.
   - If this is a function argument coming in: `loc.borrows.push(FnBarrier(stack_height))`.

-  - `initiate(new_bor)`. Note that this is a NOP if `new_bor` is already active -- in particular, if the location is frozen and this is a shared reference with interior mutability, we do *not* push anything on top of the barrier. This is important, because we do not want to push that might unfreeze the location when being reactivated.
+  - `initiate(new_bor)`. Note that this is a NOP if `new_bor` is already active -- in particular, if the location is frozen and this is a shared reference with interior mutability, we do *not* push anything on top of the barrier. This is important, because any reactivation that unfreezes this location must lead to UB while the barrier is still present.

   - Change reference tag to `new_tag`.
 * Any time a raw pointer is created from a reference, we might have to do a raw reborrow.
   - `reactivate(bor)`.
   - Change reference tag to `new_tag`.
 * Any time a raw pointer is created from a reference, we might have to do a raw reborrow.
   - `reactivate(bor)`.