From 15712018da9b13165bb5c5a72c32478c700d578e Mon Sep 17 00:00:00 2001
From: Alice Ryhl <aliceryhl@google.com>
Date: Mon, 5 Jun 2023 18:36:48 +0200
Subject: [PATCH] rt: `Scoped` should not be `Sync` (#5765)

If the `Scoped` type is `Sync`, then you can call `set` from two threads in parallel. Since it accesses `inner` without synchronization, this is a data race.

This is a soundness issue for the `Scoped` type, but since this is an internal API and we don't use it incorrectly anywhere, no harm is done.
---
 tokio/src/runtime/context/scoped.rs | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/tokio/src/runtime/context/scoped.rs b/tokio/src/runtime/context/scoped.rs
index cc9465824..7b202a16c 100644
--- a/tokio/src/runtime/context/scoped.rs
+++ b/tokio/src/runtime/context/scoped.rs
@@ -6,8 +6,6 @@ pub(super) struct Scoped<T> {
     pub(super) inner: Cell<*const T>,
 }
 
-unsafe impl<T> Sync for Scoped<T> {}
-
 impl<T> Scoped<T> {
     pub(super) const fn new() -> Scoped<T> {
         Scoped {
@@ -52,7 +50,7 @@ impl<T> Scoped<T> {
         if val.is_null() {
             f(None)
         } else {
-            unsafe { f(Some(&*(val as *const T))) }
+            unsafe { f(Some(&*val)) }
         }
     }
 }