chore: use relaxed load for unsync_load on miri (#6179)

tokio/src/loom/std/atomic_u16.rs

@@ -23,7 +23,11 @@ impl AtomicU16 {
     /// All mutations must have happened before the unsynchronized load.
     /// Additionally, there must be no concurrent mutations.
     pub(crate) unsafe fn unsync_load(&self) -> u16 {
-        core::ptr::read(self.inner.get() as *const u16)
+        // See <https://github.com/tokio-rs/tokio/issues/6155>
+        #[cfg(miri)]
+        return self.load(std::sync::atomic::Ordering::Relaxed);
+        #[cfg(not(miri))]
+        return core::ptr::read(self.inner.get() as *const u16);
     }
 }
 

tokio/src/loom/std/atomic_u32.rs

@@ -23,7 +23,11 @@ impl AtomicU32 {
     /// All mutations must have happened before the unsynchronized load.
     /// Additionally, there must be no concurrent mutations.
     pub(crate) unsafe fn unsync_load(&self) -> u32 {
-        core::ptr::read(self.inner.get() as *const u32)
+        // See <https://github.com/tokio-rs/tokio/issues/6155>
+        #[cfg(miri)]
+        return self.load(std::sync::atomic::Ordering::Relaxed);
+        #[cfg(not(miri))]
+        return core::ptr::read(self.inner.get() as *const u32);
     }
 }
 

tokio/src/loom/std/atomic_usize.rs

@@ -23,7 +23,11 @@ impl AtomicUsize {
     /// All mutations must have happened before the unsynchronized load.
     /// Additionally, there must be no concurrent mutations.
     pub(crate) unsafe fn unsync_load(&self) -> usize {
-        core::ptr::read(self.inner.get() as *const usize)
+        // See <https://github.com/tokio-rs/tokio/issues/6155>
+        #[cfg(miri)]
+        return self.load(std::sync::atomic::Ordering::Relaxed);
+        #[cfg(not(miri))]
+        return core::ptr::read(self.inner.get() as *const usize);
     }
 
     pub(crate) fn with_mut<R>(&mut self, f: impl FnOnce(&mut usize) -> R) -> R {