From 8900502a887d98a8f5a6b8774f1c756e89d4c29f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tomasz=20Mi=C4=85sko?= <tomasz.miasko@gmail.com>
Date: Sat, 4 Jul 2020 00:00:00 +0000
Subject: [PATCH] Remove unnecessary release from Arc::try_unwrap

The thread that recovers the unique access to Arc inner value (e.g., drop
when ref-count strong reaches zero, successful try_unwrap), ensures that
other operations on Arc inner value happened before by synchronizing
with release operations performed when decrementing the reference counter.

When try_unwrap succeeds, the current thread recovers the unique access
to Arc inner value, so release is unnecessary.
---
 src/liballoc/sync.rs | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/src/liballoc/sync.rs b/src/liballoc/sync.rs
index ac3ce2255c89b..2d6a3917c764e 100644
--- a/src/liballoc/sync.rs
+++ b/src/liballoc/sync.rs
@@ -419,8 +419,7 @@ impl<T> Arc<T> {
     #[inline]
     #[stable(feature = "arc_unique", since = "1.4.0")]
     pub fn try_unwrap(this: Self) -> Result<T, Self> {
-        // See `drop` for why all these atomics are like this
-        if this.inner().strong.compare_exchange(1, 0, Release, Relaxed).is_err() {
+        if this.inner().strong.compare_exchange(1, 0, Relaxed, Relaxed).is_err() {
             return Err(this);
         }