From c866ba80e4c38b0119823ab93f822f8e9dae2ce7 Mon Sep 17 00:00:00 2001
From: Amanieu d'Antras <amanieu@gmail.com>
Date: Wed, 25 Aug 2021 01:18:24 +0100
Subject: [PATCH] Fix memory orderings on rwlock upgrade.

Fixes #294
---
 src/raw_rwlock.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/raw_rwlock.rs b/src/raw_rwlock.rs
index 75a98128..19b61c81 100644
--- a/src/raw_rwlock.rs
+++ b/src/raw_rwlock.rs
@@ -362,7 +362,7 @@ unsafe impl lock_api::RawRwLockUpgrade for RawRwLock {
     unsafe fn upgrade(&self) {
         let state = self.state.fetch_sub(
             (ONE_READER | UPGRADABLE_BIT) - WRITER_BIT,
-            Ordering::Relaxed,
+            Ordering::Acquire,
         );
         if state & READERS_MASK != ONE_READER {
             let result = self.upgrade_slow(None);
@@ -377,7 +377,7 @@ unsafe impl lock_api::RawRwLockUpgrade for RawRwLock {
             .compare_exchange_weak(
                 ONE_READER | UPGRADABLE_BIT,
                 WRITER_BIT,
-                Ordering::Relaxed,
+                Ordering::Acquire,
                 Ordering::Relaxed,
             )
             .is_ok()