Downgrade context sigcontrol to read

src/sync/ordered.rs

@@ -620,6 +620,14 @@ impl<'a, L: Level, T> RwLockWriteGuard<'a, L, T> {
         drop(self.inner);
         self.lock_token
     }
+
+    /// Upgrade to RO lock
+    pub fn downgrade(self) -> RwLockReadGuard<'a, L, T> {
+        RwLockReadGuard {
+            inner: self.inner.downgrade(),
+            lock_token: self.lock_token,
+        }
+    }
 }
 
 impl<L: Level, T> core::ops::Deref for RwLockWriteGuard<'_, L, T> {

src/sync/wait_condition.rs

@@ -80,13 +80,13 @@ impl WaitCondition {
             let mut preempt = PreemptGuardL2::new(&current_context_ref, &mut token);
             let token = preempt.token();
             {
-                let mut context = current_context_ref.write(token.token());
+                let context = current_context_ref.upgradeable_read(token.token());
                 if let Some((control, pctl, _)) = context.sigcontrol()
                     && control.currently_pending_unblocked(pctl) != 0
                 {
                     return false;
                 }
-                context.block(reason);
+                context.upgrade().block(reason);
             }
 
             self.contexts