tokio-rs · hawkw · Dec 4, 2021 · Dec 4, 2021 · Dec 4, 2021 · Dec 4, 2021
diff --git a/src/rt/path.rs b/src/rt/path.rs
@@ -92,8 +92,13 @@ pub(crate) enum Thread {
 macro_rules! assert_path_len {
     ($branches:expr) => {{
         assert!(
-            $branches.len() < $branches.capacity(),
-            "Model exeeded maximum number of branches. This is often caused \
+            // if we are panicking, we may be performing a branch due to a
+            // `Drop` impl (e.g., for `Arc`, or for a user type that does an
+            // atomic operation in its `Drop` impl). if that's the case,
+            // asserting this again will double panic. therefore, short-circuit
+            // the assertion if the thread is panicking.
+            $branches.len() < $branches.capacity() || std::thread::panicking(),
+            "Model exceeded maximum number of branches. This is often caused \
              by an algorithm requiring the processor to make progress, e.g. \
              spin locks.",
         );

diff --git a/tests/double_panic_in_drop.rs b/tests/double_panic_in_drop.rs
@@ -0,0 +1,13 @@
+#[test]
+#[should_panic]
+fn double_panic_at_branch_max() {
+    let mut builder = loom::model::Builder::new();
+    builder.max_branches = 2;
+
+    builder.check(|| {
+        let _arc = loom::sync::Arc::new(());
+        loom::thread::yield_now();
+        loom::thread::yield_now();
+        loom::thread::yield_now();
+    });
+}