Ceph » crimson

    void exit() final {
      if (barrier) {
        assert(phase);
        assert(phase->core == seastar::this_shard_id());
        std::ignore = std::move(*barrier
        ).then([phase=this->phase] {
          phase->mutex.unlock();
        });
        barrier = std::nullopt;
        phase = nullptr;
      } else if (phase) {
        assert(phase->core == seastar::this_shard_id());
        phase->mutex.unlock();
        phase = nullptr;
      }
    }

phase->mutex.unlock() can occur significantly after exit() finishes. *phase will generally be embedded in a PG or a Connection, so it's often but not always safe.

https://tracker.ceph.com/issues/63647 was a more dangerous variant because *phase was part of the operation itself.