crash

thread '<unnamed>' panicked at 'already borrowed: BorrowMutError', /checkout/src/libcore/result.rs:906:4
stack backtrace:
   0:     0x560b2ac20523 - std::sys::imp::backtrace::tracing::imp::unwind_backtrace::h1070d2fb95184fa2
                               at /checkout/src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1:     0x560b2ac1e208 - std::panicking::default_hook::{{closure}}::hd87027f00dc92814
                               at /checkout/src/libstd/sys_common/backtrace.rs:69
                               at /checkout/src/libstd/sys_common/backtrace.rs:58
                               at /checkout/src/libstd/panicking.rs:381
   2:     0x560b2ac1d660 - std::panicking::rust_panic_with_hook::h97def5bc16cf8ad9
                               at /checkout/src/libstd/panicking.rs:397
                               at /checkout/src/libstd/panicking.rs:577
   3:     0x560b2ac1d0e8 - std::panicking::begin_panic::hd4ff6c8c17230ea6
                               at /checkout/src/libstd/panicking.rs:538
   4:     0x560b2ac1d069 - std::panicking::begin_panic_fmt::h2da9e717417b9bee
                               at /checkout/src/libstd/panicking.rs:522
   5:     0x560b2ac2fe3a - core::panicking::panic_fmt::h5fee652e7adf46a7
                               at /checkout/src/libstd/panicking.rs:498
   6:     0x560b2a8afee4 - core::result::unwrap_failed::hb495c03f7c450a69
   7:     0x560b2a87bd01 - std::sys_common::backtrace::__rust_begin_short_backtrace::h8345c62d94309dc9
   8:     0x560b2a8b1599 - <F as alloc::boxed::FnBox<A>>::call_box::h0ddddd44c03f10d7
   9:     0x560b2ac2c777 - std::sys::imp::thread::Thread::new::thread_start::hf0691535183b03a2
                               at /checkout/src/liballoc/boxed.rs:772
                               at /checkout/src/libstd/sys_common/thread.rs:24
                               at /checkout/src/libstd/sys/unix/thread.rs:90
  10:     0x7fb0910fa493 - start_thread
  11:     0x7fb090c25afe - __clone
  12:                0x0 - <unknown>