error[E0499]: cannot borrow `buf` as mutable more than once at a time
  --> tests/ui/dca_double_lend.rs:20:17
   |
17 |     let cpu_a = buf.cpu();
   |                 --- first mutable borrow occurs here
...
20 |     let cpu_b = buf.cpu();
   |                 ^^^ second mutable borrow occurs here
21 |     let _ = cpu_a.lend_for_read(&mut ctx);
   |             ----- first borrow later used here
