[INFO] cloning repository https://github.com/smt923/sierpinski
[INFO] running `Command { std: "git" "-c" "credential.helper=" "-c" "credential.helper=/workspace/cargo-home/bin/git-credential-null" "clone" "--bare" "https://github.com/smt923/sierpinski" "/workspace/cache/git-repos/https%3A%2F%2Fgithub.com%2Fsmt923%2Fsierpinski", kill_on_drop: false }`
[INFO] [stderr] Cloning into bare repository '/workspace/cache/git-repos/https%3A%2F%2Fgithub.com%2Fsmt923%2Fsierpinski'...
[INFO] running `Command { std: "git" "rev-parse" "HEAD", kill_on_drop: false }`
[INFO] [stdout] 7539ad79787ed1812db92f9277d9cf4f720e6219
[INFO] checking smt923/sierpinski against master#75530e9f72a1990ed2305e16fd51d02f47048f12 for pr-135899
[INFO] running `Command { std: "git" "clone" "/workspace/cache/git-repos/https%3A%2F%2Fgithub.com%2Fsmt923%2Fsierpinski" "/workspace/builds/worker-2-tc1/source", kill_on_drop: false }`
[INFO] [stderr] Cloning into '/workspace/builds/worker-2-tc1/source'...
[INFO] [stderr] done.
[INFO] [stderr] fatal: update_ref failed for ref 'HEAD': cannot update ref 'refs/heads/master': couldn't write '/workspace/builds/worker-2-tc1/source/.git/refs/heads/master.lock'


failed to checkout https://github.com/smt923/sierpinski

Caused by:
    command failed: exit status: 128