Miri hangs on running with miri-compare-exchange-weak-failure-rate=1

[alygin]

To reproduce:

cargo init miri-test
cd miri-test
echo "#[test] fn test() {}" >> src/main.rs
MIRIFLAGS="-Zmiri-compare-exchange-weak-failure-rate=1" cargo miri test

The process hangs on "Running unittests src/main.rs...", without actually running the test.

It works fine with any other valid value of miri-compare-exchange-weak-failure-rate.
The problem is not reproducible with the nightly-2022-05-22 toolchain.

[RalfJung]

Thanks for the report!

Setting the failure rate to 1 means it always fails, as it says in the docs. It is expected then that programs hang, since their weak compare exchanges never succeed, so they never can make progress.

We recently fixed a bug here with #2105; that's why you did not see this behavior before.

[alygin]

Oh, that makes sence, thanks, @RalfJung!