Re: [PATCH] xtensa: enable KCSAN

[Marco Elver]

On Wed, 20 Apr 2022 at 20:11, Max Filippov <jcmvbkbc@xxxxxxxxx> wrote:

> > Each test case is run with varying number of threads - am I correctly
> > inferring that out of all test cases, usually only one such run failed,
> > and runs with different number of threads (of the same test case)
> > succeeded?
>
> For most of the failures -- yes.
> For the test_missing_barrier and test_atomic_builtins_missing_barrier
> on the hardware it was the opposite: only one subtest succeeded while
> all others failed. Does it mean that the xtensa memory model is
> insufficiently weak?

No - KCSAN's weak memory modeling and detection of missing barriers
doesn't care what the HW does, it only approximates the LKMM. If the
test_barrier_nothreads case passed, there's nothing wrong with barrier
instrumentation. Regarding the test case failures, if at least 1
passed I'm guessing it's just flaky (not enough concurrency, or
unexpected barriers due to too many interrupts which can happen if we
enter the scheduler).

Unfortunately I don't know xtensa and if this is normal, but modulo
flakiness, I think it's fine. (I've made a note to try and deflake the
test if I can find time to try the xtensa version.)