Re: [GIT PULL] s390 updates for 5.15 merge window

[Christian Borntraeger]

On 31.08.21 19:48, Nathan Chancellor wrote:
> On Tue, Aug 31, 2021 at 05:02:15PM +0200, Marco Elver wrote:
> > On Tue, Aug 31, 2021 at 12:46PM +0200, Marco Elver wrote:
> > > On Tue, 31 Aug 2021 at 12:13, Heiko Carstens <hca@xxxxxxxxxxxxx> wrote:
> > > [...]
> > > > I really don't think this is QEMU related. The test fails are sort of
> > > > expected: we've seen KCSAN reports when the kernel boots and wanted to
> > > > fix them later.
> > > > However I have to admit that I wasn't aware of the KCSAN KUNIT tests,
> > > > and wouldn't have sent the s390 KCSAN enablement upstream if I would
> > > > have been aware of failing self tests.
> > > >
> > > > We'll fix them, and I let you know if things are supposed to work.
> > > >
> > > > Thanks a lot for making aware of this!
> > >
> > > Note: Set `CONFIG_KCSAN_REPORT_ONCE_IN_MS=100` (or smaller) instead of
> > > the default to make the test complete faster.
> > >
> > > The pattern I see from what Nathan reported is that all test cases
> > > that expect race reports don't observe them ("not ok" cases), and all
> > > those where no races are meant to be reported are fine ("ok" cases).
> > > Without actually seeing the log, I'm guessing that no races are
> > > reported at all, which is certainly not working as intended.
> >
> > I repro'd, and the problem is part QEMU TCG and a minor problem with
> > stack_trace_save() on s390:
> >
> > 1. QEMU TCG doesn't seem to want to execute threads concurrently,
> >     resulting in no "value changes" being observed. This is probably just
> >     a limitation of TCG, and if run on a real CPU, shouldn't be a problem.
> >     On QEMU, most test cases will pass with CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY=n
> >     (There's one left that requires value changes to be observable)
>
> Is this just a limitation of s390's TCG implementation or in general?
> Our CI runs on GitHub Actions, which does not support virtualization so
> I believe that all of our tests are being done with TCG and x86_64
> passes just fine:

Maybe Richard knows?

> https://github.com/ClangBuiltLinux/continuous-integration2/runs/3473222334?check_suite_focus=true
>
> Good to hear that it is working on bare metal now though, we could still
> enable build testing of it at a minimum but it would be nice to see the
> tests pass even in QEMU :)
>
> Cheers,
> Nathan