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

From: Christian Borntraeger
Subject: Re: [GIT PULL] s390 updates for 5.15 merge window
Date: Tue, 31 Aug 2021 19:49:41 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0

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@linux.ibm.com> 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 
    (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?


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 :)


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