Re: [PATCH 4/4] tests/tcg/multiarch: add vma-pthread.c

[Alex Bennée]

Peter Maydell <peter.maydell@linaro.org> writes:

> On Mon, 16 Jan 2023 at 12:40, Philippe Mathieu-Daudé <philmd@linaro.org> 
> wrote:
>>
>> On 13/1/23 18:10, Alex Bennée wrote:
>> >
>> > Peter Maydell <peter.maydell@linaro.org> writes:
>> >
>> >> On Sat, 24 Dec 2022 at 15:19, Richard Henderson
>> >> <richard.henderson@linaro.org> wrote:
>> >>>
>> >>> From: Ilya Leoshkevich <iii@linux.ibm.com>
>> >>>
>> >>> Add a test that locklessly changes and exercises page protection bits
>> >>> from various threads. This helps catch race conditions in the VMA
>> >>> handling.
>> >>>
>> >>> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
>> >>> Message-Id: <20221223120252.513319-1-iii@linux.ibm.com>
>> >>> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
>> >>
>> >> I've noticed that this newly added vma-pthread test seems to
>> >> be flaky. Here's an example from a clang-user job:
>> >> https://gitlab.com/qemu-project/qemu/-/jobs/3600385176
>> >>
>> >> TEST vma-pthread-with-libbb.so on aarch64
>> >> fail indirect write 0x5500b1eff0 (Bad address)
>> >> timeout: the monitored command dumped core
>> >> Aborted
>> >> make[1]: *** [Makefile:173: run-plugin-vma-pthread-with-libbb.so] Error 
>> >> 134
>> >>
>> >> and another from a few days earlier:
>> >> https://gitlab.com/qemu-project/qemu/-/jobs/3572970612
>> >>
>> >> TEST vma-pthread-with-libsyscall.so on s390x
>> >> fail indirect read 0x4000999000 (Bad address)
>> >> timeout: the monitored command dumped core
>> >> Aborted
>> >> make[1]: *** [Makefile:173: run-plugin-vma-pthread-with-libsyscall.so] 
>> >> Error 134
>>
>> Yet again:
>> https://gitlab.com/qemu-project/qemu/-/jobs/3608436731
>
> Yep. Could somebody write a patch to disable this test while
> we figure out why it's flaky, please?

I don't think the test is flaky - I think it is triggering a race in
QEMU code. I have not however been able to replicate it in anything other
than CI.

Although looking at the test I'm beginning to wonder what the sync point
is between the mutator and the read/write threads?

>
> thanks
> -- PMM


-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro