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

[Ilya Leoshkevich <iii@linux.ibm.com>]

On Fri, 2022-12-23 at 13:02 +0100, Ilya Leoshkevich wrote:
> 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>
> ---
>  tests/tcg/multiarch/Makefile.target  |   3 +
>  tests/tcg/multiarch/munmap-pthread.c |  16 +--
>  tests/tcg/multiarch/nop_func.h       |  25 ++++
>  tests/tcg/multiarch/vma-pthread.c    | 185
> +++++++++++++++++++++++++++
>  4 files changed, 214 insertions(+), 15 deletions(-)
>  create mode 100644 tests/tcg/multiarch/nop_func.h
>  create mode 100644 tests/tcg/multiarch/vma-pthread.c

This was meant to be a reply to the bug report for [1], but apparently
I forgot to Cc: the mailing list. Copying the original message here:

---
Hi,

Wasmtime testsuite started failing randomly, complaining that
clock_gettime() returns -EFAULT. Bisect points to this commit.

I could not see anything obviously wrong here with the manual review,
and the failure was not reproducible when running individual testcases
or using strace. So I wrote a stress test (which I will post shortly),
which runs fine on the host, but reproduces the issue with qemu-user.

When run with -strace, it also triggers an assertion:

    qemu-x86_64: ../accel/tcg/tb-maint.c:595:
tb_invalidate_phys_page_unwind: Assertion `pc != 0' failed.
    qemu-x86_64: /home/iii/qemu/include/qemu/rcu.h:102:
rcu_read_unlock: Assertion `p_rcu_reader->depth != 0' failed.

I haven't tried analyzing what is causing all this yet, but at least
now the reproducer is small (~200LOC) and fails faster than 1s.

Best regards,
Ilya
---

[1] https://lists.gnu.org/archive/html/qemu-devel/2022-12/msg03615.html