Subject: Re: [PATCH v2 2/3] selftests/powerpc: Add tm-signal-pagefault test

From: Michael Ellerman <[email-masked]>
Date: Wed, 05 Feb 2020 16:27:52 +1100

Gustavo Luiz Duarte <[email-masked]> writes:
> This test triggers a TM Bad Thing by raising a signal in transactional state
> and forcing a pagefault to happen in kernelspace when the kernel signal
> handling code first touches the user signal stack.
>
> This is inspired by the test tm-signal-context-force-tm but uses userfaultfd to
> make the test deterministic. While this test always triggers the bug in one
> run, I had to execute tm-signal-context-force-tm several times (the test runs
> 5000 times each execution) to trigger the same bug.

Using userfaultfd is a very nice touch. But it's not always enabled,
which leads to eg:

  root@mpe-ubuntu-le:~# /home/michael/tm-signal-pagefault 
  test: tm_signal_pagefault
  tags: git_version:v5.5-9354-gc1e346e7fc44
  userfaultfd() failed: Function not implemented
  failure: tm_signal_pagefault

It would be nice if that resulted in a skip, not a failure.

It looks like it shouldn't be too hard to skip if the userfaultfd call
returns ENOSYS.

cheers