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

Gustavo Luiz Duarte [off-list ref] 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