Re: [PATCH v2 46/46] selftests/mm: add HGM UFFDIO_CONTINUE and hwpoison tests

[James Houghton <jthoughton@google.com>]

> +static int test_fork(int uffd, char *primary_map, size_t len)
> +{
> +       int status;
> +       int ret = 0;
> +       pid_t pid;
> +       pthread_t uffd_thd;
> +
> +       /*
> +        * UFFD_FEATURE_EVENT_FORK will put fork event on the userfaultfd,
> +        * which we must read, otherwise we block fork(). Setup a thread to
> +        * read that event now.
> +        *
> +        * Page fault events should result in a SIGBUS, so we expect only a
> +        * single event from the uffd (the fork event).
> +        */
> +       if (read_event_from_uffd(&uffd, &uffd_thd))
> +               return -1;
> +
> +       pid = fork();
> +
> +       if (!pid) {
> +               /*
> +                * Because we have UFFDIO_REGISTER_MODE_WP and
> +                * UFFD_FEATURE_EVENT_FORK, the page tables should be copied
> +                * exactly.
> +                *
> +                * Check that everything except that last 4K has correct
> +                * contents, and then check that the last 4K gets a SIGBUS.
> +                */
> +               printf(PREFIX "child validating...\n");
> +               ret = verify_contents(primary_map, len, false) ||
> +                       test_sigbus(primary_map + len - 1, false);
> +               ret = 0;
> +               exit(ret ? 1 : 0);
> +       } else {
> +               /* wait for the child to finish. */
> +               waitpid(pid, &status, 0);
> +               ret = WEXITSTATUS(status);
> +               if (!ret) {
> +                       printf(PREFIX "parent validating...\n");
> +                       /* Same check as the child. */
> +                       ret = verify_contents(primary_map, len, false) ||
> +                               test_sigbus(primary_map + len - 1, false);
> +                       ret = 0;

I'm not sure how these 'ret = 0's got here -- they will be removed.

> +               }
> +       }

This else block also runs when fork() fails; we need to fail the test instead.

> +
> +       pthread_join(uffd_thd, NULL);
> +       return ret;
> +
> +}