[LTP] [PATCH] lib/tst_checkpoint: Retry sleep on EINTR

[Sumit Garg]

On Mon, 18 Mar 2019 at 19:13, Cyril Hrubis <chrubis@suse.cz> wrote:
>
> Previously we haven't retried on EINTR, the main reason for that was
> that all the tests using checkpoints haven't cared at all since signals
> were not involved. However I think that retry on EINTR should be done by
> default, since checkpoints returning from sleep on random signal
> delivery are broken, and no test in the tree actually depends on such
> behavior.
>
> Currently tests for tgkill have emerged on ML where child needs to sleep
> while parent sends signals to the child, this commit allows to use
> checkpoints for these tests.
>
> This commit implements the simpliest way how to retry, it's just a
> simple loop over the futex() call that repeats on EINTR. The only side
> effect is that timeout is restarted after the thread sleeping in futex()
> got signal, since we use relative timeouts after all. However the
> hypotetical worst case that can happen is that the test will timeout and
> will end up being killed by the test library in a case that one test
> would sleep on checkpoint while other would send signals in a loop.
> Hoever chances for this arrangement are quite small.
>
> Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
> CC: Sumit Garg <sumit.garg@linaro.org>
> CC: Jan Stancek <jstancek@redhat.com>

Acked-by: Sumit Garg <sumit.garg@linaro.org>

-Sumit

> ---
>  lib/tst_checkpoint.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/lib/tst_checkpoint.c b/lib/tst_checkpoint.c
> index 5455d0378..5e5b11496 100644
> --- a/lib/tst_checkpoint.c
> +++ b/lib/tst_checkpoint.c
> @@ -85,6 +85,7 @@ void tst_checkpoint_init(const char *file, const int lineno,
>  int tst_checkpoint_wait(unsigned int id, unsigned int msec_timeout)
>  {
>         struct timespec timeout;
> +       int ret;
>
>         if (id >= tst_max_futexes) {
>                 errno = EOVERFLOW;
> @@ -94,8 +95,12 @@ int tst_checkpoint_wait(unsigned int id, unsigned int msec_timeout)
>         timeout.tv_sec = msec_timeout/1000;
>         timeout.tv_nsec = (msec_timeout%1000) * 1000000;
>
> -       return syscall(SYS_futex, &tst_futexes[id], FUTEX_WAIT,
> -                      tst_futexes[id], &timeout);
> +       do {
> +               ret = syscall(SYS_futex, &tst_futexes[id], FUTEX_WAIT,
> +                             tst_futexes[id], &timeout);
> +       } while (ret == -1 && errno == EINTR);
> +
> +       return ret;
>  }
>
>  int tst_checkpoint_wake(unsigned int id, unsigned int nr_wake,
> --
> 2.19.2
>