[LTP] [PATCH] syscalls: epoll_pwait01: Work around a race

[Li Wang]

On Tue, Jan 12, 2021 at 9:28 PM Cyril Hrubis <chrubis@suse.cz> wrote:

> There was a race that would manifest on slower machines.
>
> The call to epoll_pwait() could time out before the child has chance to
> run, and that would cause the signal to be sent to the parent when it
> was already sleeping in wait().
>
> Ideally the whole test should be rewritten into new library and fixed
> properly, however as we are just before a release this is an attempt for
> a minimal fix.
>
> The logic in the test is changed so that:
>
> - epoll_wait() sleeps indefinitely
> - the child:
>   - waits for the parent to get asleep
>   - sends the signal
>   - sleeps
>   - writes to the pipe
>
> This causes the child to actually run, while the parent is blocked in
> the epoll_wait(), which greatly increases the changes of the signal
> arriving at the right time.
>
> Fixes: #765
>
> Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
>

Reviewed-by: Li Wang <liwang@redhat.com>

-- 
Regards,
Li Wang
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