Re: [PATCH] selftests: timers: set-timer-lat: fix hang when std out/err are redirected

[Greg Hackmann]

On 09/22/2017 07:42 AM, Shuah Khan wrote:
> Hi John/Greg,
>
> On 09/21/2017 02:10 PM, Shuah Khan wrote:
> > do_timer_oneshot() uses select() as a timer with FD_SETSIZE and readfs
> > is cleared with FD_ZERO without FD_SET.
> >
> > When stdout and stderr are redirected, the test hangs in select forever.
> > Fix the problem calling select() with readfds empty and nfds zero. This
> > is sufficient for using select() for timer.
> >
> > With this fix "./set-timer-lat > /dev/null 2>&1" no longer hangs.
> >
> > Signed-off-by: Shuah Khan <shuahkh@xxxxxxxxxxxxxxx>
> > ---
> >   tools/testing/selftests/timers/set-timer-lat.c | 4 +---
> >   1 file changed, 1 insertion(+), 3 deletions(-)
> >
> > diff --git a/tools/testing/selftests/timers/set-timer-lat.c b/tools/testing/selftests/timers/set-timer-lat.c
> > index ab2fe225e051..3c248f0dc0d5 100644
> > --- a/tools/testing/selftests/timers/set-timer-lat.c
> > +++ b/tools/testing/selftests/timers/set-timer-lat.c
> > @@ -229,7 +229,6 @@ int do_timer_oneshot(int clock_id, int flags)
> >   	timer_t tm1;
> >   	const int interval = 0;
> >   	struct timeval timeout;
> > -	fd_set fds;
> >   	int err;
> >   
> >   	err = setup_timer(clock_id, flags, interval, &tm1);
> > @@ -238,9 +237,8 @@ int do_timer_oneshot(int clock_id, int flags)
> >   
> >   	memset(&timeout, 0, sizeof(timeout));
> >   	timeout.tv_sec = 5;
> > -	FD_ZERO(&fds);
> >   	do {
> > -		err = select(FD_SETSIZE, &fds, NULL, NULL, &timeout);
> > +		err = select(0, NULL, NULL, NULL, &timeout);
> >   	} while (err == -1 && errno == EINTR);
> >   
> >   	timer_delete(tm1);
>
> I assume you are good with this fix. I plan to apply it to linux-kselftest fixes
> today. Please let me know if you have any objections.
>
> thanks,
> -- Shuah

Thanks for looking into this.

Acked-by: Greg Hackmann <ghackmann@xxxxxxxxxx>