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

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Date:   Fri, 22 Sep 2017 10:31:06 -0700
From:   John Stultz <john.stultz@...aro.org>
To:     Shuah Khan <shuahkh@....samsung.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Greg Hackmann <ghackmann@...gle.com>,
        Shuah Khan <shuah@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH] selftests: timers: set-timer-lat: fix hang when std
 out/err are redirected

On Fri, Sep 22, 2017 at 7:42 AM, Shuah Khan <shuahkh@....samsung.com> 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@....samsung.com>
>> ---
>>  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.

No objections from me, just has been a busy few days and haven't had a
chance to test.

thanks
-john