Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752474AbdIVOmR (ORCPT ); Fri, 22 Sep 2017 10:42:17 -0400 Received: from ec2-52-27-115-49.us-west-2.compute.amazonaws.com ([52.27.115.49]:43250 "EHLO osg.samsung.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752020AbdIVOmP (ORCPT ); Fri, 22 Sep 2017 10:42:15 -0400 Subject: Re: [PATCH] selftests: timers: set-timer-lat: fix hang when std out/err are redirected To: john.stultz@linaro.org, tglx@linutronix.de, sboyd@codeaurora.org, ghackmann@google.com, shuah@kernel.org Cc: linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, Shuah Khan , Shuah Khan References: <20170921201046.16953-1-shuahkh@osg.samsung.com> From: Shuah Khan Message-ID: <2717b5ae-fe0e-8b52-f297-90f3b4fb9b56@osg.samsung.com> Date: Fri, 22 Sep 2017 08:42:14 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: <20170921201046.16953-1-shuahkh@osg.samsung.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1611 Lines: 47 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 > --- > 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