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

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Message-Id: <20170921201046.16953-1-shuahkh@osg.samsung.com>
Date:   Thu, 21 Sep 2017 14:10:46 -0600
From:   Shuah Khan <shuahkh@....samsung.com>
To:     john.stultz@...aro.org, tglx@...utronix.de, sboyd@...eaurora.org,
        ghackmann@...gle.com, shuah@...nel.org
Cc:     Shuah Khan <shuahkh@....samsung.com>, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Subject: [PATCH] selftests: timers: set-timer-lat: fix hang when std out/err are redirected

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);
-- 
2.11.0