linux-kernel - [PATCH v2] selftests: timers: set-timer-lat: Fix hang when testing unsupported alarms

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Date:   Fri, 22 Sep 2017 11:32:56 -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 v2] selftests: timers: set-timer-lat: Fix hang when testing unsupported alarms

When timer_create() fails on a bootime or realtime clock, setup_timer()
returns 0 as if timer has been set. Callers wait forever for the timer
to expire.

This hang is seen on a system that doesn't have support for:

CLOCK_REALTIME_ALARM   ABSTIME missing CAP_WAKE_ALARM? : [UNSUPPORTED]

Test hangs waiting for a timer that hasn't been set to expire. Fix
setup_timer() to return 1, add handling in callers to detect the
unsupported case and return 0 without waiting to not fail the test.

Signed-off-by: Shuah Khan <shuahkh@....samsung.com>
---

Changes fron v1 -> v2:
- Handle unsupported case as skip and don't faile the test.

 tools/testing/selftests/timers/set-timer-lat.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/timers/set-timer-lat.c b/tools/testing/selftests/timers/set-timer-lat.c
index 9c92b7bd5641..09d20827a924 100644
--- a/tools/testing/selftests/timers/set-timer-lat.c
+++ b/tools/testing/selftests/timers/set-timer-lat.c
@@ -143,7 +143,8 @@ int setup_timer(int clock_id, int flags, int interval, timer_t *tm1)
 			printf("%-22s %s missing CAP_WAKE_ALARM?    : [UNSUPPORTED]\n",
 					clockstring(clock_id),
 					flags ? "ABSTIME":"RELTIME");
-			return 0;
+			/* Indicate timer isn't set, so caller doesn't wait */
+			return 1;
 		}
 		printf("%s - timer_create() failed\n", clockstring(clock_id));
 		return -1;
@@ -213,8 +214,9 @@ int do_timer(int clock_id, int flags)
 	int err;
 
 	err = setup_timer(clock_id, flags, interval, &tm1);
+	/* Unsupported case - return 0 to not fail the test */
 	if (err)
-		return err;
+		return err == 1 ? 0 : err;
 
 	while (alarmcount < 5)
 		sleep(1);
@@ -232,8 +234,9 @@ int do_timer_oneshot(int clock_id, int flags)
 	int err;
 
 	err = setup_timer(clock_id, flags, interval, &tm1);
+	/* Unsupported case - return 0 to not fail the test */
 	if (err)
-		return err;
+		return err == 1 ? 0 : err;
 
 	memset(&timeout, 0, sizeof(timeout));
 	timeout.tv_sec = 5;
-- 
2.11.0