linux-kernel - [PATCH] selftest: timers: Avoid signal deadlock in leap-a-day

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Date:	Wed, 17 Jun 2015 11:16:43 -0700
From:	John Stultz <john.stultz@...aro.org>
To:	lkml <linux-kernel@...r.kernel.org>
Cc:	John Stultz <john.stultz@...aro.org>,
	Prarit Bhargava <prarit@...hat.com>,
	Daniel Bristot de Oliveira <bristot@...hat.com>,
	Richard Cochran <richardcochran@...il.com>,
	Jan Kara <jack@...e.cz>, Jiri Bohac <jbohac@...e.cz>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Shuah Khan <shuahkh@....samsung.com>
Subject: [PATCH] selftest: timers: Avoid signal deadlock in leap-a-day

In 0c4a5fc95b1df (Add leap-second timer edge testing to
leap-a-day.c), we added a timer to the test which checks to make
sure timers near the leapsecond edge behave correctly.

However, the output generated from the timer uses ctime_r, which
isn't async-signal safe, and should that signal land while the
main test is using ctime_r to print its output, its possible for
the test to deadlock on glibc internal locks.

Thus this patch reworks the output to avoid using ctime_r in
the signal handler.

Cc: Prarit Bhargava <prarit@...hat.com>
Cc: Daniel Bristot de Oliveira <bristot@...hat.com>
Cc: Richard Cochran <richardcochran@...il.com>
Cc: Jan Kara <jack@...e.cz>
Cc: Jiri Bohac <jbohac@...e.cz>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Shuah Khan <shuahkh@....samsung.com>
Signed-off-by: John Stultz <john.stultz@...aro.org>
---
(This applies to tip/timers/core)

 tools/testing/selftests/timers/leap-a-day.c | 23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/tools/testing/selftests/timers/leap-a-day.c b/tools/testing/selftests/timers/leap-a-day.c
index 331c4f7..fb46ad6 100644
--- a/tools/testing/selftests/timers/leap-a-day.c
+++ b/tools/testing/selftests/timers/leap-a-day.c
@@ -141,27 +141,28 @@ void handler(int unused)
 void sigalarm(int signo)
 {
 	struct timex tx;
-	char buf[26];
 	int ret;
 
 	tx.modes = 0;
 	ret = adjtimex(&tx);
 
-	ctime_r(&tx.time.tv_sec, buf);
-	buf[strlen(buf)-1] = 0; /*remove trailing\n */
-	printf("%s + %6ld us (%i)\t%s - TIMER FIRED\n",
-					buf,
+	if (tx.time.tv_sec < next_leap) {
+		printf("Error: Early timer expiration! (Should be %ld)\n", next_leap);
+		error_found = 1;
+		printf("adjtimex: %10ld sec + %6ld us (%i)\t%s\n",
+					tx.time.tv_sec,
 					tx.time.tv_usec,
 					tx.tai,
 					time_state_str(ret));
-
-	if (tx.time.tv_sec < next_leap) {
-		printf("Error: Early timer expiration!\n");
-		error_found = 1;
 	}
 	if (ret != TIME_WAIT) {
-		printf("Error: Incorrect NTP state?\n");
+		printf("Error: Timer seeing incorrect NTP state? (Should be TIME_WAIT)\n");
 		error_found = 1;
+		printf("adjtimex: %10ld sec + %6ld us (%i)\t%s\n",
+					tx.time.tv_sec,
+					tx.time.tv_usec,
+					tx.tai,
+					time_state_str(ret));
 	}
 }
 
@@ -297,7 +298,7 @@ int main(int argc, char **argv)
 		printf("Scheduling leap second for %s", ctime(&next_leap));
 
 		/* Set up timer */
-		printf("Setting timer for %s", ctime(&next_leap));
+		printf("Setting timer for %ld -  %s", next_leap, ctime(&next_leap));
 		memset(&se, 0, sizeof(se));
 		se.sigev_notify = SIGEV_SIGNAL;
 		se.sigev_signo = signum;
-- 
1.9.1

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