linux-kernel - [PATCH] alarmtimer: don't rate limit one-shot timers

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Message-Id: <20170724171924.27898-1-ghackmann@google.com>
Date:   Mon, 24 Jul 2017 10:19:24 -0700
From:   Greg Hackmann <ghackmann@...gle.com>
To:     John Stultz <john.stultz@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Ben Fennema <fennema@...gle.com>, linux-kernel@...r.kernel.org,
        Greg Hackmann <ghackmann@...gle.com>, stable@...r.kernel.org
Subject: [PATCH] alarmtimer: don't rate limit one-shot timers

Commit ff86bf0c65f1 ("alarmtimer: Rate limit periodic intervals") sets a
minimum bound on the alarm timer interval.  This minimum bound shouldn't
be applied if the interval is 0.  Otherwise, one-shot timers will be
converted into periodic ones.

This patch is against 4.9.39, and is only needed in -stable trees.
4.13-rc2 isn't impacted due to a later refactoring.

Fixes: ff86bf0c65f1 ("alarmtimer: Rate limit periodic intervals")
Reported-by: Ben Fennema <fennema@...gle.com>
Signed-off-by: Greg Hackmann <ghackmann@...gle.com>
Cc: stable@...r.kernel.org
---
 kernel/time/alarmtimer.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/time/alarmtimer.c b/kernel/time/alarmtimer.c
index 9ba04aa740b9..d67ef56ca9bc 100644
--- a/kernel/time/alarmtimer.c
+++ b/kernel/time/alarmtimer.c
@@ -629,7 +629,8 @@ static int alarm_timer_set(struct k_itimer *timr, int flags,
 	 * Rate limit to the tick as a hot fix to prevent DOS. Will be
 	 * mopped up later.
 	 */
-	if (ktime_to_ns(timr->it.alarm.interval) < TICK_NSEC)
+	if (timr->it.alarm.interval.tv64 &&
+			ktime_to_ns(timr->it.alarm.interval) < TICK_NSEC)
 		timr->it.alarm.interval = ktime_set(0, TICK_NSEC);
 
 	exp = timespec_to_ktime(new_setting->it_value);
-- 
2.14.0.rc0.284.gd933b75aa4-goog