linux-kernel - [PATCH] timers: Fix overflow in get_next_timer

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Message-ID: <a7900f04-2a21-c9fd-67be-ab334d459ee5@nokia.com>
Date:   Tue, 1 Aug 2017 09:11:52 +0200
From:   Matija Glavinic Pecotic <matija.glavinic-pecotic.ext@...ia.com>
To:     khilman@...libre.com, tglx@...utronix.de, mingo@...nel.org,
        akpm@...ux-foundation.org, hpa@...or.com,
        linux-kernel@...r.kernel.org
Cc:     "Sverdlin, Alexander (Nokia - DE/Ulm)" <alexander.sverdlin@...ia.com>
Subject: [PATCH] timers: Fix overflow in get_next_timer_interrupt

For e.g. HZ=100, timer being 430 jiffies in the future, and 32 bit
unsigned int, there is an overflow on unsigned int right-hand side
of the expression which results with wrong values being returned.

Problem was observed on tickless core and with following applied:

	sched/nohz: add debugfs control over sched_tick_max_deferment
	https://lkml.org/lkml/2013/9/16/499

Signed-off-by: Matija Glavinic Pecotic <matija.glavinic-pecotic.ext@...ia.com>
---
 kernel/time/timer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 71ce3f4..8f5d1bf 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1495,7 +1495,7 @@ u64 get_next_timer_interrupt(unsigned long basej, u64 basem)
 		base->is_idle = false;
 	} else {
 		if (!is_max_delta)
-			expires = basem + (nextevt - basej) * TICK_NSEC;
+			expires = basem + (u64)(nextevt - basej) * TICK_NSEC;
 		/*
 		 * If we expect to sleep more than a tick, mark the base idle:
 		 */
-- 
2.1.4