Subject: Re: [PATCH] timers: Fix overflow in get_next_timer_interrupt
To: Matija Glavinic Pecotic <matija.glavinic-pecotic.ext@nokia.com>,
        <khilman@baylibre.com>, <tglx@linutronix.de>, <mingo@kernel.org>,
        <akpm@linux-foundation.org>, <hpa@zytor.com>,
        <linux-kernel@vger.kernel.org>
References: <a7900f04-2a21-c9fd-67be-ab334d459ee5@nokia.com>
From: Alexander Sverdlin <alexander.sverdlin@nokia.com>
Message-ID: <66d27e1f-5b57-aa75-bf46-91f0427b45be@nokia.com>
Date: Tue, 1 Aug 2017 10:16:30 +0200
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On 01/08/17 09:11, Matija Glavinic Pecotic wrote:
> 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@nokia.com>

Reviewed-by: Alexander Sverdlin <alexander.sverdlin@nokia.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:
>  		 */

-- 
Best regards,
Alexander Sverdlin.