linux-kernel - Re: [PATCH 2/2] sched/nohz: fix overflow error in scheduler_tick_max

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Message-ID: <20130619190604.GE21522@somewhere.redhat.com>
Date:	Wed, 19 Jun 2013 21:06:07 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Kevin Hilman <khilman@...aro.org>
Cc:	linaro-kernel@...ts.linaro.org, Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] sched/nohz: fix overflow error in
 scheduler_tick_max_deferment()

On Tue, Jun 18, 2013 at 04:58:29PM -0700, Kevin Hilman wrote:
> The conversion of the max deferment from usecs to nsecs can easily
> overflow on platforms where a long is 32-bits.  To fix, cast the usecs
> value to u64 before multiplying by NSECS_PER_USEC.
> 
> This was discovered on 32-bit ARM platform when extending the max
> deferment value.
> 
> Cc: Frederic Weisbecker <fweisbec@...il.com>
> Signed-off-by: Kevin Hilman <khilman@...aro.org>

Right, if we make it tunable we need that patch.

Thanks!

Acked-by: Frederic Weisbecker <fweisbec@...il.com>

> ---
>  kernel/sched/core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index b5d3f99..b506722 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2765,7 +2765,7 @@ u64 scheduler_tick_max_deferment(void)
>  	if (time_before_eq(next, now))
>  		return 0;
>  
> -	return jiffies_to_usecs(next - now) * NSEC_PER_USEC;
> +	return (u64)jiffies_to_usecs(next - now) * NSEC_PER_USEC;
>  }
>  #endif
>  
> -- 
> 1.8.3
> 
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