linux-kernel - Re: [PATCH] time: sched_clock: fix integer overflow

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Message-ID: <20130729055939.GK5161@tarshish>
Date:	Mon, 29 Jul 2013 08:59:39 +0300
From:	Baruch Siach <baruch@...s.co.il>
To:	John Stultz <john.stultz@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>
Cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-xtensa@...ux-xtensa.org
Subject: Re: [PATCH] time: sched_clock: fix integer overflow

Hi Thomas, John,

On Wed, Jul 17, 2013 at 12:46:53PM +0300, Baruch Siach wrote:
> The expression '(1 << 32)' happens to evaluate as 0 on ARM, but it evaluates as
> 1 on xtensa and x86_64. This zeros sched_clock_mask, and breaks sched_clock().
> Set the type of 1 to 'unsigned long long' to get the value we need.

Ping? -rc3 is out, and this bug (which currently breaks xtensa) is not fixed 
yet. Please consider applying.

baruch

> Reported-by: Max Filippov <jcmvbkbc@...il.com>
> Tested-by: Max Filippov <jcmvbkbc@...il.com>
> Acked-by: Russell King <rmk+kernel@....linux.org.uk>
> Signed-off-by: Baruch Siach <baruch@...s.co.il>
> ---
>  kernel/time/sched_clock.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c
> index a326f27..0b479a6 100644
> --- a/kernel/time/sched_clock.c
> +++ b/kernel/time/sched_clock.c
> @@ -121,7 +121,7 @@ void __init setup_sched_clock(u32 (*read)(void), int bits, unsigned long rate)
>  	BUG_ON(bits > 32);
>  	WARN_ON(!irqs_disabled());
>  	read_sched_clock = read;
> -	sched_clock_mask = (1 << bits) - 1;
> +	sched_clock_mask = (1ULL << bits) - 1;
>  	cd.rate = rate;
>  
>  	/* calculate the mult/shift to convert counter ticks to ns. */
> -- 

-- 
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