Re: [PATCH] cpuidle: idle exit_latency overflow

[AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>]

Il 16/11/23 14:26, Bo Ye ha scritto:
> From: mtk24676 <C.Cheng@mediatek.com>
> 
> In detail:
> In kernel-6.1, in the __cpuidle_driver_init function in
> driver/cpuidle/driver.c, there is a line of code that causes
> an overflow. The line is s->exit_latency_ns = s->exit_latency
> * NSEC_PER_USEC. The overflow occurs because the product of an
> int type and a constant exceeds the range of the int type.
> 
> In C language, when you perform a multiplication operation, if
> both operands are of int type, the multiplication operation is
> performed on the int type, and then the result is converted to
> the target type. This means that if the product of int type
> multiplication exceeds the range that int type can represent,
> an overflow will occur even if you store the result in a
> variable of int64_t type.
> 
> Signed-off-by: mtk24676 <C.Cheng@mediatek.com>

It all makes sense, but "mtk24676" is not the name of a person, what's going on?

> Signed-off-by: bo.ye <bo.ye@mediatek.com>

That's the same, you perhaps wanted to write "Bo Ye", not "bo.ye".

Regards,
Angelo

> ---
> 
> diff --git a/drivers/cpuidle/driver.c b/drivers/cpuidle/driver.c
> index d9cda7f..631ca16 100644
> --- a/drivers/cpuidle/driver.c
> +++ b/drivers/cpuidle/driver.c
> @@ -187,7 +187,7 @@
>   			s->target_residency = div_u64(s->target_residency_ns, NSEC_PER_USEC);
>   
>   		if (s->exit_latency > 0)
> -			s->exit_latency_ns = s->exit_latency * NSEC_PER_USEC;
> +			s->exit_latency_ns = (u64)s->exit_latency * NSEC_PER_USEC;
>   		else if (s->exit_latency_ns < 0)
>   			s->exit_latency_ns =  0;
>   		else