linux-kernel - Re: [PATCH v2] fix overflow in idle exit

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Date: Mon, 12 Feb 2024 17:09:34 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, Bo Ye <bo.ye@...iatek.com>
Cc: Daniel Lezcano <daniel.lezcano@...aro.org>, Matthias Brugger <matthias.bgg@...il.com>, 
	yongdong.zhang@...iatek.com, C Cheng <C.Cheng@...iatek.com>, 
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH v2] fix overflow in idle exit_latency

On Tue, Dec 19, 2023 at 11:56 AM AngeloGioacchino Del Regno
<angelogioacchino.delregno@...labora.com> wrote:
>
> Il 19/12/23 04:14, Bo Ye ha scritto:
> > From: C Cheng <C.Cheng@...iatek.com>
> >
> > In detail:
> >
> > 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.
> >
> > For a multiplication of two int values, it is better to use
> > mul_u32_u32() rather than s->exit_latency_ns = s->exit_latency *
> > NSEC_PER_USEC to avoid potential overflow happenning.
> >
> > Signed-off-by: C Cheng <C.Cheng@...iatek.com>
> > Signed-off-by: Bo Ye <bo.ye@...iatek.com>
>
> Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>

Applied as 6.9 material under a different subject (cpuidle: Avoid
potential overflow in integer multiplication), thanks!