Received-SPF: pass (google.com: domain of linux-kernel+bounces-61939-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:4601:e00::3 as permitted sender) client-ip=2604:1380:4601:e00::3;
Precedence: bulk
MIME-Version: 1.0
References: <20231219031444.91752-1-bo.ye@mediatek.com> <e23ebdd8-7fbe-435b-a850-0ef18a51b020@collabora.com>
In-Reply-To: <e23ebdd8-7fbe-435b-a850-0ef18a51b020@collabora.com>
From: "Rafael J. Wysocki" <rafael@kernel.org>
Date: Mon, 12 Feb 2024 17:09:34 +0100
Message-ID: <CAJZ5v0h=OKnY85EF9Mg1irsSbnea+P9oAQAdQURqjn+6_5s2PQ@mail.gmail.com>
Subject: Re: [PATCH v2] fix overflow in idle exit_latency
To: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>, Bo Ye <bo.ye@mediatek.com>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>, Matthias Brugger <matthias.bgg@gmail.com>, 
	yongdong.zhang@mediatek.com, C Cheng <C.Cheng@mediatek.com>, 
	linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, 
	linux-arm-kernel@lists.infradead.org, linux-mediatek@lists.infradead.org
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

On Tue, Dec 19, 2023 at 11:56=E2=80=AFAM AngeloGioacchino Del Regno
<angelogioacchino.delregno@collabora.com> wrote:
>
> Il 19/12/23 04:14, Bo Ye ha scritto:
> > From: C Cheng <C.Cheng@mediatek.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 =3D s->exit_latency *
> > NSEC_PER_USEC to avoid potential overflow happenning.
> >
> > Signed-off-by: C Cheng <C.Cheng@mediatek.com>
> > Signed-off-by: Bo Ye <bo.ye@mediatek.com>
>
> Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collab=
ora.com>

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