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Sat, 10 Jun 2023 21:09:28 +0100 From: David Laight To: 'Lorenzo Stoakes' , Lu Hongfei CC: Andrew Morton , Uladzislau Rezki , Christoph Hellwig , "open list:VMALLOC" , open list , "opensource.kernel@vivo.com" Subject: RE: [PATCH] mm/vmalloc: Replace the ternary conditional operator with min() Thread-Topic: [PATCH] mm/vmalloc: Replace the ternary conditional operator with min() Thread-Index: AQHZmq9RsZ2mMErDwEmVNd3QmnYBSK+Ed3Zw Date: Sat, 10 Jun 2023 20:09:28 +0000 Message-ID: References: <20230609061309.42453-1-luhongfei@vivo.com> <832d7c69-ffd5-4764-8ffe-3a02bef0efb0@lucifer.local> <3fc87d60-4e81-4f49-95f0-0503ad5cdf35@lucifer.local> In-Reply-To: <3fc87d60-4e81-4f49-95f0-0503ad5cdf35@lucifer.local> Accept-Language: en-GB, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 40077100019 X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: 1o3d8agcqhp6f95noien1qe5b1epr9ru X-HE-Tag: 1686427776-816291 X-HE-Meta: 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 eoJxwoFd wu49Glrv16um+jCg4+n/tAW0iw7gCt8ZP8bdTMvVqoUp0vqvKaOk26vccfHng+hfPdnJjfzJ7gWqmsRbm8rfDadky9E2XiCTqP0QLEi/BysXcNk90/AXwR9VLdU3LF53kEU/39dc4MexGOe/W8515p6wVXQAgkscg5/Of7qaL4qukJUiYvl23tweqVTqcDc+3z/OgBSJzuTYrXfy4PJDBQhUi8sntfrjVyfOnL3Jz6neVz40kFVLJ8KSDa9XAYOeAzqqD0jGJGu4n/XKO4AV18Idu2KIQT9DXJskU X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: From: Lorenzo Stoakes > Sent: 09 June 2023 09:49 > On Fri, Jun 09, 2023 at 08:09:45AM +0100, Lorenzo Stoakes wrote: > > On Fri, Jun 09, 2023 at 02:13:09PM +0800, Lu Hongfei wrote: > > > It would be better to replace the traditional ternary conditional > > > operator with min() in zero_iter > > > > > > Signed-off-by: Lu Hongfei > > > --- > > > mm/vmalloc.c | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > > > index 29077d61ff81..42df032e6c27 > > > --- a/mm/vmalloc.c > > > +++ b/mm/vmalloc.c > > > @@ -3571,7 +3571,7 @@ static size_t zero_iter(struct iov_iter *iter, = size_t count) > > > =09while (remains > 0) { > > > =09=09size_t num, copied; > > > > > > -=09=09num =3D remains < PAGE_SIZE ? remains : PAGE_SIZE; > > > +=09=09num =3D min(remains, PAGE_SIZE); >=20 > OK, as per the pedantic test bot, you'll need to change this to:- >=20 > num =3D min_t(size_t, remains, PAGE_SIZE); There has to be a valid reason why min/max have strong type checks. Using min_t() all the time is just subverting them and means that bugs are more likely than if the extra tests in min() were absent. The problem here is that size_t is 'unsigned int' but PAGE_SIZE 'unsigned long'. A 'safe' change is min(remains + 0ULL, PAGE_SIZE). But, in reality, min/max should always be valid when one value is a constant between 0 and MAX_INT. The constant just needs forcing to 'signed int' (eg assigning to a temporary on that type) before the comparison (etc). =09David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1= PT, UK Registration No: 1397386 (Wales)