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Tue, 20 Jun 2023 11:41:41 +0100 From: David Laight To: 'Andrew Morton' , Wang Ming CC: Mike Rapoport , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "opensource.kernel@vivo.com" Subject: RE: [PATCH v1] mm:Using div64_ul replaces do_div() function Thread-Topic: [PATCH v1] mm:Using div64_ul replaces do_div() function Thread-Index: AQHZoIwRQASXgZQ+1kWZyPY+ePpnl6+ThGqw Date: Tue, 20 Jun 2023 10:41:41 +0000 Message-ID: <5c04998fb225430e8e4966cc95f8a0ea@AcuMS.aculab.com> References: <20230615075127.6832-1-machel@vivo.com> <20230616125219.dc2346534d6f279a7527c0b0@linux-foundation.org> In-Reply-To: <20230616125219.dc2346534d6f279a7527c0b0@linux-foundation.org> 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: 85E0114000A X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: 8rz58ch5obi546shxsex4xrpp68ym3zr X-HE-Tag: 1687257706-240224 X-HE-Meta: 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 CDvCXY9s 6OTfT5g6EjCn1FOer4BAkf3VnGpVBF6wuY3JfhXRcyrkPiX/pdIeyFfIVQlgEwwHIkskHxreOTTZeh1eFTOXwLWvkaoaCyct91X1DW4OTDnHAAfexiYnAUnVhnr0WduF2NW9OuMLmKGBkkImdKHJZPfsMsLXQsal7zcJBT+PRI1llpDchQfExGQBv0W/xkMvqaTAZpEa3fQjjiUNcldff/4SKlTw3FHZQcMXSr4FzN6H4q+XQ+0NcUWOTHRR0WNK1U4f9wcG2ySIcUS8UJmqGdA4lO4ytv7kZo/f25SYxuinL1/bxKKPcDblTYw2kRjJdrsTE+6YZZGKDJEx3Jq8HkPdJFw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000039, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: From: Andrew Morton > Sent: 16 June 2023 20:52 >=20 > On Thu, 15 Jun 2023 15:51:14 +0800 Wang Ming wrote: >=20 > > Fix the following coccicheck warning: > > > > mm/mm_init.c:2492:2-8: WARNING: do_div() does a > > 64-by-32 division, please consider using div64_ul instead. >=20 > I guess coccicheck was fooled by the incorrect comment over do_div(). > do_div() returns an unsigned long. IIRC do_div() does an in-place update, but div64_ul() returns the result. So the 'fixed' code is entirely broken. The coccicheck message should really be 'check the domain/type of the divis= or'. > alloc_large_system_hash() should be using a u64 for `max'. Nobody uses > unsigned long long any more. Probably makes no difference. The issue is with 'buckesize' - probably 'long' so 64bit on 64bit systems. I guess 'max' can overflow 'long' on 32bit PAE. Although using min(nr_all_pages, 0x80000000UL >> PAGE_SHIFT >> 4) and doing everything as 'unsigned long' might be better. =09David >=20 > > --- a/mm/mm_init.c > > +++ b/mm/mm_init.c > > @@ -2508,7 +2508,7 @@ void *__init alloc_large_system_hash(const char *= tablename, > > /* limit allocation size to 1/16 total memory by default */ > > if (max =3D=3D 0) { > > max =3D ((unsigned long long)nr_all_pages << PAGE_SHIFT= ) >> 4; > > - do_div(max, bucketsize); > > + div64_ul(max, bucketsize); > > } > > max =3D min(max, 0x80000000ULL); - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1= PT, UK Registration No: 1397386 (Wales)