From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0BE5CEB64D8 for ; Tue, 20 Jun 2023 10:41:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230448AbjFTKlu convert rfc822-to-8bit (ORCPT ); Tue, 20 Jun 2023 06:41:50 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59000 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229926AbjFTKls (ORCPT ); Tue, 20 Jun 2023 06:41:48 -0400 Received: from eu-smtp-delivery-151.mimecast.com (eu-smtp-delivery-151.mimecast.com [185.58.85.151]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 89D909D for ; Tue, 20 Jun 2023 03:41:46 -0700 (PDT) Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) by relay.mimecast.com with ESMTP with both STARTTLS and AUTH (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384) id uk-mta-200-3m5ZqeQDNFqRLkrPQhChcg-1; Tue, 20 Jun 2023 11:41:43 +0100 X-MC-Unique: 3m5ZqeQDNFqRLkrPQhChcg-1 Received: from AcuMS.Aculab.com (10.202.163.6) by AcuMS.aculab.com (10.202.163.6) with Microsoft SMTP Server (TLS) id 15.0.1497.48; Tue, 20 Jun 2023 11:41:41 +0100 Received: from AcuMS.Aculab.com ([::1]) by AcuMS.aculab.com ([::1]) with mapi id 15.00.1497.048; 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: 8BIT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Andrew Morton > Sent: 16 June 2023 20:52 > > On Thu, 15 Jun 2023 15:51:14 +0800 Wang Ming wrote: > > > 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. > > 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 divisor'. > 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. David > > > --- 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 == 0) { > > max = ((unsigned long long)nr_all_pages << PAGE_SHIFT) >> 4; > > - do_div(max, bucketsize); > > + div64_ul(max, bucketsize); > > } > > max = min(max, 0x80000000ULL); - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)