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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id E0BBCC4332F for ; Wed, 12 Oct 2022 21:29:10 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 0D9D36B0071; Wed, 12 Oct 2022 17:29:10 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 088F06B0073; Wed, 12 Oct 2022 17:29:10 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E6BE76B0074; Wed, 12 Oct 2022 17:29:09 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id CE2616B0071 for ; Wed, 12 Oct 2022 17:29:09 -0400 (EDT) Received: from smtpin16.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 84C671C6D3C for ; Wed, 12 Oct 2022 21:29:09 +0000 (UTC) X-FDA: 80013588018.16.CD31D8B Received: from eu-smtp-delivery-151.mimecast.com (eu-smtp-delivery-151.mimecast.com [185.58.86.151]) by imf08.hostedemail.com (Postfix) with ESMTP id D97EF160026 for ; Wed, 12 Oct 2022 21:29:08 +0000 (UTC) Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384) id uk-mta-269-WPghBqosPyeNkdeVSYELTw-1; Wed, 12 Oct 2022 22:29:04 +0100 X-MC-Unique: WPghBqosPyeNkdeVSYELTw-1 Received: from AcuMS.Aculab.com (10.202.163.6) by AcuMS.aculab.com (10.202.163.6) with Microsoft SMTP Server (TLS) id 15.0.1497.38; Wed, 12 Oct 2022 22:29:02 +0100 Received: from AcuMS.Aculab.com ([::1]) by AcuMS.aculab.com ([::1]) with mapi id 15.00.1497.040; Wed, 12 Oct 2022 22:29:02 +0100 From: David Laight To: 'Joe Perches' , "Jason A. Donenfeld" , "linux-kernel@vger.kernel.org" CC: "linux-fbdev@vger.kernel.org" , "linux-doc@vger.kernel.org" , "linux-wireless@vger.kernel.org" , "dri-devel@lists.freedesktop.org" , "linux-mm@kvack.org" , "linux-sctp@vger.kernel.org" , "target-devel@vger.kernel.org" , "linux-mtd@lists.infradead.org" , "linux-stm32@st-md-mailman.stormreply.com" , "drbd-dev@lists.linbit.com" , "dev@openvswitch.org" , "rds-devel@oss.oracle.com" , "linux-scsi@vger.kernel.org" , "dccp@vger.kernel.org" , "linux-rdma@vger.kernel.org" , "kasan-dev@googlegroups.com" , "lvs-devel@vger.kernel.org" , "SHA-cyfmac-dev-list@infineon.com" , "coreteam@netfilter.org" , "tipc-discussion@lists.sourceforge.net" , "linux-ext4@vger.kernel.org" , "linux-media@vger.kernel.org" , "linux-actions@lists.infradead.org" , "linux-nfs@vger.kernel.org" , "linux-block@vger.kernel.org" , "dmaengine@vger.kernel.org" , "linux-nvme@lists.infradead.org" , "linux-hams@vger.kernel.org" , "ceph-devel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "cake@lists.bufferbloat.net" , "brcm80211-dev-list.pdl@broadcom.com" , "linux-raid@vger.kernel.org" , "netdev@vger.kernel.org" , "linux-usb@vger.kernel.org" , "linux-mmc@vger.kernel.org" , "linux-f2fs-devel@lists.sourceforge.net" , "linux-xfs@vger.kernel.org" , "netfilter-devel@vger.kernel.org" , "linux-crypto@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , "linuxppc-dev@lists.ozlabs.org" Subject: RE: [PATCH v1 3/5] treewide: use get_random_u32() when possible Thread-Topic: [PATCH v1 3/5] treewide: use get_random_u32() when possible Thread-Index: AQHY3m9QJDmwhr5XuUa4Hi/RfD23ja4LRXVg Date: Wed, 12 Oct 2022 21:29:02 +0000 Message-ID: References: <20221005214844.2699-1-Jason@zx2c4.com> <20221005214844.2699-4-Jason@zx2c4.com> In-Reply-To: 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 ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1665610149; a=rsa-sha256; cv=none; b=Z9bpOzd8V+l4zTWNqoBvFjTCIl/bWq8WhQCVDQH0K8iWBvvMzt1qZKyrUa7CPxZslUTUqK /RlMaAisg1unjLyRPzqgAEzoceRCSdShcWsoi4JOE7RbPtKXecuejz67HWF4Tw66ZGqe/m u6c5eJz0QByrB1MlOq/0h9Qcpo2vKCw= ARC-Authentication-Results: i=1; imf08.hostedemail.com; dkim=none; spf=pass (imf08.hostedemail.com: domain of david.laight@aculab.com designates 185.58.86.151 as permitted sender) smtp.mailfrom=david.laight@aculab.com; dmarc=pass (policy=none) header.from=aculab.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1665610149; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=DLr+AazHKqvd37FIJspzgJ5v0CvIeseJ+7IB12p8OSQ=; b=cK6D1uLBLOTsCTlRpvS0xy+ISgxy5NgH6ucLo6cVVWEPlyNXIAIBQrLI6j6cPHKKHdjhHP AkKyQQEGMVvy7g/Pg6bSfnB66McUuBaHw5BLEYgofxK3I8V4zhEsRijVgHT8yiw7JZ1PMn fndteZa1evldeS9lMsq5tpsu5c+PwDQ= X-Stat-Signature: 7mqztk77j1miqhrutzwd9byid4rqyx4n X-Rspamd-Queue-Id: D97EF160026 X-Rspam-User: Authentication-Results: imf08.hostedemail.com; dkim=none; spf=pass (imf08.hostedemail.com: domain of david.laight@aculab.com designates 185.58.86.151 as permitted sender) smtp.mailfrom=david.laight@aculab.com; dmarc=pass (policy=none) header.from=aculab.com X-Rspamd-Server: rspam06 X-HE-Tag: 1665610148-760965 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: Joe Perches > Sent: 12 October 2022 20:17 >=20 > On Wed, 2022-10-05 at 23:48 +0200, Jason A. Donenfeld wrote: > > The prandom_u32() function has been a deprecated inline wrapper around > > get_random_u32() for several releases now, and compiles down to the > > exact same code. Replace the deprecated wrapper with a direct call to > > the real function. > [] > > diff --git a/drivers/infiniband/hw/cxgb4/cm.c b/drivers/infiniband/hw/c= xgb4/cm.c > [] > > @@ -734,7 +734,7 @@ static int send_connect(struct c4iw_ep *ep) > > =09=09=09=09 &ep->com.remote_addr; > > =09int ret; > > =09enum chip_type adapter_type =3D ep->com.dev->rdev.lldi.adapter_type= ; > > -=09u32 isn =3D (prandom_u32() & ~7UL) - 1; > > +=09u32 isn =3D (get_random_u32() & ~7UL) - 1; >=20 > trivia: >=20 > There are somewhat odd size mismatches here. >=20 > I had to think a tiny bit if random() returned a value from 0 to 7 > and was promoted to a 64 bit value then truncated to 32 bit. >=20 > Perhaps these would be clearer as ~7U and not ~7UL That makes no difference - the compiler will generate the same code. The real question is WTF is the code doing? The '& ~7u' clears the bottom 3 bits. The '- 1' then sets the bottom 3 bits and decrements the (random) high bits. So is the same as get_random_u32() | 7. But I bet the coder had something else in mind. =09David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1= PT, UK Registration No: 1397386 (Wales)