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 6894BC433FE for ; Wed, 12 Oct 2022 21:30:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230135AbiJLVaG convert rfc822-to-8bit (ORCPT ); Wed, 12 Oct 2022 17:30:06 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59184 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230129AbiJLV3T (ORCPT ); Wed, 12 Oct 2022 17:29:19 -0400 Received: from eu-smtp-delivery-151.mimecast.com (eu-smtp-delivery-151.mimecast.com [185.58.86.151]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 38590120BE1 for ; Wed, 12 Oct 2022 14:29:08 -0700 (PDT) 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: 8BIT Precedence: bulk List-ID: X-Mailing-List: ceph-devel@vger.kernel.org From: Joe Perches > Sent: 12 October 2022 20:17 > > 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/cxgb4/cm.c > [] > > @@ -734,7 +734,7 @@ static int send_connect(struct c4iw_ep *ep) > > &ep->com.remote_addr; > > int ret; > > enum chip_type adapter_type = ep->com.dev->rdev.lldi.adapter_type; > > - u32 isn = (prandom_u32() & ~7UL) - 1; > > + u32 isn = (get_random_u32() & ~7UL) - 1; > > trivia: > > There are somewhat odd size mismatches here. > > 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. > > 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. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales) From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Laight Date: Wed, 12 Oct 2022 21:29:02 +0000 Subject: RE: [PATCH v1 3/5] treewide: use get_random_u32() when possible Message-Id: List-Id: References: In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: dccp@vger.kernel.org From: Joe Perches > Sent: 12 October 2022 20:17 > > 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/cxgb4/cm.c > [] > > @@ -734,7 +734,7 @@ static int send_connect(struct c4iw_ep *ep) > > &ep->com.remote_addr; > > int ret; > > enum chip_type adapter_type = ep->com.dev->rdev.lldi.adapter_type; > > - u32 isn = (prandom_u32() & ~7UL) - 1; > > + u32 isn = (get_random_u32() & ~7UL) - 1; > > trivia: > > There are somewhat odd size mismatches here. > > 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. > > 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. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales) 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 lists.sourceforge.net (lists.sourceforge.net [216.105.38.7]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 42C50C433FE for ; Wed, 12 Oct 2022 21:44:46 +0000 (UTC) Received: from [127.0.0.1] (helo=sfs-ml-1.v29.lw.sourceforge.com) by sfs-ml-1.v29.lw.sourceforge.com with esmtp (Exim 4.95) (envelope-from ) id 1oijWt-000244-Jo; Wed, 12 Oct 2022 21:44:43 +0000 Received: from [172.30.20.202] (helo=mx.sourceforge.net) by sfs-ml-1.v29.lw.sourceforge.com with esmtps (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.95) (envelope-from ) id 1oijWs-00023y-G2 for linux-f2fs-devel@lists.sourceforge.net; Wed, 12 Oct 2022 21:44:42 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=sourceforge.net; s=x; h=Content-Transfer-Encoding:Content-Type:MIME-Version :In-Reply-To:References:Message-ID:Date:Subject:CC:To:From:Sender:Reply-To: Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender: Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help:List-Unsubscribe: List-Subscribe:List-Post:List-Owner:List-Archive; bh=DLr+AazHKqvd37FIJspzgJ5v0CvIeseJ+7IB12p8OSQ=; b=jaVoRprJuw/iPRr2SoOwcOIu6N Txf3iGrIHtX2m7ku8GoSXU0bCDokv+DfCdr3Tqcg/md0/YhRso4g+ZHuI4lBhO7mwpSzPEC1jo+fr ezy7k8d8VWJTN011VXN+4R3n0MU45MdscJvp6DiwQJnzgmxJYl+YgOIajlSRO/GObYUo=; DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=sf.net; s=x ; h=Content-Transfer-Encoding:Content-Type:MIME-Version:In-Reply-To: References:Message-ID:Date:Subject:CC:To:From:Sender:Reply-To:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Id:List-Help:List-Unsubscribe:List-Subscribe: List-Post:List-Owner:List-Archive; bh=DLr+AazHKqvd37FIJspzgJ5v0CvIeseJ+7IB12p8OSQ=; b=CKrdkYXY6ONoJk440tGn6Yc/Ah rQG53K4ROl5xpG5tOp2EYh161Qv6oGIuSd/pv55qcfYW5ZUnAXLEiajXG7kENi4cBWjEFz3Xj9WZD ZKfL8jzFG+0R+R7XFlHhztwcZXR9lK4JiO+fQRHoE3RiIGkliYmX9xt1Y0cd4UWy4urQ=; Received: from eu-smtp-delivery-151.mimecast.com ([185.58.85.151]) by sfi-mx-1.v28.lw.sourceforge.com with esmtps (TLS1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.95) id 1oijWq-001aEh-3B for linux-f2fs-devel@lists.sourceforge.net; Wed, 12 Oct 2022 21:44:42 +0000 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" 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 X-Headers-End: 1oijWq-001aEh-3B Subject: Re: [f2fs-dev] [PATCH v1 3/5] treewide: use get_random_u32() when possible X-BeenThere: linux-f2fs-devel@lists.sourceforge.net X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "linux-fbdev@vger.kernel.org" , "linux-doc@vger.kernel.org" , "linux-mmc@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" , "netfilter-devel@vger.kernel.org" , "linux-ext4@vger.kernel.org" , "linux-media@vger.kernel.org" , "linux-actions@lists.infradead.org" , "brcm80211-dev-list.pdl@broadcom.com" , "linux-block@vger.kernel.org" , "linux-fsdevel@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" , "linux-nfs@vger.kernel.org" , "linux-raid@vger.kernel.org" , "netdev@vger.kernel.org" , "linux-usb@vger.kernel.org" , "linux-wireless@vger.kernel.org" , "linux-f2fs-devel@lists.sourceforge.net" , "linux-xfs@vger.kernel.org" , "tipc-discussion@lists.sourceforge.net" , "linux-crypto@vger.kernel.org" , "dmaengine@vger.kernel.org" , "linuxppc-dev@lists.ozlabs.org" Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: linux-f2fs-devel-bounces@lists.sourceforge.net From: Joe Perches > Sent: 12 October 2022 20:17 > > 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/cxgb4/cm.c > [] > > @@ -734,7 +734,7 @@ static int send_connect(struct c4iw_ep *ep) > > &ep->com.remote_addr; > > int ret; > > enum chip_type adapter_type = ep->com.dev->rdev.lldi.adapter_type; > > - u32 isn = (prandom_u32() & ~7UL) - 1; > > + u32 isn = (get_random_u32() & ~7UL) - 1; > > trivia: > > There are somewhat odd size mismatches here. > > 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. > > 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. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales) _______________________________________________ Linux-f2fs-devel mailing list Linux-f2fs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Laight Subject: Re: [PATCH v1 3/5] treewide: use get_random_u32() when possible Date: Wed, 12 Oct 2022 21:29:02 +0000 Message-ID: References: <20221005214844.2699-1-Jason@zx2c4.com> <20221005214844.2699-4-Jason@zx2c4.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: DKIM-Filter: OpenDKIM Filter v2.11.0 smtp2.osuosl.org C5243405BB DKIM-Filter: OpenDKIM Filter v2.11.0 smtp2.osuosl.org E0989400AF DKIM-Filter: OpenDKIM Filter v2.11.0 smtp3.osuosl.org 2462360AA3 DKIM-Filter: OpenDKIM Filter v2.11.0 smtp3.osuosl.org 1F53A60A81 In-Reply-To: Content-Language: en-US List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: ovs-dev-bounces-yBygre7rU0TnMu66kgdUjQ@public.gmane.org Sender: "dev" To: 'Joe Perches' , "Jason A. Donenfeld" , "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" Cc: "linux-fbdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linux-doc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linux-mmc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "dri-devel-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org" , "linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org" , "linux-sctp-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "target-devel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linux-mtd-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org" , "linux-stm32-XDFAJ8BFU24N7RejjzZ/Li2xQDfSxrLKVpNB7YpNyf8@public.gmane.org" , "drbd-dev-cunTk1MwBs8qoQakbn7OcQ@public.gmane.org" , "dev-yBygre7rU0TnMu66kgdUjQ@public.gmane.org" , "rds-devel-N0ozoZBvEnrZJqsBc5GL+g@public.gmane.org" , "linux-scsi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "dccp-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" From: Joe Perches > Sent: 12 October 2022 20:17 > > 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/cxgb4/cm.c > [] > > @@ -734,7 +734,7 @@ static int send_connect(struct c4iw_ep *ep) > > &ep->com.remote_addr; > > int ret; > > enum chip_type adapter_type = ep->com.dev->rdev.lldi.adapter_type; > > - u32 isn = (prandom_u32() & ~7UL) - 1; > > + u32 isn = (get_random_u32() & ~7UL) - 1; > > trivia: > > There are somewhat odd size mismatches here. > > 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. > > 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. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales) 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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 3614EC4167B for ; Wed, 12 Oct 2022 21:29:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:In-Reply-To:References: Message-ID:Date:Subject:CC:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=z61l7Sv0PafkN7X8Wm0ER/2vHaeH705FHXtmcKYWbjI=; b=Nk5Z2djNrx2tZB xWxE6TB7QOf/DjrNPV4oD8MFym4ZIi+U8Oqm//A3IjA1dm4aWdJPvJ3nYsm7zI+6w0yopVWhpj7gR Y2UVu/cy5mNJT7oK3s1loWarnWDEGWF+4nFQ8duY3cLBcUGKntc92lPXOzcdbW1erfk+ZeOOcd8zE +2U2ZKhCJj1yUTiz0dNo/Q3lNME8P2ZuaWePHTg7+ShYULRwaTxic7/qKtdcQYu9m0ZdzUtutZEiw UFxJAXBA/RbAmS76yw4ihHSnwzJXwOPXqxkDuNB2w2yXSx0FVOJGTw+wNYEVGxxsK/JiYLHU9RrOK 88Db7zy7XyjqQBXcn3xg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1oijI4-009OdF-LK; Wed, 12 Oct 2022 21:29:24 +0000 Received: from eu-smtp-delivery-151.mimecast.com ([185.58.86.151]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1oijHr-009OYe-9j for linux-mtd@lists.infradead.org; Wed, 12 Oct 2022 21:29:14 +0000 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 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20221012_142911_654449_CA3CD5A1 X-CRM114-Status: GOOD ( 15.41 ) X-BeenThere: linux-mtd@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-mtd" Errors-To: linux-mtd-bounces+linux-mtd=archiver.kernel.org@lists.infradead.org From: Joe Perches > Sent: 12 October 2022 20:17 > > 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/cxgb4/cm.c > [] > > @@ -734,7 +734,7 @@ static int send_connect(struct c4iw_ep *ep) > > &ep->com.remote_addr; > > int ret; > > enum chip_type adapter_type = ep->com.dev->rdev.lldi.adapter_type; > > - u32 isn = (prandom_u32() & ~7UL) - 1; > > + u32 isn = (get_random_u32() & ~7UL) - 1; > > trivia: > > There are somewhat odd size mismatches here. > > 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. > > 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. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales) ______________________________________________________ Linux MTD discussion mailing list http://lists.infradead.org/mailman/listinfo/linux-mtd/ 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 lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id A95CDC433FE for ; Wed, 12 Oct 2022 21:29:51 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4Mnm5B1L28z3dtV for ; Thu, 13 Oct 2022 08:29:50 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=aculab.com (client-ip=185.58.86.151; helo=eu-smtp-delivery-151.mimecast.com; envelope-from=david.laight@aculab.com; receiver=) Received: from eu-smtp-delivery-151.mimecast.com (eu-smtp-delivery-151.mimecast.com [185.58.86.151]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4Mnm4V5JvXz2yQg for ; Thu, 13 Oct 2022 08:29:12 +1100 (AEDT) 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" 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 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "linux-fbdev@vger.kernel.org" , "linux-doc@vger.kernel.org" , "linux-mmc@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" , "netfilter-devel@vger.kernel.org" , "linux-ext4@vger.kernel.org" , "linux-media@vger.kernel.org" , "linux-actions@lists.infradead.org" , "brcm80211-dev-list.pdl@broadcom.com" , "linux-block@vger.kernel.org" , "linux-fsdevel@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" , "linux-nfs@vger.kernel.org" , "linux-raid@vger.kernel.o rg" , "netdev@vger.kernel.org" , "linux-usb@vger.kernel.org" , "linux-wireless@vger.kernel.org" , "linux-f2fs-devel@lists.sourceforge.net" , "linux-xfs@vger.kernel.org" , "tipc-discussion@lists.sourceforge.net" , "linux-crypto@vger.kernel.org" , "dmaengine@vger.kernel.org" , "linuxppc-dev@lists.ozlabs.org" Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" 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) From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from eu-smtp-delivery-151.mimecast.com (eu-smtp-delivery-151.mimecast.com [185.58.85.151]) by mail19.linbit.com (LINBIT Mail Daemon) with ESMTP id C9210420372 for ; Wed, 12 Oct 2022 23:35:12 +0200 (CEST) From: David Laight To: 'Joe Perches' , "Jason A. Donenfeld" , "linux-kernel@vger.kernel.org" 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: MIME-Version: 1.0 Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Cc: "linux-fbdev@vger.kernel.org" , "linux-doc@vger.kernel.org" , "linux-mmc@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" , "coreteam@netfilter.org" , "netfilter-devel@vger.kernel.org" , "linux-ext4@vger.kernel.org" , "linux-media@vger.kernel.org" , "linux-actions@lists.infradead.org" , "brcm80211-dev-list.pdl@broadcom.com" , "linux-block@vger.kernel.org" , "linux-fsdevel@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" , "linux-nfs@vger.kernel.org" , "linux-raid@vger.kernel.org" , "netdev@vger.kernel.org" , "linux-usb@vger.kernel.org" , "linux-wireless@vger.kernel.org" , "SHA-cyfmac-dev-list@infineon.com" , "linux-f2fs-devel@lists.sourceforge.net" , "linux-xfs@vger.kernel.org" , "tipc-discussion@lists.sourceforge.net" , "linux-crypto@vger.kernel.org" , "dmaengine@vger.kernel.org" , "linuxppc-dev@lists.ozlabs.org" Subject: Re: [Drbd-dev] [PATCH v1 3/5] treewide: use get_random_u32() when possible List-Id: "*Coordination* of development, patches, contributions -- *Questions* \(even to developers\) go to drbd-user, please." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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) 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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id F392FC4332F for ; Wed, 12 Oct 2022 21:30:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:In-Reply-To:References: Message-ID:Date:Subject:CC:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=VRf6YPjXldZJqmdsp3fXECE/uF8K2pZ3Dyd5Vqj1v2Q=; b=P2fyUv9Y7JmMDV lRSpQeX32lyqzt4KincV/7MGK15kmxFC9FQ3zaVmo4zr7KudllF1paZoP2ODJAD2kNSpoyeo+yw7M QADOny4t3sG0XRuSgKCwni7WvTCT6DrHfZGitiFHXBE/NhAPvHC6XqKfaY7eAkO9sHNfYw1lUuhDF E6vX5x8ufsZHYyc40CRTOiw5DjIsQpf7RP8mHDiIbnWj4cfCKJBsXVA3mXXmaIojLXol4IgHRE2sk Fej/U+hnMEzGd2SgtYPJm3uKOaAQNO2hNTVkP98I/V0ScSagIXrl5s4uNSLBIPZV6F6pctMivxGdY K4nk22fazq/VlMnJjE3Q==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1oijHv-009ObU-4E; Wed, 12 Oct 2022 21:29:15 +0000 Received: from eu-smtp-delivery-151.mimecast.com ([185.58.86.151]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1oijHr-009OYg-7z for linux-arm-kernel@lists.infradead.org; Wed, 12 Oct 2022 21:29:13 +0000 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 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20221012_142911_556273_52FFD203 X-CRM114-Status: GOOD ( 16.15 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org From: Joe Perches > Sent: 12 October 2022 20:17 > > 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/cxgb4/cm.c > [] > > @@ -734,7 +734,7 @@ static int send_connect(struct c4iw_ep *ep) > > &ep->com.remote_addr; > > int ret; > > enum chip_type adapter_type = ep->com.dev->rdev.lldi.adapter_type; > > - u32 isn = (prandom_u32() & ~7UL) - 1; > > + u32 isn = (get_random_u32() & ~7UL) - 1; > > trivia: > > There are somewhat odd size mismatches here. > > 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. > > 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. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales) _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel 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 gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 4C1E7C433FE for ; Wed, 12 Oct 2022 21:29:12 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 1716A10E09A; Wed, 12 Oct 2022 21:29:11 +0000 (UTC) Received: from eu-smtp-delivery-151.mimecast.com (eu-smtp-delivery-151.mimecast.com [185.58.86.151]) by gabe.freedesktop.org (Postfix) with ESMTPS id 294FE10E09A for ; Wed, 12 Oct 2022 21:29:07 +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" 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 X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "linux-fbdev@vger.kernel.org" , "linux-doc@vger.kernel.org" , "linux-mmc@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" , "netfilter-devel@vger.kernel.org" , "linux-ext4@vger.kernel.org" , "linux-media@vger.kernel.org" , "linux-actions@lists.infradead.org" , "brcm80211-dev-list.pdl@broadcom.com" , "linux-block@vger.kernel.org" , "linux-fsdevel@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" , "linux-nfs@vger.kernel.org" , "linux-raid@vger.kernel.org" , "netdev@vger.kernel.org" , "linux-usb@vger.kernel.org" , "linux-wireless@vger.kernel.org" , "linux-f2fs-devel@lists.sourceforge.net" , "linux-xfs@vger.kernel.org" , "tipc-discussion@lists.sourceforge.net" , "linux-crypto@vger.kernel.org" , "dmaengine@vger.kernel.org" , "linuxppc-dev@lists.ozlabs.org" Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" 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)