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 6C835C433FE for ; Sat, 8 Oct 2022 22:20:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229450AbiJHWUP (ORCPT ); Sat, 8 Oct 2022 18:20:15 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58240 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229469AbiJHWUN (ORCPT ); Sat, 8 Oct 2022 18:20:13 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8605C24BE2; Sat, 8 Oct 2022 15:20:12 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 0C124B80C67; Sat, 8 Oct 2022 22:20:11 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 70236C433C1; Sat, 8 Oct 2022 22:20:03 +0000 (UTC) Authentication-Results: smtp.kernel.org; dkim=pass (1024-bit key) header.d=zx2c4.com header.i=@zx2c4.com header.b="QmEOahoB" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zx2c4.com; s=20210105; t=1665267601; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=P/cyFerOrVR1hjiF/QX04AV2aA5aZrHQbK/mKyxjv9I=; b=QmEOahoBx06KMjDzLtZ7ejYlSXdX3xXDEfCsWADs48NoQdJjnF97KJ2e9Xd8nbc1t03bHc iLLQvFEr+bqjH8bhenqpSsnO09+GKMG/IoUml8RmXTmxGyb7ZNYDfXX5MlPSK23GrIkSgB X2xrqLLCtqWzb7N/605l/YH3w7HZ3qs= Received: by mail.zx2c4.com (ZX2C4 Mail Server) with ESMTPSA id 6a6d913c (TLSv1.3:TLS_AES_256_GCM_SHA384:256:NO); Sat, 8 Oct 2022 22:20:01 +0000 (UTC) Date: Sun, 9 Oct 2022 00:19:59 +0200 From: "Jason A. Donenfeld" To: David Laight Cc: "linux-kernel@vger.kernel.org" , "patches@lists.linux.dev" , Andreas Noever , Andrew Morton , Andy Shevchenko , Borislav Petkov , Catalin Marinas , Christoph =?utf-8?Q?B=C3=B6hmwalder?= , Christoph Hellwig , Christophe Leroy , Daniel Borkmann , Dave Airlie , Dave Hansen , "David S . Miller" , Eric Dumazet , Florian Westphal , Greg Kroah-Hartman , "H . Peter Anvin" , Heiko Carstens , Helge Deller , Herbert Xu , Huacai Chen , Hugh Dickins , Jakub Kicinski , "James E . J . Bottomley" , Jan Kara , Jason Gunthorpe , Jens Axboe , Johannes Berg , Jonathan Corbet , Jozsef Kadlecsik , KP Singh , Kees Cook , Marco Elver , Mauro Carvalho Chehab , Michael Ellerman , Pablo Neira Ayuso , Paolo Abeni , Peter Zijlstra , Richard Weinberger , Russell King , Theodore Ts'o , Thomas Bogendoerfer , Thomas Gleixner , Thomas Graf , Ulf Hansson , Vignesh Raghavendra , WANG Xuerui , Will Deacon , Yury Norov , "dri-devel@lists.freedesktop.org" , "kasan-dev@googlegroups.com" , "kernel-janitors@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "linux-block@vger.kernel.org" , "linux-crypto@vger.kernel.org" , "linux-doc@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , "linux-media@vger.kernel.org" , "linux-mips@vger.kernel.org" , "linux-mm@kvack.org" , "linux-mmc@vger.kernel.org" , "linux-mtd@lists.infradead.org" , "linux-nvme@lists.infradead.org" , "linux-parisc@vger.kernel.org" , "linux-rdma@vger.kernel.org" , "linux-s390@vger.kernel.org" , "linux-um@lists.infradead.org" , "linux-usb@vger.kernel.org" , "linux-wireless@vger.kernel.org" , "linuxppc-dev@lists.ozlabs.org" , "loongarch@lists.linux.dev" , "netdev@vger.kernel.org" , "sparclinux@vger.kernel.org" , "x86@kernel.org" , Jan Kara Subject: Re: [PATCH v4 2/6] treewide: use prandom_u32_max() when possible Message-ID: References: <20221007180107.216067-1-Jason@zx2c4.com> <20221007180107.216067-3-Jason@zx2c4.com> <01fafe0e56554b1c9c934c458b93473a@AcuMS.aculab.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <01fafe0e56554b1c9c934c458b93473a@AcuMS.aculab.com> Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Sat, Oct 08, 2022 at 10:08:03PM +0000, David Laight wrote: > From: Jason A. Donenfeld > > Sent: 07 October 2022 19:01 > > > > Rather than incurring a division or requesting too many random bytes for > > the given range, use the prandom_u32_max() function, which only takes > > the minimum required bytes from the RNG and avoids divisions. > > > ... > > --- a/lib/cmdline_kunit.c > > +++ b/lib/cmdline_kunit.c > > @@ -76,7 +76,7 @@ static void cmdline_test_lead_int(struct kunit *test) > > int rc = cmdline_test_values[i]; > > int offset; > > > > - sprintf(in, "%u%s", prandom_u32_max(256), str); > > + sprintf(in, "%u%s", get_random_int() % 256, str); > > /* Only first '-' after the number will advance the pointer */ > > offset = strlen(in) - strlen(str) + !!(rc == 2); > > cmdline_do_one_test(test, in, rc, offset); > > @@ -94,7 +94,7 @@ static void cmdline_test_tail_int(struct kunit *test) > > int rc = strcmp(str, "") ? (strcmp(str, "-") ? 0 : 1) : 1; > > int offset; > > > > - sprintf(in, "%s%u", str, prandom_u32_max(256)); > > + sprintf(in, "%s%u", str, get_random_int() % 256); > > /* > > * Only first and leading '-' not followed by integer > > * will advance the pointer. > > Something has gone backwards here.... > And get_random_u8() looks a better fit. Wrong patch version. > > David > > - > Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK > Registration No: 1397386 (Wales)