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 X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 82800CA9EBC for ; Fri, 25 Oct 2019 08:53:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4E8B1222C1 for ; Fri, 25 Oct 2019 08:53:01 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=c-s.fr header.i=@c-s.fr header.b="JXqe5sri" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2437782AbfJYIxA (ORCPT ); Fri, 25 Oct 2019 04:53:00 -0400 Received: from pegase1.c-s.fr ([93.17.236.30]:34737 "EHLO pegase1.c-s.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2437618AbfJYIw7 (ORCPT ); Fri, 25 Oct 2019 04:52:59 -0400 Received: from localhost (mailhub1-int [192.168.12.234]) by localhost (Postfix) with ESMTP id 46zyYg6BYkz9vC0w; Fri, 25 Oct 2019 10:52:55 +0200 (CEST) Authentication-Results: localhost; dkim=pass reason="1024-bit key; insecure key" header.d=c-s.fr header.i=@c-s.fr header.b=JXqe5sri; dkim-adsp=pass; dkim-atps=neutral X-Virus-Scanned: Debian amavisd-new at c-s.fr Received: from pegase1.c-s.fr ([192.168.12.234]) by localhost (pegase1.c-s.fr [192.168.12.234]) (amavisd-new, port 10024) with ESMTP id 6HbhFbyFhM8v; Fri, 25 Oct 2019 10:52:55 +0200 (CEST) Received: from messagerie.si.c-s.fr (messagerie.si.c-s.fr [192.168.25.192]) by pegase1.c-s.fr (Postfix) with ESMTP id 46zyYg4vJdz9vC0r; Fri, 25 Oct 2019 10:52:55 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=c-s.fr; s=mail; t=1571993575; bh=4oDjhDK0FsO59rFVGt7Y5o7o8C55+19qgM1BU+899t4=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=JXqe5sriXNQaQXKes3qqbdy43NSrBpwRBpfMpDtkffnR5YWutoOVXs9BVvi7rzrMY QG68soKwprXrLgOAJa7ilqd/FXQFpMspM1kp2DJjaecMsPUGWDU22R2zojRhkImahW aYJ8xO9qWW+5AHxKxjlrTglXwCmCdHn/aPTlV1cw= Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id B9A698B868; Fri, 25 Oct 2019 10:52:56 +0200 (CEST) X-Virus-Scanned: amavisd-new at c-s.fr Received: from messagerie.si.c-s.fr ([127.0.0.1]) by localhost (messagerie.si.c-s.fr [127.0.0.1]) (amavisd-new, port 10023) with ESMTP id Z1aZY1cuISIS; Fri, 25 Oct 2019 10:52:56 +0200 (CEST) Received: from [192.168.4.90] (unknown [192.168.4.90]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 7BC128B895; Fri, 25 Oct 2019 10:52:54 +0200 (CEST) Subject: Re: [PATCH V7] mm/debug: Add tests validating architecture page table helpers To: Anshuman Khandual , Qian Cai Cc: linux-mm@kvack.org, Andrew Morton , Vlastimil Babka , Greg Kroah-Hartman , Thomas Gleixner , Mike Rapoport , Jason Gunthorpe , Dan Williams , Peter Zijlstra , Michal Hocko , Mark Rutland , Mark Brown , Steven Price , Ard Biesheuvel , Masahiro Yamada , Kees Cook , Tetsuo Handa , Matthew Wilcox , Sri Krishna chowdary , Dave Hansen , Russell King - ARM Linux , Michael Ellerman , Paul Mackerras , Martin Schwidefsky , Heiko Carstens , "David S. Miller" , Vineet Gupta , James Hogan , Paul Burton , Ralf Baechle , "Kirill A . Shutemov" , Gerald Schaefer , Mike Kravetz , Ingo Molnar , linux-snps-arc@lists.infradead.org, linux-mips@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-ia64@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org References: <69256008-2235-4AF1-A3BA-0146C82CCB93@lca.pw> <3cfec421-4006-4159-ca32-313ff5196ff9@c-s.fr> <763d58b4-f532-0bba-bf2b-71433ac514fb@arm.com> From: Christophe Leroy Message-ID: Date: Fri, 25 Oct 2019 10:52:54 +0200 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <763d58b4-f532-0bba-bf2b-71433ac514fb@arm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: fr Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Le 25/10/2019 à 10:24, Anshuman Khandual a écrit : > > > On 10/25/2019 12:41 PM, Christophe Leroy wrote: >> >> >> Le 25/10/2019 à 07:52, Qian Cai a écrit : >>> >>> >>>> On Oct 24, 2019, at 11:45 PM, Anshuman Khandual wrote: >>>> >>>> Nothing specific. But just tested this with x86 defconfig with relevant configs >>>> which are required for this test. Not sure if it involved W=1. >>> >>> No, it will not. It needs to run like, >>> >>> make W=1 -j 64 2>/tmp/warns >>> >> >> Are we talking about this peace of code ? >> >> +static unsigned long __init get_random_vaddr(void) >> +{ >> +    unsigned long random_vaddr, random_pages, total_user_pages; >> + >> +    total_user_pages = (TASK_SIZE - FIRST_USER_ADDRESS) / PAGE_SIZE; >> + >> +    random_pages = get_random_long() % total_user_pages; >> +    random_vaddr = FIRST_USER_ADDRESS + random_pages * PAGE_SIZE; >> + >> +    WARN_ON((random_vaddr > TASK_SIZE) || >> +        (random_vaddr < FIRST_USER_ADDRESS)); >> +    return random_vaddr; >> +} >> + >> >> ramdom_vaddr is unsigned, >> random_pages is unsigned and lower than total_user_pages >> >> So the max value random_vaddr can get is FIRST_USER_ADDRESS + ((TASK_SIZE - FIRST_USER_ADDRESS - 1) / PAGE_SIZE) * PAGE_SIZE = TASK_SIZE - 1 >> And the min value random_vaddr can get is FIRST_USER_ADDRESS (that's when random_pages = 0) > > That's right. > >> >> So the WARN_ON() is just unneeded, isn't it ? > > It is just a sanity check on possible vaddr values before it's corresponding > page table mappings could be created. If it's worth to drop this in favor of > avoiding these unwanted warning messages on x86, will go ahead with it as it > is not super important. > But you are checking what ? That the compiler does calculation correctly or what ? As mentionned just above, based on the calculation done, what you are testing cannot happen, so I'm having a hard time understanding what kind of sanity check it can be. Can you give an exemple of a situation which could trigger the warning ? Christophe