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=-3.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED 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 46161C43463 for ; Sat, 19 Sep 2020 03:37:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0202221D43 for ; Sat, 19 Sep 2020 03:37:08 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="NKq5xsKR" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726218AbgISDhI (ORCPT ); Fri, 18 Sep 2020 23:37:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35950 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726097AbgISDhH (ORCPT ); Fri, 18 Sep 2020 23:37:07 -0400 Received: from mail-qv1-xf41.google.com (mail-qv1-xf41.google.com [IPv6:2607:f8b0:4864:20::f41]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6E72AC0613CE for ; Fri, 18 Sep 2020 20:37:07 -0700 (PDT) Received: by mail-qv1-xf41.google.com with SMTP id z18so4096653qvp.6 for ; Fri, 18 Sep 2020 20:37:07 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:from:date:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=toq7L4SsqCXQkGluRvxqWyOqRcCx3zVe/9m6BQKiNj4=; b=NKq5xsKRFFkUHwl4DGXnrrp/G1OqQNLCxeoEYtd0u6KVQvJmo60LvKkqWkoHSPwTLn yoXHS+ZksyW9w16cWLkyQEfj2mXUgNvLBZKqwBMNgqve+HPqpOpMlDzoGY1755W2snyE uEJB2ArbcoEQNqUZ/2DLQ5c8nCp62P0YxMuC97EAt+ieVfbz4dgTAiU7jW1yZcWwTkB3 D5D20Q1EyxEpHzusUSIguH2YPeHLUTsB2i6cJOsIiwToNshBr1vfj2AYZb9y8Lo6kCrH W8UfBkshddz5zOINqaZSJOr7haVapA5LWMu+Kc70uES3L03qSJG4ZTqeuQUMwUBxXlJA m/Gg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:from:date:to:cc:subject:message-id :references:mime-version:content-disposition:in-reply-to; bh=toq7L4SsqCXQkGluRvxqWyOqRcCx3zVe/9m6BQKiNj4=; b=ctDkpa97oP02hm/EDGsU9HVajscn+TCJ9A1ze3S60Afid4ZqJiWdadPW3aSWkinKxb h8N7QZIDC3ezpZ1z29sI/BSK5gZxuPmT0Si1vaWJltGk+1vm6+z1fVbjrxBPV5e6u9Qp B+KtiCPX7KNcExjd6wn89O1MJBX5mtG5f7+oVh5qgZA8iNipMMMMFleTBpIvnlgmdA1A slT7CnJBshpCOhStD9ii1V1gt8MfSAlRFgG5x7U4OQWlqUI0bXtcfJ+D5IYbYEk1svZH 6ZKqkNIbLXhnN79yXxW7Ld774Rqk+RI2ZyCPpLEsSLI+19TUHqQ73MRQEApWrI48njxV 5xFg== X-Gm-Message-State: AOAM533oZRxA5Va1mI0a0mlvj+TpeZ/FeEB68qf1M5tl7r7drJlN4RVg f6ZsyhrEiBWytrcislzw6ws= X-Google-Smtp-Source: ABdhPJwEvd5oJAbcEssSmMyzVbLa0P+JOVCKw+dATnM3nOQC1r/DN9pd7rf1itdoheKAEa3WaO+1Ug== X-Received: by 2002:a05:6214:601:: with SMTP id z1mr36881818qvw.0.1600486626503; Fri, 18 Sep 2020 20:37:06 -0700 (PDT) Received: from rani.riverdale.lan ([2001:470:1f07:5f3::b55f]) by smtp.gmail.com with ESMTPSA id w194sm3400318qkb.130.2020.09.18.20.37.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 18 Sep 2020 20:37:05 -0700 (PDT) Sender: Arvind Sankar From: Arvind Sankar X-Google-Original-From: Arvind Sankar Date: Fri, 18 Sep 2020 23:37:04 -0400 To: Matthew Wilcox Cc: Arvind Sankar , Linus Torvalds , "Gustavo A. R. Silva" , Dennis Zhou , Tejun Heo , Christoph Lameter , Linux-MM , Linux Kernel Mailing List , Kees Cook Subject: Re: [GIT PULL] percpu fix for v5.9-rc6 Message-ID: <20200919033704.GA3014163@rani.riverdale.lan> References: <20200918193426.GA15213@embeddedor> <20200918200252.GH32101@casper.infradead.org> <20200918202909.GA2946008@rani.riverdale.lan> <20200918210050.GA2953017@rani.riverdale.lan> <20200918223957.GA2964553@rani.riverdale.lan> <20200919024556.GJ32101@casper.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20200919024556.GJ32101@casper.infradead.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Sep 19, 2020 at 03:45:56AM +0100, Matthew Wilcox wrote: > On Fri, Sep 18, 2020 at 06:39:57PM -0400, Arvind Sankar wrote: > > On Fri, Sep 18, 2020 at 02:18:20PM -0700, Linus Torvalds wrote: > > > On Fri, Sep 18, 2020 at 2:00 PM Arvind Sankar wrote: > > > > > > > > You could just assert that offsetof(typeof(s),flex) == sizeof(s), no? > > > > > > No, because the whole point is that I want that "sizeof(s)" to *WARN*. > > > > Ouch, offsetof() and sizeof() will give different results in the > > presence of alignment padding. > > > > https://godbolt.org/z/rqnxTK > > We really should be using offsetof() then. It's harmless because we're > currently overallocating, not underallocating. The test case I did was: > I wonder if there are cases where we know the total size, and are working out the number of elements in the flexible array by doing size - sizeof(s). Would a macro to do the inverse of struct_size(), i.e. get the count knowing the total size be useful?