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=-3.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 35941C433B4 for ; Mon, 12 Apr 2021 19:23:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0D9E061355 for ; Mon, 12 Apr 2021 19:23:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237025AbhDLTXh (ORCPT ); Mon, 12 Apr 2021 15:23:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34768 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244830AbhDLTXh (ORCPT ); Mon, 12 Apr 2021 15:23:37 -0400 Received: from mail-ej1-x62b.google.com (mail-ej1-x62b.google.com [IPv6:2a00:1450:4864:20::62b]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BB042C061756 for ; Mon, 12 Apr 2021 12:23:18 -0700 (PDT) Received: by mail-ej1-x62b.google.com with SMTP id u17so22167374ejk.2 for ; Mon, 12 Apr 2021 12:23:18 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bgdev-pl.20150623.gappssmtp.com; s=20150623; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=mELRjVqp68r+toZVxtj/nROQLw+PqRw01stMy/JKAoI=; b=RuXsPBJDF3pxAI6ljG05ZKqt8YUmS44gosy5CljDMisMK7z6FRDFFa42SQlfxTeZcm pMmiFuREi/CsiEwh3n4f9myye40LULlH6dAutk4fRQm1YLoMfR/GWhHj3j8fvco171Qj WVEHi6qmZRdbLgD9XmwL0IDXk3XH1cq1hK5hcjIn+f0FIAUa0DRmEFHP7g2GxPzv8hdk kx1AbJe5MgMR8FvTP2jpZy9wdqlHQ7VB3+PRXr524woYvd0H0j+RLlzfJw4VtRrz/98Q Pr42+gOxdhKEqRz6dM8XW2MhQA7TutftrfPsfvndRojle93KrK94IGNUc0GTCkm1vYu3 XQ+Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=mELRjVqp68r+toZVxtj/nROQLw+PqRw01stMy/JKAoI=; b=Y4LyaMQWObd1qqIZSw/Qe9TaLtSQqJ/JM28mTlNGAZ6G8P8IkynAkxxVjmR+wAttc2 6YtuXbFlCzNXJCsO8RqW4v/+hCJkWoqxHA0SybTT5/f/NG6wpeZUuI90VOHdrUAPcDDU o5AY/1JvxGHV1I71fNbJI2nlqGUIkZlM/ZWvVp152iCt+NvEPf31ST0WZp7CA9ihgAUW sZI7DEkx7YA+3EIUabsUV9JR51KFixmIHA2V5MnwdiLDS4LnSDmjYWDduZfBGUp5L4uV /zLV6rv2fByRkTVZkBlu1ZyBWSXMkSKXhmRoHpdA3yVLvCZHxCJzqPc04cbdJRZfGkg6 8hpQ== X-Gm-Message-State: AOAM533vt7brUWTpnlKjCaFXO/kApQ4onOZMyV0EdkFtrWix9GD/zh0p KkxmXpKWQPXzxeL0lpSG+SkK4YotcbQXDESF5rw5uQ== X-Google-Smtp-Source: ABdhPJwXphtNs2B1kAW+Ay203fgklD+JVIJDuKSEoScP5GErDcEj86IB5CIU+IcorY4kTj6jGjHvAx5XiZS9A93+OEk= X-Received: by 2002:a17:906:1313:: with SMTP id w19mr12522249ejb.64.1618255397479; Mon, 12 Apr 2021 12:23:17 -0700 (PDT) MIME-Version: 1.0 References: <20200629065008.27620-1-brgl@bgdev.pl> <20200629065008.27620-5-brgl@bgdev.pl> In-Reply-To: From: Bartosz Golaszewski Date: Mon, 12 Apr 2021 21:23:06 +0200 Message-ID: Subject: Re: [PATCH v2 4/6] devres: handle zero size in devm_kmalloc() To: Dmitry Torokhov Cc: Jonathan Corbet , Greg Kroah-Hartman , "Rafael J . Wysocki" , Guenter Roeck , Jean Delvare , Linux Doc Mailing List , lkml , linux-hwmon@vger.kernel.org, Bartosz Golaszewski Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-hwmon@vger.kernel.org On Sun, Apr 11, 2021 at 5:21 AM Dmitry Torokhov wrote: > > Hi Bartosz, > > On Mon, Jun 29, 2020 at 1:56 PM Bartosz Golaszewski wrote: > > > > From: Bartosz Golaszewski > > > > Make devm_kmalloc() behave similarly to non-managed kmalloc(): return > > ZERO_SIZE_PTR when requested size is 0. Update devm_kfree() to handle > > this case. > > This is wrong if you consider devm_krealloc API that you added. The > premise of devm_krealloc() is that it does not disturb devres "stack", > however in this case there is no entry in the stack. Consider: > > ptr = devm_kzalloc(dev, 0, GFP_KERNEL); > ... > more devm API calls > ... > > /* This allocation will be on top of devm stack, not bottom ! */ > ptr = devm_krealloc(dev, ptr, 16, GFP_KERNEL); > > And also: > > ptr = devm_kzalloc(dev, 16, GFP_KERNEL); > ... > more devm API calls > ... > /* Here we lose out position */ > ptr = devm_krealloc(dev, ptr, 0, GFP_KERNEL); > ... > /* and now our memory allocation will be released first */ > ptr = devm_krealloc(dev, ptr, 16, GFP_KERNEL); > > > IMO special-casing 0-size allocations for managed memory allocations > should not be done. > > Thanks. > > -- > Dmitry You're right about the ordering being lost. At the same time allocating 0 bytes is quite a special case and should result in returning ZERO_SIZE_PTR as the fault dump resulting from its dereference will indicate what the bug is. I need to give it a thought because I'm not yet sure what the right solution would be. Let me get back to you. Bartosz