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=-9.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 D9324C433EB for ; Fri, 10 Jul 2020 16:03:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B276F2078D for ; Fri, 10 Jul 2020 16:03:48 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=bgdev-pl.20150623.gappssmtp.com header.i=@bgdev-pl.20150623.gappssmtp.com header.b="rC2SRyrv" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727074AbgGJQDs (ORCPT ); Fri, 10 Jul 2020 12:03:48 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58552 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728054AbgGJQDs (ORCPT ); Fri, 10 Jul 2020 12:03:48 -0400 Received: from mail-il1-x144.google.com (mail-il1-x144.google.com [IPv6:2607:f8b0:4864:20::144]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E3B85C08C5CE for ; Fri, 10 Jul 2020 09:03:47 -0700 (PDT) Received: by mail-il1-x144.google.com with SMTP id a6so5459124ilq.13 for ; Fri, 10 Jul 2020 09:03:47 -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=DwtRvDT0fE9SjkvKFymZ3wwQRafCOuOpn69akOKMWQE=; b=rC2SRyrvMhIqnaNEsdXH5dHqfT6I0Fuwc568Cha7qAdneSqu12N31FFgng14p8uxuB jlj2/ZGgm/bYyXy7Hz7nI26zEt2sDofDxXAG3jos70408S0G57lEX/ZaeqjXvIm/4cgt QeglSiUjQy+zIx4ufn9EOyLd5ZEBM7DeasQuMKSJNRa/6EcM0fdTO9sItI7rJd0fM36D hUVVgClmAD3jrcPBlHaZe/fkC0/Eg2xyKrAnzVnawwvZDHfZV0HEwOxlj6it4hqx8U07 6g3QeJDSC2DokCFhYD7mNPEO3ID7zFws8xnzwghBPaeXvOUSqZscTV7feBTwAIPbpURl S/Mw== 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=DwtRvDT0fE9SjkvKFymZ3wwQRafCOuOpn69akOKMWQE=; b=ObKWNjbANaY6sMXl2bboxvEQ5s36qrVGfpP5iKcgTwbM4C5MaEQjL+ALjbC8CuKDwm Hdui/sc6okHhZsxgu/0W1P5l2WJKWtHJJocJZlbJaxTyhpfXEIwKpv4NvaIDess7gfKO uYoba4FrWTHG+43EJdb2nQASU7I1Sj2AvPyDdKM84JVUyBEuMMuRZewL5zDoCGYSSZIl omEAfvU2GVl+ar2GYwiuN1/hzsc4r2NlYtFUS4Hj9oUkz2WhlQDWS08HJZUvUexO5AGn 9VfPBKnv2JErxS0c5fK/mL255rQGbIr4H8PRJTV5EUPHOcwNFOF9cVPgChU8eOI2cF/t WZSA== X-Gm-Message-State: AOAM531l39FFOtQBHgg9v1qYdZTitSyB0TRA5QwD5rb1O+qis6OiUt0M gPlyFYeT7GeWrBWZZNlp3YYXSvw82jA9e/HxTHUpCg== X-Google-Smtp-Source: ABdhPJwJAZ3yGKN0TblyVdcj96DstgCQb3QGd8g40AV18tjNeGW87g9bMbpwM+p7vqduY14vMiQCR/PrO6n5L+J8oBE= X-Received: by 2002:a92:d64d:: with SMTP id x13mr52571706ilp.287.1594397027320; Fri, 10 Jul 2020 09:03:47 -0700 (PDT) MIME-Version: 1.0 References: <20200629065008.27620-1-brgl@bgdev.pl> <20200629065008.27620-5-brgl@bgdev.pl> <5c2e7514-b6d0-1331-37b0-d17a0cdb9693@nvidia.com> In-Reply-To: <5c2e7514-b6d0-1331-37b0-d17a0cdb9693@nvidia.com> From: Bartosz Golaszewski Date: Fri, 10 Jul 2020 18:03:36 +0200 Message-ID: Subject: Re: [PATCH v2 4/6] devres: handle zero size in devm_kmalloc() To: Jon Hunter Cc: Jonathan Corbet , Greg Kroah-Hartman , "Rafael J . Wysocki" , Guenter Roeck , Jean Delvare , linux-doc , Linux Kernel Mailing List , linux-hwmon@vger.kernel.org, Bartosz Golaszewski Content-Type: text/plain; charset="UTF-8" Sender: linux-hwmon-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-hwmon@vger.kernel.org On Fri, Jul 10, 2020 at 3:46 PM Jon Hunter wrote: > > Hi Bartosz, > > On 29/06/2020 07:50, 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. > > > > Signed-off-by: Bartosz Golaszewski > > --- > > drivers/base/devres.c | 9 ++++++--- > > 1 file changed, 6 insertions(+), 3 deletions(-) > > > > diff --git a/drivers/base/devres.c b/drivers/base/devres.c > > index 1df1fb10b2d9..ed615d3b9cf1 100644 > > --- a/drivers/base/devres.c > > +++ b/drivers/base/devres.c > > @@ -819,6 +819,9 @@ void *devm_kmalloc(struct device *dev, size_t size, gfp_t gfp) > > { > > struct devres *dr; > > > > + if (unlikely(!size)) > > + return ZERO_SIZE_PTR; > > + > > /* use raw alloc_dr for kmalloc caller tracing */ > > dr = alloc_dr(devm_kmalloc_release, size, gfp, dev_to_node(dev)); > > if (unlikely(!dr)) > > @@ -950,10 +953,10 @@ void devm_kfree(struct device *dev, const void *p) > > int rc; > > > > /* > > - * Special case: pointer to a string in .rodata returned by > > - * devm_kstrdup_const(). > > + * Special cases: pointer to a string in .rodata returned by > > + * devm_kstrdup_const() or NULL/ZERO ptr. > > */ > > - if (unlikely(is_kernel_rodata((unsigned long)p))) > > + if (unlikely(is_kernel_rodata((unsigned long)p) || ZERO_OR_NULL_PTR(p))) > > return; > > > > rc = devres_destroy(dev, devm_kmalloc_release, > > > This change caught a bug in one of our Tegra drivers, which I am in the > process of fixing. Once I bisected to this commit it was easy to track > down, but I am wondering if there is any reason why we don't add a > WARN_ON() if size is 0 in devm_kmalloc? It was essentially what I ended > up doing to find the bug. > > Jon > > -- > nvpublic Hi Jon, this is in line with what the regular kmalloc() does. If size is zero, it returns ZERO_SIZE_PTR. It's not an error condition. Actually in user-space malloc() does a similar thing: for size == 0 it allocates one-byte and returns a pointer to it (at least in glibc). Bartosz