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=-11.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 1189FC433E2 for ; Fri, 10 Jul 2020 16:11:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E2A1F20720 for ; Fri, 10 Jul 2020 16:11:09 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=nvidia.com header.i=@nvidia.com header.b="NEduGS65" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726496AbgGJQLJ (ORCPT ); Fri, 10 Jul 2020 12:11:09 -0400 Received: from hqnvemgate24.nvidia.com ([216.228.121.143]:1586 "EHLO hqnvemgate24.nvidia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728053AbgGJQLH (ORCPT ); Fri, 10 Jul 2020 12:11:07 -0400 Received: from hqpgpgate101.nvidia.com (Not Verified[216.228.121.13]) by hqnvemgate24.nvidia.com (using TLS: TLSv1.2, DES-CBC3-SHA) id ; Fri, 10 Jul 2020 09:09:18 -0700 Received: from hqmail.nvidia.com ([172.20.161.6]) by hqpgpgate101.nvidia.com (PGP Universal service); Fri, 10 Jul 2020 09:11:07 -0700 X-PGP-Universal: processed; by hqpgpgate101.nvidia.com on Fri, 10 Jul 2020 09:11:07 -0700 Received: from [10.26.72.135] (10.124.1.5) by HQMAIL107.nvidia.com (172.20.187.13) with Microsoft SMTP Server (TLS) id 15.0.1473.3; Fri, 10 Jul 2020 16:11:05 +0000 Subject: Re: [PATCH v2 4/6] devres: handle zero size in devm_kmalloc() To: Bartosz Golaszewski CC: Jonathan Corbet , Greg Kroah-Hartman , "Rafael J . Wysocki" , Guenter Roeck , Jean Delvare , linux-doc , Linux Kernel Mailing List , , Bartosz Golaszewski References: <20200629065008.27620-1-brgl@bgdev.pl> <20200629065008.27620-5-brgl@bgdev.pl> <5c2e7514-b6d0-1331-37b0-d17a0cdb9693@nvidia.com> From: Jon Hunter Message-ID: <9cd4521b-aba0-616b-8957-8f21b9ba3068@nvidia.com> Date: Fri, 10 Jul 2020 17:11:02 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: X-Originating-IP: [10.124.1.5] X-ClientProxiedBy: HQMAIL101.nvidia.com (172.20.187.10) To HQMAIL107.nvidia.com (172.20.187.13) Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1; t=1594397358; bh=37GibReic1eAmzIGr99yNGskjoHn0RX7lIZ5PnIec+I=; h=X-PGP-Universal:Subject:To:CC:References:From:Message-ID:Date: User-Agent:MIME-Version:In-Reply-To:X-Originating-IP: X-ClientProxiedBy:Content-Type:Content-Language: Content-Transfer-Encoding; b=NEduGS65Web3MkJIb7aFBdcebALGdw9f8SNbQn89SQwXxg6rFVvt1dtEIopjfhNp1 R2EFGBmWotyKN+LYeWUHdJRp08cl8wcGz10W3MxIEjAJIMJ19chpkmhUnBADvJWH9I XCcH4rOx1K5tdDD4LKCvmgwqNeaM3HytP40kcyUOEBd/R3bbL3/G/jfyHr4sWUCFPU DKH1LjHNGWI/qGSnpLfK8NHoYUw2tg9zLxVwxQbPKu8PlVwi/0M79b0EV5GUGIaDPu 3j0RtWi8Q1oEUyijwNFyck25EVpQY/Zbjki5OKcETIK/Yjxb+u/t8DAYqAkFLAOsK6 so8qAfbpa6vQA== Sender: linux-hwmon-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-hwmon@vger.kernel.org On 10/07/2020 17:03, Bartosz Golaszewski wrote: > 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). Yes that's fine, I was just wondering if there is any reason not to WARN as well? Cheers Jon -- nvpublic