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=-2.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, 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 9779BC433ED for ; Sun, 11 Apr 2021 03:21:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 63939610CF for ; Sun, 11 Apr 2021 03:21:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235074AbhDKDVp (ORCPT ); Sat, 10 Apr 2021 23:21:45 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51682 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234950AbhDKDVo (ORCPT ); Sat, 10 Apr 2021 23:21:44 -0400 Received: from mail-pg1-x534.google.com (mail-pg1-x534.google.com [IPv6:2607:f8b0:4864:20::534]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A3403C06138B; Sat, 10 Apr 2021 20:21:28 -0700 (PDT) Received: by mail-pg1-x534.google.com with SMTP id q10so6766130pgj.2; Sat, 10 Apr 2021 20:21:28 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=qlSJc4t6k90L7rQgXSXEIV+HoVoS9K7iCRrH/b5iwoc=; b=kQOKCmXxKQW40XZNABhPOEFiB9swRFOF1apgrL3GdicdZPT7ZUsh9L2b26Aqtd1CR9 6doqqA0afq4I2dZattSVzVYR7JgfGQv6ulGYxqYKVVDqOw0L5hzLMqi7sbxbW5bVmqCl A3OSM44MEN39B0ihmy5nfs60pxI64cqIUAeI0tYC/b7zdzPP1YxzBmVojhraKaCHorW6 SlyFDkIZB4ptDv1jAIWTlwsyjhFAls9+bv8pZA314nyK9uLHRl5vRBdU1BgR7hrmpGTb gKz17uX5KM/NjPe8bon2t3e+P0VSP5gmbp4X9oE6JG3mJX/kHkJtb//ijHnD7nT2bFFj Nu3g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=qlSJc4t6k90L7rQgXSXEIV+HoVoS9K7iCRrH/b5iwoc=; b=aH5+Ox34ne7BBqczrIrL0FiuLtJQNFZWLWD2kuWIN0GHKxCSpFoOhIU40VbLcDpbRf hcU3GtvB+/aUP9G2xTiFp4IyFFZhqP7+6obkkdiaAUkOG5MkcZdMqe8LAZqkT7epbsEO LBQmZzYOIzKUcWDdWaPEfF4ScywjelsPfLFuDwOMC3Gq/jcIYhxa6ZXvvbrstdlalaIH f4gAG6pIuoE5D2/EGudrDF/pTzWa0Q4iCYAuVH8BgxVSrxRedCSWztH/apptABYnsugV shDoN7VuxqZ32N9AT3N7OI0Vk+1WuPs65HF8vo3DFA+hOpUxQC+RJnvevjz2nMempbVJ zjtQ== X-Gm-Message-State: AOAM533VWlPekgm2Zo4REg9wal1v8KdRKbLZKWVVxIcRv+7H/GiMakrU mR5qRHZZr7EvB/8/WYx72ro= X-Google-Smtp-Source: ABdhPJy5kyvV279co0pNS7BO6amqd9zlv1DLLe/ioBFUSVUwvKOFTiapaYad9fnr9QKhGU7Ks6kMRA== X-Received: by 2002:a63:cb44:: with SMTP id m4mr20435373pgi.4.1618111287958; Sat, 10 Apr 2021 20:21:27 -0700 (PDT) Received: from google.com ([2620:15c:202:201:a9b4:ff60:6655:5c5f]) by smtp.gmail.com with ESMTPSA id t184sm6768597pgt.32.2021.04.10.20.21.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 10 Apr 2021 20:21:27 -0700 (PDT) Date: Sat, 10 Apr 2021 20:21:24 -0700 From: Dmitry Torokhov To: Bartosz Golaszewski 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 Subject: Re: [PATCH v2 4/6] devres: handle zero size in devm_kmalloc() Message-ID: References: <20200629065008.27620-1-brgl@bgdev.pl> <20200629065008.27620-5-brgl@bgdev.pl> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200629065008.27620-5-brgl@bgdev.pl> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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