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=-2.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 00835C433E0 for ; Wed, 27 May 2020 06:40:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C9F8420721 for ; Wed, 27 May 2020 06:40:25 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=web.de header.i=@web.de header.b="A3QcH1cp" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728514AbgE0GkZ (ORCPT ); Wed, 27 May 2020 02:40:25 -0400 Received: from mout.web.de ([212.227.15.4]:37985 "EHLO mout.web.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725613AbgE0GkX (ORCPT ); Wed, 27 May 2020 02:40:23 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=web.de; s=dbaedf251592; t=1590561613; bh=mfI2hFQ52IXtARQa6rbm4h5ZXG+Qg/KVDv0kdctt7Q8=; h=X-UI-Sender-Class:Subject:To:Cc:References:From:Date:In-Reply-To; b=A3QcH1cpI3UOrlNshLuZl5EnEOgCbR5NVHZ9RB6HxTCwsmEGxUp+3Mm9bweod/5vB 5l8eJrVnj3eCIt5R54IaBCGK0yb8EeW65YxXSGCCO2gEWPSzy2ZCV5vSF9mfq0ztgT ht9djQDS7EeKLCEvU3bANyWxZI4mZC99i3+Pm544= X-UI-Sender-Class: c548c8c5-30a9-4db5-a2e7-cb6cb037b8f9 Received: from [192.168.1.2] ([93.135.185.253]) by smtp.web.de (mrweb001 [213.165.67.108]) with ESMTPSA (Nemesis) id 0MRl2f-1jTCbs281R-00SzHI; Wed, 27 May 2020 08:40:13 +0200 Subject: Re: [PATCH v4] workqueue: Remove unnecessary kfree() call in rcu_free_wq() To: Zhang Qiang , Tejun Heo , Lai Jiangshan Cc: linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org References: <20200527015054.34796-1-qiang.zhang@windriver.com> From: Markus Elfring Autocrypt: addr=Markus.Elfring@web.de; prefer-encrypt=mutual; keydata= mQINBFg2+xABEADBJW2hoUoFXVFWTeKbqqif8VjszdMkriilx90WB5c0ddWQX14h6w5bT/A8 +v43YoGpDNyhgA0w9CEhuwfZrE91GocMtjLO67TAc2i2nxMc/FJRDI0OemO4VJ9RwID6ltwt mpVJgXGKkNJ1ey+QOXouzlErVvE2fRh+KXXN1Q7fSmTJlAW9XJYHS3BDHb0uRpymRSX3O+E2 lA87C7R8qAigPDZi6Z7UmwIA83ZMKXQ5stA0lhPyYgQcM7fh7V4ZYhnR0I5/qkUoxKpqaYLp YHBczVP+Zx/zHOM0KQphOMbU7X3c1pmMruoe6ti9uZzqZSLsF+NKXFEPBS665tQr66HJvZvY GMDlntZFAZ6xQvCC1r3MGoxEC1tuEa24vPCC9RZ9wk2sY5Csbva0WwYv3WKRZZBv8eIhGMxs rcpeGShRFyZ/0BYO53wZAPV1pEhGLLxd8eLN/nEWjJE0ejakPC1H/mt5F+yQBJAzz9JzbToU 5jKLu0SugNI18MspJut8AiA1M44CIWrNHXvWsQ+nnBKHDHHYZu7MoXlOmB32ndsfPthR3GSv jN7YD4Ad724H8fhRijmC1+RpuSce7w2JLj5cYj4MlccmNb8YUxsE8brY2WkXQYS8Ivse39MX BE66MQN0r5DQ6oqgoJ4gHIVBUv/ZwgcmUNS5gQkNCFA0dWXznQARAQABtCZNYXJrdXMgRWxm cmluZyA8TWFya3VzLkVsZnJpbmdAd2ViLmRlPokCVAQTAQgAPhYhBHDP0hzibeXjwQ/ITuU9 Figxg9azBQJYNvsQAhsjBQkJZgGABQsJCAcCBhUICQoLAgQWAgMBAh4BAheAAAoJEOU9Figx g9azcyMP/iVihZkZ4VyH3/wlV3nRiXvSreqg+pGPI3c8J6DjP9zvz7QHN35zWM++1yNek7Ar OVXwuKBo18ASlYzZPTFJZwQQdkZSV+atwIzG3US50ZZ4p7VyUuDuQQVVqFlaf6qZOkwHSnk+ CeGxlDz1POSHY17VbJG2CzPuqMfgBtqIU1dODFLpFq4oIAwEOG6fxRa59qbsTLXxyw+PzRaR LIjVOit28raM83Efk07JKow8URb4u1n7k9RGAcnsM5/WMLRbDYjWTx0lJ2WO9zYwPgRykhn2 sOyJVXk9xVESGTwEPbTtfHM+4x0n0gC6GzfTMvwvZ9G6xoM0S4/+lgbaaa9t5tT/PrsvJiob kfqDrPbmSwr2G5mHnSM9M7B+w8odjmQFOwAjfcxoVIHxC4Cl/GAAKsX3KNKTspCHR0Yag78w i8duH/eEd4tB8twcqCi3aCgWoIrhjNS0myusmuA89kAWFFW5z26qNCOefovCx8drdMXQfMYv g5lRk821ZCNBosfRUvcMXoY6lTwHLIDrEfkJQtjxfdTlWQdwr0mM5ye7vd83AManSQwutgpI q+wE8CNY2VN9xAlE7OhcmWXlnAw3MJLW863SXdGlnkA3N+U4BoKQSIToGuXARQ14IMNvfeKX NphLPpUUnUNdfxAHu/S3tPTc/E/oePbHo794dnEm57LuuQINBFg2+xABEADZg/T+4o5qj4cw nd0G5pFy7ACxk28mSrLuva9tyzqPgRZ2bdPiwNXJUvBg1es2u81urekeUvGvnERB/TKekp25 4wU3I2lEhIXj5NVdLc6eU5czZQs4YEZbu1U5iqhhZmKhlLrhLlZv2whLOXRlLwi4jAzXIZAu 76mT813jbczl2dwxFxcT8XRzk9+dwzNTdOg75683uinMgskiiul+dzd6sumdOhRZR7YBT+xC wzfykOgBKnzfFscMwKR0iuHNB+VdEnZw80XGZi4N1ku81DHxmo2HG3icg7CwO1ih2jx8ik0r riIyMhJrTXgR1hF6kQnX7p2mXe6K0s8tQFK0ZZmYpZuGYYsV05OvU8yqrRVL/GYvy4Xgplm3 DuMuC7/A9/BfmxZVEPAS1gW6QQ8vSO4zf60zREKoSNYeiv+tURM2KOEj8tCMZN3k3sNASfoG fMvTvOjT0yzMbJsI1jwLwy5uA2JVdSLoWzBD8awZ2X/eCU9YDZeGuWmxzIHvkuMj8FfX8cK/ 2m437UA877eqmcgiEy/3B7XeHUipOL83gjfq4ETzVmxVswkVvZvR6j2blQVr+MhCZPq83Ota xNB7QptPxJuNRZ49gtT6uQkyGI+2daXqkj/Mot5tKxNKtM1Vbr/3b+AEMA7qLz7QjhgGJcie qp4b0gELjY1Oe9dBAXMiDwARAQABiQI8BBgBCAAmFiEEcM/SHOJt5ePBD8hO5T0WKDGD1rMF Alg2+xACGwwFCQlmAYAACgkQ5T0WKDGD1rOYSw/+P6fYSZjTJDAl9XNfXRjRRyJSfaw6N1pA Ahuu0MIa3djFRuFCrAHUaaFZf5V2iW5xhGnrhDwE1Ksf7tlstSne/G0a+Ef7vhUyeTn6U/0m +/BrsCsBUXhqeNuraGUtaleatQijXfuemUwgB+mE3B0SobE601XLo6MYIhPh8MG32MKO5kOY hB5jzyor7WoN3ETVNQoGgMzPVWIRElwpcXr+yGoTLAOpG7nkAUBBj9n9TPpSdt/npfok9ZfL /Q+ranrxb2Cy4tvOPxeVfR58XveX85ICrW9VHPVq9sJf/a24bMm6+qEg1V/G7u/AM3fM8U2m tdrTqOrfxklZ7beppGKzC1/WLrcr072vrdiN0icyOHQlfWmaPv0pUnW3AwtiMYngT96BevfA qlwaymjPTvH+cTXScnbydfOQW8220JQwykUe+sHRZfAF5TS2YCkQvsyf7vIpSqo/ttDk4+xc Z/wsLiWTgKlih2QYULvW61XU+mWsK8+ZlYUrRMpkauN4CJ5yTpvp+Orcz5KixHQmc5tbkLWf x0n1QFc1xxJhbzN+r9djSGGN/5IBDfUqSANC8cWzHpWaHmSuU3JSAMB/N+yQjIad2ztTckZY pwT6oxng29LzZspTYUEzMz3wK2jQHw+U66qBFk8whA7B2uAU1QdGyPgahLYSOa4XAEGb6wbI FEE= Message-ID: <067566d5-9392-c155-fb8e-f2662fb5f60f@web.de> Date: Wed, 27 May 2020 08:40:12 +0200 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: <20200527015054.34796-1-qiang.zhang@windriver.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: quoted-printable X-Provags-ID: V03:K1:mkKZNRBgSgIeD86dJGArPlxO9RkBDSPymeUmxAPqA88QollIOUi 9cLWAmWYa0hZZzkbtnOEi0tPJrcPKRtXUxWVjH1PCVbcpe+n20ykqJEE/hnYBEiVNUjvRFj wg+2DznCQDfEJKDTFY26/Yg/7kpF/DUUPlYSyf2OsBw5CsZAWrrQHz/duKMQuv5iZ5oQ9GK +UzoG4TiSqFDqmncKZl1A== X-UI-Out-Filterresults: notjunk:1;V03:K0:qXYxUwt3wCM=:PfzgaYyZGNxv9+YCr9OBH9 92GZX2OV3GscVsB0lIWTn9Twqx0sDZp7HBviMutkgG6ewtXG2IjsoktNkd0jv3/++iCF9zlRB rH+jLF0eVOE/H/oAd4b21Cf1DIEHGtVkUK3nc63Ix8c3HUI3C29BKRzzEc/yl/t1Q5i6KSxp5 4uNM/GY7WkhWrTEwJBRkdopZRwT1za4GKrMMEOqR4Fu6M1TpuIEs1yw8CvhdWfY4vb9WuvQEM XgRuOSPOI381qekenTBNtVLAzaPwVyLzUfQ/XddPKtAGDfIFxRYZP5WReNf28CB3mJwT/NwB3 E6lYHevD4YxX0F2/YQpUIxAMRhh2dYuvhGsj91QkEdgXcM+oTKIbPWgSNJvnBoEdcyyBbFqbM Y/gNRDZtMq2x/xOTjEKZ13RWtTr7evzOJzSFMTxsgqbt4NKaZIjBv2Ky1gTEaMlAmwbXGaxLJ 1P273VCpKpiZ8/goldpeOG46kmfLB6Z1m4vvPbnnULMoxOW+uzvpZJ9/7ARK6mrsM9mXFYvWB rXjUfwN4F8D3YoEk+4cTuPJh+vKNQaL9GFB/E10rOBRcoXhpzuF3sbMzCUHblL6NRrhONoWfa 6QKiYAYzN6e4DGjkvh1gW0OlZ7HyhxitZDaUsOaZti4spRIrLEvJPkFItoOTBCaG7MT0/FTWW 3J5bdt0dwQCtjZSpMzNGxTdVCc+12D0yjXyqu/RvZ4JQW01nw0Ns+JL70aqdiqoeb9JhenMQD XONGWy0+BOjvkfXuxBwnlrq45RZXRdtyE9uaUIDGT5qV3QNdGW2ufX2uNX32KaHO7B6YAq7SI 9ricrEVb0jLM00T/QSPT5x9s9d434AABj7ACTqWYlV69m3ZWPCTKk998z3XyQQXy53Yxp/+3I BQa0907b6Vtm/voVApMNeTxxJXEVFbpYgW9O6uSzc40Z66GzRJaMKGniysBhB7MJP2msQA27M uXpaOx0uB0MZOGCBeacgwxlHvlnU4v1fvPyF1E1/YTX67jGI9kU9VpzdkkiCSeFNAxnmEwwut pdawq9O9a+I7Qq0LkB8uWfeWFMrmsGhO8D4/6o4qCBmyZdsxKRcqHP/KZ36CPddhCAI+X6YBt UvuzQkYtN9eZKyF98g0kz37rpLFWWRVFdwFfU/4H4B2YC43QH1kZmdWnfVGNHtYlioqxFMfYL 7Mcu0g5Hy8bKviG1sy8PIn0Pxm/Zje2TDEbJLRxyh11Bq69ZwZBLRPAnnU1OdDEMQ8cYLNRk8 aFEQAa1Bi2KTsN/Uw Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > The callback function "rcu_free_wq" could be called after memory > was released for "wq->rescuer" already and assignment is empty. so > remove unnecessary kfree(NULL). I have got the impression that also this wording approach contains weaknes= ses. How do you think about a wording variant like the following? The data structure member =E2=80=9Cwq->rescuer=E2=80=9D was reset to a = null pointer in one if branch. It was passed to a call of the function =E2=80=9Ckfre= e=E2=80=9D in the callback function =E2=80=9Crcu_free_wq=E2=80=9D (which was event= ually executed). The function =E2=80=9Ckfree=E2=80=9D does not perform more meaningful d= ata processing for a passed null pointer (besides immediately returning from such a ca= ll). Thus delete this function call which became unnecessary with the refere= nced software update. > Fixes: def98c84b6cd ("workqueue: Fix spurious sanity check failures in d= estroy_workqueue()") This change triggered another collateral evolution finally. Would you like to detect similarly questionable function calls by advanced source code analysis? > Fixes: 8efe1223d73c ("workqueue: Fix missing kfree(rescuer) in destroy_w= orkqueue()") Please delete this tag from the change description (because I find that it is not so relevant here.) > v1->v2->v3->v4: > Modify wrong submission information. Will it be nicer to mention the adjustment of the commit message? Regards, Markus