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[23.128.96.18]) by mx.google.com with ESMTP id h16si10951902edj.301.2020.05.25.03.06.09; Mon, 25 May 2020 03:06:32 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; dkim=pass header.i=@web.de header.s=dbaedf251592 header.b=jYzGloPJ; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389734AbgEYKCI (ORCPT + 99 others); Mon, 25 May 2020 06:02:08 -0400 Received: from mout.web.de ([212.227.15.4]:33699 "EHLO mout.web.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389407AbgEYKCI (ORCPT ); Mon, 25 May 2020 06:02:08 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=web.de; s=dbaedf251592; t=1590400920; bh=I4AC220AsvLo1AfbrJuiQXJY0TZLYS/i5UQOwj/yE4M=; h=X-UI-Sender-Class:Subject:To:Cc:References:From:Date:In-Reply-To; b=jYzGloPJe0SLYyvc21IyK/j1R07xIoVZaIrHmbhPjsjE2kUBWaQID2HIqIuPsiIvz zwKcPGiI1WmrytKo24kLYhyyVsoCY/3Zzhv4TV30n3ZE6KOpsXOugPQKu/B1Nop9Mx 6cP+lnZXLCD4zB7QibuWigfsB/21Y6FbvO0+77jA= X-UI-Sender-Class: c548c8c5-30a9-4db5-a2e7-cb6cb037b8f9 Received: from [192.168.1.2] ([93.135.186.124]) by smtp.web.de (mrweb003 [213.165.67.108]) with ESMTPSA (Nemesis) id 0LbIyo-1j9uj40lC6-00l0A9; Mon, 25 May 2020 12:02:00 +0200 Subject: Re: [PATCH v3] workqueue: Fix double kfree for rescuer To: Zhang Qiang , Tejun Heo , Lai Jiangshan Cc: linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org References: <20200525093019.2253-1-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: <167233e4-a389-5627-f5ad-3b21f337b7f7@web.de> Date: Mon, 25 May 2020 12:01:59 +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: <20200525093019.2253-1-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:Md1GAGRj5JlDBAaAHiwR+oAh5JkziCypIQq+EnLN2dpoeE9fwm4 QVIsndg/vPBuZuZ6s01tF96ETSdDEKE8oQwDGwPqHrlCEksyPhr72VZDoGGL7W//ZBoKjQw t+6szl5+PVaCvAou4e29X3sxkM9h3x2lebGF7HssrTbi2tWctUIzLd1IJpogehixu0AaFi6 rISwGnm0amRGGOZzxgfrg== X-Spam-Flag: NO X-UI-Out-Filterresults: notjunk:1;V03:K0:aA0XnEizI0o=:uIqUbdqHg21MGNe/wqpXXl 970o1Nva8oAyBpP742uVFfEcONUE0jmGQO1UydyPXXTZtuUfet0Z2F8bbUgmr+l2XKnCQvhCs fpwPtHAvtYvESzW8X1daKghQ62Sp3wO3XLX8uSg25+ZnoIk3HbluR3HIHlvnLHECHvtXZo8Ut AhGfiea4vxXqgPrBtHzJOiIGHmgK1oNXt9iVI93CCob6vTrzTtoO6kqpaAuTU7XxhGU9IPP7h Fbyt7UsTNEmJBZ0lMaNWEXHwr4zpqG9LmpGFiCb5d689Q/93KRms+OQP1gKXNiGNfYn6mqD66 SgynYekYDLAOnvb6dzdHzQM6XvcOXlvS9WvjJzd6ZW+UiMpSJhSfBvXVb5voycY5Tvzm2yZNx zeYryRgrFdnKWjO+PDmJG/LkvwiQv6pigtwbkmbpKVoXDmRrAYcW9Qe1U8jAZmXBGu/rjJ0LD ctKGaSfoAxrLduVnA1veO4+hO8jTvM0fvGZiiZZdr9jLN5TU7SCha28140Lp1bE1lqUFaqD3v 52tlPrZsS1nAtXPrrK68fuabvftDYMBdKfEqCI+ljsx+ryyQNvig+bgLFfce14PYBKjgmIla3 e1ZrEbuDDM385P6d3OZLNZcWOYo5gb6uso4s6xNTU12NXoce507MkCaYKZ03I9j+SacaCIo8c QpBP03JEFs2QNEeh06nq0zhs3XHX+coHXzONYJQUB3fOWz7NM9IOdLogdfD2HDmACscz5kLDR T24zHsmCUCQIvTAQmW275zU8mIt4Zvrq2Xh4P1Rmb+pc3KH/iiU0zHaPuFiwc9Y5Ejh8OuwEH YWl308dmQfSs56sNliNrbc19VS0zjtotzDIQp+SCgV3iy/zqodjR0zE/psbc0Cgq8pxv4dHqu u9aB+t4Kz0F+GrMXCxQw//NHhIvL62wR5v2aU7tvoManqbzTnCCK/OPyg1RlhSaTqMVLMjWHH WoL426u3GqD+P3NY8Ttl9cVplXYlji88oCwMHf1h4nWXJYWXGiALul/sVHA/dNMrXaZ3qa89Z FDNVw55WC3BJmGjZdo8MU/GZLsrQdLW1h1X0m6K0gOuxakGTu4GEm6sglOf4pmVGyg0ptcZcg jrMhe18Z/tGE3/fULCj5LIxTAsfFEYPq7/NsXOzHbVTl3WpOgGTjOyNSNEhCpjaTXc7Hxt0eu Gr1RPDIHof7YES5898b3e5aO5xtUW59DYrZ5bCFZDJToJRCLlbRtlpjVJsLhST1FEXyv7ocCk OtKpjhFtd4bBRh6mY 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 "rescuer" already, Thus delete a misplaced call > of the function "kfree". I got into the mood to follow your interpretation of the software situation for a moment. I have taken another look also at the implementation of the function =E2= =80=9Cdestroy_workqueue=E2=80=9D. * The function call =E2=80=9Ckfree(rescuer)=E2=80=9D can be performed ther= e in an if branch after the statement =E2=80=9Cwq->rescuer =3D NULL=E2=80=9D was executed. * This data processing is independent from a possible call of the function =E2=80=9Ccall_rcu(&wq->rcu, rcu_free_wq)=E2=80=9D in another if= branch. Thus it seems that a null pointer is intentionally passed by a data stru= cture member to this callback function on demand. The corresponding call of the function =E2=80=9Ckfree=E2=80=9D can toler= ate this special case. Now I find that the proposed change can be inappropriate. I'm sorry for undesirable confusion because of this patch review. Regards, Markus