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=-10.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 CF7A1C4361B for ; Thu, 10 Dec 2020 12:24:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A0B6B23C44 for ; Thu, 10 Dec 2020 12:24:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728455AbgLJMYQ (ORCPT ); Thu, 10 Dec 2020 07:24:16 -0500 Received: from frasgout.his.huawei.com ([185.176.79.56]:2241 "EHLO frasgout.his.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729976AbgLJMX5 (ORCPT ); Thu, 10 Dec 2020 07:23:57 -0500 Received: from fraeml739-chm.china.huawei.com (unknown [172.18.147.206]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4CsCfD3BjJz67NBM; Thu, 10 Dec 2020 20:19:48 +0800 (CST) Received: from lhreml724-chm.china.huawei.com (10.201.108.75) by fraeml739-chm.china.huawei.com (10.206.15.220) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2106.2; Thu, 10 Dec 2020 13:23:11 +0100 Received: from [10.210.172.228] (10.210.172.228) by lhreml724-chm.china.huawei.com (10.201.108.75) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2106.2; Thu, 10 Dec 2020 12:23:09 +0000 Subject: Re: [RFC PATCH] blk-mq: Clean up references when freeing rqs From: John Garry To: Ming Lei CC: , , , , , , , References: <1606827738-238646-1-git-send-email-john.garry@huawei.com> <20201202033134.GD494805@T590> <20201203005505.GB540033@T590> <7beb86a2-5c4b-bdc0-9fce-1b583548c6d0@huawei.com> <20201209010102.GA1217988@T590> <13327a68-6f86-96da-0c5f-5fa0be326d6f@huawei.com> <20201210020745.GA1363446@T590> Message-ID: <76190c94-c5c1-9553-5509-9969fc323544@huawei.com> Date: Thu, 10 Dec 2020 12:22:35 +0000 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.1.2 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.210.172.228] X-ClientProxiedBy: lhreml729-chm.china.huawei.com (10.201.108.80) To lhreml724-chm.china.huawei.com (10.201.108.75) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Ming, > > So I'll try an experiment today to prove your concern about > blk_mq_queue_tag_busy_iter(). Then look at possible solution which > builds on patch in $subject, and compare. JFYI, I was able to trigger this: [ 1651.324150] ================================================================== [ 1651.331400] BUG: KASAN: use-after-free in bt_iter+0xa0/0x120 [ 1651.337054] Read of size 8 at addr ffff00108d589300 by task fio/3052 [ 1651.344891] CPU: 32 PID: 3052 Comm: fio Tainted: GW 5.10.0-rc4-64839-g2dcf1ee5054f #693 [ 1651.354281] Hardware name: Huawei Taishan 2280 /D05, BIOS Hisilicon D05 IT21 Nemo 2.0 RC0 04/18/2018 [ 1651.363407] Call trace: [ 1651.365861] dump_backtrace+0x0/0x2d0 [ 1651.369519] show_stack+0x18/0x68 [ 1651.372833] dump_stack+0x100/0x16c [ 1651.376316] print_address_description.constprop.12+0x6c/0x4e8 [ 1651.382146] kasan_report+0x130/0x200 [ 1651.385801] __asan_load8+0x9c/0xd8 [ 1651.389284] bt_iter+0xa0/0x120 [ 1651.392419] blk_mq_queue_tag_busy_iter+0x2d8/0x540 [ 1651.397293] blk_mq_in_flight+0x80/0xb8 [ 1651.401121] part_stat_show+0xd8/0x238 [ 1651.404867] dev_attr_show+0x44/0x90 [ 1651.408439] sysfs_kf_seq_show+0x128/0x1c8 [ 1651.412530] kernfs_seq_show+0xa0/0xb8 [ 1651.416274] seq_read_iter+0x1ec/0x6a0 [ 1651.420019] seq_read+0x1d0/0x250 [ 1651.423331] kernfs_fop_read+0x70/0x330 [ 1651.427161] vfs_read+0xe4/0x250 [ 1651.430382] ksys_read+0xc8/0x178 [ 1651.433690] __arm64_sys_read+0x44/0x58 [ 1651.437524] el0_svc_common.constprop.2+0xc4/0x1e8 [ 1651.442309] do_el0_svc+0x90/0xa0 [ 1651.445619] el0_sync_handler+0x128/0x178 [ 1651.449623] el0_sync+0x158/0x180 [ 1651.454418] The buggy address belongs to the page: [ 1651.459208] page:00000000140c0813 refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x108d589 [ 1651.468683] flags: 0xbfffc0000000000() [ 1651.472432] raw: 0bfffc0000000000 0000000000000000 ffffffff42150201 0000000000000000 [ 1651.480173] raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000 [ 1651.487909] page dumped because: kasan: bad access detected [ 1651.494956] Memory state around the buggy address: [ 1651.499744] ffff00108d589200: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff [ 1651.506960] ffff00108d589280: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff [ 1651.514176] >ffff00108d589300: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff [ 1651.521389] ^ [ 1651.524611] ffff00108d589380: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff [ 1651.531827] ffff00108d589400: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff [ 1651.539044] ================================================================== [ 1651.546258] Disabling lock debugging due to kernel taint john@ubuntu:~$ So I run fio on disk providing root partition and another disk, and constantly change IO scheduler on other disk. I did also add this delay to trigger in reasonable timeframe: +++ b/block/blk-mq-tag.c @@ -215,8 +215,11 @@ static bool bt_iter(struct sbitmap *bitmap, unsigned int bitnr, void *data) * We can hit rq == NULL here, because the tagging functions * test and set the bit before assigning ->rqs[]. */ - if (rq && rq->q == hctx->queue && rq->mq_hctx == hctx) - return iter_data->fn(hctx, rq, iter_data->data, reserved); + if (rq) { + mdelay(50); + if (rq->q == hctx->queue && rq->mq_hctx == hctx) + return iter_data->fn(hctx, rq, iter_data->data, reserved); + } return true; } Thanks, John