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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,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 633ADC433E0 for ; Mon, 4 Jan 2021 15:35:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 34E072225E for ; Mon, 4 Jan 2021 15:35:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727468AbhADPfX (ORCPT ); Mon, 4 Jan 2021 10:35:23 -0500 Received: from frasgout.his.huawei.com ([185.176.79.56]:2287 "EHLO frasgout.his.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727040AbhADPfX (ORCPT ); Mon, 4 Jan 2021 10:35:23 -0500 Received: from fraeml740-chm.china.huawei.com (unknown [172.18.147.207]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4D8fh85SVDz67XjM; Mon, 4 Jan 2021 23:30:00 +0800 (CST) Received: from lhreml724-chm.china.huawei.com (10.201.108.75) by fraeml740-chm.china.huawei.com (10.206.15.221) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2106.2; Mon, 4 Jan 2021 16:34:41 +0100 Received: from [10.47.2.42] (10.47.2.42) 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; Mon, 4 Jan 2021 15:34:40 +0000 Subject: Re: [RFC PATCH v2 2/2] blk-mq: Lockout tagset iter when freeing rqs To: Bart Van Assche , , CC: , , , , , References: <1608203273-170555-1-git-send-email-john.garry@huawei.com> <1608203273-170555-3-git-send-email-john.garry@huawei.com> <4d2004bb-4444-7a63-7c72-1759e3037cfd@huawei.com> <31de2806-bbc1-dcc3-b9eb-ce9257420432@acm.org> <33e41110-b3b2-ac16-f131-de1679ce8238@acm.org> <7bdd562d-b258-43a2-0de0-966091086cff@huawei.com> <0ab85ab8-c5c7-01aa-6b39-da731b3db829@acm.org> From: John Garry Message-ID: Date: Mon, 4 Jan 2021 15:33:41 +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: <0ab85ab8-c5c7-01aa-6b39-da731b3db829@acm.org> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: [10.47.2.42] X-ClientProxiedBy: lhreml719-chm.china.huawei.com (10.201.108.70) To lhreml724-chm.china.huawei.com (10.201.108.75) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 23/12/2020 15:47, Bart Van Assche wrote: > On 12/23/20 3:40 AM, John Garry wrote: >> Sorry, I got the 2x iter functions mixed up. >> >> So if we use mutex to solve blk_mq_queue_tag_busy_iter() problem, then we >> still have this issue in blk_mq_tagset_busy_iter() which I report previously >> [0]: >> >> [  319.771745] BUG: KASAN: use-after-free in bt_tags_iter+0xe0/0x128 >> [  319.777832] Read of size 4 at addr ffff0010b6bd27cc by task more/1866 >> [  319.784262] >> [  319.785753] CPU: 61 PID: 1866 Comm: more Tainted: G        W >> 5.10.0-rc4-18118-gaa7b9c30d8ff #1070 >> [  319.795312] Hardware name: Huawei Taishan 2280 /D05, BIOS Hisilicon >> D05 IT21 Nemo 2.0 RC0 04/18/2018 >> [  319.804437] Call trace: >> [  319.806892]  dump_backtrace+0x0/0x2d0 >> [  319.810552]  show_stack+0x18/0x68 >> [  319.813865]  dump_stack+0x100/0x16c >> [  319.817348]  print_address_description.constprop.12+0x6c/0x4e8 >> [  319.823176]  kasan_report+0x130/0x200 >> [  319.826831]  __asan_load4+0x9c/0xd8 >> [  319.830315]  bt_tags_iter+0xe0/0x128 >> [  319.833884]  __blk_mq_all_tag_iter+0x320/0x3a8 >> [  319.838320]  blk_mq_tagset_busy_iter+0x8c/0xd8 >> [  319.842760]  scsi_host_busy+0x88/0xb8 >> [  319.846418]  show_host_busy+0x1c/0x48 >> [  319.850079]  dev_attr_show+0x44/0x90 >> [  319.853655]  sysfs_kf_seq_show+0x128/0x1c8 >> [  319.857744]  kernfs_seq_show+0xa0/0xb8 >> [  319.861489]  seq_read_iter+0x1ec/0x6a0 >> [  319.865230]  seq_read+0x1d0/0x250 >> [  319.868539]  kernfs_fop_read+0x70/0x330 >> [  319.872369]  vfs_read+0xe4/0x250 >> [  319.875590]  ksys_read+0xc8/0x178 >> [  319.878898]  __arm64_sys_read+0x44/0x58 >> [  319.882730]  el0_svc_common.constprop.2+0xc4/0x1e8 >> [  319.887515]  do_el0_svc+0x90/0xa0 >> [  319.890824]  el0_sync_handler+0x128/0x178 >> [  319.894825]  el0_sync+0x158/0x180 >> [  319.898131] >> [  319.899614] The buggy address belongs to the page: >> [  319.904403] page:000000004e9e6864 refcount:0 mapcount:0 >> mapping:0000000000000000 index:0x0 pfn:0x10b6bd2 >> [  319.913876] flags: 0xbfffc0000000000() >> [  319.917626] raw: 0bfffc0000000000 0000000000000000 fffffe0000000000 >> 0000000000000000 >> [  319.925363] raw: 0000000000000000 0000000000000000 00000000ffffffff >> 0000000000000000 >> [  319.933096] page dumped because: kasan: bad access detected >> [  319.938658] >> [  319.940141] Memory state around the buggy address: >> [  319.944925]  ffff0010b6bd2680: ff ff ff ff ff ff ff ff ff ff ff ff ff >> ff ff ff >> [  319.952139]  ffff0010b6bd2700: ff ff ff ff ff ff ff ff ff ff ff ff ff >> ff ff ff >> [  319.959354] >ffff0010b6bd2780: ff ff ff ff ff ff ff ff ff ff ff ff ff >> ff ff ff >> [  319.966566] ^ >> [  319.972131]  ffff0010b6bd2800: ff ff ff ff ff ff ff ff ff ff ff ff ff >> ff ff ff >> [  319.979344]  ffff0010b6bd2880: ff ff ff ff ff ff ff ff ff ff ff ff ff >> ff ff ff >> [  319.986557] >> ================================================================== >> [  319.993770] Disabling lock debugging due to kernel taint >> >> So to trigger this, I start fio on a disk, and then have one script >> which constantly enables and disables an IO scheduler for that disk, and >> another script which constantly reads /sys/class/scsi_host/host0/host_busy . >> >> And in this problem, the driver tag we iterate may point to a stale IO sched >> request. > > Hi John, Hi Bart, Sorry for the slow reply, but I was on vacation since before you sent this mail. > > I propose to change the order in which blk_mq_sched_free_requests(q) and > blk_mq_debugfs_unregister(q) are called. Today blk_mq_sched_free_requests(q) > is called by blk_cleanup_queue() before blk_put_queue() is called. > blk_put_queue() calls blk_release_queue() if the last reference is dropped. > blk_release_queue() calls blk_mq_debugfs_unregister(). I prefer removing the > debugfs attributes earlier over modifying the tag iteration functions > because I think removing the debugfs attributes earlier is less risky. But don't we already have this following path to remove the per-hctx debugfs dir earlier than blk_mq_sched_free_requests() or blk_release_queue(): blk_cleanup_queue() -> blk_mq_exit_queue() -> blk_mq_exit_hw_queues() -> blk_mq_debugfs_unregister_hctx() -> blk_mq_debugfs_unregister_hctx(hctx->debugfs_dir) Having said that, I am not sure how this is related directly to the problem I mentioned. In that problem, above, we trigger the blk_mq_tagset_busy_iter() from the SCSI host sysfs file, and the use-after-free comes about from disabling the elevator (and freeing the sched requests) in parallel. > Although this will make it harder to debug lockups that happen while > removing a request queue, kernel developers who are analyzing such an issue > can undo this change in their development kernel tree. > Thanks, John