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=-15.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY, 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 6C711C4743C for ; Tue, 22 Jun 2021 02:26:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 453F76128C for ; Tue, 22 Jun 2021 02:26:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231179AbhFVC2d (ORCPT ); Mon, 21 Jun 2021 22:28:33 -0400 Received: from out30-42.freemail.mail.aliyun.com ([115.124.30.42]:36912 "EHLO out30-42.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230338AbhFVC2c (ORCPT ); Mon, 21 Jun 2021 22:28:32 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R181e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04426;MF=jefflexu@linux.alibaba.com;NM=1;PH=DS;RN=6;SR=0;TI=SMTPD_---0UdGhKea_1624328775; Received: from admindeMacBook-Pro-2.local(mailfrom:jefflexu@linux.alibaba.com fp:SMTPD_---0UdGhKea_1624328775) by smtp.aliyun-inc.com(127.0.0.1); Tue, 22 Jun 2021 10:26:15 +0800 Subject: Re: [dm-devel] [RFC PATCH V2 3/3] dm: support bio polling To: Ming Lei Cc: Jens Axboe , Mike Snitzer , linux-block@vger.kernel.org, dm-devel@redhat.com, Christoph Hellwig References: <20210617103549.930311-1-ming.lei@redhat.com> <20210617103549.930311-4-ming.lei@redhat.com> <5ba43dac-b960-7c85-3a89-fdae2d1e2f51@linux.alibaba.com> <9b42601a-ca54-4748-e592-3720b7994d7b@linux.alibaba.com> From: JeffleXu Message-ID: Date: Tue, 22 Jun 2021 10:26:15 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 6/21/21 10:04 PM, Ming Lei wrote: > On Mon, Jun 21, 2021 at 07:33:34PM +0800, JeffleXu wrote: >> >> >> On 6/18/21 10:39 PM, Ming Lei wrote: >>> From 47e523b9ee988317369eaadb96826323cd86819e Mon Sep 17 00:00:00 2001 >>> From: Ming Lei >>> Date: Wed, 16 Jun 2021 16:13:46 +0800 >>> Subject: [RFC PATCH V3 3/3] dm: support bio polling >>> >>> Support bio(REQ_POLLED) polling in the following approach: >>> >>> 1) only support io polling on normal READ/WRITE, and other abnormal IOs >>> still fallback on IRQ mode, so the target io is exactly inside the dm >>> io. >>> >>> 2) hold one refcnt on io->io_count after submitting this dm bio with >>> REQ_POLLED >>> >>> 3) support dm native bio splitting, any dm io instance associated with >>> current bio will be added into one list which head is bio->bi_end_io >>> which will be recovered before ending this bio >>> >>> 4) implement .poll_bio() callback, call bio_poll() on the single target >>> bio inside the dm io which is retrieved via bio->bi_bio_drv_data; call >>> dec_pending() after the target io is done in .poll_bio() >>> >>> 4) enable QUEUE_FLAG_POLL if all underlying queues enable QUEUE_FLAG_POLL, >>> which is based on Jeffle's previous patch. >>> >>> Signed-off-by: Ming Lei >>> --- >>> V3: >>> - covers all comments from Jeffle >>> - fix corner cases when polling on abnormal ios >>> >> ... >> >> One bug and one performance issue, though I haven't investigated deep >> for both. >> >> >> kernel base: based on Jens' for-next, applying Christoph and Leiming's >> patchset. >> >> >> 1. One bug when there's DM device stack, e.g., dm-linear upon another >> dm-linear. Can be reproduced by following steps: >> >> ``` >> $ sudo dmsetup create tmpdev --table '0 2097152 linear /dev/nvme0n1 0' >> >> $ cat tmp.table >> 0 2097152 linear /dev/mapper/tmpdev 0 >> 2097152 2097152 linear /dev/nvme0n1 0 >> >> $ cat tmp.table | dmsetup create testdev >> >> $ fio -name=test -ioengine=io_uring -iodepth=128 -numjobs=1 -thread >> -rw=randread -direct=1 -bs=4k -time_based -runtime=10 -cpus_allowed=6 >> -filename=/dev/mapper/testdev -hipri=1 >> ``` >> >> >> BUG: unable to handle page fault for address: ffffffffc01a6208 >> #PF: supervisor write access in kernel mode >> #PF: error_code(0x0003) - permissions violation >> PGD 39740c067 P4D 39740c067 PUD 39740e067 PMD 1035db067 PTE 1ddf6f061 >> Oops: 0003 [#1] SMP PTI >> CPU: 6 PID: 5899 Comm: fio Tainted: G S >> 5.13.0-0.1.git.81bcdc3.al7.x86_64 #1 >> Hardware name: Inventec K900G3-10G/B900G3, BIOS A2.20 06/23/2017 >> RIP: 0010:dm_submit_bio+0x171/0x3e0 [dm_mod] > > It has been fixed in my local repo: > > @@ -1608,6 +1649,7 @@ static void init_clone_info(struct clone_info *ci, struct mapped_device *md, > ci->map = map; > ci->io = alloc_io(md, bio); > ci->sector = bio->bi_iter.bi_sector; > + ci->submit_as_polled = false; > It doesn't work in my test environment. Actually the following fix should be applied. @@ -1390,6 +1403,8 @@ static int clone_bio(struct dm_target_io *tio, struct bio *bio, if (bio_integrity(bio)) bio_integrity_trim(clone); + clone->bi_opf &= ~REQ_SAVED_END_IO; + return 0; } The rationale is that, REQ_SAVED_END_IO should be cleared once the bio *passes through* the device stack layer. Or the cloned bio for next layer will inherit REQ_SAVED_END_IO flag, in which case 'cloned_bio->bi_end_io' (actually acts as the hlist head) won't be initialized in dm_setup_polled_io(), and thus it gets crashed when trying to insert into this hash list in __split_and_process_bio(). -- Thanks, Jeffle