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=-11.2 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 1E2B9C4320A for ; Tue, 31 Aug 2021 02:27:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 06ECE600CD for ; Tue, 31 Aug 2021 02:27:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239416AbhHaC2f (ORCPT ); Mon, 30 Aug 2021 22:28:35 -0400 Received: from szxga02-in.huawei.com ([45.249.212.188]:14438 "EHLO szxga02-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239363AbhHaC2f (ORCPT ); Mon, 30 Aug 2021 22:28:35 -0400 Received: from dggemv711-chm.china.huawei.com (unknown [172.30.72.57]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4Gz9wc3kQGzbftq; Tue, 31 Aug 2021 10:23:44 +0800 (CST) Received: from dggemi759-chm.china.huawei.com (10.1.198.145) by dggemv711-chm.china.huawei.com (10.1.198.66) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256) id 15.1.2176.2; Tue, 31 Aug 2021 10:27:29 +0800 Received: from [127.0.0.1] (10.40.192.131) by dggemi759-chm.china.huawei.com (10.1.198.145) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.2308.8; Tue, 31 Aug 2021 10:27:28 +0800 From: luojiaxing Subject: Re: rq pointer in tags->rqs[] is not cleared in time and make SCSI error handle can not be triggered To: Ming Lei CC: , , Jens Axboe , "Martin K. Petersen" , References: Message-ID: Date: Tue, 31 Aug 2021 10:27:28 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Originating-IP: [10.40.192.131] X-ClientProxiedBy: dggems701-chm.china.huawei.com (10.3.19.178) To dggemi759-chm.china.huawei.com (10.1.198.145) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org Hi, Ming Sorry to reply so late, This issue occur in low probability, so it take some time to confirm. On 2021/8/26 15:29, Ming Lei wrote: > On Thu, Aug 26, 2021 at 11:00:34AM +0800, luojiaxing wrote: >> Dear all: >> >> >> I meet some problem when test hisi_sas driver(under SCSI) based on 5.14-rc4 >> kernel, it's found that error handle can not be triggered after >> >> abnormal IO occur in some test with a low probability. For example, >> circularly run disk hardreset or disable all local phy of expander when >> running fio. >> >> >> We add some tracepoint and print to see what happen, and we got the >> following information: >> >> (1).print rq and rq_state at bt_tags_iter() to confirm how many IOs is >> running now. >> >> <4>[  897.431182] bt_tags_iter: rqs[2808]: 0xffff202007bd3000; rq_state: 1 >> <4>[  897.437514] bt_tags_iter: rqs[3185]: 0xffff0020c5261e00; rq_state: 1 >> <4>[  897.443841] bt_tags_iter: rqs[3612]: 0xffff00212f242a00; rq_state: 1 >> <4>[  897.450167] bt_tags_iter: rqs[2808]: 0xffff00211d208100; rq_state: 1 >> <4>[  897.456492] bt_tags_iter: rqs[2921]: 0xffff00211d208100; rq_state: 1 >> <4>[  897.462818] bt_tags_iter: rqs[1214]: 0xffff002151d21b00; rq_state: 1 >> <4>[  897.469143] bt_tags_iter: rqs[2648]: 0xffff0020c4bfa200; rq_state: 1 >> >> The preceding information show that rq with tag[2808] is found in different >> hctx by bt_tags_iter() and with different pointer saved in tags->rqs[]. >> >> And tag[2808] own the same pointer value saved in rqs[] with tag[2921]. It's >> wrong because our driver share tag between all hctx, so it's not possible > What is your io scheduler? I guess it is deadline, yes > and can you observe > such issue by switching to none? Yes, it happen when switched to none > > The tricky thing is that one request dumped may be re-allocated to other tag > after returning from bt_tags_iter(). > >> to allocate one tag to different rq. >> >> >> (2).check tracepoints(temporarily add) in blk_mq_get_driver_tag() and >> blk_mq_put_tag() to see where this tag is come from. >> >>     Line 1322969:            <...>-20189   [013] .... 893.427707: >> blk_mq_get_driver_tag: rqs[2808]: 0xffff00211d208100 >>     Line 1322997:  irq/1161-hisi_s-7602    [012] d..1 893.427814: >> blk_mq_put_tag_in_free_request: rqs[2808]: 0xffff00211d208100 >>     Line 1331257:            <...>-20189   [013] .... 893.462663: >> blk_mq_get_driver_tag: rqs[2860]: 0xffff00211d208100 >>     Line 1331289:  irq/1161-hisi_s-7602    [012] d..1 893.462785: >> blk_mq_put_tag_in_free_request: rqs[2860]: 0xffff00211d208100 >>     Line 1338493:            <...>-20189   [013] .... 893.493519: >> blk_mq_get_driver_tag: rqs[2921]: 0xffff00211d208100 >> >> As we can see this rq is allocated to tag[2808] once, and finially come to >> tag[2921], but rqs[2808] still save the pointer. > Yeah, we know this kind of handling, but not see it as issue. > >> There will be no problem until we encounter a rare situation. >> >> For example, tag[2808] is reassigned to another hctx for execution, then >> some IO meet some error. > I guess the race is triggered when 2808 is just assigned, meantime > ->rqs[] isn't updated. As we shared tag between hctx, so if 2808 was assinged to other hctx. So previous hctx's rqs will not updated。 >> Before waking up the error handle thread, SCSI compares the values of >> scsi_host_busy() and shost->host_failed. >> >> If the values are different, SCSI waits for the completion of some I/Os. >> According to the print provided by (1), the return value of scsi_host_busy() >> should be 7 for tag [2808] is calculated twice, >> >> and the value of shost->host_failed is 6. As a result, this two values are >> never equal, and error handle cannot be triggered. >> >> >> A temporary workaround is provided and can solve the problem as: >> >> diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c >> index 2a37731..e3dc773 100644 >> --- a/block/blk-mq-tag.c >> +++ b/block/blk-mq-tag.c >> @@ -190,6 +190,7 @@ void blk_mq_put_tag(struct blk_mq_tags *tags, struct >> blk_mq_ctx *ctx, >>                 BUG_ON(tag >= tags->nr_reserved_tags); >>                 sbitmap_queue_clear(tags->breserved_tags, tag, ctx->cpu); >>         } >> +       tags->rqs[tag] = NULL; >>  } >> >> >> Since we did not encounter this problem in some previous kernel versions, we >> wondered if the community already knew about the problem or could provide >> some solutions. > Can you try the following patch? I tested it. it can fix the bug. However, if there is still a problem in the following scenario? For example, driver tag 0 is assigned to rq0 in hctx0, and reclaimed after rq completed. Next time driver tag 0 is still assigned to rq0 but in hctx1. So at this time,  bt_tags_iter will still got two rqs. Thanks Jiaxing > > diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c > index 86f87346232a..97557ba0737f 100644 > --- a/block/blk-mq-tag.c > +++ b/block/blk-mq-tag.c > @@ -301,7 +301,7 @@ static bool bt_tags_iter(struct sbitmap *bitmap, unsigned int bitnr, void *data) > return true; > > if (!(iter_data->flags & BT_TAG_ITER_STARTED) || > - blk_mq_request_started(rq)) > + (blk_mq_request_started(rq) && rq->tag == bitnr)) > ret = iter_data->fn(rq, iter_data->data, reserved); > if (!iter_static_rqs) > blk_mq_put_rq_ref(rq); > > > > Thanks, > Ming > > > . >