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=-17.6 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,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 472B9C433F5 for ; Mon, 6 Sep 2021 08:16:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 28BFF60295 for ; Mon, 6 Sep 2021 08:16:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240437AbhIFIRT (ORCPT ); Mon, 6 Sep 2021 04:17:19 -0400 Received: from szxga01-in.huawei.com ([45.249.212.187]:19008 "EHLO szxga01-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240260AbhIFIRS (ORCPT ); Mon, 6 Sep 2021 04:17:18 -0400 Received: from dggemv711-chm.china.huawei.com (unknown [172.30.72.53]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4H31Mw2dwgzbmBZ; Mon, 6 Sep 2021 16:12:12 +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 15.1.2308.8; Mon, 6 Sep 2021 16:16:11 +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; Mon, 6 Sep 2021 16:16:11 +0800 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: From: luojiaxing Message-ID: Date: Mon, 6 Sep 2021 16:16:10 +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: dggems706-chm.china.huawei.com (10.3.19.183) 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 On 2021/9/1 17:36, Ming Lei wrote: > On Tue, Aug 31, 2021 at 10:27:28AM +0800, luojiaxing wrote: >> 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. > Each hctx has its own rq pool so far, so no such issue you worried. > > John's patch works towards sharing rq pool among hctxs in case of > shared sbitmap, not merged yet, but ->rqs[] should be shared too, still > no such issue. > > Follows the revised patch for handling the stale request in ->rqs[] issue: Following patch can fix the issue. Tested-by: Luo Jiaxing Thanks Jiaxing > > > diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c > index 86f87346232a..ff5caeb82542 100644 > --- a/block/blk-mq-tag.c > +++ b/block/blk-mq-tag.c > @@ -208,7 +208,7 @@ static struct request *blk_mq_find_and_get_req(struct blk_mq_tags *tags, > > spin_lock_irqsave(&tags->lock, flags); > rq = tags->rqs[bitnr]; > - if (!rq || !refcount_inc_not_zero(&rq->ref)) > + if (!rq || rq->tag != bitnr || !refcount_inc_not_zero(&rq->ref)) > rq = NULL; > spin_unlock_irqrestore(&tags->lock, flags); > return rq; > > > Thanks, > Ming > > > . >