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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4E41CC19F21 for ; Wed, 27 Jul 2022 03:09:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240090AbiG0DJE (ORCPT ); Tue, 26 Jul 2022 23:09:04 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40618 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239918AbiG0DIz (ORCPT ); Tue, 26 Jul 2022 23:08:55 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id E0F7C3C8DF for ; Tue, 26 Jul 2022 20:08:53 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1658891333; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=32axq/VfQhSlDfqHI2UD/a9LuuHQ/A3908wmtNoQ7lo=; b=SlPFIdOefoa2ZV5E9vOI/11EMbtwoZWUwzKS0DwD4zx7zs2xNDG0ZoW/UAEmbC6oEgfydK Bc5r+qHcomtdnwCmQVDWXoihM9ebAkWZjB0V8ASPDaIHh0e++gIFJVJ/6AWcuLTCnf52op oxz4osYGHfKs8dW+QJ/WRErEvUqlYoQ= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-231-3z542prMMcGtTLhGBYgXgg-1; Tue, 26 Jul 2022 23:08:48 -0400 X-MC-Unique: 3z542prMMcGtTLhGBYgXgg-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 2CDAF85A581; Wed, 27 Jul 2022 03:08:48 +0000 (UTC) Received: from T590 (ovpn-8-20.pek2.redhat.com [10.72.8.20]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E9F87C15D4F; Wed, 27 Jul 2022 03:08:43 +0000 (UTC) Date: Wed, 27 Jul 2022 11:08:38 +0800 From: Ming Lei To: Yu Kuai Cc: axboe@kernel.dk, osandov@fb.com, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, yukuai3@huawei.com, yi.zhang@huawei.com Subject: Re: [PATCH v3] blk-mq: fix io hung due to missing commit_rqs Message-ID: References: <20220726122224.1790882-1-yukuai1@huaweicloud.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220726122224.1790882-1-yukuai1@huaweicloud.com> X-Scanned-By: MIMEDefang 2.85 on 10.11.54.8 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 26, 2022 at 08:22:24PM +0800, Yu Kuai wrote: > From: Yu Kuai > > Currently, in virtio_scsi, if 'bd->last' is not set to true while > dispatching request, such io will stay in driver's queue, and driver > will wait for block layer to dispatch more rqs. However, if block > layer failed to dispatch more rq, it should trigger commit_rqs to > inform driver. > > There is a problem in blk_mq_try_issue_list_directly() that commit_rqs > won't be called: > > // assume that queue_depth is set to 1, list contains two rq > blk_mq_try_issue_list_directly > blk_mq_request_issue_directly > // dispatch first rq > // last is false > __blk_mq_try_issue_directly > blk_mq_get_dispatch_budget > // succeed to get first budget > __blk_mq_issue_directly > scsi_queue_rq > cmd->flags |= SCMD_LAST > virtscsi_queuecommand > kick = (sc->flags & SCMD_LAST) != 0 > // kick is false, first rq won't issue to disk > queued++ > > blk_mq_request_issue_directly > // dispatch second rq > __blk_mq_try_issue_directly > blk_mq_get_dispatch_budget > // failed to get second budget > ret == BLK_STS_RESOURCE > blk_mq_request_bypass_insert > // errors is still 0 > > if (!list_empty(list) || errors && ...) > // won't pass, commit_rqs won't be called > > In this situation, first rq relied on second rq to dispatch, while > second rq relied on first rq to complete, thus they will both hung. > > Fix the problem by also treat 'BLK_STS_*RESOURCE' as 'errors' since > it means that request is not queued successfully. > > Same problem exists in blk_mq_dispatch_rq_list(), 'BLK_STS_*RESOURCE' > can't be treated as 'errors' here, fix the problem by calling > commit_rqs if queue_rq return 'BLK_STS_*RESOURCE'. > > Fixes: d666ba98f849 ("blk-mq: add mq_ops->commit_rqs()") > Signed-off-by: Yu Kuai Reviewed-by: Ming Lei Thanks, Ming