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=-6.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 D263AC433DF for ; Mon, 17 Aug 2020 11:07:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A37DC2072D for ; Mon, 17 Aug 2020 11:07:05 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="SjFT5Ok5" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726685AbgHQLHF (ORCPT ); Mon, 17 Aug 2020 07:07:05 -0400 Received: from us-smtp-1.mimecast.com ([207.211.31.81]:25765 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726341AbgHQLHD (ORCPT ); Mon, 17 Aug 2020 07:07:03 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1597662422; 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=vaeJYlqz4i43h2jN+zYN6KdI8iVkdCIzTxfaFW4qgUs=; b=SjFT5Ok5A+ubsWNdhVc2bfzj8RoK+7aDXZoqzFyRrqacGSPgK/O+Vcc79qJwJYqeiC42TA g/DS9Xg9xMfpSChPLVwVy4MVjqlnb/p1GJ87D7YZUUhGajWaDPMSYYOnJ5NOiTAFGacUl6 c162TQTgKOppV4Y+WJR3sHTiK/+24Ss= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-225-xoXRQM56NEiUy0GdfqN1jw-1; Mon, 17 Aug 2020 07:06:56 -0400 X-MC-Unique: xoXRQM56NEiUy0GdfqN1jw-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 08E1E1014DEE; Mon, 17 Aug 2020 11:06:55 +0000 (UTC) Received: from T590 (ovpn-13-146.pek2.redhat.com [10.72.13.146]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 56ADD7DFC0; Mon, 17 Aug 2020 11:06:48 +0000 (UTC) Date: Mon, 17 Aug 2020 19:06:43 +0800 From: Ming Lei To: Christoph Hellwig Cc: Jens Axboe , linux-block@vger.kernel.org, Bart Van Assche , David Jeffery , kernel test robot , stable@vger.kernel.org Subject: Re: [PATCH RESEND] blk-mq: order adding requests to hctx->dispatch and checking SCHED_RESTART Message-ID: <20200817110643.GA2486425@T590> References: <20200817100115.2495988-1-ming.lei@redhat.com> <20200817101539.GB25336@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200817101539.GB25336@lst.de> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Mon, Aug 17, 2020 at 12:15:39PM +0200, Christoph Hellwig wrote: > On Mon, Aug 17, 2020 at 06:01:15PM +0800, Ming Lei wrote: > > SCHED_RESTART code path is relied to re-run queue for dispatch requests > > in hctx->dispatch. Meantime the SCHED_RSTART flag is checked when adding > > requests to hctx->dispatch. > > > > memory barriers have to be used for ordering the following two pair of OPs: > > > > 1) adding requests to hctx->dispatch and checking SCHED_RESTART in > > blk_mq_dispatch_rq_list() > > > > 2) clearing SCHED_RESTART and checking if there is request in hctx->dispatch > > in blk_mq_sched_restart(). > > > > Without the added memory barrier, either: > > > > 1) blk_mq_sched_restart() may miss requests added to hctx->dispatch meantime > > blk_mq_dispatch_rq_list() observes SCHED_RESTART, and not run queue in > > dispatch side > > > > or > > > > 2) blk_mq_dispatch_rq_list still sees SCHED_RESTART, and not run queue > > in dispatch side, meantime checking if there is request in > > hctx->dispatch from blk_mq_sched_restart() is missed. > > > > IO hang in ltp/fs_fill test is reported by kernel test robot: > > > > https://lkml.org/lkml/2020/7/26/77 > > > > Turns out it is caused by the above out-of-order OPs. And the IO hang > > can't be observed any more after applying this patch. > > > > Cc: Bart Van Assche > > Cc: Christoph Hellwig > > Cc: David Jeffery > > Reported-by: kernel test robot > > Cc: > > Signed-off-by: Ming Lei > > Can you add a Fixes: tag so that the commit gets backported? Fixes: bd166ef183c2 ("blk-mq-sched: add framework for MQ capable IO schedulers") Thanks, Ming