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=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable 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 594C7C10F14 for ; Thu, 3 Oct 2019 17:07:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2C84320673 for ; Thu, 3 Oct 2019 17:07:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1570122455; bh=uz0yh/ZK6cChfUY3IqA6SxiaK6OQKPgqLLWkm4NAiSA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=NamzYzX8fgnSyKizy0TE+W5QXhXo3apQpg9B74lO0+NHuhjfa2N+3xrZ+7XZdWyIZ 6E93kxUmlK2q1uYreweHos7ovm87rXWWUrV3jpWt/e1eK54erSupqBfpF4sDuUsLih 09VvTifmc/yNXDZClq8od7g6KwOP8S0ji0e8jZCc= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2404436AbfJCQgf (ORCPT ); Thu, 3 Oct 2019 12:36:35 -0400 Received: from mail.kernel.org ([198.145.29.99]:45670 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2404384AbfJCQg1 (ORCPT ); Thu, 3 Oct 2019 12:36:27 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 0DE9420830; Thu, 3 Oct 2019 16:36:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1570120586; bh=uz0yh/ZK6cChfUY3IqA6SxiaK6OQKPgqLLWkm4NAiSA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=AQMfZNJ5Cus48FVw6//qKktYY4kvK663U0wmgS6A06ZSa8eEjE2cJOO0DQvnEjOAN HLRrDFu5FEJXXkkuja/lpdiWPDKeC6onkNN2YfukZdORLvkZMUi1irH/ii9rhfdHlV 0q3Yl0e6WIAvPB8qEZqm2L3juFVMMyf2duN844L8= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Hans Holmberg , Hans Holmberg , Christoph Hellwig , Damien Le Moal , Jens Axboe Subject: [PATCH 5.2 276/313] block: mq-deadline: Fix queue restart handling Date: Thu, 3 Oct 2019 17:54:14 +0200 Message-Id: <20191003154600.232127235@linuxfoundation.org> X-Mailer: git-send-email 2.23.0 In-Reply-To: <20191003154533.590915454@linuxfoundation.org> References: <20191003154533.590915454@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Damien Le Moal commit cb8acabbe33b110157955a7425ee876fb81e6bbc upstream. Commit 7211aef86f79 ("block: mq-deadline: Fix write completion handling") added a call to blk_mq_sched_mark_restart_hctx() in dd_dispatch_request() to make sure that write request dispatching does not stall when all target zones are locked. This fix left a subtle race when a write completion happens during a dispatch execution on another CPU: CPU 0: Dispatch CPU1: write completion dd_dispatch_request() lock(&dd->lock); ... lock(&dd->zone_lock); dd_finish_request() rq = find request lock(&dd->zone_lock); unlock(&dd->zone_lock); zone write unlock unlock(&dd->zone_lock); ... __blk_mq_free_request check restart flag (not set) -> queue not run ... if (!rq && have writes) blk_mq_sched_mark_restart_hctx() unlock(&dd->lock) Since the dispatch context finishes after the write request completion handling, marking the queue as needing a restart is not seen from __blk_mq_free_request() and blk_mq_sched_restart() not executed leading to the dispatch stall under 100% write workloads. Fix this by moving the call to blk_mq_sched_mark_restart_hctx() from dd_dispatch_request() into dd_finish_request() under the zone lock to ensure full mutual exclusion between write request dispatch selection and zone unlock on write request completion. Fixes: 7211aef86f79 ("block: mq-deadline: Fix write completion handling") Cc: stable@vger.kernel.org Reported-by: Hans Holmberg Reviewed-by: Hans Holmberg Reviewed-by: Christoph Hellwig Signed-off-by: Damien Le Moal Signed-off-by: Jens Axboe Signed-off-by: Greg Kroah-Hartman --- block/mq-deadline.c | 19 +++++++++---------- 1 file changed, 9 insertions(+), 10 deletions(-) --- a/block/mq-deadline.c +++ b/block/mq-deadline.c @@ -377,13 +377,6 @@ done: * hardware queue, but we may return a request that is for a * different hardware queue. This is because mq-deadline has shared * state for all hardware queues, in terms of sorting, FIFOs, etc. - * - * For a zoned block device, __dd_dispatch_request() may return NULL - * if all the queued write requests are directed at zones that are already - * locked due to on-going write requests. In this case, make sure to mark - * the queue as needing a restart to ensure that the queue is run again - * and the pending writes dispatched once the target zones for the ongoing - * write requests are unlocked in dd_finish_request(). */ static struct request *dd_dispatch_request(struct blk_mq_hw_ctx *hctx) { @@ -392,9 +385,6 @@ static struct request *dd_dispatch_reque spin_lock(&dd->lock); rq = __dd_dispatch_request(dd); - if (!rq && blk_queue_is_zoned(hctx->queue) && - !list_empty(&dd->fifo_list[WRITE])) - blk_mq_sched_mark_restart_hctx(hctx); spin_unlock(&dd->lock); return rq; @@ -560,6 +550,13 @@ static void dd_prepare_request(struct re * spinlock so that the zone is never unlocked while deadline_fifo_request() * or deadline_next_request() are executing. This function is called for * all requests, whether or not these requests complete successfully. + * + * For a zoned block device, __dd_dispatch_request() may have stopped + * dispatching requests if all the queued requests are write requests directed + * at zones that are already locked due to on-going write requests. To ensure + * write request dispatch progress in this case, mark the queue as needing a + * restart to ensure that the queue is run again after completion of the + * request and zones being unlocked. */ static void dd_finish_request(struct request *rq) { @@ -571,6 +568,8 @@ static void dd_finish_request(struct req spin_lock_irqsave(&dd->zone_lock, flags); blk_req_zone_write_unlock(rq); + if (!list_empty(&dd->fifo_list[WRITE])) + blk_mq_sched_mark_restart_hctx(rq->mq_hctx); spin_unlock_irqrestore(&dd->zone_lock, flags); } }