From patchwork Tue Sep 1 15:10:27 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg Kroah-Hartman X-Patchwork-Id: 310448 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=-10.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 C83C7C43461 for ; Tue, 1 Sep 2020 15:43:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 90CBA207D3 for ; Tue, 1 Sep 2020 15:43:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598975007; bh=Tyu91bH63gG6nmgdD1zZbuSXVaxKlvW0YzojL9UrOcA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=oVT8Is3dic83gxF5HH8ZtDFLwNBhb3+JeHSFX/Fns5ZcuzJk+yMATl0gpbFcx1qGF hHf0ulnETHfQ5Yz4XvsNtcIX8Y6sHIBPbF7o0cwsZu3rkwE+t7iuZ8ipLMb4UHAIem XEj03xyEgIqbRX+98wSzh5tkonKYzR1o4qkcNhJM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728318AbgIAPnZ (ORCPT ); Tue, 1 Sep 2020 11:43:25 -0400 Received: from mail.kernel.org ([198.145.29.99]:57360 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731659AbgIAPnX (ORCPT ); Tue, 1 Sep 2020 11:43:23 -0400 Received: from localhost (83-86-74-64.cable.dynamic.v4.ziggo.nl [83.86.74.64]) (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 B39F9206EB; Tue, 1 Sep 2020 15:43:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598975002; bh=Tyu91bH63gG6nmgdD1zZbuSXVaxKlvW0YzojL9UrOcA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ZWhjIEb7B4HjzxiFZBqykuoi7Mg/9906cchD1DEtBrt8kM4/U1tv30cNQ+XlIArp/ WYLxnIS1KpIAwYY7A50O5/ZciM7aFyWFBW2RYPN8qA59QoJQq5oFENoy+IxjZkDru2 FA1TJFD6bOZl6Oi9jNKPn2zbm0bxBWnXfmt1QHBY= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, kernel test robot , Ming Lei , Christoph Hellwig , Bart Van Assche , David Jeffery , Jens Axboe Subject: [PATCH 5.8 171/255] blk-mq: order adding requests to hctx->dispatch and checking SCHED_RESTART Date: Tue, 1 Sep 2020 17:10:27 +0200 Message-Id: <20200901151008.889544975@linuxfoundation.org> X-Mailer: git-send-email 2.28.0 In-Reply-To: <20200901151000.800754757@linuxfoundation.org> References: <20200901151000.800754757@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Ming Lei commit d7d8535f377e9ba87edbf7fbbd634ac942f3f54f upstream. 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. Fixes: bd166ef183c2 ("blk-mq-sched: add framework for MQ capable IO schedulers") Reported-by: kernel test robot Signed-off-by: Ming Lei Reviewed-by: Christoph Hellwig Cc: Bart Van Assche Cc: Christoph Hellwig Cc: David Jeffery Cc: Signed-off-by: Jens Axboe Signed-off-by: Greg Kroah-Hartman --- block/blk-mq-sched.c | 9 +++++++++ block/blk-mq.c | 9 +++++++++ 2 files changed, 18 insertions(+) --- a/block/blk-mq-sched.c +++ b/block/blk-mq-sched.c @@ -77,6 +77,15 @@ void blk_mq_sched_restart(struct blk_mq_ return; clear_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state); + /* + * Order clearing SCHED_RESTART and list_empty_careful(&hctx->dispatch) + * in blk_mq_run_hw_queue(). Its pair is the barrier in + * blk_mq_dispatch_rq_list(). So dispatch code won't see SCHED_RESTART, + * meantime new request added to hctx->dispatch is missed to check in + * blk_mq_run_hw_queue(). + */ + smp_mb(); + blk_mq_run_hw_queue(hctx, true); } --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -1324,6 +1324,15 @@ bool blk_mq_dispatch_rq_list(struct requ spin_unlock(&hctx->lock); /* + * Order adding requests to hctx->dispatch and checking + * SCHED_RESTART flag. The pair of this smp_mb() is the one + * in blk_mq_sched_restart(). Avoid restart code path to + * miss the new added requests to hctx->dispatch, meantime + * SCHED_RESTART is observed here. + */ + smp_mb(); + + /* * If SCHED_RESTART was set by the caller of this function and * it is no longer set that means that it was cleared by another * thread and hence that a queue rerun is needed.