From patchwork Wed Jan 13 10:09:25 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jan Kara X-Patchwork-Id: 12016375 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=-16.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 0D0ECC433E6 for ; Wed, 13 Jan 2021 10:10:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C17E3233A2 for ; Wed, 13 Jan 2021 10:10:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727229AbhAMKKU (ORCPT ); Wed, 13 Jan 2021 05:10:20 -0500 Received: from mx2.suse.de ([195.135.220.15]:44664 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726960AbhAMKKT (ORCPT ); Wed, 13 Jan 2021 05:10:19 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id F189CB771; Wed, 13 Jan 2021 10:09:37 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id B53F81E0804; Wed, 13 Jan 2021 11:09:37 +0100 (CET) From: Jan Kara To: Jens Axboe Cc: , Paolo Valente , Jan Kara , stable@vger.kernel.org Subject: [PATCH 1/3] bfq: Avoid false bfq queue merging Date: Wed, 13 Jan 2021 11:09:25 +0100 Message-Id: <20210113100937.8278-1-jack@suse.cz> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20200605140837.5394-1-jack@suse.cz> References: <20200605140837.5394-1-jack@suse.cz> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org bfq_setup_cooperator() uses bfqd->in_serv_last_pos so detect whether it makes sense to merge current bfq queue with the in-service queue. However if the in-service queue is freshly scheduled and didn't dispatch any requests yet, bfqd->in_serv_last_pos is stale and contains value from the previously scheduled bfq queue which can thus result in a bogus decision that the two queues should be merged. This bug can be observed for example with the following fio jobfile: [global] direct=0 ioengine=sync invalidate=1 size=1g rw=read [reader] numjobs=4 directory=/mnt where the 4 processes will end up in the one shared bfq queue although they do IO to physically very distant files (for some reason I was able to observe this only with slice_idle=1ms setting). Fix the problem by invalidating bfqd->in_serv_last_pos when switching in-service queue. Fixes: 058fdecc6de7 ("block, bfq: fix in-service-queue check for queue merging") CC: stable@vger.kernel.org Acked-by: Paolo Valente Signed-off-by: Jan Kara --- block/bfq-iosched.c | 1 + 1 file changed, 1 insertion(+) diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index 9e4eb0fc1c16..dc5f12d0d482 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -2937,6 +2937,7 @@ static void __bfq_set_in_service_queue(struct bfq_data *bfqd, } bfqd->in_service_queue = bfqq; + bfqd->in_serv_last_pos = -1; } /*