From patchwork Fri Jun 5 14:16:16 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jan Kara X-Patchwork-Id: 11589781 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 315A5912 for ; Fri, 5 Jun 2020 14:16:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2045D20835 for ; Fri, 5 Jun 2020 14:16:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728253AbgFEOQc (ORCPT ); Fri, 5 Jun 2020 10:16:32 -0400 Received: from mx2.suse.de ([195.135.220.15]:42444 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728241AbgFEOQb (ORCPT ); Fri, 5 Jun 2020 10:16:31 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 13E65AAD0; Fri, 5 Jun 2020 14:16:33 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 4D67A1E0267; Fri, 5 Jun 2020 16:16:29 +0200 (CEST) From: Jan Kara To: Cc: Paolo Valente , Jan Kara , stable@vger.kernel.org Subject: [PATCH 1/3] bfq: Avoid false bfq queue merging Date: Fri, 5 Jun 2020 16:16:16 +0200 Message-Id: <20200605141629.15347-1-jack@suse.cz> X-Mailer: git-send-email 2.16.4 In-Reply-To: <20200605140837.5394-1-jack@suse.cz> References: <20200605140837.5394-1-jack@suse.cz> Sender: linux-block-owner@vger.kernel.org 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 Signed-off-by: Jan Kara Acked-by: Paolo Valente Acked-by: Paolo Valente --- block/bfq-iosched.c | 1 + 1 file changed, 1 insertion(+) diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index 3d411716d7ee..50017275915f 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 = 0; } /*