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=-13.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 30FDDC433B4 for ; Thu, 20 May 2021 07:21:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 143D961074 for ; Thu, 20 May 2021 07:21:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231136AbhETHWy (ORCPT ); Thu, 20 May 2021 03:22:54 -0400 Received: from mail.itouring.de ([85.10.202.141]:58404 "EHLO mail.itouring.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231142AbhETHWy (ORCPT ); Thu, 20 May 2021 03:22:54 -0400 X-Greylist: delayed 348 seconds by postgrey-1.27 at vger.kernel.org; Thu, 20 May 2021 03:22:53 EDT Received: from tux.applied-asynchrony.com (p5b07e8e5.dip0.t-ipconnect.de [91.7.232.229]) by mail.itouring.de (Postfix) with ESMTPSA id 10C9FE0; Thu, 20 May 2021 09:15:43 +0200 (CEST) Received: from [192.168.100.221] (hho.applied-asynchrony.com [192.168.100.221]) by tux.applied-asynchrony.com (Postfix) with ESMTP id AA65BF01624; Thu, 20 May 2021 09:15:42 +0200 (CEST) Subject: Re: [PATCH BUGFIX] block, bfq: fix delayed stable merge check To: Luca Mariotti , Paolo Valente , Jens Axboe Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Pietro Pedroni References: From: =?UTF-8?Q?Holger_Hoffst=c3=a4tte?= Organization: Applied Asynchrony, Inc. Message-ID: Date: Thu, 20 May 2021 09:15:42 +0200 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 2021-05-18 12:43, Luca Mariotti wrote: > When attempting to schedule a merge of a given bfq_queue with the currently > in-service bfq_queue or with a cooperating bfq_queue among the scheduled > bfq_queues, delayed stable merge is checked for rotational or non-queueing > devs. For this stable merge to be performed, some conditions must be met. > If the current bfq_queue underwent some split from some merged bfq_queue, > one of these conditions is that two hundred milliseconds must elapse from > split, otherwise this condition is always met. > > Unfortunately, by mistake, time_is_after_jiffies() was written instead of > time_is_before_jiffies() for this check, verifying that less than two > hundred milliseconds have elapsed instead of verifying that at least two > hundred milliseconds have elapsed. > > Fix this issue by replacing time_is_after_jiffies() with > time_is_before_jiffies(). > > Signed-off-by: Luca Mariotti > Signed-off-by: Paolo Valente > Signed-off-by: Pietro Pedroni > --- > block/bfq-iosched.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c > index acd1f881273e..2adb1e69c9d2 100644 > --- a/block/bfq-iosched.c > +++ b/block/bfq-iosched.c > @@ -2697,7 +2697,7 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq, > if (unlikely(!bfqd->nonrot_with_queueing)) { > if (bic->stable_merge_bfqq && > !bfq_bfqq_just_created(bfqq) && > - time_is_after_jiffies(bfqq->split_time + > + time_is_before_jiffies(bfqq->split_time + > msecs_to_jiffies(200))) { > struct bfq_queue *stable_merge_bfqq = > bic->stable_merge_bfqq; > Not sure why but with this patch I quickly got a division-by-zero in BFQ and complete system halt. Unfortunately I couldn't capture the exact stack trace, but it read something like bfq_calc_weight() or something ike that. I looked through the code and found bfq_delta(), so maybe weight got reduced to 0? -h