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=-18.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,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 4232DC43381 for ; Mon, 1 Mar 2021 21:49:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 01C90601FD for ; Mon, 1 Mar 2021 21:49:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244462AbhCAVs2 (ORCPT ); Mon, 1 Mar 2021 16:48:28 -0500 Received: from mail.kernel.org ([198.145.29.99]:48856 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238249AbhCARYA (ORCPT ); Mon, 1 Mar 2021 12:24:00 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 12E2465068; Mon, 1 Mar 2021 16:48:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1614617331; bh=LhcZVeNCRJS1Z6vXuuq/RF6MV1TwjipyFenDsbvlGMM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=1BRd3kAuUxlJ/IQ0F1kPn1f9oTPlWKlKrRy4xVSl/YLhoX3zMyWRfKXiwuJLydIwF 6gkbA9eWF7bKSkNzVi2dVt039rVLvvZYDH6ypWdGVHpLqncm5HbAiC7ZapUXK9ik4O b8W0PN3paQhS9K5rxgRuAMSDxHe8VxRJJund+h3g= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Jan Kara , Paolo Valente , Jens Axboe Subject: [PATCH 5.4 009/340] bfq: Avoid false bfq queue merging Date: Mon, 1 Mar 2021 17:09:13 +0100 Message-Id: <20210301161048.765559820@linuxfoundation.org> X-Mailer: git-send-email 2.30.1 In-Reply-To: <20210301161048.294656001@linuxfoundation.org> References: <20210301161048.294656001@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Jan Kara commit 41e76c85660c022c6bf5713bfb6c21e64a487cec upstream. 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 Signed-off-by: Jens Axboe Signed-off-by: Greg Kroah-Hartman --- block/bfq-iosched.c | 1 + 1 file changed, 1 insertion(+) --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -2937,6 +2937,7 @@ static void __bfq_set_in_service_queue(s } bfqd->in_service_queue = bfqq; + bfqd->in_serv_last_pos = 0; } /*