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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4CB04C76188 for ; Mon, 3 Apr 2023 14:21:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233157AbjDCOVS (ORCPT ); Mon, 3 Apr 2023 10:21:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42154 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233074AbjDCOVJ (ORCPT ); Mon, 3 Apr 2023 10:21:09 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9B2D32D7D9 for ; Mon, 3 Apr 2023 07:20:49 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id DAF6561D2B for ; Mon, 3 Apr 2023 14:20:46 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id F1BD0C433EF; Mon, 3 Apr 2023 14:20:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1680531646; bh=G7LSSRoHa3o5x+mUN5YLL63FpHLw8VRIA0LkyNNtO6A=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=VWrN5hUP3EwP+MO0IGnLPfttKv1sl5hk0BieTuliFQF2/MG5gwMQSw6UL3blzpfk2 qKB5HzUEIWzAq8Ncs9uXaIzluiWomNvrBp5mDt5NM3au8RoaEvy7Y1ORqaa5EqhBxr NP4sKanfa0PoTEreUCTk1Y8OdS4pNke4CN+ijd8s= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Zhang Qiao , Roman Kagan , "Peter Zijlstra (Intel)" Subject: [PATCH 5.4 056/104] sched/fair: sanitize vruntime of entity being placed Date: Mon, 3 Apr 2023 16:08:48 +0200 Message-Id: <20230403140406.500673368@linuxfoundation.org> X-Mailer: git-send-email 2.40.0 In-Reply-To: <20230403140403.549815164@linuxfoundation.org> References: <20230403140403.549815164@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Zhang Qiao commit 829c1651e9c4a6f78398d3e67651cef9bb6b42cc upstream. When a scheduling entity is placed onto cfs_rq, its vruntime is pulled to the base level (around cfs_rq->min_vruntime), so that the entity doesn't gain extra boost when placed backwards. However, if the entity being placed wasn't executed for a long time, its vruntime may get too far behind (e.g. while cfs_rq was executing a low-weight hog), which can inverse the vruntime comparison due to s64 overflow. This results in the entity being placed with its original vruntime way forwards, so that it will effectively never get to the cpu. To prevent that, ignore the vruntime of the entity being placed if it didn't execute for much longer than the characteristic sheduler time scale. [rkagan: formatted, adjusted commit log, comments, cutoff value] Signed-off-by: Zhang Qiao Co-developed-by: Roman Kagan Signed-off-by: Roman Kagan Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20230130122216.3555094-1-rkagan@amazon.de Signed-off-by: Greg Kroah-Hartman --- kernel/sched/fair.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -3881,6 +3881,7 @@ static void place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial) { u64 vruntime = cfs_rq->min_vruntime; + u64 sleep_time; /* * The 'current' period is already promised to the current tasks, @@ -3905,8 +3906,18 @@ place_entity(struct cfs_rq *cfs_rq, stru vruntime -= thresh; } - /* ensure we never gain time by being placed backwards. */ - se->vruntime = max_vruntime(se->vruntime, vruntime); + /* + * Pull vruntime of the entity being placed to the base level of + * cfs_rq, to prevent boosting it if placed backwards. If the entity + * slept for a long time, don't even try to compare its vruntime with + * the base as it may be too far off and the comparison may get + * inversed due to s64 overflow. + */ + sleep_time = rq_clock_task(rq_of(cfs_rq)) - se->exec_start; + if ((s64)sleep_time > 60LL * NSEC_PER_SEC) + se->vruntime = vruntime; + else + se->vruntime = max_vruntime(se->vruntime, vruntime); } static void check_enqueue_throttle(struct cfs_rq *cfs_rq);