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=-6.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 1A664C43219 for ; Tue, 30 Apr 2019 12:06:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D2C612075E for ; Tue, 30 Apr 2019 12:06:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1556625977; bh=qRmKrYYbqkg1FwSL1lD95/YIPLn4v7ox5OG63TAr2ZE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=WyUd0Qzep7REq1KUMjUtMyJ5CGMDdyT1AzWP65R+Zk3DmvmShsMeZoSUb4ANecWD1 lWOemcrqnW1dhTGfCyiYZ5HId2qJccGYNZKdQLkPlvBnK/khSFEIMxmgAvZVcO57j2 N57qbQTISYqG887wMdV4/7b7QCKg0gVkNCNnTITk= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729260AbfD3MGQ (ORCPT ); Tue, 30 Apr 2019 08:06:16 -0400 Received: from mail.kernel.org ([198.145.29.99]:48896 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727992AbfD3LlW (ORCPT ); Tue, 30 Apr 2019 07:41:22 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id C14E921670; Tue, 30 Apr 2019 11:41:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1556624481; bh=qRmKrYYbqkg1FwSL1lD95/YIPLn4v7ox5OG63TAr2ZE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Ig2rSMqPuAGDv0kQchaR05pqMQ0PzekHV/DzUArNf9LRxfVOzbxKYtnQnw2jYutH0 k4ETFoSpe3vX3R3HZgkJE3QF9vTv3E6mGenaR7k9zUX0SxHqJdWaejJSBrY/zKr0Pe WF+dzj3qJauwOZoo9QTVq8uxxlkP+b5FKqllpNqg= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Xie XiuQi , "Peter Zijlstra (Intel)" , Linus Torvalds , Thomas Gleixner , cj.chengjian@huawei.com, Ingo Molnar Subject: [PATCH 4.14 10/53] sched/numa: Fix a possible divide-by-zero Date: Tue, 30 Apr 2019 13:38:17 +0200 Message-Id: <20190430113552.326734493@linuxfoundation.org> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20190430113549.400132183@linuxfoundation.org> References: <20190430113549.400132183@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Xie XiuQi commit a860fa7b96e1a1c974556327aa1aee852d434c21 upstream. sched_clock_cpu() may not be consistent between CPUs. If a task migrates to another CPU, then se.exec_start is set to that CPU's rq_clock_task() by update_stats_curr_start(). Specifically, the new value might be before the old value due to clock skew. So then if in numa_get_avg_runtime() the expression: 'now - p->last_task_numa_placement' ends up as -1, then the divider '*period + 1' in task_numa_placement() is 0 and things go bang. Similar to update_curr(), check if time goes backwards to avoid this. [ peterz: Wrote new changelog. ] [ mingo: Tweaked the code comment. ] Signed-off-by: Xie XiuQi Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: cj.chengjian@huawei.com Cc: Link: http://lkml.kernel.org/r/20190425080016.GX11158@hirez.programming.kicks-ass.net Signed-off-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman --- kernel/sched/fair.c | 4 ++++ 1 file changed, 4 insertions(+) --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -2026,6 +2026,10 @@ static u64 numa_get_avg_runtime(struct t if (p->last_task_numa_placement) { delta = runtime - p->last_sum_exec_runtime; *period = now - p->last_task_numa_placement; + + /* Avoid time going backwards, prevent potential divide error: */ + if (unlikely((s64)*period < 0)) + *period = 0; } else { delta = p->se.avg.load_sum / p->se.load.weight; *period = LOAD_AVG_MAX;