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=-7.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED 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 EF4FBC282C0 for ; Fri, 25 Jan 2019 14:31:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B4294218D0 for ; Fri, 25 Jan 2019 14:31:57 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=linaro.org header.i=@linaro.org header.b="SKOJ4pwp" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726999AbfAYOb4 (ORCPT ); Fri, 25 Jan 2019 09:31:56 -0500 Received: from mail-it1-f194.google.com ([209.85.166.194]:39638 "EHLO mail-it1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726122AbfAYObz (ORCPT ); Fri, 25 Jan 2019 09:31:55 -0500 Received: by mail-it1-f194.google.com with SMTP id a6so9844376itl.4 for ; Fri, 25 Jan 2019 06:31:54 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc:content-transfer-encoding; bh=t9i4bOBLGTAvNS6M38apgzthf/lmEx7fFpXcnbxk9Yg=; b=SKOJ4pwp5B/7u/ji5UhMDJzbTj+tY9nExd9hSZYcHWWGPMOWD5f+fgDxOdFPxc9c1p uZ5scGeIVdc8JnKwYF6jQFekZxaC1T0jujfELGf0iRjAo9la9kwTewUojhcbZkQO+GsR JPj0pdiy+jeyu/zFvpRbdiBaVDinA+yYWbweA= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc:content-transfer-encoding; bh=t9i4bOBLGTAvNS6M38apgzthf/lmEx7fFpXcnbxk9Yg=; b=mlj4s3MPzziqAC+KROCkq3yd+WM27HYPQITUoQXojj8UsPtaNcvTHBmt4xh2ufHWpN iihvVsAbTUdZuIDsbyqA6yildvJwMIbDlEyqTYvCZgwFoDqbF72ajSxWpm099fdm1A3B YD9VizISkeKtGHZFqHVOahDZgRBCgBtXWSRcBKOVFCZ2m5otnMdGFJU8h/1RC9seRjMj aajfed51D6lQt3kZrVkAUrLjyX7aSXv2KqSmztfjTaFGr35Cu7eRuLjl2o6s5t1pVTuc CAHCpkrRzbTK6yqbcfSOcm/jVPPy02ua5l8nFY778wxms8Kx1+2ZJttDGLgkcWTrr9dD wJhA== X-Gm-Message-State: AJcUuketb4bVjUzof03zy83O2fHd7xVq2nFga2QtJIxK8rnijjVMbqdB oAB+8D2ALGo4XOPNvoZ3bxfmnLTzo33FewcEvommGidsCfg= X-Google-Smtp-Source: ALg8bN5eaPZ7aYnAf/tuuouaRVgbC7wqULTX/r0oSefopsjuA8SyS5IgANqVaut/80pAlZT59TLrH4LApPEMVbS8xq8= X-Received: by 2002:a05:660c:a8f:: with SMTP id m15mr4184470itk.114.1548426714130; Fri, 25 Jan 2019 06:31:54 -0800 (PST) MIME-Version: 1.0 References: <20190121144628.GA28655@linaro.org> In-Reply-To: <20190121144628.GA28655@linaro.org> From: Vincent Guittot Date: Fri, 25 Jan 2019 15:31:43 +0100 Message-ID: Subject: Re: Crash in list_add_leaf_cfs_rq due to bad tmp_alone_branch To: Sargun Dhillon Cc: LKML , Ingo Molnar , Peter Zijlstra , Tejun Heo , Peter Zijlstra , Gabriel Hartmann , Gabriel Hartmann Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Sargun, On Mon, 21 Jan 2019 at 15:46, Vincent Guittot wrote: > > Hi Sargun, > > Le Friday 18 Jan 2019 =C3=A0 15:06:28 (+0100), Vincent Guittot a =C3=A9cr= it : > > On Fri, 18 Jan 2019 at 11:16, Vincent Guittot > > wrote: > > > > > > On Wed, 9 Jan 2019 at 23:43, Sargun Dhillon wrote: > > > > > > > > On Wed, Jan 9, 2019 at 2:14 PM Sargun Dhillon wr= ote: > > > > > > > > > > I picked up c40f7d74c741a907cfaeb73a7697081881c497d0 sched/fair: = Fix > > > > > infinite loop in update_blocked_averages() by reverting a9e7f6544= b9c > > > > > and put it on top of 4.19.13. In addition to this, I uninlined > > > > > list_add_leaf_cfs_rq for debugging. > > > > With the fix above applied, the code that manages the leaf_cfs_rq_list > > is the same since v4.9. > > Have you noticed similar problem on other older kernel version between > > v4.9 and v4.19 ? The problem might have been introduce while modifying > > other part of the scheduler like the sequence for adding/removing > > cgroup. > > > > Knowing the most recent kernel version without the problem could help > > to narrow the problem > > > > Thanks, > > Vincent > > > > > > > > > > > > This revealed a new bug that we didn't get to because we kept get= ting > > > > > crashes from the previous issue. When we are running with cgroups= that > > > > > are rapidly changing, with CFS bandwidth control, and in addition > > > > > using the cpusets cgroup, we see this crash. Specifically, it see= ms to > > > > > occur with cgroups that are throttled and we change the allowed > > > > > cpuset. > > > > > > Thanks for the context, I will try to reproduce the problem and > > > understand how we can stop in the middle of walking to the > > > sched_entity branch with a parent not already added > > > > > > How many cgroup level have you got in you setup ? > > > > > > > > > > > > > > > > This patch from Gabriel should fix the problem: > > > > > > > > > > > > [PATCH] sched/fair: Reset tmp_alone_branch on cfs_rq delete > > > > > > > > When a child cfs_rq is added to the leaf cfs_rq list before its par= ent > > > > tmp_alone_branch is set to point to the child in preparation for th= e > > > > parent being added. > > > > > > > > If the child is deleted before the parent is added then tmp_alone_b= ranch > > > > points to a freed cfs_rq. Any future reference to tmp_alone_branch = will > > > > result in a use after free. > > > > > > So, the patch below is a temporary fix that helps to recover from the > > > situation where tmp_alone_branch doesn't finished back to > > > rq->leaf_cfs_rq_list > > > But this situation should not happened at the beginning > > I have been able to reproduce the situation where tmp_alone_branch doesn'= t > point to rq->leaf_cfs_rq_list after enqueuing a task. > > Can you try the patch below which ensures all cfs_rq of a cgroup branch w= ill > be added in the list even if throttled ? Did you get a chance to test this patch ? Regards, Vincent > > The algorithm used to order cfs_rq in rq->leaf_cfs_rq_list assumes that > it will walk down to root the 1st time a cfs_rq is used and we will finis= hed > to add either a cfs_rq without parent or a cfs_rq with a parent that is a= lready > on the list. But this is not always true in presence of throttling. > Because a cfs_rq can be throttled even if it has never been used but othe= r CPUS > of the cgroup have already used all the bandwdith, we are not sure to go = down to > the root and add all cfs_rq in the list. > > Ensure that all cfs_rq will be added in the list even if they are throttl= ed. > > Signed-off-by: Vincent Guittot > --- > kernel/sched/fair.c | 17 +++++++++++++++++ > 1 file changed, 17 insertions(+) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 6483834..ae468ab 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -352,6 +352,20 @@ static inline void list_del_leaf_cfs_rq(struct cfs_r= q *cfs_rq) > } > } > > +static inline void list_add_branch_cfs_rq(struct sched_entity *se, struc= t rq *rq) > +{ > +struct cfs_rq *cfs_rq; > + > + for_each_sched_entity(se) { > + cfs_rq =3D cfs_rq_of(se); > + list_add_leaf_cfs_rq(cfs_rq); > + > + /* If parent is already in the list, we can stop */ > + if (rq->tmp_alone_branch =3D=3D &rq->leaf_cfs_rq_list) > + break; > + } > +} > + > /* Iterate through all leaf cfs_rq's on a runqueue: */ > #define for_each_leaf_cfs_rq(rq, cfs_rq) \ > list_for_each_entry_rcu(cfs_rq, &rq->leaf_cfs_rq_list, leaf_cfs_r= q_list) > @@ -5177,6 +5191,9 @@ enqueue_task_fair(struct rq *rq, struct task_struct= *p, int flags) > > } > > + /* Ensure that all cfs_rq have been added to the list */ > + list_add_branch_cfs_rq(se, rq); > + > hrtick_update(rq); > } > > > > > > > > > > > > > > > > > Signed-off-by: Gabriel Hartmann > > > > Reported-by: Sargun Dhillon > > > > --- > > > > kernel/sched/fair.c | 5 +++++ > > > > 1 file changed, 5 insertions(+) > > > > > > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > > > > index 7137bc343b4a..0987629cbb76 100644 > > > > --- a/kernel/sched/fair.c > > > > +++ b/kernel/sched/fair.c > > > > @@ -347,6 +347,11 @@ static inline void list_add_leaf_cfs_rq(struct > > > > cfs_rq *cfs_rq) > > > > static inline void list_del_leaf_cfs_rq(struct cfs_rq *cfs_rq) > > > > { > > > > if (cfs_rq->on_list) { > > > > + struct rq *rq =3D rq_of(cfs_rq); > > > > + > > > > + if (rq->tmp_alone_branch =3D=3D &cfs_rq->leaf_cfs_rq_list) > > > > + rq->tmp_alone_branch =3D &rq->leaf_cfs_rq_list; > > > > + > > > > list_del_rcu(&cfs_rq->leaf_cfs_rq_list); > > > > cfs_rq->on_list =3D 0; > > > > }