linux-kernel - Re: [Linux 5.18-rc1] WARNING: CPU: 1 PID: 0 at kernel/sched/fair.c:3355 update_blocked

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Message-ID: <000457c2-57af-95e3-7dff-2cbd99f0de5f@arm.com>
Date:   Wed, 6 Apr 2022 14:21:19 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Ammar Faizi <ammarfaizi2@...weeb.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc:     Ben Segall <bsegall@...gle.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        GNU/Weeb Mailing List <gwml@...r.gnuweeb.org>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Mel Gorman <mgorman@...e.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: Re: [Linux 5.18-rc1] WARNING: CPU: 1 PID: 0 at
 kernel/sched/fair.c:3355 update_blocked_averages

On 05/04/2022 15:13, Ammar Faizi wrote:
> On 4/5/22 7:21 PM, Dietmar Eggemann wrote:
>> Tried to recreate the issue but no success so far. I used you config
>> file, clang-14 and a Xeon CPU E5-2690 v2 (2 sockets 40 CPUs) with 20
>> two-level cgoupv1 taskgroups '/X/Y' with 'hackbench (10 groups, 40 fds)
>> + idling' running in all '/X/Y/'.
>>
>> What userspace are you running?
> 
> HP Laptop, Intel i7-1165G7, 8 CPUs, with 16 GB of RAM. Ubuntu 21.10.
> Just for
> daily workstation. Compiling kernel, browsing and coding stuff.

Can you check that CFS Bandwidth control (CONFIG_CFS_BANDWIDTH=y) is
still not used on Ubuntu desktop 21.10?

It shouldn't but I can't verify since I'm still on 20.04 LTS Desktop:

$ mount | grep "cgroup2\|\bcpu\b"
cgroup2 on /sys/fs/cgroup/unified type cgroup2 (rw,nosuid,nodev,noexec,relatime,nsdelegate)
cgroup on /sys/fs/cgroup/cpu,cpuacct type cgroup (rw,nosuid,nodev,noexec,relatime,cpu,cpuacct)

CPU controller is still used in cgroupv1. So cgroupv2 can't use it:

$ cat /sys/fs/cgroup/unified/cgroup.controllers
/* empty */

And there is no cgroupv1 hierarchy under /sys/fs/cgroup/cpu,cpuacct/ .

No cpu.cfs_quota_us files with something other than -1.

So CFS Bandwidth control is not used.

[...]