linux-kernel - Re: 5.6-rc3: WARNING: CPU: 48 PID: 17435 at kernel/sched/fair.c:380 enqueue_task

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Message-Id: <805cbe05-2424-7d74-5e11-37712c189eb6@de.ibm.com>
Date:   Wed, 4 Mar 2020 20:38:16 +0100
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     Dietmar Eggemann <dietmar.eggemann@....com>,
        Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: 5.6-rc3: WARNING: CPU: 48 PID: 17435 at kernel/sched/fair.c:380
 enqueue_task_fair+0x328/0x440



On 04.03.20 20:19, Dietmar Eggemann wrote:
>> I just realized that this system has something special. Some month ago I created 2 slices
>> $ head /etc/systemd/system/*.slice
>> ==> /etc/systemd/system/machine-production.slice <==
>> [Unit]
>> Description=VM production
>> Before=slices.target
>> Wants=machine.slice
>> [Slice]
>> CPUQuota=2000%
>> CPUWeight=1000
>>
>> ==> /etc/systemd/system/machine-test.slice <==
>> [Unit]
>> Description=VM production
>> Before=slices.target
>> Wants=machine.slice
>> [Slice]
>> CPUQuota=300%
>> CPUWeight=100
>>
>>
>> And the guests are then put into these slices. that also means that this test will never use more than the 2300%.
>> No matter how much CPUs the system has.
> 
> If you could run this debug patch on top of your un-patched kernel, it would tell us which task (in the enqueue case)
> and which taskgroup is causing that.
> 
> You could then further dump the appropriate taskgroup directory under the cpu cgroup mountpoint
> (to see e.g. the CFS bandwidth data). 
> 
> I expect more than one hit since assert_list_leaf_cfs_rq() uses SCHED_WARN_ON, hence WARN_ONCE.

That was quick. FWIW, I messed up dumping the cgroup mountpoint (since I restarted my guests after this happened).
Will retry. See the dmesg attached. 

View attachment "output" of type "text/plain" (49696 bytes)