linux-kernel - Re: [External] Re: Fwd: WARNING: CPU: 13 PID: 3837105 at kernel/sched/sched.h:1561 __cfsb_csd

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Message-ID: <3544d5e3-3070-9ddc-fa6c-a05ed35dfd14@bytedance.com>
Date:   Thu, 7 Sep 2023 16:59:22 +0800
From:   Hao Jia <jiahao.os@...edance.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Benjamin Segall <bsegall@...gle.com>,
        Bagas Sanjaya <bagasdotme@...il.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Igor Raits <igor.raits@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Regressions <regressions@...ts.linux.dev>,
        Linux Stable <stable@...r.kernel.org>
Subject: Re: [External] Re: Fwd: WARNING: CPU: 13 PID: 3837105 at
 kernel/sched/sched.h:1561 __cfsb_csd_unthrottle+0x149/0x160



On 2023/9/5 Peter Zijlstra wrote:
> On Thu, Aug 31, 2023 at 04:48:29PM +0800, Hao Jia wrote:
> 
>> If I understand correctly, rq->clock_update_flags may be set to
>> RQCF_ACT_SKIP after __schedule() holds the rq lock, and sometimes the rq
>> lock may be released briefly in __schedule(), such as newidle_balance(). At
>> this time Other CPUs hold this rq lock, and then calling
>> rq_clock_start_loop_update() may trigger this warning.
>>
>> This warning check might be wrong. We need to add assert_clock_updated() to
>> check that the rq clock has been updated before calling
>> rq_clock_start_loop_update().
>>
>> Maybe some things can be like this?
> 
> Urgh, aside from it being white space mangled, I think this is entirely
> going in the wrong direction.
> 
> Leaking ACT_SKIP is dodgy as heck.. it's entirely too late to think
> clearly though, I'll have to try again tomorrow.

Hi Peter,

Do you think this fix method is correct? Or should we go back to the 
beginning and move update_rq_clock() from unthrottle_cfs_rq()?

Thanks,
Hao