linux-kernel - RE: [PATCH] [RFC] rt: kernel/sched/core: fix kthread_park() pending too long when CPU un-plugged

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Date:   Fri, 8 Jan 2021 09:27:25 +0000
From:   Ran Wang <ran.wang_1@....com>
To:     Sebastian Siewior <bigeasy@...utronix.de>
CC:     Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jiafei Pan <jiafei.pan@....com>,
        "linux-rt-users@...r.kernel.org" <linux-rt-users@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] [RFC] rt: kernel/sched/core: fix kthread_park() pending
 too long when CPU un-plugged

Hi Sebastian,

On Friday, January 8, 2021 5:05 PM, Sebastian Siewior wrote:
> 
> On 2021-01-08 08:45:14 [+0000], Ran Wang wrote:
> > Hi Sebastian, Peter
> Hi,
> 
> > > I had a similar patch in -RT and dropped it in v5.10-rc7-rt16.
> > > It was added because RT couldn't boot since creating the boot-threads didn't work before the ksoftirqd was up. This was fixed by commit
> > >    26c7295be0c5e ("kthread: Do not preempt current task if it is
> > > going to call schedule()")
> >
> > I tried applying above commit to linux-5.6.y-rt, it could resolve my problem on LX2160ARDB, THANKS!
> 
> so in other words all this could have been avoided by using a supported or maintained RT series. The v5.4 series has this patch, v5.6 isn't
> maintained anymore so it is likely that there is more missing.

Thanks for let me know this.

The reason I trying linux-5.6-rt is that I have encountered other more serious issues on later RT version (even with v5.10-rc7-rt16), one of them
is CPU hot plug got stuck in irq_work_sync() which called by sugov_stop(), failure happen at 1st loop stress test every time.
I will try to collect more information and create another mail thread later.

Thanks & Regards,
Ran

> Sebastian