linux-kernel - Re: [REGRESSION 4.20-rc1] 45975c7d21a1 ("rcu: Define RCU-sched API in terms of RCU for Tree RCU PREEMPT builds")

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Message-ID: <20190205130559.GA12858@localhost.localdomain>
Date:   Tue, 5 Feb 2019 21:05:59 +0800
From:   Tom Li <tomli@...li.me>
To:     Aaro Koskinen <aaro.koskinen@....fi>
Cc:     paulmck@...ux.ibm.com, ak@...ux.intel.com, bp@...en8.de,
        hpa@...or.com, linux-kernel@...r.kernel.org, mingo@...hat.com,
        rjw@...ysocki.net, ville.syrjala@...ux.intel.com,
        viresh.kumar@...aro.org, linux-mips@...r.kernel.org
Subject: Re: [REGRESSION 4.20-rc1] 45975c7d21a1 ("rcu: Define RCU-sched API
 in terms of RCU for Tree RCU PREEMPT builds")

On Tue, Feb 05, 2019 at 11:58:09AM +0200, Aaro Koskinen wrote:
> Can you try below fix? It works on my Loongson.

Hello Aaro, thanks for your response. But in case you've missed
the original thread, please check it at:

https://lkml.org/lkml/2018/11/13/857

My problem is NOT about how to fix the problem on Loongson (or
x86): the patch in the original thread (only has one-line-of-code,
simply changes timing of cpufreq_core_init), or your patch, is
indeed working. But they are workarounds, the real issue is the race
condition in cpufreq.

My question is

1. What's the progress and current consensus about how the underlying
problem can be fixed.

2. If there's no consensus since November, is it possible that we land
a hotfix patch to linux-stable as a temporary workaround?

Cheers,
Tom Li.