linux-kernel - Re: [PATCH v2 0/2] cpufreq: Fix a circular lock dependency problem

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Message-ID: <11110536.k4alKVjaiY@aspire.rjw.lan>
Date:   Thu, 26 Jul 2018 11:06:58 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Waiman Long <longman@...hat.com>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Subject: Re: [PATCH v2 0/2] cpufreq: Fix a circular lock dependency problem

On Tuesday, July 24, 2018 8:26:03 PM CEST Waiman Long wrote:
>  v2:
>   - Remove the retry loop in the store method.
> 
> This patchset works around a circular lock dependency issue in the
> cpufreq driver reported by lockdep. The two locks involved are the
> cpu_hotplup_lock and the reference count of a sysfs file.
> 
> The cpufreq_register_driver() function uses the lock sequence:
> 
>   cpus_read_lock --> kn->count
> 
> Whereas the cpufreq sysfs store method uses the sequence:
> 
>   kn->count --> cpus_read_lock
> 
> This is not really an issue as a shared lock is used on the
> cpu_hotplup_lock. However, the lockdep code isn't able to handle
> shared locking. So one way to work around this is to define a
> cpus_read_trylock() function and uses it in the store method instead.
> 
> Waiman Long (2):
>   cpu/hotplug: Add a cpus_read_trylock() function
>   cpufreq: Fix a circular lock dependency problem
> 
>  drivers/cpufreq/cpufreq.c | 7 ++++++-
>  include/linux/cpu.h       | 2 ++
>  kernel/cpu.c              | 6 ++++++
>  3 files changed, 14 insertions(+), 1 deletion(-)
> 
> 

I'm queuing up this series for 4.19.

If anyone has any concerns regarding it, please let me know.

Thanks,
Rafael