linux-kernel - Re: [RFC PATCH 11/19] cpufreq: assert policy->rwsem is held in __cpufreq

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Message-ID: <20160112102025.GC1084@ubuntu>
Date:	Tue, 12 Jan 2016 15:50:25 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Juri Lelli <juri.lelli@....com>
Cc:	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	peterz@...radead.org, rjw@...ysocki.net, mturquette@...libre.com,
	steve.muckle@...aro.org, vincent.guittot@...aro.org,
	morten.rasmussen@....com, dietmar.eggemann@....com
Subject: Re: [RFC PATCH 11/19] cpufreq: assert policy->rwsem is held in
 __cpufreq_governor

On 11-01-16, 17:35, Juri Lelli wrote:
> __cpufreq_governor works on policy, so policy->rwsem has to be held.
> Add assertion for such condition.
> 
> Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
> Cc: Viresh Kumar <viresh.kumar@...aro.org>
> Signed-off-by: Juri Lelli <juri.lelli@....com>
> ---
>  drivers/cpufreq/cpufreq.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index f1f9fbc..e7fc5c9 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -1950,6 +1950,9 @@ static int __cpufreq_governor(struct cpufreq_policy *policy,
>  	/* Don't start any governor operations if we are entering suspend */
>  	if (cpufreq_suspended)
>  		return 0;
> +
> +	lockdep_assert_held(&policy->rwsem);
> +

We had an ABBA problem with the EXIT governor callback and so this
rwsem is dropped just before that from set_policy()..

commit 955ef4833574 ("cpufreq: Drop rwsem lock around
CPUFREQ_GOV_POLICY_EXIT")

-- 
viresh