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

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Date:	Sat, 30 Jan 2016 12:49:03 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Saravana Kannan <skannan@...eaurora.org>
Cc:	Viresh Kumar <viresh.kumar@...aro.org>,
	Juri Lelli <juri.lelli@....com>, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org, peterz@...radead.org,
	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 Friday, January 29, 2016 04:33:39 PM Saravana Kannan wrote:
> On 01/12/2016 02:20 AM, Viresh Kumar wrote:
> > 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")
> >
> 
> AFAIR, the ABBA issue was between the sysfs lock and the policy lock. 
> The fix for that issue should not be dropping the lock around 
> POLICY_EXIT.

Right.  Dropping the lock is a mistake (which I overlooked, sadly).

Thanks,
Rafael