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SubjectRe: [RFC PATCH 11/19] cpufreq: assert policy->rwsem is held in __cpufreq_governor
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@rjwysocki.net>
>> Cc: Viresh Kumar <viresh.kumar@linaro.org>
>> Signed-off-by: Juri Lelli <juri.lelli@arm.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. The proper fix is to have the governor "export" the
attributes it wants to add/remove and have the cpufreq framework do the
adding/removing of the attributes from sysfs for the governor.

Thanks,
Saravana

--
Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project

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