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SubjectRe: [PATCH 2/2] cpufreq: Fix a circular lock dependency problem
On Mon, Jul 23, 2018 at 9:16 PM, Peter Zijlstra <peterz@infradead.org> wrote:
> On Mon, Jul 23, 2018 at 01:49:39PM -0400, Waiman Long wrote:
>> drivers/cpufreq/cpufreq.c | 16 +++++++++++++++-
>> 1 file changed, 15 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
>> index b0dfd32..9cf02d7 100644
>> --- a/drivers/cpufreq/cpufreq.c
>> +++ b/drivers/cpufreq/cpufreq.c
>> @@ -922,8 +922,22 @@ static ssize_t store(struct kobject *kobj, struct attribute *attr,
>> struct cpufreq_policy *policy = to_policy(kobj);
>> struct freq_attr *fattr = to_attr(attr);
>> ssize_t ret = -EINVAL;
>> + int retries = 3;
>>
>> - cpus_read_lock();
>> + /*
>> + * cpus_read_trylock() is used here to work around a circular lock
>> + * dependency problem with respect to the cpufreq_register_driver().
>> + * With a simple retry loop, the chance of not able to get the
>> + * read lock is extremely small.
>> + */
>> + while (!cpus_read_trylock()) {
>> + if (retries-- <= 0)
>> + return -EBUSY;
>> + /*
>> + * Sleep for about 50ms and retry again.
>> + */
>> + msleep(50);
>> + }
>
> That's atrocious.

Agreed.

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