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SubjectRe: [PATCH 2/2] cpufreq: Fix a circular lock dependency problem
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.


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