On Mon, Jul 23, 2018 at 9:16 PM, Peter Zijlstra <pet...@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.