On 09/12/2013 10:55 AM, Viresh Kumar wrote:
> This broke after a recent change "cedb70a cpufreq: Split __cpufreq_remove_dev()
> into two parts" from Srivatsa..
>
> Consider a scenario where we have two CPUs in a policy (0 & 1) and we are
> removing cpu 1. On the call to __cpufreq_remove_dev_prepare() we have cleared 1
> from policy->cpus and now on a call to __cpufreq_remove_dev_finish() we read
> cpumask_weight of policy->cpus, which will come as 1 and this code will behave
> as if we are removing the last cpu from policy :)
>
> Fix it by clearing cpu mask in __cpufreq_remove_dev_finish() instead of
> __cpufreq_remove_dev_prepare().
>
Oops! Good catch!
That said, your fix doesn't look correct. See below.
> Signed-off-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
> ---
> drivers/cpufreq/cpufreq.c | 14 +++++++-------
> 1 file changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 0e11fcb..b556d46 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -1175,12 +1175,9 @@ static int __cpufreq_remove_dev_prepare(struct device *dev,
> policy->governor->name, CPUFREQ_NAME_LEN);
> #endif
>
> - WARN_ON(lock_policy_rwsem_write(cpu));
> + lock_policy_rwsem_read(cpu);
> cpus = cpumask_weight(policy->cpus);
> -
> - if (cpus > 1)
> - cpumask_clear_cpu(cpu, policy->cpus);
> - unlock_policy_rwsem_write(cpu);
> + unlock_policy_rwsem_read(cpu);
>
> if (cpu != policy->cpu) {
> if (!frozen)
Around here, we call cpufreq_nominate_new_policy_cpu(), and if we haven't cleared
the CPU by then, there is a chance that it will nominate the same CPU that we are
taking offline. So its important to clear the CPU before that point.
> @@ -1222,9 +1219,12 @@ static int __cpufreq_remove_dev_finish(struct device *dev,
> return -EINVAL;
> }
>
> - lock_policy_rwsem_read(cpu);
> + WARN_ON(lock_policy_rwsem_write(cpu));
> cpus = cpumask_weight(policy->cpus);
> - unlock_policy_rwsem_read(cpu);
> +
> + if (cpus > 1)
> + cpumask_clear_cpu(cpu, policy->cpus);
> + unlock_policy_rwsem_write(cpu);
>
Perhaps we can retain the above as a read operation, ...
> /* If cpu is last user of policy, free policy */
> if (cpus == 1) {
>
... and change this suitably (from 1 to 0 etc..) ? To add to it, it will look more
clear as well:
if (cpus == 0) {
/* No cpus in policy, so free it */
} else {
/* Restart governor */
}
Regards,
Srivatsa S. Bhat
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