Re: [PATCH v2 01/10] drivers base/arch_topology: free cpumask cpus_to_visit

From: Dietmar Eggemann
Date: Fri Jul 07 2017 - 11:50:52 EST

On 06/07/17 12:15, Viresh Kumar wrote:
> On 06-07-17, 11:59, Juri Lelli wrote:
>> On 06/07/17 15:52, Viresh Kumar wrote:


>> If that's the case I'm wondering however if we need explicit
>> synchronization though. Otherwise both threads can read the mask as
>> full, clear only their bits and not schedule the workfn?
> Maybe not as the policies are created one by one only, not concurrently.
>> But, can the policies be concurrently initialized? Or is the
>> initialization process serialized or the different domains?
> There can be complex cases here. For example consider this.
> Only the little CPUs are brought online at boot. Their policy is set and they
> are cleared from the cpus_to_visit mask. Now we try to bring any big CPU online
> and at the same time try changing min/max from sysfs for the LITTLE CPU policy.
> The notifier may get called concurrently here I believe and cause the problem I
> mentioned earlier.

I chatted with Juri and your proposed fix to do the unregister before
the free makes sense to us. Thanks for spotting this! I will change in
the next version.