Re: [PATCH 2/5] sched/topology: Wrappers for sched_domains_mutex

[Waiman Long <llong@redhat.com>]

On 3/7/25 4:32 AM, Juri Lelli wrote:
> On 05/03/25 10:52, Juri Lelli wrote:
>> On 04/03/25 11:01, Waiman Long wrote:
>>> On 3/4/25 10:05 AM, Waiman Long wrote:
>>>>> --- a/kernel/sched/topology.c
>>>>> +++ b/kernel/sched/topology.c
>>>>> @@ -6,6 +6,19 @@
>>>>>    #include <linux/bsearch.h>
>>>>>      DEFINE_MUTEX(sched_domains_mutex);
>>>>> +#ifdef CONFIG_SMP
>>>>> +void sched_domains_mutex_lock(void)
>>>>> +{
>>>>> +    mutex_lock(&sched_domains_mutex);
>>>>> +}
>>>>> +void sched_domains_mutex_unlock(void)
>>>>> +{
>>>>> +    mutex_unlock(&sched_domains_mutex);
>>>>> +}
>>>>> +#else
>>>>> +void sched_domains_mutex_lock(void) { }
>>>>> +void sched_domains_mutex_unlock(void) { }
>>>>> +#endif
>>>>>      /* Protected by sched_domains_mutex: */
>>>>>    static cpumask_var_t sched_domains_tmpmask;
>>>>> @@ -2791,7 +2804,7 @@ void partition_sched_domains_locked(int
>>>>> ndoms_new, cpumask_var_t doms_new[],
>>>>>    void partition_sched_domains(int ndoms_new, cpumask_var_t doms_new[],
>>>>>                     struct sched_domain_attr *dattr_new)
>>>>>    {
>>>>> -    mutex_lock(&sched_domains_mutex);
>>>>> +    sched_domains_mutex_lock();
>>>>>        partition_sched_domains_locked(ndoms_new, doms_new, dattr_new);
>>>>> -    mutex_unlock(&sched_domains_mutex);
>>>>> +    sched_domains_mutex_unlock();
>>>>>    }
>>>> There are two "lockdep_assert_held(&sched_domains_mutex);" statements in
>>>> topology.c file and one in cpuset.c. That can be problematic in the
>>>> non-SMP case. Maybe another wrapper to do the assert?
>>> Ignore that as both topology.c and cpuset.c will only be compiled if
>>> CONFIG_SMP is defined. IOW, you don't need the the "#ifdef CONFIG_SMP"
>>> above.
>> Indeed!
> Ah, actually I believe next patch (3/5) introduce usage for the !SMP
> case in sched_rt_handler()
>
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index 4b8e33c615b1..8cebe71d2bb1 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -2910,6 +2910,7 @@ static int sched_rt_handler(const struct ctl_table *table, int write, void *buff
>          int ret;
>
>          mutex_lock(&mutex);
> +       sched_domains_mutex_lock();
>          old_period = sysctl_sched_rt_period;
>          old_runtime = sysctl_sched_rt_runtime;
>
> @@ -2936,6 +2937,7 @@ static int sched_rt_handler(const struct ctl_table *table, int write, void *buff
>                  sysctl_sched_rt_period = old_period;
>                  sysctl_sched_rt_runtime = old_runtime;
>          }
> +       sched_domains_mutex_unlock();
>          mutex_unlock(&mutex);
>
>          return ret;
>
> So, I will need to add the ifdef back I guess (I removed it on v2). Do
> you agree?

You are right. That change does introduce the need to define the 
!CONFIG_SMP case. I was looking the existing uses o domains_mutex when 
making that suggestions.

It is a good catch.

Cheers,
Longman