linux-kernel - Re: [PATCH v13 03/11] cpuset: Simply allocation and freeing of cpumasks

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Date:   Mon, 15 Oct 2018 14:43:22 -0400
From:   Waiman Long <longman@...hat.com>
To:     Tom Hromatka <tom.hromatka@...cle.com>, Tejun Heo <tj@...nel.org>,
        Li Zefan <lizefan@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>
Cc:     cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, kernel-team@...com, pjt@...gle.com,
        luto@...capital.net, Mike Galbraith <efault@....de>,
        torvalds@...ux-foundation.org, Roman Gushchin <guro@...com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Patrick Bellasi <patrick.bellasi@....com>
Subject: Re: [PATCH v13 03/11] cpuset: Simply allocation and freeing of
 cpumasks

On 10/15/2018 02:35 PM, Tom Hromatka wrote:
>
>
> On 10/12/2018 11:55 AM, Waiman Long wrote:
>> The previous commit introduces a new subparts_cpus mask into the cpuset
>> data structure and a new tmpmasks structure.  Managing the allocation
>> and freeing of those cpumasks is becoming more complex.
>>
>> So a number of helper functions are added to simplify and streamline
>> the management of those cpumasks. To make it simple, all the cpumasks
>> are now pre-cleared on allocation.
>>
>> Signed-off-by: Waiman Long <longman@...hat.com>
>> ---
>>   kernel/cgroup/cpuset.c | 104
>> +++++++++++++++++++++++++++++++++----------------
>>   1 file changed, 71 insertions(+), 33 deletions(-)
>>
>> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
>> index 29a2bdc..9ac5f94 100644
>> --- a/kernel/cgroup/cpuset.c
>> +++ b/kernel/cgroup/cpuset.c
>> @@ -456,6 +456,57 @@ static int is_cpuset_subset(const struct cpuset
>> *p, const struct cpuset *q)
>>   }
>>     /**
>> + * alloc_cpumasks - allocate three cpumasks for cpuset
>> + * @cs:  the cpuset that have cpumasks to be allocated.
>> + * @tmp: the tmpmasks structure pointer
>> + * Return: 0 if successful, -ENOMEM otherwise.
>> + *
>> + * Only one of the two input arguments should be non-NULL.
>> + */
>> +static inline int alloc_cpumasks(struct cpuset *cs, struct tmpmasks
>> *tmp)
>> +{
>> +    cpumask_var_t *pmask1, *pmask2, *pmask3;
>> +
>> +    if (cs) {
>> +        pmask1 = &cs->cpus_allowed;
>> +        pmask2 = &cs->effective_cpus;
>> +        pmask3 = &cs->subparts_cpus;
>> +    } else {
>> +        pmask1 = &tmp->new_cpus;
>> +        pmask2 = &tmp->addmask;
>> +        pmask3 = &tmp->delmask;
>> +    }
>> +
>> +    if (!zalloc_cpumask_var(pmask1, GFP_KERNEL))
>> +        return -ENOMEM;
>> +
>> +    if (!zalloc_cpumask_var(pmask2, GFP_KERNEL))
>> +        goto free_one;
>> +
>> +    if (!zalloc_cpumask_var(pmask3, GFP_KERNEL))
>> +        goto free_two;
>> +
>> +    return 0;
>> +
>> +free_two:
>> +    free_cpumask_var(*pmask2);
>> +free_one:
>> +    free_cpumask_var(*pmask1);
>> +    return -ENOMEM;
>> +}
>> +
>> +/**
>> + * free_cpumasks - free cpumasks in a tmpmasks structure
>> + * @tmp: the tmpmasks structure pointer
>> + */
>> +static inline void free_cpumasks(struct tmpmasks *tmp)
>> +{
>> +    free_cpumask_var(tmp->new_cpus);
>> +    free_cpumask_var(tmp->addmask);
>> +    free_cpumask_var(tmp->delmask);
>> +}
>> +
>
> I hesitate to bring this up, but since you're respinning this
> patch for a different bug...
>
> Would it make sense to have free_cpumasks() have a similar
> API and behavior to alloc_cpumasks()?  I could see this potentially
> causing bugs/confusion in future patches.
>
> Thanks.
>
> Tom
>
>
Thanks for the comment. Yes I will make the change.

-Longman