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

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Date:   Mon, 15 Oct 2018 12:35:39 -0600
From:   Tom Hromatka <tom.hromatka@...cle.com>
To:     Waiman Long <longman@...hat.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 10/12/2018 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