Re: [PATCH -next v5 2/3] cpuset: separate tmpmasks and cpuset allocation logic

[Waiman Long <llong@redhat.com>]

On 8/24/25 11:23 PM, Chen Ridong wrote:
> From: Chen Ridong <chenridong@huawei.com>
>
> The original alloc_cpumasks() served dual purposes: allocating cpumasks
> for both temporary masks (tmpmasks) and cpuset structures. This patch:
>
> 1. Decouples these allocation paths for better code clarity
> 2. Introduces dedicated alloc_tmpmasks() and dup_or_alloc_cpuset()
>     functions
> 3. Maintains symmetric pairing:
>     - alloc_tmpmasks() ↔ free_tmpmasks()
>     - dup_or_alloc_cpuset() ↔ free_cpuset()
>
> Signed-off-by: Chen Ridong <chenridong@huawei.com>
> ---
>   kernel/cgroup/cpuset.c | 127 ++++++++++++++++++++++-------------------
>   1 file changed, 69 insertions(+), 58 deletions(-)
>
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index aebda14cc67f..7b0b81c835bf 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -411,51 +411,47 @@ static void guarantee_online_mems(struct cpuset *cs, nodemask_t *pmask)
>   }
>   
>   /**
> - * alloc_cpumasks - allocate three cpumasks for cpuset
> - * @cs:  the cpuset that have cpumasks to be allocated.
> - * @tmp: the tmpmasks structure pointer
> + * alloc_cpumasks - Allocate an array of cpumask variables
> + * @pmasks: Pointer to array of cpumask_var_t pointers
> + * @size: Number of cpumasks to allocate
>    * Return: 0 if successful, -ENOMEM otherwise.
>    *
> - * Only one of the two input arguments should be non-NULL.
> + * Allocates @size cpumasks and initializes them to empty. Returns 0 on
> + * success, -ENOMEM on allocation failure. On failure, any previously
> + * allocated cpumasks are freed.
>    */
> -static inline int alloc_cpumasks(struct cpuset *cs, struct tmpmasks *tmp)
> +static inline int alloc_cpumasks(cpumask_var_t *pmasks[], u32 size)
>   {
> -	cpumask_var_t *pmask1, *pmask2, *pmask3, *pmask4;
> +	int i;
>   
> -	if (cs) {
> -		pmask1 = &cs->cpus_allowed;
> -		pmask2 = &cs->effective_cpus;
> -		pmask3 = &cs->effective_xcpus;
> -		pmask4 = &cs->exclusive_cpus;
> -	} else {
> -		pmask1 = &tmp->new_cpus;
> -		pmask2 = &tmp->addmask;
> -		pmask3 = &tmp->delmask;
> -		pmask4 = NULL;
> +	for (i = 0; i < size; i++) {
> +		if (!zalloc_cpumask_var(pmasks[i], GFP_KERNEL)) {
> +			while (--i >= 0)
> +				free_cpumask_var(*pmasks[i]);
> +			return -ENOMEM;
> +		}
>   	}
> -
> -	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;
> -
> -	if (pmask4 && !zalloc_cpumask_var(pmask4, GFP_KERNEL))
> -		goto free_three;
> -
> -
>   	return 0;
> +}
>   
> -free_three:
> -	free_cpumask_var(*pmask3);
> -free_two:
> -	free_cpumask_var(*pmask2);
> -free_one:
> -	free_cpumask_var(*pmask1);
> -	return -ENOMEM;
> +/**
> + * alloc_tmpmasks - Allocate temporary cpumasks for cpuset operations.
> + * @tmp: Pointer to tmpmasks structure to populate
> + * Return: 0 on success, -ENOMEM on allocation failure
> + */
> +static inline int alloc_tmpmasks(struct tmpmasks *tmp)
> +{
> +	/*
> +	 * Array of pointers to the three cpumask_var_t fields in tmpmasks.
> +	 * Note: Array size must match actual number of masks (3)
> +	 */
> +	cpumask_var_t *pmask[3] = {
> +		&tmp->new_cpus,
> +		&tmp->addmask,
> +		&tmp->delmask
> +	};
> +
> +	return alloc_cpumasks(pmask, ARRAY_SIZE(pmask));
>   }
>   
>   /**
> @@ -470,26 +466,46 @@ static inline void free_tmpmasks(struct tmpmasks *tmp)
>   }
>   
>   /**
> - * alloc_trial_cpuset - allocate a trial cpuset
> - * @cs: the cpuset that the trial cpuset duplicates
> + * dup_or_alloc_cpuset - Duplicate or allocate a new cpuset
> + * @cs: Source cpuset to duplicate (NULL for a fresh allocation)
> + *
> + * Creates a new cpuset by either:
> + * 1. Duplicating an existing cpuset (if @cs is non-NULL), or
> + * 2. Allocating a fresh cpuset with zero-initialized masks (if @cs is NULL)
> + *
> + * Return: Pointer to newly allocated cpuset on success, NULL on failure
>    */
> -static struct cpuset *alloc_trial_cpuset(struct cpuset *cs)
> +static struct cpuset *dup_or_alloc_cpuset(struct cpuset *cs)
>   {
>   	struct cpuset *trial;
>   
> -	trial = kmemdup(cs, sizeof(*cs), GFP_KERNEL);
> +	/* Allocate base structure */
> +	trial = cs ? kmemdup(cs, sizeof(*cs), GFP_KERNEL) :
> +		     kzalloc(sizeof(*cs), GFP_KERNEL);
>   	if (!trial)
>   		return NULL;
>   
> -	if (alloc_cpumasks(trial, NULL)) {
> +	/* Setup cpumask pointer array */
> +	cpumask_var_t *pmask[4] = {
> +		&trial->cpus_allowed,
> +		&trial->effective_cpus,
> +		&trial->effective_xcpus,
> +		&trial->exclusive_cpus
> +	};
> +
> +	if (alloc_cpumasks(pmask, ARRAY_SIZE(pmask))) {
>   		kfree(trial);
>   		return NULL;
>   	}
>   
> -	cpumask_copy(trial->cpus_allowed, cs->cpus_allowed);
> -	cpumask_copy(trial->effective_cpus, cs->effective_cpus);
> -	cpumask_copy(trial->effective_xcpus, cs->effective_xcpus);
> -	cpumask_copy(trial->exclusive_cpus, cs->exclusive_cpus);
> +	/* Copy masks if duplicating */
> +	if (cs) {
> +		cpumask_copy(trial->cpus_allowed, cs->cpus_allowed);
> +		cpumask_copy(trial->effective_cpus, cs->effective_cpus);
> +		cpumask_copy(trial->effective_xcpus, cs->effective_xcpus);
> +		cpumask_copy(trial->exclusive_cpus, cs->exclusive_cpus);
> +	}
> +
>   	return trial;
>   }
>   
> @@ -2332,7 +2348,7 @@ static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs,
>   	if (cpumask_equal(cs->cpus_allowed, trialcs->cpus_allowed))
>   		return 0;
>   
> -	if (alloc_cpumasks(NULL, &tmp))
> +	if (alloc_tmpmasks(&tmp))
>   		return -ENOMEM;
>   
>   	if (old_prs) {
> @@ -2476,7 +2492,7 @@ static int update_exclusive_cpumask(struct cpuset *cs, struct cpuset *trialcs,
>   	if (retval)
>   		return retval;
>   
> -	if (alloc_cpumasks(NULL, &tmp))
> +	if (alloc_tmpmasks(&tmp))
>   		return -ENOMEM;
>   
>   	if (old_prs) {
> @@ -2820,7 +2836,7 @@ int cpuset_update_flag(cpuset_flagbits_t bit, struct cpuset *cs,
>   	int spread_flag_changed;
>   	int err;
>   
> -	trialcs = alloc_trial_cpuset(cs);
> +	trialcs = dup_or_alloc_cpuset(cs);
>   	if (!trialcs)
>   		return -ENOMEM;
>   
> @@ -2881,7 +2897,7 @@ static int update_prstate(struct cpuset *cs, int new_prs)
>   	if (new_prs && is_prs_invalid(old_prs))
>   		old_prs = PRS_MEMBER;
>   
> -	if (alloc_cpumasks(NULL, &tmpmask))
> +	if (alloc_tmpmasks(&tmpmask))
>   		return -ENOMEM;
>   
>   	err = update_partition_exclusive_flag(cs, new_prs);
> @@ -3223,7 +3239,7 @@ ssize_t cpuset_write_resmask(struct kernfs_open_file *of,
>   	if (!is_cpuset_online(cs))
>   		goto out_unlock;
>   
> -	trialcs = alloc_trial_cpuset(cs);
> +	trialcs = dup_or_alloc_cpuset(cs);
>   	if (!trialcs) {
>   		retval = -ENOMEM;
>   		goto out_unlock;
> @@ -3456,15 +3472,10 @@ cpuset_css_alloc(struct cgroup_subsys_state *parent_css)
>   	if (!parent_css)
>   		return &top_cpuset.css;
>   
> -	cs = kzalloc(sizeof(*cs), GFP_KERNEL);
> +	cs = dup_or_alloc_cpuset(NULL);
>   	if (!cs)
>   		return ERR_PTR(-ENOMEM);
>   
> -	if (alloc_cpumasks(cs, NULL)) {
> -		kfree(cs);
> -		return ERR_PTR(-ENOMEM);
> -	}
> -
>   	__set_bit(CS_SCHED_LOAD_BALANCE, &cs->flags);
>   	fmeter_init(&cs->fmeter);
>   	cs->relax_domain_level = -1;
> @@ -3920,7 +3931,7 @@ static void cpuset_handle_hotplug(void)
>   	bool on_dfl = is_in_v2_mode();
>   	struct tmpmasks tmp, *ptmp = NULL;
>   
> -	if (on_dfl && !alloc_cpumasks(NULL, &tmp))
> +	if (on_dfl && !alloc_tmpmasks(&tmp))
>   		ptmp = &tmp;
>   
>   	lockdep_assert_cpus_held();
Reviewed-by: Waiman Long <longman@redhat.com>