Re: [PATCH v2 6/6] slab: Introduce kmalloc_nolock() and kfree_nolock().

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 2025-07-08 18:53:03 [-0700], Alexei Starovoitov wrote:
> @@ -4555,6 +4707,53 @@ static void __slab_free(struct kmem_cache *s, struct slab *slab,
>  	discard_slab(s, slab);
>  }
>  
> +static DEFINE_PER_CPU(struct llist_head, defer_free_objects);
> +static DEFINE_PER_CPU(struct irq_work, defer_free_work);

static DEFINE_PER_CPU(struct llist_head, defer_free_objects) = LLIST_HEAD_INIT(defer_free_objects);
static DEFINE_PER_CPU(struct irq_work, defer_free_work) = IRQ_WORK_INIT(free_deferred_objects);

would allow you to avoid init_defer_work().

> +static void free_deferred_objects(struct irq_work *work)
> +{
> +	struct llist_head *llhead = this_cpu_ptr(&defer_free_objects);
> +	struct llist_node *llnode, *pos, *t;
…
> +}
> +
> +static int __init init_defer_work(void)
> +{
> +	int cpu;
> +
> +	for_each_possible_cpu(cpu) {
> +		init_llist_head(per_cpu_ptr(&defer_free_objects, cpu));
> +		init_irq_work(per_cpu_ptr(&defer_free_work, cpu),
> +			      free_deferred_objects);
> +	}
> +	return 0;
> +}
> +late_initcall(init_defer_work);
> +
> +static void defer_free(void *head)
> +{
> +	if (llist_add(head, this_cpu_ptr(&defer_free_objects)))
> +		irq_work_queue(this_cpu_ptr(&defer_free_work));

If you group &defer_free_objects and &defer_free_work into a struct you
could avoid using this_cpu_ptr twice.
Having both in one struct would allow to use container_of() in
free_deferred_objects() to get the free list.

> +}
…
> @@ -4844,6 +5064,62 @@ void kfree(const void *object)
>  }
>  EXPORT_SYMBOL(kfree);
>  
> +/*
> + * Can be called while holding raw_spin_lock or from IRQ and NMI,
raw_spinlock_t

> + * but only for objects allocated by kmalloc_nolock(),
> + * since some debug checks (like kmemleak and kfence) were
> + * skipped on allocation. large_kmalloc is not supported either.
> + */
> +void kfree_nolock(const void *object)
> +{
…

Sebastian