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SubjectRe: [PATCH -mm] slub: fix cpu hotplug offline/online path
On Thu, 11 Oct 2007, Akinobu Mita wrote:

> > Why would get_cpu_slab not work?
>
>
> case CPU_DEAD:
> case CPU_DEAD_FROZEN:
> down_read(&slub_lock);
> list_for_each_entry(s, &slab_caches, list) {
> struct kmem_cache_cpu *c = get_cpu_slab(s, cpu);
>
> local_irq_save(flags);
> __flush_cpu_slab(s, cpu);
> local_irq_restore(flags);
> free_kmem_cache_cpu(c, cpu);
> s->cpu_slab[cpu] = NULL; <----------------------
> }
> up_read(&slub_lock);
> break;
>
> When CPU is offlined, cpu-hotplug notifier sets s->cpu_slab[cpu] = NULL.
> This means get_cpu_slab() always return NULL when CPU is being onlined.
> So I can't use get_cpu_slab to check whether kmem_cache_cpu_free
> initalization for the CPU has already been done or not.

If you have set it to NULL then the earlier kmem_cache_cpu structures has
been freed. Why is it a problem to allocate another one when the cpu comes
up again?
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