Re: [PATCH -mm v2 5/8] slub: make slab_free non-preemptable

Christoph Lameter
2014-06-09T13:52:29Z

On Mon, 9 Jun 2014, Vladimir Davydov wrote:

> The whole function (unfreeze_partials) is currently called with irqs
> off, so this is effectively a no-op. I guess we can restore irqs here
> though.

We could move the local_irq_save from put_cpu_partial() into
unfreeze_partials().

> If we just freed the last slab of the cache and then get preempted
> (suppose we restored irqs above), nothing will prevent the cache from
> destruction, which may result in use-after-free below. We need to be
> more cautious if we want to call for page allocator with preemption and
> irqs on.

Hmmm. Ok.
>
> However, I still don't understand what's the point in it. We *already*
> call discard_slab with irqs disabled, which is harder, and it haven't
> caused any problems AFAIK. Moreover, even if we enabled preemption/irqs,
> it wouldn't guarantee that discard_slab would always be called with
> preemption/irqs on, because the whole function - I mean kmem_cache_free
> - can be called with preemption/irqs disabled.
>
> So my point it would only complicate the code.

Ok.

Acked-by: Christoph Lameter <cl@linux.com>