Re: [PATCH-next v3] mm/memcg: Properly handle memcg_stock access for PREEMPT_RT

[Davidlohr Bueso <dave@xxxxxxxxxxxx>]

On Tue, 14 Dec 2021, Waiman Long wrote:

> @@ -2189,7 +2194,7 @@ static void drain_local_stock(struct work_struct *dummy)
> 	 * drain_stock races is that we always operate on local CPU stock
> 	 * here with IRQ disabled
> 	 */
> -	local_irq_save(flags);
> +	local_lock_irqsave(&memcg_stock.lock, flags);
>
> 	stock = this_cpu_ptr(&memcg_stock);
> 	drain_obj_stock(&stock->irq_obj);

So here there is still the problem that you can end up taking sleeping locks
with irqs disabled via obj_cgroup_put() >> obj_cgroup_release() - ie: the
percpu_ref_switch_lock and css_set_lock. It had occurred to me to promote
the former to a raw spinlock, but doubt we can get away with the latter.

Thanks,
Davidlohr