Messages in this thread | | | Date | Wed, 15 Dec 2021 11:58:45 -0500 | Subject | Re: [PATCH-next v3] mm/memcg: Properly handle memcg_stock access for PREEMPT_RT | From | Waiman Long <> |
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On 12/14/21 23:36, Davidlohr Bueso wrote: > 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.
Yes, it is tricky to avoid all these. One possibility to to delay obj_cgroup_release() through RCU. However, this is outside the scope of this patch.
Cheers, Longman
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