Messages in this thread | | | Date | Fri, 10 Dec 2021 11:37:20 -0500 | Subject | Re: [PATCH-next v2] mm/memcg: Properly handle memcg_stock access for PREEMPT_RT | From | Waiman Long <> |
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On 12/10/21 11:34, Sebastian Andrzej Siewior wrote: > On 2021-12-10 11:29:31 [-0500], Waiman Long wrote: >> On 12/10/21 08:01, Sebastian Andrzej Siewior wrote: >>> On 2021-12-09 21:52:28 [-0500], Waiman Long wrote: >>> … >>>> --- a/mm/memcontrol.c >>>> +++ b/mm/memcontrol.c >>> … >>>> @@ -2210,7 +2211,7 @@ static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages) >>>> struct memcg_stock_pcp *stock; >>>> unsigned long flags; >>>> - local_irq_save(flags); >>>> + local_lock_irqsave(&memcg_stock.lock, flags); >>> Why is this one using the lock? It isn't accessing irq_obj, right? >> Well, the lock isn't just for irq_obj. It protects the whole memcg_stock >> structure which include irq_obj. Sometimes, data in irq_obj (or task_obj) >> will get transfer to nr_pages and vice versa. So it is easier to use one >> single lock for the whole thing. > This needs way better documentation what protects what any why. > I don't like the quick slapping for RT only usage without any kind of > explanation. Once you think you know it is irq_obj only you end up here > where you have the lock again for no obvious reason.
Sure, I will update the patch description and add comments to document that. Let's see what other feedback I have before I make the update.
Cheers, Longman
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