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. > > Cheers, > Longman Sebastian
