> > > @@ -2231,7 +2244,7 @@ __mem_cgroup_commit_charge_swapin(struct
> > >
> > > id = swap_cgroup_record(ent, 0);
> > > rcu_read_lock();
> > > - memcg = mem_cgroup_lookup(id);
> > > + memcg = id_to_memcg(id);
> > > if (memcg) {
> > > /*
> > > * This recorded memcg can be obsolete one. So, avoid
> > > @@ -2240,9 +2253,10 @@ __mem_cgroup_commit_charge_swapin(struct
> > > if (!mem_cgroup_is_root(memcg))
> > > res_counter_uncharge(&memcg->memsw, PAGE_SIZE);
> > > mem_cgroup_swap_statistics(memcg, false);
> > > + rcu_read_unlock();
> > > mem_cgroup_put(memcg);
> > > - }
> > > - rcu_read_unlock();
> > > + } else
> > > + rcu_read_unlock();
> > > }
> > > /*
> > > * At swapin, we may charge account against cgroup which has no tasks.
> > > @@ -2495,7 +2509,7 @@ void mem_cgroup_uncharge_swap(swp_entry_
> > >
> > > id = swap_cgroup_record(ent, 0);
> > > rcu_read_lock();
> > > - memcg = mem_cgroup_lookup(id);
> > > + memcg = id_to_memcg(id);
> > > if (memcg) {
> > > /*
> > > * We uncharge this because swap is freed.
> > > @@ -2504,9 +2518,10 @@ void mem_cgroup_uncharge_swap(swp_entry_
> > > if (!mem_cgroup_is_root(memcg))
> > > res_counter_uncharge(&memcg->memsw, PAGE_SIZE);
> > > mem_cgroup_swap_statistics(memcg, false);
> > > + rcu_read_unlock();
> > > mem_cgroup_put(memcg);
> > > - }
> > > - rcu_read_unlock();
> > > + } else
> > > + rcu_read_unlock();
> > > }
> > >
> > > /**
> > Could you explain why we need rcu_read_unlock() before mem_cgroup_put() ?
> > I suspect that it's because mem_cgroup_put() can free the memcg, but do we
> > need mem->valid then ?
> >
> mem_cgroup_put() may call synchronize_rcu(). So, we have to unlock before it.
>
Ah, I see. Thank you for your explanation.
Daisuke Nishimura.
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