On Tue, 24 Aug 2010 01:35:37 -0700
Greg Thelen <gthelen@xxxxxxxxxx> wrote:
> > rcu_read_lock() is just for delaying to discard object, not for avoiding
> > racy updates. All _updates_ requires proper lock or speculative logic as
> > atomic_inc_not_zero() etc... Basically, RCU is for avoiding use-after-free.
>
>
> Thanks for the info. Referring to your original patch:
> > @@ -2014,11 +2025,11 @@ static int mem_cgroup_move_account(struc
> > {
> > int ret = -EINVAL;
> > lock_page_cgroup(pc);
> > - if (PageCgroupUsed(pc) && pc->mem_cgroup == from) {
> > + if (PageCgroupUsed(pc) && id_to_memcg(pc->mem_cgroup, true) == from) {
> > __mem_cgroup_move_account(pc, from, to, uncharge);
> > ret = 0;
> > }
> > - unlock_page_cgroup(pc);
> > + rcu_read_unlock();
> >
>
> It seems like mem_cgroup_move_account() is not balanced. Why is
> lock_page_cgroup(pc) used to lock but rcu_read_unlock() used to unlock?
>
Nice catch. It's bug. It seems my eyes were corrupted..
Will be fixed in the next version. Sorry for bad code.
Thanks,
-Kame
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