Re: [PATCH v2 1/2] blk-iocost: add refcounting for iocg

[Yu Kuai]

Hi,

在 2023/01/11 2:36, Tejun Heo 写道:
> Hello,
>
> On Tue, Jan 10, 2023 at 09:39:44AM +0800, Yu Kuai wrote:
> > As I tried to explain before, we can make sure blkg_free() is called
> > in order, but blkg_free() from remove cgroup can concurrent with
> > deactivate policy, and we can't guarantee the order of ioc_pd_free()
> > that is called both from blkg_free() and blkcg_deactivate_policy().
> > Hence I don't think #3 is possible.
>
> Hahaha, sorry that I keep forgetting that. This doesn't really feel like
> that important or difficult part of the problem tho. Can't it be solved by
> synchronizing blkg free work item against the deactivate path with a mutex?

I'm not sure, of course this can fix the problem, but two spinlock
'blkcg->lock' and 'q->queue_lock' are used to protect blkg_destroy()
currently, add a mutex（disk level?) requires a refactor, which seems
complex to me.

Thanks,
Kuai