Re: [PATCH] blk-iocost: do not WARNING if iocg has already offlined

[Li Nan]

在 2024/4/19 0:14, Tejun Heo 写道:
> Hello,
>
> On Thu, Apr 18, 2024 at 03:23:40PM +0800, linan666@xxxxxxxxxxxxxxx wrote:
> > From: Li Nan <linan122@xxxxxxxxxx>
> >
> > In iocg_pay_debt(), warn is triggered if 'active_list' is empty, which
> > is intended to confirm iocg is avitve when it has debt. However, warn
> > can be triggered during removing cgroup controller, as
>
> Maybe saying "a blkcg is being removed" is clearer?

Thanks for your suggestion. I will correct my expression in next version.

> > iocg_waitq_timer_fn() is awakened at that time.
> >
> >    WARNING: CPU: 0 PID: 2344971 at block/blk-iocost.c:1402 iocg_pay_debt+0x14c/0x190
> >    Call trace:
> >    iocg_pay_debt+0x14c/0x190
> >    iocg_kick_waitq+0x438/0x4c0
> >    iocg_waitq_timer_fn+0xd8/0x130
> >    __run_hrtimer+0x144/0x45c
> >    __hrtimer_run_queues+0x16c/0x244
> >    hrtimer_interrupt+0x2cc/0x7b0
> >
> > The warn in this situation is meaningless. Since this iocg is being
> > removed, the state of the 'active_list' is irrelevant, and 'waitq_timer'
> > is canceled after removing 'active_list' in ioc_pd_free(), which ensure
> > iocg is freed after iocg_waitq_timer_fn() returns.
> >
> > Therefore, add the check if iocg has already offlined to avoid warn
> > when removing cgroup controller.
> >
> > Signed-off-by: Li Nan <linan122@xxxxxxxxxx>
> > ---
> >   block/blk-iocost.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/block/blk-iocost.c b/block/blk-iocost.c
> > index baa20c85799d..2e109c016a39 100644
> > --- a/block/blk-iocost.c
> > +++ b/block/blk-iocost.c
> > @@ -1440,7 +1440,7 @@ static void iocg_pay_debt(struct ioc_gq *iocg, u64 abs_vpay,
> >   	lockdep_assert_held(&iocg->waitq.lock);
> >   
> >   	/* make sure that nobody messed with @iocg */
> > -	WARN_ON_ONCE(list_empty(&iocg->active_list));
> > +	WARN_ON_ONCE(list_empty(&iocg->active_list) && iocg->pd.online);
>
> Can you add a comment explaining why we need the pd.online test?

Yeah, I will add comment in next version.

> Other than the above nits, looks great to me. Please feel free to add
>
>    Acked-by: Tejun Heo <tj@xxxxxxxxxx>
>
> Thanks.

--
Thanks,
Nan