Re: [PATCH -next v2 9/9] blk-iocost: fix walk_list corruption

[Yu Kuai]

Hi,

在 2022/12/01 4:59, Tejun Heo 写道:
> On Wed, Nov 30, 2022 at 09:21:56PM +0800, Li Nan wrote:
> > From: Yu Kuai <yukuai3@xxxxxxxxxx>
> >
> > Our test report a problem:
> >
> > ------------[ cut here ]------------
> > list_del corruption. next->prev should be ffff888127e0c4b0, but was ffff888127e090b0
> > WARNING: CPU: 2 PID: 3117789 at lib/list_debug.c:62 __list_del_entry_valid+0x119/0x130
> > RIP: 0010:__list_del_entry_valid+0x119/0x130
> > RIP: 0010:__list_del_entry_valid+0x119/0x130
> > Call Trace:
> >   <IRQ>
> >   iocg_flush_stat.isra.0+0x11e/0x230
> >   ? ioc_rqos_done+0x230/0x230
> >   ? ioc_now+0x14f/0x180
> >   ioc_timer_fn+0x569/0x1640
> >
> > We haven't reporduced it yet, but we think this is due to parent iocg is
> > freed before child iocg, and then in ioc_timer_fn, walk_list is
> > corrupted.
> >
> > 1) Remove child cgroup can concurrent with remove parent cgroup, and
> > ioc_pd_free for parent iocg can be called before child iocg. This can be
> > fixed by moving the handle of walk_list to ioc_pd_offline, since that
> > offline from child is ensured to be called before parent.
>
> Which you already did in a previous patch, right?

yes, this is already did in patch 7.

> > 2) ioc_pd_free can be triggered from both removing device and removing
> > cgroup, this patch fix the problem by deleting timer before deactivating
> > policy, so that free parent iocg first in this case won't matter.
>
> Okay, so, yeah, css's pin parents but blkg's don't. I think the right thing
> to do here is making sure that a child blkg pins its parent (and eventually
> ioc).

Ok, I can try to do that.

> > Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
> > Signed-off-by: Li Nan <linan122@xxxxxxxxxx>
> > ---
> >   block/blk-iocost.c | 3 ++-
> >   1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/block/blk-iocost.c b/block/blk-iocost.c
> > index 710cf63a1643..d2b873908f88 100644
> > --- a/block/blk-iocost.c
> > +++ b/block/blk-iocost.c
> > @@ -2813,13 +2813,14 @@ static void ioc_rqos_exit(struct rq_qos *rqos)
> >   {
> >   	struct ioc *ioc = rqos_to_ioc(rqos);
> >   
> > +	del_timer_sync(&ioc->timer);
> > +
> >   	blkcg_deactivate_policy(rqos->q, &blkcg_policy_iocost);
> >   
> >   	spin_lock_irq(&ioc->lock);
> >   	ioc->running = IOC_STOP;
> >   	spin_unlock_irq(&ioc->lock);
> >   
> > -	del_timer_sync(&ioc->timer);
>
> I don't about this workaround. Let's fix properly?

Ok, and by the way, is there any reason to delete timer after
deactivate policy? This seems a litter wreid to me.

Thanks,
Kuai
>