Hi,
在 2022/12/20 5:28, Tejun Heo 写道:
On Sat, Dec 17, 2022 at 11:05:25AM +0800, Yu Kuai wrote:
From: Yu Kuai <yukuai3@xxxxxxxxxx>
bio will grab blkg reference, however, blkcg->online_pin is not grabbed,
hence cgroup can be removed after thread exit while bio is still in
progress. Bypass io in this case since it doesn't make sense to
throttle bio while cgroup is removed.
I don't get it. Why wouldn't that make sense? ISTR some occasions where we
clear the config to mitigate exits stalling for too long but in general a
policy being active on a draining cgroup shouldn't be a problem.
The main reason here for patch 2/3 is for patch 4, since bio can still
reach rq_qos after pd_offline_fn is called.
Currently, it's not consistent and seems messy how different policies
implement pd_alloc/free_fn, pd_online/offline_fn, and pd_init_fn. For
iocost, iocg is exited in pd_free_fn, and parent iocg can exits before
child, which will cause many problems.
Patch 2/3 are not necessary if we don't choose to fix such problems by
exiting iocg in ioc_pd_offline() in patch 4.
I'll try to think about how to use refcnting, either from blkg layer or
add refcnting for iocg.
Thanks,
Kuai
Thanks.
