Hi,
在 2023/01/05 5:44, Tejun Heo 写道:
On Tue, Dec 27, 2022 at 08:55:01PM +0800, Yu Kuai wrote:
From: Yu Kuai <yukuai3@xxxxxxxxxx>
iocost requires that child iocg must exit before parent iocg, otherwise
kernel might crash in ioc_timer_fn(). However, currently iocg is exited
in pd_free_fn(), which can't guarantee such order:
1) remove cgroup can concurrent with deactivate policy;
2) blkg_free() triggered by remove cgroup is asynchronously, remove
child cgroup can concurrent with remove parent cgroup;
Fix the problem by add refcounting for iocg, and child iocg will grab
reference of parent iocg, so that parent iocg will wait for all child
iocg to be exited.
Wouldn't it be better to do this refcnting in the blk-cgroup core code
rather than in blk-iocost?
The problem is that I can't find a proper way to fix the competition
that pd_free_fn() can be called from different context:
1) from blkg_free() that is called asynchronously from removing cgroup;
2) from blkcg_deactivate_policy() that is called from removing device;
1) is related to blkg, while 2) is not, hence refcnting from blkg can't
fix the problem. refcnting from blkcg_policy_data should be ok, but I
see that bfq already has the similar refcnting, while other policy
doesn't require such refcnting.
Any suggestions?
Thanks,
Kuai
Thanks.
