Messages in this thread | | | Subject | Re: [PATCH v2 1/2] blk-iocost: add refcounting for iocg | From | Yu Kuai <> | Date | Thu, 5 Jan 2023 09:14:07 +0800 |
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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@huawei.com> >> >> 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. >
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