Re: [PATCH v10 3/3] blk-cgroup: Flush stats at blkgs destruction path

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On Fri, Nov 04, 2022 at 08:59:02PM -0400, Waiman Long wrote:
> As noted by Michal, the blkg_iostat_set's in the lockless list
> hold reference to blkg's to protect against their removal. Those
> blkg's hold reference to blkcg. When a cgroup is being destroyed,
> cgroup_rstat_flush() is only called at css_release_work_fn() which is
> called when the blkcg reference count reaches 0. This circular dependency
> will prevent blkcg from being freed until some other events cause
> cgroup_rstat_flush() to be called to flush out the pending blkcg stats.
> 
> To prevent this delayed blkcg removal, add a new cgroup_rstat_css_flush()
> function to flush stats for a given css and cpu and call it at the blkgs
> destruction path, blkcg_destroy_blkgs(), whenever there are still some
> pending stats to be flushed. This will ensure that blkcg reference
> count can reach 0 ASAP.
> 
> Signed-off-by: Waiman Long <longman@xxxxxxxxxx>

Acked-by: Tejun Heo <tj@xxxxxxxxxx>

Thanks.

-- 
tejun



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