Re: [PATCH v2] blk-throttle: fix race between blkcg_bio_issue_check and cgroup_rmdir

[Joseph Qi <joseph.qi@linux.alibaba.com>]

On 18/3/5 04:23, Tejun Heo wrote:
> Hello, Joseph.
> 
> Sorry about late reply.
> 
> On Wed, Feb 28, 2018 at 02:52:10PM +0800, Joseph Qi wrote:
>> In current code, I'm afraid pd_offline_fn() as well as the rest
>> destruction have to be called together under the same blkcg->lock and
>> q->queue_lock.
>> For example, if we split the pd_offline_fn() and radix_tree_delete()
>> into 2 phases, it may introduce a race between blkcg_deactivate_policy()
>> when exit queue and blkcg_css_free(), which will result in
>> pd_offline_fn() to be called twice.
> 
> So, yeah, the sync scheme aroung blkg is pretty brittle and we'd need
> some restructuring to separate out blkg offlining and release, but it
> looks like that'd be the right thing to do, no?
> 
Agree, except the restriction above, as of now I don't find any more.
I'll try to fix in the way you suggested and post v3.

Thanks,
Joseph