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Date: Thu, 6 Sep 2018 16:46:30 -0400
From: Dennis Zhou <dennisszhou@gmail.com>
To: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>, Johannes Weiner <hannes@cmpxchg.org>,
	Josef Bacik <josef@toxicpanda.com>, kernel-team@fb.com,
	linux-block@vger.kernel.org, cgroups@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 13/15] blkcg: change blkg reference counting to use
 percpu_ref
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References: <20180831015356.69796-1-dennisszhou@gmail.com>
 <20180831015356.69796-14-dennisszhou@gmail.com>
 <20180901003159.GK1488037@devbig004.ftw2.facebook.com>
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On Fri, Aug 31, 2018 at 05:31:59PM -0700, Tejun Heo wrote:
> Hello,
> 
> On Thu, Aug 30, 2018 at 09:53:54PM -0400, Dennis Zhou wrote:
> > @@ -217,6 +240,10 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg,
> >  		blkg_get(blkg->parent);
> >  	}
> >  
> > +	ret = percpu_ref_init(&blkg->refcnt, __blkg_release, 0, GFP_KERNEL);
> 
> So, while this would work in some configs, you can't depend on RCU
> grace period inside percpu_ref.  blkg is now percpu-reference counted
> and rcu protected object - it has to explicitly go through a rcu grace
> period before release.
> 

Ah ok. I've made it into a call_rcu which should work.

Thanks,
Dennis