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From: Tejun Heo <tj@kernel.org>
To: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Jens Axboe <axboe@kernel.dk>,
	xuejiufei <jiufei.xue@linux.alibaba.com>,
	Caspar Zhang <caspar@linux.alibaba.com>,
	linux-block <linux-block@vger.kernel.org>,
	cgroups@vger.kernel.org
Subject: Re: [PATCH v2] blk-throttle: fix race between blkcg_bio_issue_check and cgroup_rmdir
Date: Thu, 22 Feb 2018 07:18:27 -0800	[thread overview]
Message-ID: <20180222151721.GA1641506@devbig577.frc2.facebook.com> (raw)
In-Reply-To: <19009bad-8429-c210-dd91-2b20771a66bd@linux.alibaba.com>

Hello,

On Thu, Feb 22, 2018 at 02:14:34PM +0800, Joseph Qi wrote:
> I still don't get how css_tryget can work here.
> 
> The race happens when:
> 1) writeback kworker has found the blkg with rcu;
> 2) blkcg is during offlining and blkg_destroy() has already been called.
> Then, writeback kworker will take queue lock and access the blkg with
> refcount 0.

Yeah, then tryget would fail and it should go through the root.

Thanks.

-- 
tejun

  reply	other threads:[~2018-02-22 15:18 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-02-07  8:40 [PATCH v2] blk-throttle: fix race between blkcg_bio_issue_check and cgroup_rmdir Joseph Qi
     [not found] ` <6f136c90-faa9-4bc0-b02f-3a112b4d8360-KPsoFbNs7GizrGE5bRqYAgC/G2K4zDHf@public.gmane.org>
2018-02-07 21:38   ` Tejun Heo
2018-02-07 21:38     ` Tejun Heo
     [not found]     ` <20180207213811.GF695913-4dN5La/x3IkLX0oZNxdnEQ2O0Ztt9esIQQ4Iyu8u01E@public.gmane.org>
2018-02-08  2:29       ` Joseph Qi
2018-02-08  2:29         ` Joseph Qi
     [not found]         ` <b590caed-1423-4776-966d-cd9e346a8ea1-KPsoFbNs7GizrGE5bRqYAgC/G2K4zDHf@public.gmane.org>
2018-02-08 15:23           ` Tejun Heo
2018-02-08 15:23             ` Tejun Heo
2018-02-09  2:15             ` Joseph Qi
     [not found]               ` <aac95b90-786d-95bf-b93d-87ecca79f846-KPsoFbNs7GizrGE5bRqYAgC/G2K4zDHf@public.gmane.org>
2018-02-12 17:11                 ` Tejun Heo
2018-02-12 17:11                   ` Tejun Heo
2018-02-22  6:14                   ` Joseph Qi
2018-02-22 15:18                     ` Tejun Heo [this message]
2018-02-23  1:56                       ` xuejiufei
2018-02-23 14:23                         ` Tejun Heo
2018-02-24  1:45                           ` Joseph Qi
2018-02-27  3:18                             ` Joseph Qi
2018-02-27 18:33                             ` Tejun Heo
2018-02-28  6:52                               ` Joseph Qi
2018-03-04 20:23                                 ` Tejun Heo
2018-03-05  1:17                                   ` Joseph Qi

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