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From: "yukuai (C)" <yukuai3@huawei.com>
To: "Michal Koutný" <mkoutny@suse.com>
Cc: <hch@infradead.org>, <tj@kernel.org>, <axboe@kernel.dk>,
	<cgroups@vger.kernel.org>, <linux-block@vger.kernel.org>,
	<linux-kernel@vger.kernel.org>, <yi.zhang@huawei.com>
Subject: Re: [PATCH v4 2/2] block: cancel all throttled bios in del_gendisk()
Date: Sat, 4 Dec 2021 16:03:53 +0800	[thread overview]
Message-ID: <c8a16fe9-4ad2-682d-0d34-1049dc217d62@huawei.com> (raw)
In-Reply-To: <20211203102739.GB64349@blackbody.suse.cz>

在 2021/12/03 18:27, Michal Koutný 写道:
> On Fri, Dec 03, 2021 at 03:50:01PM +0800, "yukuai (C)" <yukuai3@huawei.com> wrote:
>> blkg_destroy() is protected by the queue_lock，so I think queue_lock can
>> protect such concurrent scenario.
> 
> blkg_destroy() is not as destroying :-) as actual free, you should
> synchronize against (the queue_lock ensures this for
> pd_free_fn=throtl_pd_free but you may still trip on blkcg after
> blkcg_css_free()).

Hi, Michal

I was thinking that if there are active blkgs, holding queue_lock will 
ensure blkcg won't be freed. However, if there are no active blkgs in
the first place, it seems right rcu_read_lock() can prevent this
iteration concurrent with css_release->css_release_work_fn->
css_free_rwork_fn.

By the way, does spin_lock can guarantee this since it disables preempt
like what rcu_read_lock() does?

Thanks,
Kuai

> 
> [Actually, I think you should see a warning in your situation if you
> enable CONFIG_PROVE_RCU.]
> 
> HTH,
> Michal
> 

  reply	other threads:[~2021-12-04  8:04 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-02 13:04 [PATCH v4 0/2] cancel all throttled bios in del_gendisk() Yu Kuai
2021-12-02 13:04 ` [PATCH v4 1/2] blk-throtl: move WARN_ON_ONCE() from throtl_rb_first() to it's caller Yu Kuai
2021-12-02 13:04 ` [PATCH v4 2/2] block: cancel all throttled bios in del_gendisk() Yu Kuai
2021-12-02 14:48   ` Michal Koutný
2021-12-03  7:50     ` yukuai (C)
2021-12-03 10:27       ` Michal Koutný
2021-12-04  8:03         ` yukuai (C) [this message]
2021-12-06 15:43           ` Michal Koutný

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