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From: Tejun Heo <tj@kernel.org>
To: Yufen Yu <yuyufen@huawei.com>
Cc: axboe@kernel.dk, linux-block@vger.kernel.org, jack@suse.cz,
	bvanassche@acm.org
Subject: Re: [PATCH] bdi: fix use-after-free for bdi device
Date: Thu, 13 Feb 2020 08:58:09 -0500	[thread overview]
Message-ID: <20200213135809.GH88887@mtj.thefacebook.com> (raw)
In-Reply-To: <fa6183c5-b92c-c431-37ab-09638f890f6c@huawei.com>

Hello,

On Thu, Feb 13, 2020 at 03:51:40PM +0800, Yufen Yu wrote:
> If we destroy the device asynchronously by call_rcu(), we may need to
> add a new member 'rcu_head' into struct backing_dev_info. Right?

Yes.

> The code may be like:
> 
> bdi_unregister()
> {
> 	...
> 	if (bdi->dev) {
> 		...
> 		device_get(bdi->dev);
> 		device_unregister(bdi->dev);
> 		bdi->dev = NULL; //XXX
> 		bdi_get(bdi); //avoiding bdi to be freed before calling bdi_release_device
> 		call_rcu(&bdi->rcu_head, bdi_release_device);
> 	}
> 		...
> }
> 
> bdi_release_device()
> {
> 	...
> 	put_device(bdi->dev);//XXX
> 	bdi_put(bdi);
> }
> 
> But, the problem is how do we get 'bdi->dev' in bdi_release_device().
> If we do not set bdi->dev as 'NULL', re-registration bdi may cannot work well.

So, unregistering can leave ->dev along and re-registering can test
whether it's NULL and if not put the existing one and put a new one
there. Wouldn't that work?

Thanks.

-- 
tejun

  reply	other threads:[~2020-02-13 13:58 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-11 14:00 [PATCH] bdi: fix use-after-free for bdi device Yufen Yu
2020-02-11 13:57 ` Yufen Yu
2020-02-12 21:33   ` Tejun Heo
2020-02-13  2:46     ` Yufen Yu
2020-02-13  3:48       ` Tejun Heo
2020-02-13  7:51         ` Yufen Yu
2020-02-13 13:58           ` Tejun Heo [this message]
2020-02-14  2:50             ` Yufen Yu
2020-02-14 14:05               ` Tejun Heo
2020-02-15 13:54                 ` Yufen Yu
2020-02-19 12:55                   ` Jan Kara
2020-02-19 15:12                     ` Tejun Heo
2020-02-20 11:07                     ` Yufen Yu
2020-02-20 12:07                       ` Jan Kara

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