linux-kernel - Re: Subject: [PATCH] kobject: fix the race between kobject_del and get_device

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Message-ID: <5459992B.1040700@huawei.com>
Date:	Wed, 5 Nov 2014 11:27:39 +0800
From:	Yijing Wang <wangyijing@...wei.com>
To:	Tejun Heo <tj@...nel.org>
CC:	Weng Meiling <wengmeiling.weng@...wei.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	Frans Klaver <fransklaver@...il.com>,
	"Jens Axboe" <axboe@...nel.dk>, <akpm@...ux-foundation.org>,
	<adilger.kernel@...ger.ca>, Jan Kara <jack@...e.cz>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Xiang Rui <rui.xiang@...wei.com>,
	Li Zefan <lizefan@...wei.com>,
	Huang Qiang <h.huangqiang@...wei.com>,
	Zhao Hongjiang <zhaohongjiang@...wei.com>
Subject: Re: Subject: [PATCH] kobject: fix the race between kobject_del and
 get_device_parent

On 2014/11/5 11:13, Tejun Heo wrote:
> Hello,
> 
> On Wed, Nov 05, 2014 at 10:01:39AM +0800, Yijing Wang wrote:
>>> So, yeah, this looks like a correct approach; however, do we even need
>>> to clear the glue directories? 
>>
>> Yes. In our platform, the glue directories
>> /sys/devices/virtual/block will be removed once the last child
>> device call device_del().
> 
> What I mean is why are we even trying to remove the parent directory?
> Can't we just keep them around once created?

We remove the parent directory because parent ref count is equal to children
device numebr, every child device will get/add parent's ref count when child
device be created.

Keep the parent directory looks good to me,  we could only add kobject_get(&parent)
after the parent dir be created.

....
		/* or create a new class-directory at the parent device */
		k = class_dir_create_and_add(dev->class, parent_kobj);
		/* do not emit an uevent for this simple "glue" directory */
		kobject_get(k);  <--------add parent ref count for first child device.
		mutex_unlock(&gdp_mutex);
		return k;
....

> 
> Thanks.
> 


-- 
Thanks!
Yijing

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