linux-kernel - Re: [PATCH RFC] sysfs: fix the race of "parent deleted before child added"

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Message-ID: <CAA9_cmfc7_d_s9XjeyqY_T6uZPbWjY0Dw=2aeFbL+9hCu8k_aA@mail.gmail.com>
Date:	Fri, 1 Aug 2014 09:54:18 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	Jianyu Zhan <nasa4836@...il.com>
Cc:	Tejun Heo <tj@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jianyu Zhan <Jianyu.Zhan@....com>
Subject: Re: [PATCH RFC] sysfs: fix the race of "parent deleted before child added"

On Fri, Aug 1, 2014 at 4:18 AM, Jianyu Zhan <nasa4836@...il.com> wrote:
> From: Jianyu Zhan <Jianyu.Zhan@....com>
>
> I've met such a race conditon the same as what commit 3a198886
> ("sysfs: handle 'parent deleted before child added'") tackled.
>
> The senario got triggered under a torturing test of quick disk
> removal and plugging.
>
> The forementioned commit 3a198886 didn't really fix this race,
> it just narrows down the racy window.

You misread the changelog.  It was never meant to be a fix, its there
to prevent abuses from crashing this system and rather return an
error.

The commit that fixed the race I was seeing is here:

https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=3b661a92

Perhaps you have found another occasion where a device is being
device_del()'d right before a device_add() attempt?
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