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From: Kay Sievers <kay.sievers@vrfy.org>
Date: Sat, 23 May 2009 22:46:27 +0200
Message-ID: <ac3eb2510905231346n6f7ba736we0c4f9bce8e5e59f@mail.gmail.com>
Subject: Re: [PATCH 04/20] sysfs: Handle the general case of removing of 
	directories with subdirectories
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Tejun Heo <tj@kernel.org>, Andrew Morton <akpm@linux-foundation.org>,
       Greg Kroah-Hartman <gregkh@suse.de>, linux-kernel@vger.kernel.org,
       Cornelia Huck <cornelia.huck@de.ibm.com>, linux-fsdevel@vger.kernel.org,
       "Eric W. Biederman" <ebiederm@aristanetworks.com>
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On Sat, May 23, 2009 at 22:09, Eric W. Biederman <ebiederm@xmission.com> wrote:
> Kay Sievers <kay.sievers@vrfy.org> writes:
>> What's the problem in /sys/dev/? There are just a bunch of symlinks,
>> one for every device with a dev_t, and all in flat directories, and no
>> directory to remove.
>
> device_shutdown called during reboot removes /sys/dev/block and /sys/dev/char.
> The current sysfs_remove_dir (because it empties directories)
> removes all of those symlinks.
>
> The problem is that it is the device objects for each individual
> device that owns those symlinks, and normally removes those symlinks.
>
> Which means that in theory we could have double deletion going on.
>
> In practice today it doesn't matter because this is at reboot.
>
> And as far as that goes it is wrong to remove anything from sysfs during
> device_shutdown so the fix is just to not call kobject_put there.

Yes, that's just a bug. These directories should never be removed.

Thanks,
Kay