From mboxrd@z Thu Jan  1 00:00:00 1970
From: Li Zefan <lizefan@huawei.com>
Subject: Re: 3.15 regression: wrong cgroup magic
Date: Tue, 3 Jun 2014 09:18:25 +0800
Message-ID: <538D2261.70406@huawei.com>
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Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Tejun Heo <tj@kernel.org>,
	Linux FS Devel <linux-fsdevel@vger.kernel.org>,
	"Linus Torvalds" <torvalds@linux-foundation.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Jianyu Zhan <nasa4836@gmail.com>
To: Andy Lutomirski <luto@amacapital.net>
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Cc: Greg
Cc: Jianyu Zhan

On 2014/6/3 8:56, Andy Lutomirski wrote:
> Sorry I didn't notice this earlier.  Linux 3.15 breaks my production

But 3.15 hasn't been released. :)

> system :(  The cause appears to be:
> 
> commit 2bd59d48ebfb3df41ee56938946ca0dd30887312
> Author: Tejun Heo <tj@kernel.org>
> Date:   Tue Feb 11 11:52:49 2014 -0500
> 
>     cgroup: convert to kernfs
> 
> In particular, this piece:
> 
> -       sb->s_magic = CGROUP_SUPER_MAGIC;
> 
> The result is that cgroup shows up with the wrong magic number, so my
> code goes "oh crap, cgroupfs isn't mounted" and fails.
> 
> I can change my code to hack around this, but I can imagine other
> things getting tripped up.  Is there still time to fix this?
> 

This should be fixed by "kernfs: move the last knowledge of sysfs out from kernfs".

It's in driver-core-next.

https://git.kernel.org/cgit/linux/kernel/git/gregkh/driver-core.git/commit/?h=driver-core-next&id=26fc9cd200ec839e0b3095e05ae018f27314e7aa