linux-kernel - Re: [PATCH] sysfs: fix namespace refcnt leak

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Date:	Thu, 20 Feb 2014 09:30:18 -0500
From:	Tejun Heo <tj@...nel.org>
To:	Li Zefan <lizefan@...wei.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Cgroups <cgroups@...r.kernel.org>
Subject: Re: [PATCH] sysfs: fix namespace refcnt leak

Hello, Li.

On Wed, Feb 19, 2014 at 09:39:28AM +0800, Li Zefan wrote:
> > Can we make it optional so that users who don't care about it can
> > ignore it?
> 
> cgroupfs also needs this to fix refcnt leak.

Ah, okay.

> Because success in finding an existing cgroup_root doesn't mean no new
> superblock is needed. For example:
> 
>   # mount -t cgroup -o cpuacct xxx /cgroup
>   # mkdir /cgroup/tmp
>   # umount /cgroup    <--- sb will be freed but cgroup_root won't
> 
>   // this will allocate new sb, but we find the cgroup_root is there.
>   # mount -t cgroup -o cpuacct xxx /cgroup
> 
> But debugfs won't need this if it's converted to kernfs.
> 
> How about I keep kernfs_mount() API intact, and when this fix gets
> merged into mainline, you merge the fix into cgroup-next, and then
> I make a fix for cgroup by changing kernfs_mount()?

If we need kernfs_mount() modified anyway, let's do it in this patch.
I still think it'd be better to allow the parameter to be NULL but
other than that, no objection.

Thanks!

-- 
tejun
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