linux-kernel - Re: [PATCH] Revert "cgroup: remove redundant variable in cgroup

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Message-ID: <20140926050457.GB14426@htj.dyndns.org>
Date:	Fri, 26 Sep 2014 01:04:57 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Zefan Li <lizefan@...wei.com>, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Revert "cgroup: remove redundant variable in
 cgroup_mount()"

On Fri, Sep 26, 2014 at 05:53:52AM +0100, Al Viro wrote:
> On Fri, Sep 26, 2014 at 12:26:17AM -0400, Tejun Heo wrote:
> > On Fri, Sep 26, 2014 at 12:03:25PM +0800, Zefan Li wrote:
> > > This reverts commit 0c7bf3e8cab7900e17ce7f97104c39927d835469.
...
> > > Cc: Al Viro <viro@...IV.linux.org.uk>
> > > Reported-by: Andrey Wagin <avagin@...il.com>
> > > Signed-off-by: Zefan Li <lizefan@...wei.com>
> > 
> > Applied to cgroup/for-3.18.
> 
> Er?  It's a clear regression since 3.16; shouldn't it go into mainline
> before 3.17-final?  Another thing: AFAICS, if kernfs_fill_super() fails,

Hmmm?  This is reverting 0c7bf3e8cab7 which was committed six days ago
to cgroup/for-3.18.

> you get unbalanced kernfs_put() on the cleanup path - kernfs_kill_sb()
> will be called in those cases as well.  IOW, we'd better move that
>         kernfs_get(info->root->kn);
> in kernfs_fill_super() all way up to the point before kernfs_get_inode().
> Something like this:
> 
> Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
> ---
> diff --git a/fs/kernfs/mount.c b/fs/kernfs/mount.c
> index f973ae9..e5e92e3 100644
> --- a/fs/kernfs/mount.c
> +++ b/fs/kernfs/mount.c
> @@ -74,6 +74,7 @@ static int kernfs_fill_super(struct super_block *sb, unsigned long magic)
>  	sb->s_magic = magic;
>  	sb->s_op = &kernfs_sops;
>  	sb->s_time_gran = 1;
> +	kernfs_get(info->root->kn);
>  
>  	/* get root inode, initialize and unlock it */
>  	mutex_lock(&kernfs_mutex);
> @@ -90,7 +91,6 @@ static int kernfs_fill_super(struct super_block *sb, unsigned long magic)
>  		pr_debug("%s: could not get root dentry!\n", __func__);
>  		return -ENOMEM;
>  	}
> -	kernfs_get(info->root->kn);

Ooh, right.  Will test & send the patch to Greg.

Thanks.

-- 
tejun
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