linux-kernel - Re: [PATCH 03/79] ovl: rearrange ovl_follow_link to it doesn't need to call ->put

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Date:	Tue, 05 May 2015 15:12:28 +0800
From:	"Hillf Danton" <hillf.zj@...baba-inc.com>
To:	"'NeilBrown'" <neilb@...e.de>
Cc:	"'Al Viro'" <viro@...iv.linux.org.uk>,
	"linux-kernel" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 03/79] ovl: rearrange ovl_follow_link to it doesn't need to call ->put_link

> 
> From: NeilBrown <neilb@...e.de>
> 
> ovl_follow_link current calls ->put_link on an error path.
> However ->put_link is about to change in a way that it will be
> impossible to call it from ovl_follow_link.
> 
> So rearrange the code to avoid the need for that error path.
> Specifically: move the kmalloc() call before the ->follow_link()
> call to the subordinate filesystem.
> 
> Signed-off-by: NeilBrown <neilb@...e.de>
> Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
> ---
>  fs/overlayfs/inode.c | 25 ++++++++++++-------------
>  1 file changed, 12 insertions(+), 13 deletions(-)
> 
> diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
> index 04f1248..1b4b9c5e 100644
> --- a/fs/overlayfs/inode.c
> +++ b/fs/overlayfs/inode.c
> @@ -145,6 +145,7 @@ static void *ovl_follow_link(struct dentry *dentry, struct nameidata *nd)
>  	void *ret;
>  	struct dentry *realdentry;
>  	struct inode *realinode;
> +	struct ovl_link_data *data = NULL;
> 
>  	realdentry = ovl_dentry_real(dentry);
>  	realinode = realdentry->d_inode;
> @@ -152,25 +153,23 @@ static void *ovl_follow_link(struct dentry *dentry, struct nameidata *nd)
>  	if (WARN_ON(!realinode->i_op->follow_link))
>  		return ERR_PTR(-EPERM);
> 
> -	ret = realinode->i_op->follow_link(realdentry, nd);
> -	if (IS_ERR(ret))
> -		return ret;
> -
>  	if (realinode->i_op->put_link) {
> -		struct ovl_link_data *data;
> -
>  		data = kmalloc(sizeof(struct ovl_link_data), GFP_KERNEL);
> -		if (!data) {
> -			realinode->i_op->put_link(realdentry, nd, ret);
> +		if (!data)
>  			return ERR_PTR(-ENOMEM);
> -		}
>  		data->realdentry = realdentry;
> -		data->cookie = ret;
> +	}
> 
> -		return data;
> -	} else {
> -		return NULL;
> +	ret = realinode->i_op->follow_link(realdentry, nd);
> +	if (IS_ERR(ret)) {
> +		kfree(data);
> +		return ret;
>  	}
> +
> +	if (data)

No need to check again(see the above kfree(data) please).

> +		data->cookie = ret;
> +
> +	return data;
>  }
> 
>  static void ovl_put_link(struct dentry *dentry, struct nameidata *nd, void *c)
> --
> 2.1.4

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