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

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

[Hillf Danton]

> 
> From: NeilBrown <neilb@suse.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@suse.de>
> Signed-off-by: Al Viro <viro@zeniv.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

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

[NeilBrown]

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On Tue, 05 May 2015 15:12:28 +0800 "Hillf Danton" <hillf.zj@alibaba-inc.com>
wrote:

> > 
> > From: NeilBrown <neilb@suse.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@suse.de>
> > Signed-off-by: Al Viro <viro@zeniv.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).

kfree(NULL) is perfectly valid.

NeilBrown


> 
> > +		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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[PATCH 03/79] ovl: rearrange ovl_follow_link to it doesn't need to call ->put_link

[Al Viro]

From: NeilBrown <neilb@suse.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@suse.de>
Signed-off-by: Al Viro <viro@zeniv.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)
+		data->cookie = ret;
+
+	return data;
 }
 
 static void ovl_put_link(struct dentry *dentry, struct nameidata *nd, void *c)
-- 
2.1.4