linux-kernel - [PATCH v3 003/110] ovl: rearrange ovl_follow_link to it doesn't need to call ->put

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Message-Id: <1431367690-5223-3-git-send-email-viro@ZenIV.linux.org.uk>
Date:	Mon, 11 May 2015 19:06:23 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Neil Brown <neilb@...e.de>, Christoph Hellwig <hch@...radead.org>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: [PATCH v3 003/110] 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)
+		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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