Fix a reference counting bug in cgroupfs

As part of the extraction of cpusetfs to cgroupfs, a call to
cpuset_get_dentry() was lost (justified by the fact that the dentry in
question was now being passed down by the caller).  Since
cpuset_get_dentry() called lookup_one_len(), this resulted in a reference
count being missed from the directory dentry.

This patch removes cgroup_get_dentry() and replaces it with direct calls
to lookup_one_len(); the initialization of cgroupfs dentry ops is done
now in cgroup_create_file() at dentry creation time.

Signed-off-by: Paul Menage <menage@google.com>

---
 kernel/cgroup.c |   24 +++++++-----------------
 1 file changed, 7 insertions(+), 17 deletions(-)

Index: linux-2.6.23-rc4-mm1-new/kernel/cgroup.c
===================================================================
--- linux-2.6.23-rc4-mm1-new.orig/kernel/cgroup.c
+++ linux-2.6.23-rc4-mm1-new/kernel/cgroup.c
@@ -604,19 +604,6 @@ static void cgroup_diput(struct dentry *
 	iput(inode);
 }
 
-static struct dentry *cgroup_get_dentry(struct dentry *parent,
-					   const char *name)
-{
-	struct dentry *d = lookup_one_len(name, parent, strlen(name));
-	static struct dentry_operations cgroup_dops = {
-		.d_iput = cgroup_diput,
-	};
-
-	if (!IS_ERR(d))
-		d->d_op = &cgroup_dops;
-	return d;
-}
-
 static void remove_dir(struct dentry *d)
 {
 	struct dentry *parent = dget(d->d_parent);
@@ -1507,6 +1494,10 @@ static struct inode_operations cgroup_di
 static int cgroup_create_file(struct dentry *dentry, int mode,
 				struct super_block *sb)
 {
+	static struct dentry_operations cgroup_dops = {
+		.d_iput = cgroup_diput,
+	};
+
 	struct inode *inode;
 
 	if (!dentry)
@@ -1532,7 +1523,7 @@ static int cgroup_create_file(struct den
 		inode->i_size = 0;
 		inode->i_fop = &cgroup_file_operations;
 	}
-
+	dentry->d_op = &cgroup_dops;
 	d_instantiate(dentry, inode);
 	dget(dentry);	/* Extra count - pin the dentry in core */
 	return 0;
@@ -1553,13 +1544,12 @@ static int cgroup_create_dir(struct cgro
 	int error = 0;
 
 	parent = cont->parent->dentry;
-	if (IS_ERR(dentry))
-		return PTR_ERR(dentry);
 	error = cgroup_create_file(dentry, S_IFDIR | mode, cont->root->sb);
 	if (!error) {
 		dentry->d_fsdata = cont;
 		inc_nlink(parent->d_inode);
 		cont->dentry = dentry;
+		dget(dentry);
 	}
 	dput(dentry);
 
@@ -1581,7 +1571,7 @@ int cgroup_add_file(struct cgroup *cont,
 	}
 	strcat(name, cft->name);
 	BUG_ON(!mutex_is_locked(&dir->d_inode->i_mutex));
-	dentry = cgroup_get_dentry(dir, name);
+	dentry = lookup_one_len(name, dir, strlen(name));
 	if (!IS_ERR(dentry)) {
 		error = cgroup_create_file(dentry, 0644 | S_IFREG,
 						cont->root->sb);

--
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