[Devel] [PATCH] Containers: Fix refcount bug

[Paul Menage]

Fix a reference counting bug in containerfs

As part of the extraction of cpusetfs to containerfs, 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 container_get_dentry() and replaces it with direct
calls to lookup_one_len(); the initialization of containerfs dentry
ops is done now in container_create_file() at dentry creation time.

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

---
 kernel/container.c |   26 ++++++++------------------
 1 file changed, 8 insertions(+), 18 deletions(-)

Index: container-2.6.23-rc3-mm1/kernel/container.c
===================================================================
--- container-2.6.23-rc3-mm1.orig/kernel/container.c
+++ container-2.6.23-rc3-mm1/kernel/container.c
@@ -603,19 +603,6 @@ static void container_diput(struct dentr
 	iput(inode);
 }
 
-static struct dentry *container_get_dentry(struct dentry *parent,
-					   const char *name)
-{
-	struct dentry *d = lookup_one_len(name, parent, strlen(name));
-	static struct dentry_operations container_dops = {
-		.d_iput = container_diput,
-	};
-
-	if (!IS_ERR(d))
-		d->d_op = &container_dops;
-	return d;
-}
-
 static void remove_dir(struct dentry *d)
 {
 	struct dentry *parent = dget(d->d_parent);
@@ -1506,6 +1493,10 @@ static struct inode_operations container
 static int container_create_file(struct dentry *dentry, int mode,
 				struct super_block *sb)
 {
+	static struct dentry_operations container_dops = {
+		.d_iput = container_diput,
+	};
+
 	struct inode *inode;
 
 	if (!dentry)
@@ -1531,7 +1522,7 @@ static int container_create_file(struct 
 		inode->i_size = 0;
 		inode->i_fop = &container_file_operations;
 	}
-
+	dentry->d_op = &container_dops;
 	d_instantiate(dentry, inode);
 	dget(dentry);	/* Extra count - pin the dentry in core */
 	return 0;
@@ -1552,13 +1543,12 @@ static int container_create_dir(struct c
 	int error = 0;
 
 	parent = cont->parent->dentry;
-	if (IS_ERR(dentry))
-		return PTR_ERR(dentry);
 	error = container_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);
 
@@ -1580,7 +1570,7 @@ int container_add_file(struct container 
 	}
 	strcat(name, cft->name);
 	BUG_ON(!mutex_is_locked(&dir->d_inode->i_mutex));
-	dentry = container_get_dentry(dir, name);
+	dentry = lookup_one_len(name, dir, strlen(name));
 	if (!IS_ERR(dentry)) {
 		error = container_create_file(dentry, 0644 | S_IFREG,
 						cont->root->sb);
@@ -2586,7 +2576,7 @@ int container_clone(struct task_struct *
 	/* Hold the parent directory mutex across this operation to
 	 * stop anyone else deleting the new container */
 	mutex_lock(&inode->i_mutex);
-	dentry = container_get_dentry(parent->dentry, nodename);
+	dentry = lookup_one_len(nodename, parent->dentry, strlen(nodename));
 	if (IS_ERR(dentry)) {
 		printk(KERN_INFO
 		       "Couldn't allocate dentry for %s: %ld\n", nodename,


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