GIT: unionfs2-2.6.27.y: revert changes to new_dentry_private_data and document it

[Erez Zadok]

commit 71afb20079196b71d8f041c9c8513ddfec9451dc
Author: Erez_Zadok <ezk at cs.sunysb.edu>
Date:   Mon Jun 11 10:52:21 2007 -0400

    revert changes to new_dentry_private_data and document it
    
    Revert bad changes to this function, but this time explain better its precise
    semantics.  It can take a dentry whose private unionfs 'info' node exists or
    not, and it should allocate and un/lock it only if it's NULL.
    
    Signed-off-by: Erez Zadok <ezk at cs.sunysb.edu>

diff --git a/fs/unionfs/lookup.c b/fs/unionfs/lookup.c
index dadfd14..ea5bba1 100644
--- a/fs/unionfs/lookup.c
+++ b/fs/unionfs/lookup.c
@@ -477,24 +477,31 @@ void free_dentry_private_data(struct unionfs_dentry_info *udi)
 /*
  * Allocate new dentry private data, free old one if necessary.
  * On success, returns a dentry whose ->info node is locked already.
+ *
+ * Note: this function may get a dentry with an already existing *and*
+ * locked info node!
  */
 int new_dentry_private_data(struct dentry *dentry)
 {
 	int size;
 	struct unionfs_dentry_info *info = UNIONFS_D(dentry);
 	void *p;
+	int unlock_on_err = 0;
 
-	BUG_ON(info);
+	if (!info) {
+		dentry->d_fsdata = kmem_cache_alloc(unionfs_dentry_cachep,
+						    GFP_ATOMIC);
+		info = UNIONFS_D(dentry);
+		if (!info)
+			goto out;
 
-	dentry->d_fsdata = kmem_cache_alloc(unionfs_dentry_cachep,
-					    GFP_ATOMIC);
-	info = UNIONFS_D(dentry);
-	if (!info)
-		goto out;
+		mutex_init(&info->lock);
+		unionfs_lock_dentry(dentry);
+		unlock_on_err = 1;
+
+		info->lower_paths = NULL;
+	}
 
-	mutex_init(&info->lock);
-	info->lower_paths = NULL;
-	unionfs_lock_dentry(dentry);
 
 	info->bstart = info->bend = info->bopaque = -1;
 	info->bcount = sbmax(dentry->d_sb);
@@ -513,7 +520,10 @@ int new_dentry_private_data(struct dentry *dentry)
 	return 0;
 
 out_free:
-	unionfs_unlock_dentry(dentry);
+	kfree(info->lower_paths);
+	if (unlock_on_err)
+		unionfs_unlock_dentry(dentry);
+
 out:
 	free_dentry_private_data(info);
 	dentry->d_fsdata = NULL;