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@cs.sunysb.edu>

diff --git a/fs/unionfs/lookup.c b/fs/unionfs/lookup.c
index dadfd14b61466664f00e0e577e342ae7600cf1e6..ea5bba1350b57f9f8f1d5b067a331c11df0d3c9f 100644 (file)
--- 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;