[PATCH] dentry->d_count fixes: d_invalidate

From: Maneesh Soni <maneesh@in.ibm.com>

- d_invalidate() can incorrectly return success instead of returning -EBUSY
  as we can have situations where lockless d_lookup has found a dentry
  successfully before d_invalidate drops it

fs/dcache.c

@@ -232,14 +232,17 @@ int d_invalidate(struct dentry * dentry)
 	 * we might still populate it if it was a
 	 * working directory or similar).
 	 */
+	spin_lock(&dentry->d_lock);
 	if (atomic_read(&dentry->d_count) > 1) {
 		if (dentry->d_inode && S_ISDIR(dentry->d_inode->i_mode)) {
+			spin_unlock(&dentry->d_lock);
 			spin_unlock(&dcache_lock);
 			return -EBUSY;
 		}
 	}
 
 	__d_drop(dentry);
+	spin_unlock(&dentry->d_lock);
 	spin_unlock(&dcache_lock);
 	return 0;
 }