Fix sb_read and umount cache not be freed

dir.c

@@ -60,9 +60,11 @@ static int simplefs_iterate(struct file *dir, struct dir_context *ctx)
                 goto release_bh;
             }
             dblock = (struct simplefs_dir_block *) bh2->b_data;
-            if (dblock->files[0].inode == 0)
+            if (dblock->files[0].inode == 0) {
+                brelse(bh2);
+                bh2 = NULL;
                 break;
-
+            }
             /* Iterate every file in one block */
             for (; fi < SIMPLEFS_FILES_PER_BLOCK; fi++) {
                 f = &dblock->files[fi];

fs.c

@@ -58,6 +58,8 @@ static int __init simplefs_init(void)
 
 err_inode:
     simplefs_destroy_inode_cache();
+    /* Only after rcu_barrier() is the memory guaranteed to be freed. */
+    rcu_barrier();
 err:
     return ret;
 }
@@ -69,6 +71,8 @@ static void __exit simplefs_exit(void)
         pr_err("Failed to unregister file system\n");
 
     simplefs_destroy_inode_cache();
+    /* Only after rcu_barrier() is the memory guaranteed to be freed. */
+    rcu_barrier();
 
     pr_info("module unloaded\n");
 }

inode.c

@@ -749,8 +749,8 @@ static int simplefs_rename(struct inode *old_dir,
                     break;
                 }
             }
-            if (new_pos < 0)
-                brelse(bh2);
+
+            brelse(bh2);
         }
     }
 

super.c

@@ -37,6 +37,9 @@ int simplefs_init_inode_cache(void)
 /* De-allocate the inode cache */
 void simplefs_destroy_inode_cache(void)
 {
+    /* wait for call_rcu() and prevent the free cache be used */
+    rcu_barrier();
+
     kmem_cache_destroy(simplefs_inode_cache);
 }