Re: [PATCH] hfsplus: Supports freeing newly created tree head

[Viacheslav Dubeyko]

On Sat, 2026-04-18 at 17:37 +0800, Edward Adam Davis wrote:
> On Fri, 17 Apr 2026 15:03:17 -0700, Viacheslav Dubeyko wrote:
> > > hfs_bnode_put() does not support deallocating a newly created btree
> > > head node; therefore, regardless of whether hfsplus_bnode_find() succeeds
> > > or fails, it cannot effectively reclaim the memory allocated for a newly
> > > created head node.
> > > 
> > > When finding a head node, if the node is a newly created one, we can use
> > > hfs_bnode_free() to reclaim its memory.
> > > 
> > > [1]
> > > BUG: memory leak
> > > unreferenced object 0xffff88811cabc840 (size 96):
> > >   backtrace (crc 3e2dadb7):
> > >     __hfs_bnode_create+0x59/0x310 fs/hfsplus/bnode.c:469
> > >     hfsplus_bnode_find+0x13e/0x580 fs/hfsplus/bnode.c:547
> > >     hfsplus_btree_open+0x2fa/0x6d0 fs/hfsplus/btree.c:382
> > >     hfsplus_fill_super+0x272/0x880 fs/hfsplus/super.c:548
> > 
> > I need slightly more detailed and clear explanation how the issue has been
> > happened and why we need to fix it in a such way. Currently, I don't have the
> > complete picture how this happened. I am sure that you have the complete
> > picture. :) Could you please share what you have in your mind? :) Don't hide the
> > wisdom. ;)
>     fc_mount()
>      vfs_get_tree()
>       get_tree_bdev_flags()
>        hfsplus_fill_super() 

We have multiple calls of hfsplus_btree_open(). Which particular b-tree do you
mean here?

>         hfsplus_btree_open() 

I assume that you mean hfs_btree_open().

>          hfsplus_bnode_find(tree, HFSPLUS_TREE_HEAD)
> 

We call hfs_bnode_find() here.

>  
>           __hfs_bnode_create()
> 	   ...
> 	   node->this = cnid; // cnid is HFSPLUS_TREE_HEAD, it is 0
> 	   ...
> 	  ...
> 	  desc = (struct hfs_bnode_desc *)(kmap_local_page(node->page[0])
> 	  node->type = desc->type;
> 	  switch (node->type) {
> 	  ...
> 	  default:  // because node->type is 127, so run here
> 	  	goto node_error;

I think, maybe, we need to add some error message(s) when some error is
happened. What do you think?

> 	  ...
> 	  hfs_bnode_put()
> 	   ...
> 	   if (test_bit(HFS_BNODE_DELETED, &node->flags)) { /* head node not set HFS_BNODE_DELETED flag
> 							     * so, the node will never be freed.
> 							     * Furthermore, even if the node were marked
> 							     * with the HFS_BNODE_DELETED flag, hfs_bmap_free()
> 							     * would still trigger BUG_ON(!node->this).
> 	   						     */

 node_error:
 	set_bit(HFS_BNODE_ERROR, &node->flags);
-	clear_bit(HFS_BNODE_NEW, &node->flags);
-	wake_up(&node->lock_wq);
+	if (num != HFSPLUS_TREE_HEAD) {

Why do we need to distinguish is it HFSPLUS_TREE_HEAD or not? I don't see any
difference in node processing.

+		clear_bit(HFS_BNODE_NEW, &node->flags);

I think that we don't need to clear the HFS_BNODE_NEW. Because, we need to
analyze HFS_BNODE_ERROR in hfs_bnode_put().

+		wake_up(&node->lock_wq);

I assume that wake_up() should be called anyway. Why have you removed this call
for HFSPLUS_TREE_HEAD case?

+	}
 	hfs_bnode_put(node);
 	return ERR_PTR(-EIO);

@@ -694,6 +698,10 @@ void hfs_bnode_put(struct hfs_bnode *node)
 			hfs_bnode_free(node);
 			return;
 		}
+		if (test_bit(HFS_BNODE_NEW, &node->flags)) {

I suggest to analyze HFS_BNODE_ERROR here.

+			hfs_bnode_unhash(node);
+			hfs_bnode_free(node);
+		}

@@ -598,14 +598,18 @@ struct hfs_bnode *hfs_bnode_find(struct hfs_btree *tree,
u32 num)
 		if (key_size >= entry_size || key_size & 1)
 			goto node_error;
 	}
-	clear_bit(HFS_BNODE_NEW, &node->flags);
-	wake_up(&node->lock_wq);
+	if (num != HFSPLUS_TREE_HEAD) {
+		clear_bit(HFS_BNODE_NEW, &node->flags);
+		wake_up(&node->lock_wq);

What the point in this code? Why have you change the logic here?

+	}
 	return node;

And, could you please add these new details into the commit message?

Thanks,
Slava.