Re: [PATCH] btrfs: take delayed_node mutex when releasing item

[Leo Martins <loemra.dev@gmail.com>]

On Wed, 12 Nov 2025 08:09:25 +0100 David Sterba <dsterba@suse.cz> wrote:

> On Tue, Nov 11, 2025 at 04:22:57PM -0800, Leo Martins wrote:
> > The error path in btrfs_delete_delayed_dir_index does not take
> > the delayed_node mutex when releasing delayed item.
> > btrfs_release_delayed_item -> __btrfs_remove_delayed_item which
> > has lockdep_assert_held(&delayed_node->mutex)
> > 
> > Fix this by taking the mutex when releasing.
> > 
> > Fixes: 933c22a7512c ("btrfs: delayed-inode: Kill the BUG_ON() in btrfs_delete_delayed_dir_index()")
> > Signed-off-by: Leo Martins <loemra.dev@gmail.com>
> > ---
> >  fs/btrfs/delayed-inode.c | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/fs/btrfs/delayed-inode.c b/fs/btrfs/delayed-inode.c
> > index e77a597580c5..30dd067e2db3 100644
> > --- a/fs/btrfs/delayed-inode.c
> > +++ b/fs/btrfs/delayed-inode.c
> > @@ -1662,7 +1662,9 @@ int btrfs_delete_delayed_dir_index(struct btrfs_trans_handle *trans,
> >  		btrfs_err(trans->fs_info,
> >  "metadata reservation failed for delayed dir item deletion, index: %llu, root: %llu, inode: %llu, error: %d",
> >  			  index, btrfs_root_id(node->root), node->inode_id, ret);
> > +		mutex_lock(&node->mutex);
> >  		btrfs_release_delayed_item(item);
> > +		mutex_unlock(&node->mutex);
> 
> I don't think it's needed, the item has been just allocated but not yet
> added to the rbtree (__btrfs_add_delayed_item() a few lines below).
> 
> In btrfs_release_delayed_item() there's a check if the item is in the
> rbtree, if not then nothing is done. Otherwise the lockdep assertion is
> checked, and the locking would be needed.

Whoops, you're right, good catch.